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- 09/23/14--02:38: _A “Walk on the Moon...
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- 12/14/14--08:35: _2014 Posts That Nev...
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- 12/22/15--01:50: _2015 Geology Posts ...
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- 12/21/17--02:48: _2017 Geology Posts ...
- 11/28/14--12:40: Richard E. Byrd III’s National Champion Eastern Hophornbeam Tree
- 12/14/14--08:35: 2014 Posts That Never Quite Made It - A Lustrous Pearl for an Illustrious New Year; William Smith's Map That Changed the World; The Longitude Problem; Plaster of Paris Meets the Father of Comparative Anatomy; The Seine's Epic Journey to the Sea; Blue Sky, Green Water and Red Rocks on the Stove Pipe Trail; Born to Reproduce; The Oldest Cut Granite Building in America; The Granite Railway; and The Bridge that Spans Two Geologic Eras
- 11/20/13--17:59: Roadside America: Part III - Weird, Wacky, Tacky and Wonderful
From the Dartmouth College motto adapted from the Gospel of Mark and
subtitle of Merle Graffam's treatise entitled Fossils from the Tropic Shale
Although some dinosaurs may have spent time feeding in open water and possibly a few may have become strongly amphibious as implied by some trackways, it’s a common misconception that dinosaurs colonized the seas. If so, what were the bones of a terrestrial dinosaur – a new species of therizinosaur - doing amongst the marine fauna of the Late Cretaceous Tropic Shale, at least 60 miles from the nearest dry land at the time?
Artist Victor Leshyk’s portrayal of the proto-feathered, Late Cretaceous dinosaur Nothronychus graffami dining upon mangroves growing marginal to the Western Interior Seaway. The therizinosaur is thought capable of balancing tripodally on its massive pelvis while raking in tree branches with its long slender claws, which it passed to its toothless beak.|
From the Museum of Northern Arizona. Visit Victor here. Visit MNA here.
WELCOME TO THE MOON
If you’ve ever visited the badlands outside of the tiny southern Utah town of Big Water, you know the meaning of the word “barren”. The landscape consists of a coarse, brownish sandstone bedrock covered by a monotonous repetition of eroding, low-slung, blue-gray mounds of fine mud turned-to-shale against a backdrop of buff-colored, sandstone cliffs littered at the base with dislodged blocks of stone. Little grows and nothing moves, other than the wind and the imperceptible forces of gravity and erosion that are incessantly at work.
The region is so drab and desolate that locals call it ‘The Moon.’ To geologists and paleontologists – who are of the same ilk - it’s all hauntingly beautiful and exciting beyond anything imaginable, not just for its appearance but for the story of its formation and the bounty of lifeforms that are preserved. Personally, I couldn’t wait to get out there with geologist and acclaimed author Wayne Ranney, and Merle Graffam - namesake of the dinosaur Nothronychus graffami.
INTRODUCING MERLE GRAFFAM
Indeed, there’s nary a sole in sight on The Moon unless you stumble upon Merle - retired commercial artist, Big Water resident, Bureau of Land Management Park Ranger at the Big Water Visitor Center, and amateur paleontologist par excellence. Merle takes regular walks on the Moon, combing the ancient seabed for marine fossils with the intuition, trained eye, laser focus and insatiable curiosity of a seasoned field expert.
CREATURES OF, ABOVE AND ALONGSIDE THE SEA
Merle knows The Moon and the fossils preserved within in it, all creatures of a long gone sea - megafaunal marine and brackish-water invertebrates such as oysters, gastropods, solitary corals, inoceramid bivalves and ammonites, and marine vertebrates such as fish, rays and sharks, turtles, crocodilians and an occasional short-necked plesiosaur. Above the sea soared pterosaurs and early avians with toothed-beaks. As bleak and depauperate as the landscape looks now, at one time, The Moon was the site of a thriving marine ecosystem.
Creatures above and within the Late Cretaceous Western Interior Seaway|
Adapted from nd.gov
Terrestrial deposits marginal to the sea preserve extensive skeletal remains and trackways that attest to a diverse dinosaur fauna that plied the shoreline's habitats, while diminutive, insectivorous mammals hid in the shadows amongst the gymnosperms and newly-evolved angiosperm plants. It takes considerable imagination to view this ancient land and seascape while standing on the landscape of The Moon.
AS LUCK WOULD HAVE IT
On one of Merle's lunar constitutionals in 2000, he made an unsuspecting discovery that would change his life. What's more, it would rewrite a portion of dinosaur phylogeny, offer a new perception of dietary plasticity amongst theropods and expand our knowledge of biodiversity within the Cretaceous ecosystem.
Merle discovered a small toe-bone - a phalange - in the Tropic Shale that eventually would lead to the remains of a spectacular dinosaur skeleton at the crest of a small hillock of eroding marine sediments of the Tropic Shale. It proved to be the most complete therizinosaurid yet discovered in North America.
|Very excited at the excavation site, Merle exclaimed, "Here's the spot!"|
LET'S GET OUR BEARINGS
With a population barely of 475, the settlement of Big Water is a tiny speck on the map (green laser dot) located in Kane County on Highway 89 in southernmost Utah near the Arizona border. On maps from the late 50’s and early 60’s, it's called Glen Canyon City and housed workers who built the nearby Glen Canyon Dam.
The name Big Water seems a misnomer, since the high desert and badlands are as dry as a bone with an average rainfall of barely six inches a year. The nearest “big water” is a slender arm of Lake Powell called Wahweap Bay about 10 miles down the highway to the southeast, where a trip downstream leads to the dam that impounds the Colorado River. So where’s all the water at Big Water?
|Wayne Ranney aims his laser-pointer at Big Water on a topographical relief map at the Big Water Visitor Center. The highway takes you down and across the Glen Canyon Dam that impounds Lake Powell.|
Big Water is actually named for the Navajo Aquifer, an underground formation with an estimated 400 million acre-feet of potable water that spans most of southwestern Utah and some of northern Arizona. Yet geologically, the name is highly appropriate, since a much earlier actual “big water” submerged the entire region and a wide swath of North America during the Late Cretaceous. That sea was responsible for the layered deposits at the Moon of Big Water – and as we shall see - much more.
The three sections of the Monument record sedimentation throughout the Mesozoic. The centrally-located Kaiparowits Plateau section is exemplified by plateaus, buttes and mesas carved in rocks acquired in the Cretaceous when the region was situated along the western shore of an extensive inland body of shallow water called the Western Interior Seaway.
|Three sections of the Grand Staircase-Escalante National Monument in southern Utah with Big Water on Highway 89 near the Arizona border.|
Modified from Utah Geological Association, Second Edition DVD.
LOAD-INDUCED SUBSIDENCE AND SEDIMENTATION
The Sevier front consisted of a fault zone, an active volcanic arc, low-angle thrust slices and a broad foreland basin. The retroarc basin - so called because it was 140-200 km cratonward of the thrust front - was an asymmetric depression created in response to the load superimposed by the east-advancing wedge of thrust sheets that downwarped the lithosphere. In response to ongoing Sevier thrusting, the foreland migrated eastward and continued to rapidly subside. The basin received massive amounts of detritus delivered by rivers across alluvial plains from the encroaching front from the west and southwest.
BIRTH OF AN INLAND SEA
In the Early Cretaceous (Aptian to Albian), the basin began to flood with marine waters from the north and south, connecting the Boreal and Tethyan seas. By the Late Cretaceous, long arms of the sea converged forming an inland epicontinental sea (epi is Greek for above). Nearest the front, deep-water sediments pass upward into shallow-water sediments recorded with conglomerates that pass into sandstones and shales, which in turn pass into carbonate marine sediments well to the east.
Late Cretaceous oblique, north view of the asymmetric Western Interior Seaway illustrating the subducting Farallon slab, the Sevier orogen and Western Interior Seaway.|
Modified from Wikipedia
"WHENCE THE FLOOD COMETH" - GEOLOGICAL NOT BIBLICAL
The development of the inland sea occurred by active subsidence of the foreland but was assisted at a time of eustasy (global high seas). Sea level changes are affected by the volume of water contained in the ocean basins and the volume of water displaced from the basins. For example, melting polar ice adds to the basins causing glacioeustasy, and shifting plates and shallowing basins removes water called tectonoeustasy. It's a rather simplistic scenario but not far from reality.
Pangaea's aridity during the Triassic and Jurassic - demonstrated by widespread eolian sandstones and evaporites in the west - was replaced by a humid, subtropical climate in the Cretaceous, as North America drifted out of lower, equatorial latitudes. Concurrently, as Atlantic seafloor spreading increased, the ocean basin shallowed, displacing vast quantities of water, while extrusive continental volcanics associated with rifting elevated temperatures 18°F (10°C) higher than average.
Submitting to the global greenhouse, melting polar ice further drove seas higher. Low-lying regions - coasts, interior lowlands and cratonic platforms - drowned worldwide including the subsiding basin of the Sevier foreland. And in its wake, the seas left vast sequences of sedimentary rocks. The great flood is known as the Zuni transgression - the greatest of six major high water events of the Phanerozoic. As an aside, our modern world with rising seas is in a state of Holocene (post-Pleistocene) glacioeustasy. Now back to the Cretaceous Seaway!
The six major transgressions of the Phanerozoic Eon with the Cretaceous Zuni highlighted.|
Modified from Earth System History, Second Edition, 2005 and msubillings.edu.
THE WESTERN INTERIOR SEAWAY
At its zenith in the Late Cretaceous, the Western Interior Seaway in places was almost 300 meters deep. Inland seas are built on buoyant continental platforms and are relatively shallow compared to deeper-denser ocean basins. The sea connected the Arctic Ocean and Hudson Bay with the Gulf of Mexico, and stretched from Utah in the west to the western Appalachians in the east. It split North America into two massive landmasses - eastern Appalachia and western Laramidia - and divided the terrestrial ecosystem forcing it to pursue independent courses of evolution, as did the resident faunal populations riding on Pangaea's drifting continental siblings.
Also in the Late Cretaceous, Laramidia formed an arctic land-based connection with northeast Asia called Beringia. The loosely defined region in the vicinity of the Bering Strait has intermittently persisted through Recent times. During the Pleistocene, an Ice House climatic condition created regressive global seas exposing the land bridge; whereas during the Greenhouse conditions of the Cretaceous, the land was devoid of polar ice, having formed tectonically from a series of accretionary events. Like the Pleistocene connection that allowed the passage of Paleo-Indians and mammalian megafauna (the Asian saber-toothed cat comes to mind), the Cretaceous bridge (up to a 1,000 miles wide) likely allowed faunal and floral exchange in a similar manner in both directions.
Approximate extent of the Beringia Land Bridge|
Adapted from ic.arizona.edu
In the Late Cretaceous, Laramidia experienced a major evolutionary radiation of dinosaurs possibly related to new biomes generated by the Sevier front and foreland, and may have been infused by immigrant fauna that migrated across the bridge from Asia (or vice-versa). The relevance of Cretaceous paleography will become relevant in our forthcoming discussion of therizinosaurs from Laurasia (the combined landmasses of North America and Eurasia that formed Pangaea with Gondwana of the Southern Hemisphere).
TRANGRESSIONS, REGRESSIONS AND DEPOSITIONAL SEQUENCES OF THE VACILLATING SEA
During the Late Cretaceous for nearly 25 million years, the Western Interior Seaway dominated paleography and sedimentation over a vast area of the Southwest. At least two major and numerous minor transgression-regression sequences - called cyclothems - are recorded in the rock record.
Marine waters advanced onto the continent's downwarping interior, rising and falling with starts and stops while the shoreline shifted to and fro from east to west. As the sea advanced onto land, the sandy shore was buried by new, higher shores, while previously deeper muds migrated as well. Terrestrial deposits met marine that vied for space in an overlapping, alternating geometry, all related to the whim of the vacillating sea. When the sea eventually reversed its direction, the opposite layered architecture was deposited as newer shorelines formed on previously deeper muds called a transgressive-regressive sequence - visible stratigraphically.
The west part of the GSENM was elevated by Sevier tectonics before sediments were deposited in coastal areas ahead of the encroaching inland sea from the east. All Upper Jurassic and a good part of Middle Jurassic rocks were removed by erosion before Cretaceous sediments were deposited.
THE FIRST TRANSGRESSIVE SEQUENCE
Initial alluvial plain and coastal plain deposits were met by the sea's rapidly-rising westward advance called the Greenhorn Cyclothem (late Cenomanian to middle Turonian). Deposited in the sea's first transgression in the early Late Cretaceous about 95 million years ago came coarse, yellow-brown beach sands of the shallow marine Dakota Formation, deposited on either the Morrison Formation (east) or the Entrada Sandstone (west). The Dakota contains a record of shallow brackish and marine water environments, lush coastal swamps and sandy expanses incised by rivers and streams emptying into the sea.
In deeper waters, the Dakota grades into dark, organic-rich Mancos Shale - called the Tropic Shale regionally - and consists of exceptionally fossiliferous blue-gray silts and muds formed about 93 million years ago. The type section crops out around the town of Tropic, Utah, about 50 miles to the northwest. Elsewhere in Utah, Tropic stratigraphic equivalents have been referred to the Tununk Member of the Mancos Shale, the Tropic equivalent in most of the Southwest.
On top of the sequence with the sea retreated to the east lies the four-membered Straight Cliffs Formation, an overall regressive sequence rich in coal that followed the previous marine incursion about 85 million years ago. The sea returned again bringing with it another sequence of deposits, seen elsewhere on the Kaiparowits Plateau and in the Grays Cliffs of the Grand Staircase.
The aforementioned lithologies are conformable and form a classic transgressive-regressive sequence that documents the greatest widespread rise in sea level of the Cretaceous recognized worldwide. In summary, the foreland basin's sedimentary infill represents a record Sevier orogen tectonics, flexural subsidence, weathering and sedimentation and eustatic sea level change.
|The dissected landscape rocks of The Moon of Big Water preserve Upper Cretaceous transgressive Dakota sandstone, shale and some coal buried beneath eroding gray Mancos muds and regressive cliff-forming Straight Cliffs sands and coals.|
"HEY DAVE! WHAT'S THIS?"
In 2000, at the conclusion of a large plesiosaur excavation in the Tropic, Merle turned to Dr. Dave Gillette - Utah's former state paleontologist and current Colbert Curator of Vertebrate Paleontology at the Museum of Northern Arizona in Flagstaff. Pulling a bone from his pocket, Merle uttered the now famous phrase "Hey Dave! What's this?"
Dave recognized the toe bone, but it was clearly not from a plesiosaur, the large marine reptile found with increasing frequency on the Tropic seabed thanks to Merle's keen eye of discovery. The bone was too small to be from a hadrosaur, a terrestrial, duck-bill dinosaur found in large numbers along the shoreline far to the west.
Stumped by the implication of a dinosaur bone so far from land, they later returned to the site, found more bones and initiated an excavation. The dinosaur's identity was a mystery well into the dig. According to Dave, “We weren’t thinking ‘therizinosaur’ at first, because at that time they were known only from Asia. From that first toe bone, we thought maybe we had a big ‘raptor’ (an agile, hunting dinosaur). But when we found peculiar bones of the massive hips, we knew we had a sickle-claw dinosaur. They were like nothing we’d ever seen.”
The active therizinosaur excavation site in the Tropic Shale. A project can require the removal of up to 20 tons of overburden and take a thousand hours of field and laboratory time. |
Photo by Dave Gillette
For Merle's discovery and contribution, Graffam became the species namesake. Following the dinosaur's reconstruction, the therizinosaur was featured in an exhibit at the Museum of Northern Arizona from 2007-2009 and at the Carl Hayden Visitor Center at the Glen Canyon Dam in 2012.
For half a century, therizinosaurs have remained a poorly known and understood group of theropod dinosaurs with an extremely unusual combination of anatomical features. That's changed largely in the last decade with new discoveries in Cretaceous deposits in Mongolia, China and western North America.
Unlike earlier theropod dinosaurs that exhibit predatory morphological adaptations and carnivorous inclinations, therizinosaurs exhibit the characteristics inherent of herbivores. These are thought to include: tightly-packed, leaf-shaped cheek teeth (as opposed to elongate, typically Theropod meat-cutting teeth), an inset tooth row (suggesting fleshy cheeks necessary for plant mastication) in tandem with a rostral rhampotheca (keratinous, toothless bird-like beak to facilitate an herbivorous diet), a massive, highly derived pelvis (to accommodate a large gut synonymous with plant digestion), the development of large load-bearing hind limbs (to support a large abdomen), the loss of cursorial hind-limb adaptions (typical of predatory, swift carnivorous theropods) and an increased vertebral count (long neck speculated to increase browsing range similar to sauropods).
Therizinosaurs, especially more derived forms such as Nothronychus graffami, are thought to have been slow, large waddling, pot-bellied creatures rather than the quick, graceful gaited members of related Theropod predators. In spite of their likely herbivory, the group is thought to possess defensive capabilities with its powerful claws.
The tail was short and unnecessary for its mode of non-predatory diminished speed and thought to have provided upright, tripodal support for plant consumption. Unlike most theropods, the pes was curiously tetradactyl (four toes, which is a throwback to the ancestral dinosaur condition) with blunt unguals (claws), while its manus was tridactyl (three fingers) with elongated, recurved claws - the distinctive anatomical feature that gives the clade its name. Therizinosaur means "sickle-claw reptile". These Therizinosauroid features became increasing expressed from basal forms through more derived forms.
What's more, being members of Theropoda, the entire clade was thought to possess rudimentary proto-feathers - integumentary-derived structures such as hair, scales and nails. Please visit my daughter's post on feathers here for the evolution of this dinosaurian structure.
An imaginative interpretation of a proto-feathered adult therizinosaur accompanied by juveniles|
Used with permission by artist Damir G. Martin. Visit him here.
Taking their singular, albeit bizarre morphology and fragmentary fossil record into account, it comes as no surprise that therizinosaurs have endured a convoluted taxonomic history within Dinosauria and have been variously assigned to nearly all of its major subclades.
At one time, the family Therizinosauridae was referred to as the now-outmoded, group Segnosauria (segnis means slow in Latin) based on their heavy bodies, short legs, and sloth-like claws with a comparable lifestyle. They have been variously regarded as gigantic turtles, aberrant theropods and sauropodomorphs. Based on their retroverted (opisthopubic) pelvis (posteroventrally-directed pubis bone which was aimed backwards as in ornithischian, bird-hipped dinosaurs), they were considered to be phylogenetic intermediates between herbivorous prosauropods and early ornithischians.
UNEQUIVOCAL PHYLOGENETIC RESOLUTION
With increasing numbers of discoveries in Asia and North America from the Cretaceous, the diversity of therizinosaurs has begun to exhibit remarkable growth. Yet, a significant impediment to ascertaining phylogenetic relationships has been the paucity of both ancestral and transitional forms. Speculation is gradually being replaced with resolution.
Therizinosaurs are now considered to be unequivocal descendants not only of theropods but of the coelurosaurian clade and maniraptoran subclade with a sister relationship with Oviraptorosauria (see below). Thus, therizinosaurs are Saurischian, Theropodal, Tetanurian, Coelurosaurian, Maniraptoran dinosaurs and members of the family Therizinosauridea.
Therizinosaurs also share the tree with more highly derived Avialae (birds) and possess avian-associated characters such as a pneumatic-skeleton (hollow light-weight bones that facilitate a high rate of respiration, and later, powered flight), a pygostyle (shortened tail with fused vertebrae), feathers (for thermo-regulation, sexual dimorphism and brooding) and an avian-trending brain (for enhanced sight, sound and mechano-reception).
UNCLEAR FAMILY INTERRELATIONSHIPS
Interrelationships between specific therizinosaur taxa remains less clear. Until recently, the fossil record was restricted to Asia. With discoveries in North America such as Nothronychus mckinleyi (the first undisputed North American therizinosaurid from the Upper Cretaceous of New Mexico) and Falcarius utahensis (the third therizinosaur discovered in America, the most morphologically primitive therizinosaur yet discovered and a sister taxon to the clade of Therizinosauroidea from the Lower Cretaceous Cedar Mountain Formation of east-central Utah), we can begin to ask questions about origination, geographic and stratigraphic range, and even potential faunal mixing between immigrant and endemic clades.
One of many parsimonious phylogenies proposed for therizinosaurs|
50% Majority-rule consensus tree
Modified from Pu et al, 2013.
QUESTIONS WITHOUT ANSWERS
Did basalmost Falcarius utahensis originate in North America and certain populations expand into Asia? With recent finds in China such as Eshanosaurusdeguchiianus from the Early Jurassic, the presence of derived coelurosaurian lineages including therizinosaurians is being pushed back earlier. Did therizinosaurs differentiate from coelurosaurian ancestors before the breakup of Pangaea into Eurasia and North America and/or did they migrate across the tectonic Beringia Land Bridge that was established in the Early Cretaceous between northeast Asia and northwest North America? Was there more than one dispersal event? At various times, Asian endemic therizinosaurids show faunal similarities with North American forms. Did endemic forms mix with immigrant forms? Do North American therizinosaur taxa exhibit an Asian affinity or vice versa?
VEGETARIANS WITHIN A FAMILY OF CARNIVORES
Based on therizinosaur's osteological anatomy and soft tissue reconstructions, taking into account the habitats in which they likely thrived, and using animal analogues such as the sloth, certain dietary assumptions have been made about therizinosaurs and the Coelurosaurian clade in which they belong - once thought to have been obligate carnivores. In a little over a decade, doubt has been shed on that notion, raising the possibility or even likelihood that "dietary diversification was more commonplace among 'predatory' dinosaurs than previously appreciated" (Zanno, 2009).
In fact, therizinosaurs are the most widely regarded candidate for herbivory among theropods. Dietary plasticity and facultative (capable of rather than restricted to) herbivory (omnivory) is thought to have afforded the group the potential to invade and exploit ecospaces early in evolution for survival.
With a similar body shape and large claws on their front feet, Nothronychus graffami is shown as a bipedal browser analogous to the Giant Ground Sloth of the Ice Age.|
Artist Victor Leshyk
Wayne Ranney and I met Merle bright and early at the Visitor Center in Big Water for a tour of the Moon. Crossing the dry streambed of Wahweap Creek, we travelled on a planar surface of Tropic mudstone, occasionally bouncing around on the hummocky, eroded terrain. The easiest places to build roads on the Colorado Plateau, although the most difficult places to maintain them, are on the Mancos-Tropic Shale. The soft rock weathers readily, forming broad, flat expanses and easy routes to get from here to there.
Our first destination was the very spot of Merle's once-in-a-lifetime discovery. After a surprisingly short drive from the Visitor Center, we left our vehicle and began to ascend a large, loose mound of gray mudstone and claystone to a noticeably beveled off area.
Standing at the site of the former dig, let's let Merle tell the story. Although he's recounted the details many times in well over a decade since the find, it's clear that his enthusiasm hasn't diminished one iota. I'm filming, while Wayne is interjecting commentary.
|Merle and Wayne debate the mysterious circumstances of the terrestrial therizinosaur's burial at sea.|
BURIAL AT SEA - BUT BY WHAT MEANS?
One important question that has plagued paleontologists is how the dinosaur came to be buried in marine mud 60 miles out to sea with the nearest shore confirmed geologically near present-day Cedar City? To date, no definitive answer exists, although theories include "bloat and float" - having died on or near land and washed out to sea buoyed by decomposing body-gases followed by burial- and "lost at sea" - a less plausible scenario of having been caught by a flood or storm, floated out to sea alive, perhaps attacked by predators, and eventually buried nearly fully articulated. The skeleton of N. graffami was located in a supine position, belly-up, implying that it settled to its final resting place in the Tropic mud while buoyed by gases in a typical death pose.
I've seen the same "bloat and float" taphonymous (mode of fossilization) entity in New Jersey where terrestrial duck-billed dinosaur remains (the state fossil) have been found buried in glauconitic sands of the flooded Late Cretaceous continental shelf on Jersey farmland.
As the Tropic continues to erode, a few small osseous remnants of N. graffami have weathered to the surface since its excavation over a decade ago. It's that fact, among many others, that keeps Merle coming back to The Moon. There's always something new to be found on the ever-changing landscape. Come back the next day, and a new discovery will be awaiting you. What appears to be a static landscape is entirely the opposite!
HEADING DOWN DRY WAHWEAP CREEK
• First Definitive Therizinosaurid From North America by James I. Kirkland and Douglas G. Wolfe, 2001.
• Fossils from the Tropic Shale by Merle H. Grafam, 2000. Personal copy from the author.
• Geological Evolution of the Colorado Plateau of Eastern Utah and Western Colorado by Robert Fillmore, 2011.
• The Geology of the Grand Staircase in Southern Utah by the Geological Society of America, 2002.
• The Pectoral Girdle and Forelimb of the Primitive Therizinosaiuriod Falcarius Utahensis by Lindsay A. Zanno, 2006.
• Therizinosaur – Mystery of the Sickle-Claw Dinosaur by David D. Gillette, Ph.D., Plateau, Museum of Northern Arizona, 2007.
• Vertebrate Paleontology by Michael J. Benton, 2005.
In “101 American Geo-Sites You’ve Gotta See,” author Albert B. Dickas listed Maryland's Calvert Cliffs as number 32. With curiosity piqued and the Cliffs renowned for their diverse and well-preserved fossiliferous assemblages - having attracted tourists and scientists as early as 1770 - I decided to visit the site in July. Only a 90 minute drive southeast of Washington, the Calvert Cliffs is a spectacular and scenic, almost continuous 50 km wavecut bluff along the western side of the Chesapeake Bay.
A geological contradiction to the Eastern Seaboard's otherwise flat Coastal Plain, the Cliffs rise in places to as much as 40 meters. They are cut into actively eroding, unconsolidated sandy, silty and clayey sediments of the lowermost portion of the Chesapeake Group. Throughout much of the Miocene, the region was the site of a shallow, inland arm of the temperate Atlantic Ocean during climatic cooling, uplift of the Atlantic Coastal Plain and eustatic changes in sea level. The stratal package preserves the best available record of middle Miocene marine and, less frequently, terrestrial life along the East Coast of North America.
WHO WAS CALVERT AND WHERE ARE WE?
The recorded history of the Chesapeake region is as varied as the geology, which began with the Spanish. The cartographer Diego Gutierrez recorded the Chesapeake on a map, calling it “Bahia de Santa Maria.” The English arrived with John White in 1585 and again in 1608 with John Smith’s entry onto the Calvert Peninsula. His mission was to explore the Chesapeake region, find riches, and locate a navigable route to the Pacific, all the while making maps and claiming land for England. On John Smith’s 1606 map (below), the Calvert Cliffs were originally called “Rickard’s Cliffes”, after his mother’s family name.
The first English settlement in Southern Maryland dates to somewhere between 1637 and 1642, although the county was actually organized in 1654. Established by Cecelius Calvert, the second Lord Baltimore, English gentry were the first settlers, followed by Puritans, Huguenots, Quakers, and Scots. In 1695, Calvert County was partitioned into St. Mary's, Charles, and Prince George's, and its boundaries became substantially what they are today. Statehood wasn’t granted to Maryland until 1788. The Revolutionary War, the War of 1812 and the Civil War waged in the region. In fact, the peninsula was the training site for Navy and Marine detachments, and the invasion of Normandy was simulated on the lower Cliffs of Calvert.
The Cliffs of Calvert reside on the broad, flat, seaward-sloping landform of the Coastal Plain of Maryland on the western shore of the Chesapeake Bay in Calvert and southernmost Anne Arundel Counties. Located on finger-like Calvert Peninsula, the Cliffs are on the higher western section of the Plain, while the lower section, known as the Eastern Shore (always capitalized), is a flat-lying tidal stream-dissected plain, generally less than 60 feet above sea level.
Red arrow indicates the region of Calvert Cliffs on the Atlantic Coastal Plain of the eastern shore of the Calvert Peninsula within the Chesapeake Bay.|
Modified from USGS map
Chesapeake Bay is an estuary - the largest of 130 in the United States - with a mix of freshwater from the Appalachians and brackish water from its tidal connection to the Atlantic Ocean. The Bay's central axis formed by the drowning of the ancestral Susquehanna River by the sea that flowed to the Atlantic from the north during the last glacial maximum of the Pleistocene Ice Age some 20,000 years ago - when the planet's water was bound up in ice and global seas were lower.
Multiple advances of the Laurentide Ice Sheet blanketed Canada and a large portion of northern United States during Quaternary glacial epochs. Its advance never reached the region of Chesapeake Bay, having extended to about 38 degrees latitude. Being in a contemporary interglacial period - the Holocene - global seas are higher, but not at the level during the deposition of the Chesapeake Group at Calvert Cliffs during the Miocene.
During the time of deposition of the Calvert Cliffs, fluctuating seas drowned portions of southern Maryland. A shallow, protected basin of the Atlantic Ocean called the Salisbury Embayment was located in Virginia, Maryland, Delaware and southern New Jersey. It was one of many depocenters along the Eastern Seaboard, separated by adjoining highs or arches. The Salisbury Embayment structurally represents a westward extension of the Baltimore Canyon Trough that extends into the central Atlantic on the continent's shelf and slope.
The depositional history and relief of the Cliffs of Calvert are testimony to the elevated level of the seas in the Miocene. In addition, the Embayment resides on the “passive” margin of North America’s east coast, which is typified by subsidence and sedimentation rather than seismic faulting and volcanic activity found on the continent’s “active” west margin. The Embayment was and is in a constant dynamic state - passive but far from inactive.
THE GEOLOGIC PROCESSES THAT SHAPED THE EASTERN COAST OF NORTH AMERICA
The orogen's remnants form the Anti-Atlas Mountains in western Africa, the Caledonides in Greenland and northern Europe, the Variscan-Hercynian system in central Europe and central Asia, the Ouachita-Marathons in south-central North America, the Cordillera Oriental in Mexico, and the Venezuelan Andes in northwestern South America. As a result of Pangaea's fragmentation, the region of the future Calvert Cliffs (red dot) was finally positioned in proximity to the sea, awaiting the orogen to erode and Cenozoic eustasy to flood the landscape and deposit the Chesapeake Group during the Miocene.
A glowing Maryland sunrise illuminates the strata of the Calvert Cliffs looking south.|
Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum
Location of Calvert Cliffs on the Chesapeake Bay's western shore of the Atlantic Coastal Plain (light colored)|
Modified from USGS map
MIOCENE STRATIGRAPHY OF CALVERT CLIFFS
The Calvert Cliffs consist largely of relatively undeformed and unlithified strata of silts, sands and clays of the Calvert, Choptank and St. Mary's formations (Shattuck, 1904) in ascending order of the Chesapeake Group. The formations are interrupted by a series of erosional unconformities and other hiatal intervals and preserve nearly 10 million years of elapsed time.
The Miocene succession was deposited as a complex package representing a first-order transgressive-regressive cycle with numerous superimposed smaller-scale perturbations of sea level. Overall, the record is one of gradual shallowing within the Salisbury Embayment and is reflected in the character of the strata that progresses from inner to middle shelf to tidally-influenced, lower-salinity coastal embayments. Deposition occurred under subtropical and warm temperate conditions in a shallow marine shelf environment at a maximum water depth of more than ~40-50 meters.
The exposures include not only the Calvert Cliffs but the Westmoreland and Nomini Cliffs along the Virginia Shore of the Potomac River. Debated for more than a century, estimates for the basal Calvert range from early Early Miocene to mid-Middle Miocene.
RECESSION OF THE COASTAL BLUFFS
A general absence of beaches below the cliffs is a characteristic of the region. Direct wave undercutting at the cliff-toe, freeze-thaw erosion, underground seepage at sand-clay interfaces and mass-wasting (the average inclination is 70 degrees) are accompanied by rapid wave removal of colluvium (slope debris). Long-term rates can exceed 1 m/yr. Slumps, rotational slides and fallen trees are constantly being generated and removed. For these reasons, beachcombing for fossils and excavating the cliff-toes is a dangerous and prohibited venture. Collected is allowed in designated parks along the shoreline such as Calvert Cliffs State Park, Flag Ponds Nature Park and Brownies Beach, and private beaches given the owner's permission.
Two vying factions in regards to the Cliffs are scientists that reap the benefit of ongoing erosion and the homeowners, who seek real estate in close proximity to the cliff edge for the sake of a bay view. For the former, the best way to preserve the Cliffs is to let them erode naturally, while the latter would like to riprap (with stone or concrete), bulkhead, sandbag and groin-field the Cliffs to preserve them and their property. In dealing with Mother Nature, in this regard, shoreline protection reduces the risk of cliff failure, although it doesn't eliminate it. It's only a matter of geologic time.
To reach otherwise inaccessible sections of the Cliffs and lessen the inherent dangers of collapse and burial, this mode of exploration employs descent from above. Excavation into the unlithified substrate is facilitated by an air-powered drill using a scuba tank's compressed air.
|From Google Science Fair 2014. See the video here.|
THE CLIFF'S FOSSILIFEROUS BOUNTY
The formations preserve more than 600 largely marine species that include diatoms, dinoflagellates, foraminiferans, sponges, corals, polychaete worms, mollusks, ostracods, decapods, crustaceans, barnacles, brachiopods and echinoderms. The macrobenthic fauna (large organisms living on or in the sea bottom) act as good indicators of salinity. The Calvert and Choptank are dominated by diverse assemblages of stenohaline organisms (tolerating a narrow range of salinity); whereas, the younger St. Mary's Formation exhibits an increasing prevalence of euryhaline molluscan assemblages (tolerating a wide range of salinity). The changes within the assemblages reflect the fluctuating freshwater conditions within the Salisbury Embayment.
Vertebrate taxa include sharks and rays, actinopterygian fish, turtles, crocodiles, pelagic (open sea) birds, seals, sea cows, odontocetes and mysticetes (whales, porpoises and dolphins).
In addition, the Cliffs preserve isolated and fragmentary remains of large terrestrial mammals (peccaries, rhinos, antelope, camels, horses and an extinct group of elephants called gomphotheres), palynomorphs (pollens and spores), and even land plants (from cypress and pine to oak) that bordered the Miocene Atlantic Coast and were carried to the sea by floodplains, rivers and streams sourced by the Appalachians.
|Miocene River Environment by Karen Carr with permission|
SIFTING THE SURF FOR FOSSILS
Armed with a plastic garden rake in hand from the local hardware store, I collected this fossil potpourri (below) on a brief 60 minute stroll along the beach at Flag Ponds. Their abundance and availability is a testimony to the richness and diversity of the Miocene marine fauna. The fossils are continually being generated from the eroding cliffs and their underwater extensions.
I am uncertain as to the specific origin of the mammalian bony fragments, but I suspect they are largely from marine fauna (i.e. dolphin, whale, seal, etc.) rather than terrestrial, since the former vastly outnumber the latter. Cetaceans such as the whale have repurposed an air-adapted mammalian ear for the differentiation of underwater sounds. The shell-like otic tympanic bulla is a thickened portion of the temporal bone located below the middle ear complex of bones. The large dense bone is well preserved and can easily be mistaken for an eroded fragment of rock.
The crocodile tooth is an indication that rivers and swampy habitats existed in the marginal marine environment of Calvert Cliffs. Shark teeth are the most common vertebrate fossils preserved at the Cliffs. Their numbers are commentary on the favorable paleoenvironmental conditions that existed in the Salisbury Embayment. Of course, sharks continually produce and shed teeth throughout their lives, facilitated by the absence of a long, retentive root structure, and are composed of durable and insoluble biogenic apatite, which favors their preservation. Calvert Museum collections contain as many as 15 genera. The main constituents are Carcharhinus, Hemipristis, Galeocerdo, Isurus and Carchrius. Carcharhiniformes shed about 35,000 teeth in a lifetime!
Appearing in the fossil record about 395 million years ago (middle Devonian), the Class Chondrichthyes (cartilaginous skeletal fish) is divided into two subclasses: Elasmobranchii, which includes sharks, rays and skates, and Holocephali (chimaeras). Elasmobranchii are distinguished by their 5-7 pairs of gill clefts, rigid dorsal fin, presence or absence of an anal fin, placoid dermal scales, teeth arranged in series within the jaws and the upper jaw being not fused to the cranium. Along with a dolphin tooth and a few gastropods, here are a few specimens collected from the surf at Calvert Cliffs State Park, about five miles southeast of Flag Ponds.
From these small samples, one can glean the ancient habitat at Calvert Cliffs during the Miocene. The combined study of both fossils and rock layers are essential in reconstructing the paleo-geography of the Cliffs.
By far, the largest but rarest shark teeth at Calvert Cliffs (but widely distributed within the world's oceans) are those of a "Megalodon," an extinct species of shark that lived from the late Oligocene to early Pleistocene (~28 to 1.5 million years ago). Its distinctive triangular, strongly serrated teeth are morphologically similar to those of a Great White shark (Carcharodon carcharias), a fact that fuels the debate over convergent dental evolution versus an ancestral relationship.
The controversy has resulted in a taxonomic name of either Carcharodon megalodon or Carcharocles megalodon - commonly abbreviated as C. megalodon. The “Meg” is regarded as one of the most powerful apex predators in vertebrate history. On rare occasion, extinct cetacean fossilized vertebrae have been uncovered with bite-marks suggestive of mega-tooth shark predation or scavenging. Megalodon is represented in the fossil record by teeth and vertebral centra, since the majority of its cartilaginous skeleton is poorly preserved.
C. megalodon dining on cetaceans|
With permission from artist Karen Carr with permission
SKULLS AND BURROWS OF A NEW SPECIES
Dr. Stephen Godfrey of the Calvert Marine Museum has been conducting paleontological studies in the Calvert Cliffs for some 15 years. After rafting along the shoreline to the excavation site, this paleontologist is taking measurements of a trace fossil interpreted as an infilled tilefish burrow from the Plum Point Member of the Calvert Formation deposited some 16 million years ago. In a 2014 paper in the JVP (see reference below), well preserved, partially complete, largely cranial remains of tilefish are described. They have been collected over the past three decades from Miocene deposits outcropping in Maryland and Virginia.
Ruler in hand, paleontologist W. Johns investigates the exposed tilefish burrow.|
Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum
Lopholatilus ereborensis, a new species of family Malacanthidae and teleost (infraclass of advanced ray-finned fish), inhabited long funnel-shaped vertical burrows that it excavated for refuge within the cohesive bottoms of the outer continental shelf of the Salisbury Embayment that likely inhabited other parts of the warm, oxygenated waters of the western North Atlantic outer shelf and slope. The species name was derived from 'Erebor,' the fictional name for the Lonely Mountain in J.R.R. Tolkien's The Hobbit. Like the mountain-clan of dwarves, the tilefish mined the substrate.
COLONIAL SMOKING PIPE
In an attempt to see what fossilized remains might have filtered down from overlying Miocene and more recent strata, I walked the beach until finding a break where a wash had carved a trough through the bluffs. I immediately spotted a white object glistening in the sun in a stream bed filled with gravel and tiny sharks teeth that turned out to be the worn remnants of a Colonial-era smoking pipe.
Pipes of clay were first smoked in England after the introduction of tobacco from Virginia in the late 16th century. Sir Walter Raleigh, an English sea captain, was one of the first to promote this novel habit acquired from Native Americans that practiced its ritual use for many centuries. By the mid-17th century clay pipe manufacture was well established with millions produced in England, mainland Europe, and the colonies of Maryland and Virginia. For various reasons, clay pipe demand declined by the 1930’s.
Clay pipes were very fragile and broke easily, and along with their popularity, they are commonly found at Maryland and Virginia colonial home sites. In Colonial-era taverns, clay pipes that were passed around were supposedly broken off at the stem for the next user in the interest of hygiene. Some clay pipes can be dated by the manufacturer's stamp located on the bowl, which was unfortunately missing in this lucky (but well calculated) find.
HIGHLY RECOMMENDED REFERENCES
• Evolution of Equilibrium Slopes at Calvert Cliffs, Maryland by Inga Clark et at, Shore and Beach, 2014.
•Frequency of Effective Wave Activity and the Recession of Coastal Bluffs: Calvert Cliffs, Maryland by Peter R. Wilcock et al, Journal of Coastal Research, 1998.
• Geologic Evolution of the Eastern United States by Art Schultz and Ellen Compton-Gooding, Virginia Museum of Natural History, 1991.
• Maryland's Cliffs of Calvert: A Fossiliferous Record of Mid-Miocene Inner Shelf and Coastal Environments by Peter R. Vogt and Ralph Eshelman, G.S.A. Field Guide, Northeastern Section, 1987.
• Miocene Cetaceans of the Chesapeake Group by Michael D. Gottfried, Proceedings of the San Diego Society of Natural History, 1994.
• Miocene Rejuvenation of Topographic Relief in the Southern Appalachians by Sean F. Gallen et al, GSA Today, February 2013.
• Molluscan Biostratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America by Lauck W. Ward, Virginia Museum of Natural History, 1992.
• Slope Evolution at Calvert Cliffs, Maryland by Martha Herzog, USGS.
• Stargazer (Teleostei, Uranoscopidae) Cranial Remains from the Miocene Calvert Cliffs, Maryland, U.S.A. by Giorgio Carnevale, Stephen J. Godfrey and Theodore W. Pietsch, Journal of Vertebrate Paleontology, November 2011.
• Stratigraphy of the Calvert, Choptank, and St. Mary's Formations (Miocene) in the Chesapeake Bay Area, Maryland and Virginia by Lauck W. Ward and George W. Andrews, Virginia Museum of Natural History, Memoir Number 9, 2008.
• The Ecphora Newsletter, September 2009.
• Tilefish (Teleostei, Malacanthidae) Remains from the Miocene Calvert Formation, Maryland and Virginia: Taxonomical and Paleoecological Remarks by Giorgio Carnevale and Stephen J. Godfrey, Journal of Vertebrate Paleontology, September 2014.
•Variation in Composition and Abundance of Miocene Shark Teeth from Calvert Cliffs, Maryland by Christy C. Visaggi and Stephen J. Godfrey, Journal of Vertebrate Paleontology, January 2010.
WITH GREAT APPRECIATION
I wish to express my gratitude and thanks to Stephen J. Godfrey, PhD., Curator of Paleontology of the Calvert Marine Museum, for providing valuable support (personal communications, October 2014), documentation and photographs of Calvert Cliffs and his recent excavation and publication.
Calvert Cliffs Marine Museum was founded in 1970 at the mouth of the Patuxent River in Solomons, Maryland. Visit them here, but do go there! You can join the museum here.
The Ecphora is the quarterly newsletter of the Calvert Marine Museum Fossil Club. Ecphora gardnerae gardnerae is an extinct, Oligocene to Pliocene, predatory gastropod and the Maryland State Fossil, whose first description appeared in paleontological writings as early as 1770. Sadly, riprapping (rock used to protect shorelines from erosion) has covered one of only two localities in the State of Maryland where the fossil can be found. The other is on private land and off limits without permission. Ironically, Marylanders can find their state fossil in Miocene strata of Virginia. Download copies of current and past newsletters here or simply subscribe.
DOES YOUR TREE MEASURE UP?
WHAT'S A HOPHORNBEAM?
The Eastern or American Hophornbeam - Ostrya virginiania if you're trying to impress Dick - is a member of the birch family of trees. Also known as ironwood, hardhack (in New England) and leverwood, it's generally a small short-lived tree scattered in the understory of hardwood forests. The tree is generally a subordinate species or minor member of most forest communities, when present. That's another unique aspect of Dick's champion - its unusually large size. Perhaps thriving in "the open" and Dick's nurturing nature has facilitated its large growth.
The Eastern Hophornbeam is a rugged, shade-tolerant tree with an oval or round canopy that grows to 50 feet in height. Dick's champion tops out at 66! It's found throughout the eastern United States and within the mountains of Mexico, south to El Salvador and Honduras. Over this large native range, it thrives in a diversity of climatic conditions and soils. Its small nutlets, which ripen in summer and fall, are used by birds and mammals during the winter.
It's often grown as an ornamental plant and sometimes used as a street tree. Because of its hardness, it has been used to make tool handles for mallets and posts. It should not be confused with the hornbeam, which is also a member of the birch family. The bark of a hophornbeam has loose strips of reddish brown to gray, creating a rough "clawed" bark.
|The hophornbeam's leaf is doubly-serrated with fine teeth at the margin and 2-4 inches long.|
I asked Dick what he knew of the age of his champion, it being slow-growing and having achieved such a large size. His best guess was about 135 years based on the age of his house. Dick speaks with the knowledge and ecological pride that comes from his BS in Forestry that he received from the University of Maine, although he doesn't pursue that profession, other than avocationally.
Gazing up at the hophornbeam and shaking his head, Dick says that it has lost a good two-thirds of its crown, and that it wasn't registered until it lost the first third. "After losing the first third, no one would ever know that you have a champion. That's why I registered it. I looked up the previous champion - a tree in Michigan. The Commonwealth came to measure it near the end of 2008."
Dick continued, "These types of trees are often culled early for pulpwood." Given its age and the deteriorated condition of its trunk, he fears that its days are numbered. "One good nor'easter, and that's it!" He's thought of cutting it down but is obviously highly reluctant.
Even before I met Dick, I couldn't help but notice the tree as I jogged through the neighborhood. Maybe it was the signage that he proudly placed on the tree that caught my eye - one high and the other low. "Why the low signage?" I asked. "It's for the kids, and it's fun for everyone to read about it." Unfortunately, the bark that held the signs has rotted off, and they're now displayed on the logs.
I was grateful for Dick telling me the story of his Eastern Hophornbeam and seeing his arboreal pride. He walked me back to my car, and quite sincerely added, "It's nice to find somebody that appreciates a championship tree!" And that I did! I must admit that I sneaked back the next morning to catch the morning sun illuminating its still majestic crown.
HOW TO MEASURE TRUNK CIRCUMFERENCE
1. Measure the distance around the trunk of the tree, in inches, at 4 ½ feet above ground level. This point is called the diameter breast height or dbh.
2. If the tree forks at or below 4 ½ feet, record the smallest trunk circumference below the lowest fork. Record the height at which the measurement was taken. Trees should be considered separate if the circumference measurement below the lowest fork places the measurement on the ground.
3. If the tree is on a slope, measure 4 ½ feet up the trunk on the high and low sides of the slope. The dbh is the average between both points. If the tree is on a steep slope, take the measurement at 4 ½ feet above the midpoint of the trunk.
4. If the tree is leaning, measure the circumference at 4 ½ feet along the axis of the trunk. Make sure the measurement is taken at a right (90 degree) angle to the trunk.
HOW TO MEASURE TREE HEIGHT
Measure the vertical distance, in feet, between the base of the trunk and the topmost twig. Height is accurately measured using a clinometer, laser, hypsometer, or other specialized tools. If these tools are not available, height can be estimated using the following “stick method.”
1. Find a straight stick or ruler.
2. Hold the stick vertically at arm’s length, making sure that the length of the stick above your hand equals the distance from your hand to your eye.
3. Walk backward away from the tree. Stop when the stick above your hand is the same length as the tree.
4. Measure the distance from the tree to where you are standing. Record that measurement to the closest foot.
HOW TO MEASURE THE CROWN SPREAD
Two measurements of the crown spread are taken and recorded, in feet, at right angles to one another.
1. Measure the widest crown spread, which is the greatest distance between any two points along the tree’s drip line. The drip line is the area defined by the outermost circumference of the tree’s canopy where water drips to the ground.
2. Turn the axis of measurement 90 degrees and find the narrow crown spread.
3. Calculate the average of the two crown spread measurements using this formula: (wide spread + narrow spread)/2 = average crown spread.
Every blogger knows the challenge. What shall I blog about next? What photos should I use? By the time the end of the year rolls around, there are always a few posts that never quite made it. And so, with this final post of the year, here they are from here and there. Please visit the same for 2013 here and 2012 here.
Pearls begin as foreign bodies within the mantle of a mollusk. The bivalve’s response is to secrete layer after layer of nacre (NAY-ker), a hard crystalline substance around the irritant for protection. The result is a pearl, which is similar in finish to the shiny inside of oysters and mussels, known as mother of pearl and can take 5 to 20 years to form (1 to 6 years for freshwater pearls). Light passing through the nacreous substance is reflected and refracted, which gives the pearl its luster and iridescence. This is because the thickness of the platelets of aragonite - a form of calcium carbonate (the other being calcite) - is close to the wavelength of visible light. Unlike gemstones that are cut and polished to bring out their beauty, pearls require no such treatment.
Finding a pearl is considered to be good luck, and looking back on this year, I would affirm that superstition.
|This is a High Dynamic Range photograph|
|This is a High Dynamic Range photograph|
It was from Quincy Granite’s unique mineral composition. The high percentage of alkali feldspar, as opposed to the plagioclase variety, affords the rock its dusty gray, greenish tint, aided by its variety of black quartz. Formed from the slow crystallization of magma some 450 million years ago when the micro-terrane of Avalon was in transit to Laurentia, the granite’s characteristic mineral of riebeckite, a brittle prismatic amphibole, allows the rock to achieve a high polish, in addition to its lack of micas. Quincy Granite was the rock that Willard sought - attractive, distinctive, stately, transports well, available, highly polishable and weather-resistant.
Thankfully, the natural beauty of the Palisades cliffs rising above the west bank of the Hudson has long been appreciated by generations of residents and visitors to the metropolitan area. But now, LG Electronics, a South Korean multinational electronics corporation, is planning to build an office tower that will rise high above the trees, and for the first time, violate the unspoiled ridgeline. Interested in preserving the Hudson River Palisades? Visit “Protect the Palisades” here.
to be a glass-bottomed boat sailing through a Late Cretaceous sea busy with life.”
|Big Brook at a slightly high water level as seen from the Hillsdale Road bridge facing east|
A WINDOW INTO A LATE CRETACEOUS CONTINENTAL SHELF
Step into the waters of this very ordinary-looking brook, and you’ll go back in time to North America’s continental shelf only a few million years before the Great Extinction that ended the Age of the Dinosaurs. In its lazy and short course to the Atlantic, Big Brook has carved a shallow, curvy trough through New Jersey's Inner Coastal Plain through the upper sediments of a Late Cretaceous paleoshelf. In so doing, weathering of the streambank provides a steady supply of fossils that are washed into the streambed.
Big Brook is one of the East Coast’s classic fossil-collecting localities with both amateurs and professionals alike. As early as 1863, the Smithsonian Institute in New York sent an expedition to explore and gather fossils from the brook and others within Monmouth County. Less widely appreciated amongst amateurs is that the strata through which Big Brook transects preserves an outstanding sedimentological record of the transition from an inner to an outer shelf environment during the Late Cretaceous as sea level rose.
APALEONTOLOGICAL GRAB BAG
A Late Cretaceous terrestrial fauna similar in some respects to eastern North America|
From National Geographic
The Late Cretaceous marine ecosystem teemed with life. |
In addition, abundant macro-invertebrate remains include brachiopods, bryozoans and molluscs (bivalves such as oysters, snails, belemnites and ammonites) and disarticulated arthropod carapaces and claws (lobster, crab and shrimp), all from the Late Cretaceous shelf ecosystem.
|The shelf's benthic and demersal zone was rich and diverse with brachiopods, bryozoans, molluscs and arthropods.|
From Matthew McCullough on Flickr and license here.
WHERE ARE WE?
Big Brook is barely 50 miles south of New York City via the Garden State Parkway off exit 109 west. The brook winds its way through the rural New Jersey hamlets of Colts Neck and Marlboro to the Navesink River near the borough of Red Bank, and ultimately the Atlantic Ocean. Besides Big Brook, other nearby fossil-bearing tributaries include Poricy Brook in Middletown Township, Ramanessin Brook in Holmdel and Shark River (Eocene and Miocene) in Neptune and Wall Townships. They're all located in gentrified and well-healed Monmouth County, which is in the top 1.2% of counties by wealth in the United States. The County's website advertises itself as the "Gateway to the Jersey Shore", while locals know it as Springsteen country (“…sprung from cages on highway nine…”).
|The arrow points to the location of Big Brook within Monmouth County.|
Modified from Roadside Geology of New Jersey
BIG PICTURE TECTONIC STUFF
Some sixty-seven million years ago, this lazy, oak-shaded stream and the surrounding countryside were a tiny submerged section of the newly-formed, Atlantic continental shelf. During the Late Cretaceous, global high seas drowned the shelf that now represents the broad, low relief of the Atlantic Coastal Plain through which Big Brook flows. But the geological story of the plain begins well before the Cretaceous.
Paleozoic tectonic convergence...
Beginning in the early Paleozoic, Laurentia - the rifted megacontinental sibling of the Late Proterozoic supercontinent of Rodinia - was converged upon by a procession of magmatic arcs, micro-continents and megacontinents and their intervening ocean basins.
Birth of Pangaea...
In a parade of orogenic events, they accreted to Laurentia's growing ancestral core - building mountains and adding crust with each collision. By the Pennsylvanian Period of the Paleozoic (below), their cumulative convergence had constructed the supercontinent of Pangaea and built a massive, centrally-located mountainous spine. By the Late Permian at the close of the Paleozoic, the mountains had been ravaged by erosion.
Demise of Pangaea...
In the Late Triassic, Pangaea’s fragmentation began. As the Atlantic Ocean began to open within the schism, the remnants of Pangaea's central mountainous spine began to fragment as well. A portion remained astride the Atlantic Coast in newly-formed eastern North America - today's Appalachians - while other remnants were carried across the globe on the backs of Pangaea's rifted siblings. Pangaea's breakup also endowed North America (and of course New Jersey) with a new passive shoreline characterized by seismic and volcanic inactivity, and most importantly, subsidence and sedimentation.
Subsidence and sedimentation of the Atlantic margin...
Beginning probably during Jurassic time, lithospheric cooling of North America's newly-formed passive margin, in concert with the weight of voluminous sedimentation, promoted rapid subsidence and provided a vast accommodation space for the accumulation of clastic erosive products. With subsidence, the Atlantic margin was broken into a series of faulted-blocks, which experienced differential movements.
Downward movement created embayments - deep indentations of the ancient shoreline in which sediments accumulated in greater thicknesses in greater water depths. Upward movement created structural highs, arches or uplifts - with thinner sequences and even the absence of deposition. One such coastal geo-indentation that would become a portion of the Coastal Plain - the Raritan embayment - influenced sedimentation in New Jersey between Staten Island at the western end of Long Island and Jersey's northern Coastal Plain.
Formation of the Atlantic Coastal Plain...
Concomitant with crustal cooling and subsidence, deposition in the coastal plain began in earnest in the Early Cretaceous with fluvial sedimentation from the highlands of the Appalachians. However, in the Late Cretaceous (below), marine incursions representative of global high seas flooded low-lying regions of the world that included the newly-formed, low-lying Atlantic coast.
Progressing from the shoreline seaward, gravel and sand on the inner continental shelf gave way to silt and clay, and, in progressively deeper water, glauconitic sand and silt. The deposits record a progressive but discontinuous and fluctuating rise in sea level - perhaps four in Late Cretaceous time and three in the Cenozoic. Thus, the landform of the Atlantic Coastal Plain gradually developed, representative of some 150 million years of sedimentation.
Of course, the flood waters of the Cretaceous have receded exposing the broad Coastal Plain on the eastern seaboard. Although global seas continued to vacillate, erosion became the dominant geological process through the Tertiary. Ice Age glaciers made it to northern New Jersey but not to the south, while the Coastal Plain continued to receive a thin and varied veneer of colluvial and alluvial Quaternary and Holocene debris. Today, the modern shoreline is 10 miles to the east of Big Brook as it lethargically dissects its way to the sea through Late Cretaceous sediments.
A COLORFUL TAPESTRY OF TERRAIN AND TIME
The Paleozoic collisions that assembled North America formed geomorphic provinces that are seen in the colorful mosaic of the Tapestry of Terrain and Time map by the USGS here. The yellow and tan Cretaceous and Cenozoic deposits of New Jersey (within the ellipse) illustrates the extent of the Coastal Plain within the state, which is continuous with that of the entire Atlantic and Gulf Coasts from Cape Cod and Long Island, through northern Jersey at Sandy Hook to southern New Jersey at Cape May, and down to Florida and around to the Gulf of Mexico. Let's take a closer look at the provinces of New Jersey.
The geomorphic provinces of Northeastern and Mid-Atlantic North America with New Jersey encircled. |
Modified from the USGS Tapestry of Time bedrock map located here.
NEW JERSEY’S GEOMORPHIC PROVINCES
For an area its size, New Jersey has a diverse geological history. From west to east, from the mountains to the sea, and across the multitude of orogens that formed eastern North America, New Jersey’s main geological subdivisions or provinces are the Valley and Ridge, the Highlands (equivalent to the familiar Blue Ridge down south), the Piedmont and the Coastal Plain.
By definition, the four geomorphic or physiographic regions are each unique as to relief, landforms and geology. Being inherited subsequent to the tectonic collisions that occurred throughout the Paleozoic, they're on strike from northeast to southwest in accordance with the direction of tectonic convergence. A fifth smaller province - in accordance with tectonic divergence - is the Newark Basin (green and red), which lies interposed within the Piedmont. It's a sediment-filled rift-basin, one of many along the east coast that formed during the initial stages of Atlantic opening in the Late Triassic and Jurassic.
THE COASTAL PLAIN
The Coastal Plain Province is relatively featureless, save a few gently undulating hills, and overlaps the rocks of the Piedmont Province to the west. It covers the entire lower half of New Jersey (see above map), dipping seaward from 10 to 60 feet per mile to the the southeast and extending beneath the Atlantic Ocean to the edge of the Continental Shelf at the Baltimore Canyon Trough. Its unconsolidated and compacted (but not cemented) sediments range in age from the Cretaceous to the Miocene. The composition of its bedrock and fossils confirms that it was submerged by Late Cretaceous high seas.
THE INNER AND OUTER REGIONS OF THE COASTAL PLAIN
The Coastal Plain is further subdivided into two regions. Because it was uplifted, weathered and dissected, the Inner Coastal Plain is higher in altitude than the Outer Plain but not by much. Its composition is largely a mix of quartz sand, glauconitic sand, silt and clay. This fertile agricultural zone gave rise to New Jersey’s nickname as the Garden State. It's also the location of Big Brook within Monmouth County. The Outer Plain is a region of lower altitude where low-relief terraces are bounded by subtle erosional scarps. It consists of Tertiary and Quaternary sand, and being acidic and less fertile, is the location of Jersey’s heavily forested cedar swamps and pine-scrub oak of the Pine Barrens.
THE MONMOUTH GROUP
As mentioned, in the Early Cretaceous the Coastal Plain region of New Jersey received deltaic and floodplain-derived (non-marine) sediments from the Appalachian highlands to the west. In the Late Cretaceous and into the early Paleocene, sea levels rose and flooded the coastal region in a series of transgressions over land and regressions back again. Layer after layer, sequence after sequence (packages of strata deposited during a single cycle of sea level rise and fall), sediments of the sea were laid down beginning with the earliest Late Cretaceous Raritan Bass River Formation upon the latest Early Cretaceous fluvial Potomac Formation (chart below).
In the late Late Cretaceous - from the Campanian into the Maastrichtian - the Monmouth Group, the state's youngest Cretaceous package, was laid down - a unit that is compacted but unlithified. New Jersey's Monmouth Group includes the basal Mount Laurel sand (5-60 feet thick), the transgressive marl of the Navesink (25-60 feet thick), the regressive silt and sand of the Redbank Formation (thin film to 100 feet thick) and the Tinton Formation's coarse quartzose and glaucontic sand (20-40 feet thick).
As the sea transgressed and regressed, shorelines moved accordingly. Existing sediments were eroded, reworked and redeposited, leaving behind unconformities. Breaks between sequences were punctuated by lag deposits or "shell beds." The great majority of fossils at Big Brook such as within the Navesink Formation, which we will visit, were eroded from lag deposits and released into the streambed. They were deposited within the neritic zone - the relatively shallow waters of the ocean from the littoral zone (closest to the shore) to the drop-off at the edge of the continental shelf.
|This map depicts the channel of Big Brook. The red arrow points to the car park on the north side of the Hillsdale Road bridge.|
Modified from the Bedrock Geologic Map of the Freehold and Marlboro Quadrangles, New Jersey, 1996.
TWO PORTALS TO BIG BROOK
|The bucolic Hillsdale Road bridge over Big Brook facing south|
The Department of Recreation and Parks of the Township of Colts Neck has determined that "there is an increasing need for the preservation of the many natural resources located within Big Brook Preserve. It has been observed that natural resources such as fossils have been taken from the park in large quantities. It has also been observed that certain other dangerous conditions continue to threaten the natural beauty, assets and environmental resources within Big Brook Park."
Therefore, "Fossil extraction is prohibited from the walls of the streambed above the stream waterline", and "No person may harvest more than five fossils per day." With all that in mind, you’re ready to “beachcomb” at Big Brook, panning and sifting for treasures buried within the streambed.
|The short path through the woods to Big Brook|
The Hillsdale Road bridge seen from Big Brook. |
The water level is somewhat high here, so the mudflats would be the best option for fossil-foraging.
|Seen here at high water, the brook's bed, gravel bars and mudflats are less accessible for foraging.|
|Geologic bedrock map of Late Cretaceous and Paleogene Formations of New Jersey's Inner Coastal Plain|
Modified from Zehdra Allen-Lafayette
|Standing directly in Big Brook's stream, this cut bank is within the Navesink Formation with a portion of the overlying Red Bank Formation. The voids are where large clusters of bivalves have avulsed (or were excavated) from the glauconitic matrix.|
|Close-up of a heavily bioturbinated and water-saturated Navesink bank with an iron-rich mineral seep.|
|A gravel bar alongside the streambed of Big Brook|
|A 35 mm long Scapanorhynchus anterior tooth|
|Shark teeth from Archaeolamna-Cretolamna (?) and Squalicorax|
|Top Row: Squalicorax, Odontaspis, Archaeolamna and Scapanorhynchus. |
Bottom Row: Two Squalicorax, Four unidentified and Enchodus.
|Vertebral centra from a shark and a ray|
|Calcitic rostra from belemnites|
|Diagram of a belemnite from ukfossils.co.uk|
Exogyra is an extinct genus of saltwater oyster, a common marine bivalve mollusc, that lived in great abundance within the benthic zone (just above, at and below the sediment surface) of the warm Cretaceous sea. Five species have been reported from New Jersey (C. cancellata, C. costata, C. erraticostata, C. spinifera and C. ponderosa), some of which are found at Big Brook. Exogyra and pycnodonte oysters are preserved in great numbers within the Navesink Formation's muddy glauconitic sands of Big Brook, typical of an outer shelf environment. Assemblages of the bivalves Exogyra, Pycnodonte and Agerostrea form biofacies horizons within the Navesink.
PYCNODONTE MUTABILIS WITH CLIONA CRETACICA BORINGS AND EXOGYRA
Another extinct Cretaceous saltwater oyster in the same family as exogyra, Pycnodonte is also a bivalve that is well represented at Big Brook. Many of the upper valves (referred to as "left") preserve the original shell coloration in the form of reddish brown radial bands, which are often discontinuous or offset indicating growth lines. The upper valve is strongly convex with concentric growth rings. Pycnodonte can reach up to 10 cm across.
Many modern oysters fall victim to predation from crustaceans such as lobsters and crabs, and gastropods. The oyster might survive the invasive attempts by continually accreting new shell layers. Back in the Cretaceous, the predatory sponge Cliona cretacica created trace holes by boring into Pycnodonte's shell (lower left). The shell on the right is the lower (or "right") valve of Exogyra.
|Top row are artifacts; bottom row are remnants of crustacean carapaces and claws.|
|Note the morphological similarities of Ophiomorpha from the Upper Cretaceous Blackhawk Formation of Utah to the burrows found at Big Brook.|
|A heavily bioturbinated and deer-trampled mudflat alongside Big Brook|
Most assuredly, there's a lot to experience and comprehend in the "piddly little dribble" of Big Brook.
OUTSTANDING SOURCES OF GEOLOGICAL AND PALEONTOLOGICAL INFORMATION
• Bedrock Geologic Map of Central and Southern New Jersey by James P. Owens et al, 1998.
• Bedrock Geologic Map of of the Freehold and Marlboro Quadrangles, Middlesex and Monmouth Counties, New Jersey by Peter J. Sugarman and James P. Owens, 1996.
• Big and Ramanessin Brooks by the New York Paleontological Society, Field Trip 2002.
• Callainassid, Burrowing Bivalve, and Gryphaeid Oyster Biofacies in the Upper Cretaceous Navesink Formation, Central New Jersey: Paleoecological Implications and Sedimentological Implications by J.B. Bennington et al, Department of Biology, Hofstra University.
• Cretaceous Fossils of New Jersey - Part I by Horace G. Richards et al, 1958.
• Cretaceous Stratigraphy of the Atlantic Coastal Plain, Atlantic Highlands of New Jersey by Richard L. Ollson, Department of Geological Sciences, Rutgers University, GSA Centenial Field Guide-Northeastern Section, 1987.
• Geology Map of New Jersey, Department of Environmental Protection, Geological Survey, 1999.
• Greensand and Greensand Soils of New Jersey: A Review by J.C.F. Tedrow, 2002.
• New York Paleontological Society. Established in 1970, individual and family memberships are open to all, regardless of education or previous experience, It's a fantastic way to visit Big Brook and many other fossil-collecting localities in the Northeast with an enthusiastic and well-informed group of amateurs and professionals. Meetings are held in the American Museum of Natural History in New York City and includes an outstanding newsletter. Visit them here to join. Yes, I am a member.
• Paleocommunities and Depositional Environments of the Upper Cretaceous Navesink Formation by J. Bret Bennington et al, Department of Geology, Hofstra University, 1999.
• Paleontology and Sequence Stratigraphy of the Upper Cretaceous Navesink Formation, New Jersey by J. Bret Bennington, Hofstra University, Long Island Geologists Field Trip, 2003.
• Pictorial Guide to Fossils by Gerard R. Case, 1992.
• Roadside Geology of New Jersey by David P. Garper, Mountain Press Publishing Company, 2013.
• Shell Color and Predation in the Cretaceous Oyster Pycnodonte Convexa from New Jersey by J. Bret Bennington. Hofstra University.
• Summary of Lithostratigraphy and Biostratigraphy of the Atlantic Coastal Plain by Richard K. Ollson, Rutgers University.
• Uppermost Campanian-Maestrichian Strontium Isotopic, Biostratigraphic and Sequence Stratigraphic Framework of the New Jersey Coastal Plain by Peter J. Sugarman et al, GSA Bulletin, 1995.
Mushrooms and toadstools. Mold and mildew. Puffballs and earthballs. Jellies and slime. Rusts and smuts. Stinkhorns and bloodfoots. The only thing more colorful than their names is their staggering diversity and bizarre biologies. This post is a continuation of the mycological mission I initiated in Part I (here), in which I discussed the lifecycle of the mushroom. In this final fungi post, I document some of the more remarkable specimens sprouting in my yard and down the street.
Amanita muscaria var. guessowii
“Esteemed by both maggots and mystics” (David Arora), this hemispherical-shaped, yellow-capped, conifer-loving beauty is known as the American Eastern Yellow Fly Agaric. The “fly” designation, according to one source, refers to its use in Eastern Europe as an insecticide, supposedly lethal to flies when mixed with milk.
The warts on the cap’s surface are remnants of the “universal veil”
that shrouded the juvenile mushroom as it germinated through the soil.
Amanita is a study in contradictions. While some are wildly hallucinogenic and delicious beyond compare, a few are the most toxic of all mushrooms with names such Death Cap and Destroying Angel. After the ingestion of a toxic Amanita, it can take a few days for symptoms to appear, which is particularly dangerous since its toxins insidiously demolish one’s kidneys and liver.
In his memoires, Voltaire recounted Holy Roman Emperor Charles VI’s death from eating sautéed amanita as, “The dish of mushrooms that changed the destiny of Europe.” Because amanita resembles several other edible species, fungiphile and author Arora warns, “When in doubt, throw it out.”
Of the 16,000 species of mushrooms identified by mycologists, the red and white-spotted fly agaric
is the iconic mushroom. It's often referred to as a toadstool due to its poisonous and psychoactive properties.
Like an annual time clock during the second week of August, dense clusters of bright orange mushrooms appear at the foot of an aging oak down the street. With the same regularity, my neighbor frustratingly digs up the crop in hopes of eradicating it, only to see it return the following year. Picking apples in an attempt to eradicate the tree is futile. As long as the "rooted" mycelium remains viable within the soil, the fungus will continue to spawn new mushrooms.
Mushrooms are fruiting through a crack in the sidewalk where the tree’s roots have barely broken the surface.
Omphalotus is also known as the Jack O’Lantern mushroom likely due to its pumpkin-color, although some sources attribute the name to its eerie property of neon-green bioluminescence. About 90 species of fungi glow in the dark along with certain bacteria, algae, marine creatures and insects such as the familiar firefly. Anyone can observe it in a forest on a dark summer’s night, although I’ve failed to photograph the phenomenon in my dark basement three years running.
Some references state that bioluminosity occurs at all stages of the fungi’s lifecycle, while others indicate that it only occurs in fresh specimens in which spores are still forming, so timing is critical. Light-emission is the result of oxidation involving an enzyme called luciferase. One theory is that insects receptive to the emissions are attracted to the luminescence, which assists in spore dispersal.
The mushroom caps start out flat but become centrally depressed, eventually becoming wavy and lobed.
Omphalotus is frequently mistaken for its lookalike, the prized chanterelle mushroom Cantharellus, a $1.5 billion global market, hence its occasional reference as False Chanterelle. The similarity is potentially hazardous, since chanterelles are highly edible and our Jack O’Lantern is deadly poisonous. Muscarine, its neurotoxin, produces GI symptoms, visual disturbances, irregular pulse and respiratory failure.
In Polish, there’s a phrase, "A sapper (field soldier) and a mushroom collector make a mistake only once." In spite of its toxicity, Irofulven, a chemically modified version of the mushroom’s toxin, is currently undergoing clinical trials as an anti-tumor agent.
With a delicate, pleated cap, many of the Coprinus mushrooms are extremely ephemeral, often lasting only a few hours in the morning. The reason is that its gills autolyse (self-digest) and deliquesce (turn to liquid) at maturity into a black, inky fluid that drips to the ground, hence their common name of Inky Caps. Autodigestion is a unique method of spore dispersal. As the spores at the mushroom’s periphery ripen first, the release of enzymes causes the cap to curl back spreading the gills and discharging the spores into the air. What’s left is a ragged stalk.
The autodigestive-spore releasing process is recalled in Shelley’s memorable lines of The Sensitive Plant:
Till the thick stalk stuck like a murderer’s stake;
Where rags of loose flesh yet tremble on high,
Infecting the winds that wander by.”
This leathery bracket fungus is primarily a pathogen of spruce forests but also infects other evergreens. It was fruiting in my back yard at the base of a tall, old spruce. It’s frequently associated with infections of tree roots and their mortality. Last year, I cut down two nearby spruces and wonder if this one will be next. The fungus is often associated with spruce beetles.
In New England, it’s very common to find massive, slow-growing, beeches on the grounds of stately old homes, churches and cemeteries, planted for their dense shade and botanical grandeur. For years, this thin-barked beech up the street began to host an array of huge bracket fungi on its south-facing side. Passersby couldn’t resist stopping for a look. I took the presence of the fungi as an indication of ill health. Sadly, this summer the majestic tree suddenly became leafless and was cut down. It left a huge void both on the ground and amongst the canopy of the surrounding trees.
Appearing somewhat near the base of the tree, the polypore is gray to brown in color, and often green with algae. They are also called Artists’ Conks since lasting pictures can be carved onto their undersurface. When they fruit on live trees, they are often parasitic and allow insects and woodpeckers to invade the bark.
Its layers are an indication of its age. A large specimen can liberate up to 30 billion spores a day for 6 months of the year. Multiply that by its age of about 10 years for the polypore seen below! High spore production illustrates the mathematics of survival, since most spores fall upon a nutritionless, hostile substrate.
Like Ganoderma, this Red-Banded polypore is a common, perennial bracket fungus that was boldly attached to another spruce in my back yard. Its concentrically grooved bands of yellow to orange and red, its thick pizza crust margin, and its resin-coated surface make it both hard to miss and misidentify. Its preference is dead wood (conifers in particular), rotting logs and stumps rather than live trees.
This Earthball, along with related puffballs, earthstars, bird’s nest fungi and stinkhorns, produces its spores inside the fruitbody rather than on the undersurface of mushrooms. At maturity, the fruitbody ruptures, such as during a rain, exposing a purple-brown spore-mass, freeing the spores to inoculate the wind. Unlike puffballs that develop an aperture through which the spores escape, earthballs break up to release their bounty.
This spherical yellow-brown Earthball with its ornately decorated, raised mosaic pattern was fruiting in the woods in my neighborhood. They’re all classified as Gasteromycetes or “stomach fungi.”
Fusicolla merismoides (possibly)
Also in the woods, this amoeba-like slime mold appeared after a soaking summer rain. The gelatinous oozing, vomitous blob looked like something out of a B-movie. Slime molds (mould is the British version) produce spores and thus were formerly classified as Fungi, but many taxonomists consider them as protists (see post Part I for a taxonomic explanation here). Since mycologists traditionally group and discuss them with fungi, so have I, especially since they appeared along with the mushrooms this summer.
Typically found on soil, lawns, mulch and on the forest floor where shady and damp, they can travel several feet and climb any object to feed on microorganisms that live on dead plant material such as bacteria and fungi, and contribute to its decomposition. The slime searches for a host, surrounds it, and then secretes enzymes to digest it. Protoplasm at the cell’s periphery creates a type of movement called “shuttle streaming.”
Slime molds, while brainless, are smarter than they look. Amazingly, some are capable of navigating and solving an agar maze in search of food. This display of “intelligence” occurs by anticipating thermal changes at predictable time intervals. When it’s time to fruit they even migrate to a more desirable site for spore dispersal, often quickly at night to minimize the risk of dehydration. Despite being a single cell, each part of the plasmodium reacts to environmental information independently. By combining the reactions, the mass responds without even a conscious thought. “Nothing can stop it!”
The yellowish, bile-colored Dog Vomit (or Scrambled Egg) slime mold was believed to be used by witches to spoil their neighbors’ milk. I found this specimen hiding under a rotting log in a nearby woods. Like the slime above, the amoeboid mass migrates in search of nutrients. Under adverse conditions such as dryness or cold temperatures, the slime can form a hardened, resistant structure called a sclerotium, which is capable of reforming and reinitiating its protoplasmic exploitations.
Its yellow pigment, fuligorubin A, chelates metals and converts then into inactive forms, which accounts for the slimes high resistance to toxic levels of metals (up to 20,000 ppm). The pigment is also thought to be involved in photoreception for purposes of energy. Not that you’re tempted, but it’s inedible.
Genus Ramaria (possibly)
Another member of phylum Basidiomycota, coral fungi come in many colors, and many are tasty. The fruitbody is densely branched and fruits on the ground in woods. Although related to mushrooms and not the marine animal for which they resemble, corals bear no anatomical likeness to mushrooms. But like the undersurface of mushrooms’ caps, their many branches provide a high surface area for the basidia, the spore-producing structure of the fungus, similar to mushroom’s gills, pores, teeth and folds (see Part I).
There are many forms of coral fungi, originally lumped into one unwieldy genus. Now there are over 30 genera, looking coral-like due to convergent evolution.
My “Neighborhood Fungus Watch” wouldn’t be complete without mention of the ubiquitous gray-green rosettes on trees, tangled masses of hair suspended from branches, miniature goblets on the ground and yellow-orange crusts on rocks. Lichens are neither plants nor single organisms but are “miniature ecosystems” (Hinds).
They are a partnership of two, and sometimes three, lifeforms that coexist as one for their mutual benefit. It’s a symbiotic association between a species of fungus (the mycobiont) and a species of photosynthetic algae (a photobiont, usually Trebouxia).
The algal component is either eukaryotic green algae or prokaryotic blue-green algae (explained in Part I). With over 14,000 species to date, lichens are classified within Kingdom Fungi based on the Latin name of the fungal partner (which is usually an Ascomycota or “cup” fungi), since the relationship is largely fungal (90%). Therefore, lichens are often referred to as “lichenized” fungi. Most of the vegetative body of the lichen, called the thallus, is formed by the fungus.
The algal component lives not within the actual cells of the fungus but sandwiched within the body of the fungus (the medulla) between the upper and lower fungal cortex. Anastomosing hyphae form a loosely arranged network that are in communication with the algal cells. Strands of root-like hyphae (rhizines) attach the lichen to the substrate.
Schematic cross section through the thallus (body) of a flat, leaf-like (foliose) lichen.|
The algal member provides energy to the fungus in the form of manufactured simple carbs such as glucose or sorbitol. In return, the alga gets a happy home with a favorable microenvironment from desiccation, protection from excessive UV radiation and mineral nutrients from the attachment-substrate and the atmosphere. Most vascular plants would be incapable of populating the lichen’s exposed, inhospitable, nutrient-poor habitats.
Therein lies the enigma of lichens! They are the hardiest of “plants” capable of surviving arctic cold, desert heat and extreme drought. In a 2005 test, lichens even survived 15 days of exposure to the vacuum of space on a Russian rocket. Yet, they are incredibly sensitive to pollution since they absorb water and nutrients from the air. Devoid of lichens, industrial regions of the world are referred to as “lichen deserts.” In my nearby Boston, you don’t start seeing lichen-covered rock walls until several miles from the city until reaching the “clean air” of the suburbs. Thus, lichens are bio-indicators of air quality. There's even a profound association between lichen presence and a reduced risk of lung cancer. Another reason to look down at the ground!
Lichens are divided into groups or growth forms based on modes of substrate attachment. The three most common are: crustose (crust-like), foliose (leaf-like) and fruticose (long and hairy often with cups).
|Evernia prunastri is an antler-like fruticose (hairy), “oakmoss” lichen that favors growth on decaying oak.|
They are commercially harvested in Europe and sent to France for their fragrant compounds used in perfumes.
Amazing lichen facts that your friends probably don’t know:
1.) Lichen symbiosis may have been one of the first steps in the colonization of land. In the Precambrian, lichens may have lowered CO2 levels sufficiently to plunge the Earth into global glaciation typified by Snowball Earth between 750-580 Mya. Their eventual terrestrial colonization may have raised the atmospheric O2 levels enough to permit the Cambrian Explosion.
2.) Lichens can physically weather a granite substrate by penetrating intergranular surface boundaries, voids and cleavage planes. The swelling and contraction of hyphae can then break up the rock. They can chemically weather granite by leaching out potassium and iron. On calcareous (limestone) rocks, lichens produce weak acids that dissolve the substrate.
3.) Beatrix Potter, the celebrated author of Peter Rabbit fame, was a pioneering mycologist who studied and experimented with fungus germination under the microscope as early as 1887. She published Les Champignons on fungus and lichens with over 65 original, watercolor drawings. Her scientific fungal paper was read by a male colleague before the men-only Linnaean Society of London, but it was rejected from publication because of her gender. Fortunately for children everywhere, her artistic talents found creativity elsewhere.
4.) Fungi and algae, although capable of forming an intimate partnership, are totally unrelated phylogenetically. Fungi and humans share a common ancestor and are more closely related. One would expect that all lichens are more closely related than they would be to other fungi. Instead, the lichen partnership has evolved a myriad of times, because the DNA and genes of different lichen species are more closely related to non-lichen fungi than they are to other lichen. (Gargas et al, Multiple origins of lichen symbiosis in fungi suggested by SSU rDNA phylogeny. Science 268: 1492-1495, 1995).
In spite of ourselves.
Our kind multiplies:
We shall by morning
Inherit the earth.
With great appreciation, I thank professional mycologist Taylor Lockwood and amateur “mushroom expert” Michael Kuo for their expertise in identifying many of the more obscure mushrooms in my neighborhood. Their respective links are below.
VERY INFORMATIVE PUBLISHED RESOURCES
Kingdom Fungi by Steven L. Stephenson
Macrolichens of New England by James W. and Patricia L. Hinds
Mushroom by Nicholas P. Money
Mushrooms Demystified by David Arora
Mushrooms of Northeast North America by George Barron
Mushrooms, Simon and Schuster’s Guide by Gary H. Lincoff
VERY INFORMATIVE LINKS
Tom Volk here
Michael Kuo here
Michael Wood here
Taylor Lockwood here
North American Mycological Association here
Virtually every geology-based road trip I've been on has had its share of unforgettable side trips, off beat detours and unplanned turn offs. The best part, second to the geology, was the adventure of the unexpected and the inexplicable waiting at every turn.
That’s when you see the unusual signage, the eccentric pieces of art, the unique architecture, the kitschy sculptures, the cheesy tourist stops, the poignant juxtapositions, and all the wacky, tacky, bizarre and oddball attractions that are so characteristic of Roadside America. It’s also when you find remnants of vanishing America - the diners, drive-ins, juke-joints and storefronts that have been thoughtfully preserved or recklessly abandoned to the ravages of time.
Here's what I stumbled on this November while traveling with my friend and geologist Wayne Ranney on the roads and backroads between Phoenix, Arizona and the Mexican border. This is my third post in this series in what has become a tradition following our geological excursions. The other two may be found in the "Index to Topics" in the column to the right under "Roadside America."
Literally across the street, beer and chicken headline a newer version of the menu today. Nothing gets my digestive juices flowing more than an enormous chicken alongside my table.
This "masthead" decorates one corner of the building.|
This demising wall across the street was intensely muralled. Notice the graffiti proclaiming "Old Bisbee."|
And this creative gallery sign was next door. The "Five C's" of Arizona's economy are: Cattle, Copper, Citrus, Cotton and Climate. Bisbee deserves a sixth "C" for Creative.|
Here's a 60's mega food-sculpture in newer Bisbee, down in the flats below the Lavender Pit mine.|
Bisbee is the nation's southernmost mile-high city.
Believe me now?|
When was the last time you saw a gas pump that looked like this? That's glass not plastic!|
In far southern Arizona, this sign was a first for me. Any guesses precisely where we are?|
Here's a hint.|
We're in Naco, Arizona, at the Border Fence or Wall between Mexico and the United States. 96.6% of apprehensions along the 1,951-mile border between the two countries occurs along the country's southwest boundary and traverses a variety of terrains including urban areas and deserts. The barrier strategically exists where illegal crossings and drug trafficking have existed in the past. In addition to the physical barrier, a "virtual fence" of motion sensors and video cameras watches everything and everyone that moves. Note three of them on tall poles down the road. We counted over two dozen white Border Patrol vehicles on maneuvers in one hour. Critics in Arizona and Texas assert that the fence adversely isolates endangered species in critical migration corridors and jeopardizes fragile ecosystems much the way roads and canals have compartmentalized the Florida Everglades (recent post here). In 2010, a Rasmussens Reports survey indicated that 68% of Americans are in favor of the U.S.-Mexico Border Fence.|
Right next door was an antique railroad car gradually decomposing into the landscape.|
You never know what you're gonna find.
Back in Tucson, after a 1,300-mile geological road trip and mystery tour, we got an early start to investigate the metamorphic core complexes that encompass the valley. I did a double take at this raptorian red light.|
In the Tucson Mountains west of Tucson, Arizona, lies the unsuspecting rocky outcrop of Signal Hill. Just a short hike from the scenic Bajada Loop Drive through the Sonoran Desert in Saguaro National Park West brings you to the hillock’s rubble-covered crest of sun-baked boulders where a millennium-old gallery of petroglyphs (Greek for "stone-carvings") is on display.
Members of the pre-Columbian Hohokam (HO-HO-kam) created the rock renderings with a stone and hammerstone. By chipping, incising and abrading through a micro-thin, dark coating of desert varnish into the lighter, underlying rock, they fashioned images commonly called rock art. Leaving no written history, the images afford us an opportunity to look into the past and gain insight into the Hohokam's lives and thoughts.
|This High Dynamic Range photograph centers on a one-foot diameter Hohokam spiral geometric.|
"THOSE WHO CAME BEFORE"
The Hohokam people thrived in central and southern Arizona from about 400 to 1450 AD. They were farmers, hunters and gatherers, who built over 1,000 miles of elaborate canals in the Phoenix area and cultivated crops of corn, cotton, squash and beans. In the region of Signal Hill, they occupied the river valleys and deserts between the Tucson Mountains and the Rincons.
After thriving in the Sonoran Desert for over 1,000 years, Hohokam society began to decline and collapse over the course of several generations. During the Protohistoric Period, between the Hohokam occupation and Spanish contact, the area appears to have been occupied by Sobiapuri (Upper Pimam) and Tohono O'odham people.
When Spanish explorers arrived in the 1500's, they found Hohokam villages in ruins. Their fate is both controversial and mysterious, whether related to droughts, soil depletion, warfare, disease or internal strife. Archaeologists that search for clues also look for direct links to indigenous Native Americans like the O’odham Nation that practice Hohokam’s desert traditions such as the annual saguaro cactus fruit harvest.
COMMUNICATION, DECORATION OR CULTURAL REFLECTION?
The Hohokam’s petroglyphs at Signal Hill are reminiscent of life forms such as snakes, lizards, bighorn sheep, dogs, plants and stick-figure humans, but the majority are abstract geometrics of circles, spirals and lines. Their meaning remains unknown, whether pre-historic graffiti, artistic, symbolic conveyance of a message to passersby or their descendants, astronomical, religious or ceremonial. Perhaps their significance lies in the very act of creating the images rather than the message they convey.
|Petroglyphs litter the crest of Signal Hill seen from the trail|
PETROGLYPHS AND PICTOGRAPHS
Found throughout the Southwest, and in fact worldwide, desert varnish is the canvas on which many Native American cultures engraved their rock art. Pictographs are often confused with petroglyphs, which are literally drawn or painted on rock faces with naturally-occurring pigments made from clays and minerals. Pictographs are not as durable as petroglyphs unless located in protected settings such as rock shelters or caves.
Desert varnish is typically found on resistant rock surfaces that are subjected to periodic wetting and drying in arid regions of the world. "Rock" varnish is a more appropriate term, since it also occurs in tropical, arctic and alpine environments. Its coating ends with an abrupt boundary on rocky substrates. The sharp demarcation is suggestive that it is derived from external sources. A long standing debate exists as to whether the varnish's formation is microbially-mediated, deposited by inorganic processes or more likely a combination of biological, physical and chemical processes.
Micro-fungi have been cultured from the varnish, but it remains unclear whether fungi or bacteria precipitate the varnish or if microbial components complex with metals in the varnish-forming process. It has been theorized that the varnish’s thin patina protects underlying microbes from exposure to desiccation and UV radiation. The following schematics summarize three popular models for the formation of desert varnish.
Numerous chemical elements are found in varnish but predominantly clays and oxides of manganese and iron, making it appear black and reddish-brown, and at far greater levels than the neighboring substrate and soils. Mixtures of oxides are responsible for intermediate shades of brown. The varnish is almost as hard as quartz and yet extremely thin, commonly a hundredth of a millimeter in thickness (<200 µm).
It takes thousands to tens of thousands of years to coat a rock with varnish in the arid conditions of the Southwest with growth rates from <1 to 40 µm per thousand years. That qualifies desert varnish as the slowest forming terrestrial sedimentary deposit! Varnish's structure appears micro-laminated in microscopic cross-section, reminiscent of a stromatolite's onion-layered macro-stratification.
Attempts to utilize varnish for paleo-dating have proven unreliable; however, its usage as a paleo-climate indicator does shows promise. Incidentally, varnish may have planetary analogues, Mars in particular, which has fueled speculation of its potential usefulness in the search for life on other planets.
The bedrock rock type in the immediate region of Signal Hill is granodiorite, a coarse-grained, intrusive igneous rock intermediate in composition between granite and diorite. These rocks were generated within a volcanic caldera, a collapsed magma chamber, at the end of the Cretaceous from a subduction zone (Sevier-Laramide compression) at the continent’s western margin, a time when at least seven volcanoes were active in southeastern Arizona.
Long after the cessation of volcanic activity and related to continued plate subduction with an altered geometry around 30-35 million years ago, extension (pulling-apart) and heat from within the Earth's crust separated the landscape into linear ranges with intervening basins. Portions of the extinct caldera were faulted upward into a range, the Tucson Mountains, while other portions dropped into the nearby basin and were covered by basin fill sediment.
Brittle, faulted-blocks of the Tucson Mountains represent an unmetamorphosed “upper plate” (not to be confused with a tectonic plate) of an arched "metamorphic core complex." Complexes are enigmatic, controversial and only recently described geologic features of Arizona’s Basin and Range province. The Tucson-upper plate slid off (detached) from the “lower plate” along an intervening, near-horizontal “detachment fault”, which bowed upward into a blister-like uplift.
Uplift occurs in response to tectonic denudation (i.e. erosion) and the inflow of hot, middle crust. Portions of the lower plate are exposed by erosion and others lay buried within the Tucson basin (called a graben, German for grave). The metamorphic core of the “lower plate”, stretched and deformed plastically rather than brittlely, forms the Santa Catalina Mountains across the basin. These domal uplifts are not confined to the Basin and Range of Arizona but follow a sinuous belt from southern Canada to northwestern Mexico.
A CELEBRATION OF SONORAN LIGHT
The ruggedness and colors, the distinctive look and feel, the topography and climate, and the rocks exposed in Saguaro National Park West are a compendium of the state’s billion year-plus geologic history. On our return hike from Signal Hill, the setting sun and rising moon, the billowy clouds and blue sky, the saguaro and prickly pear, and the spirits of the Hohokam were in exquisite balance. Please enjoy the following photos as our day gloriously gave way to night.
|High Dynamic Range digital photograph|
Every blogger knows the challenge. What shall I blog about next? What photos should I use? By the time the end of the year rolls around, there are always a few posts that never quite made it. And so, with this final post of the year, here they are from here and there. Please visit the same for 2012 here.
Flying High Above Boston’s West African Harbor Islands
On an Appalachian-Derived Beach at Fort Lauderdale
Living Cretaceous Fossils in Bloom in Boston’s Backbay
Luxuriating in the Grenville-Age High Peaks of the Adirondacks
A Summer’s Wade in the Late Cretaceous Marl of Big Brook
Monster Mushrooms in Chestnut Hill, Massachusetts
My Lofty Visit to an Alpine Bog in New Hampshire
High Atop Laccolithic Katahdin in the Remote North Woods of Maine
The Remnants of Historic Fort Bowie within the Apache Pass Fault Zone
Oblivious to most passersby alongside Beacon Street, a major thoroughfare out of Boston, is a cross-section of an ancient streambed embedded within a cliff wall. The stream bed appears as a semi-circular channel outlined perfectly by fallen leaves. The transected bed and its banks consist of fine-grained, thinly-bedded, fissile (easily split along its planes) siltstone (mud rock) that displays a large infill of conglomerate rock over its entirety. The siltstone preserves the contours of an ancient landscape that was buried by subsequent deposition.
Upon close inspection, laminations within the streambed display whorls of sediment indicative of stream turbidity currents and slump features indicative of settling. The manmade wall at the top is composed of stacked conglomerate boulders.
The flat-lying rocks of the entire assemblage, being sedimentary, were deposited horizontally under the action of gravity. Subsequent to their deposition, compaction, cementation and lithification (conversion to solid rock), the assemblage and the rocks in the region were tilted by tectonic forces, which accounts for the angulation seen in the photo. These rocks belong to the Roxbury Conglomerate, a 2,000 foot thick formation of coarse arkosic sandstone with small to medium-size, rounded clasts (rounded fragments of stones). In 1830, the American poet Oliver Wendell Holmes likened the Roxbury to puddingstone, its common name, since it reminded him of raisins in English bread pudding.
The puddingstone's sandy matrix and rocky inclusions indicate they were deposited in a high-energy depositional and/or transport system such as a cascading mountain stream or a massive submarine flow. The Roxbury is exposed almost everywhere in the neighboring towns to the west and southwest of Boston. The channel's siltstone is a facies change, a clastless sediment within the Roxbury Formation. Along with the Cambridge Argillite (or Slate), the Roxbury Conglomerate comprises the sedimentary strata of the Boston Bay Group. As mentioned in the first vignette at the top of this post, the group was deposited on the microcontinent of Avalonia in an extensional regime, such as a faulted rift basin in Late Proterozoic-time between 595 and 540 million years ago.
Avalonia originated as an elongate volcanic island chain along the edge of the megacontinent of Gondwana, possibly of West Africa cratonic provenance in the southern hemisphere. Avalonia’s deeper basement is volcanic in origin, and, in the vicinity of the Boston Basin, they include the Brighton, Dedham, Mattapan, Lynn and Westwood granites, which underlie the rocks of the Boston Bay Group. During the Acadian orogeny, Avalonia welded to the continent of Laurentia about 370 million years ago. Can't get enough of the Roxbury Conglomerate? Check out my previous post here.
The "unnoticed" streambed is an example of my masthead statement at the top of my blog. "Geology is all around us, scarcely thought of as we go about our lives." Perhaps I should add, "but not by all of us!"
|High Dynamic Range digital photograph|
WELCOME TO BAKER'S BRIDGE
If you follow the Animas River some 14 miles upstream from Durango, Colorado, you’ll arrive at Baker’s Bridge in the southern foothills of the San Juan Mountains. The short bridge traverses the amazingly green-hued waters of small but strikingly scenic Animas Gorge, formed by erosion-resistant, varnish-stained walls of pale brownish-red Bakers Bridge granite. The region's beauty is a compendium of almost two billion years of geological evolution.
|Animas Gorge from atop Baker's Bridge looking north|
On this hot summer’s day throngs of locals were sunning, swimming and jumping from the bridge in what has been described as a right of passage in these parts. Chances are you won't notice (I didn’t) that this locale was used in the filming of the escape scene in the 1969 movie "Butch Cassidy and the Sundance Kid." The two leaders of the Hole-in-the-Wall Gang are cornered on a cliff by the approaching posse and make a dramatic, expletive-echoing leap to freedom from a ledge of Bakers Bridge granite into the Animas Gorge.
Camera magic made the cliff appear higher than it really is, as Robert Redford and Paul Newman leaped into the Animas, purportedly photographed somewhere in California. Hollywood has never been concerned with geological correctness, as every geologist knows. Here’s the jump scene from the movie. Check out the Bakers Bridge granite.
|Robert Redford and Paul Newman making a leap from Bakers Bridge granite|
THE GREAT UNCONFORMITY AT BAKER'S BRIDGE
We're not here for a photo op or to take the plunge. A stone's throw from the bridge, our draw is geological. Where Precambrian and Paleozoic rocks are in contact, there exists a temporal discontinuity or gap in time of enormous proportions. It's on the order of 1.2 to 1.3 billion years - 25% of the earth's history missing from the geological record. It's called the Great Unconformity, distinguished with capital letters by geologists in honor of its immensity. It's at Baker's Bridge, yet it exists globally, providing you know where to look.
|The Great Unconformity at Baker's Bridge just west of the gorge|
The Great Unconformity at Baker's Bridge spans the contact between underlying medium to coarse-grained igneous rock of late Early to early Middle Proterozoic (~1700 Ma) Bakers Bridge granite. Above the contact are marine sandstones of the Upper Cambrian(?) Ignacio Formation, the Tapeats sandstone equivalent found in the Grand Canyon and on the Colorado Plateau. The question mark denotes uncertainty on the part of geologists concerning the Ignacio's age at the time of deposition. More on that later.
SO WHO WAS BAKER?
Charles Baker arrived in the region with one thing on his mind - mineral wealth, but he wasn't the first to seek his fortune in the San Juans. El Dorado-seeking Spanish explored for gold deeply into the mountains during the eighteenth century, evidenced by their abandoned openings and discarded prospecting tools. In 1860 and 1861, Charles and his mining party established camp on the Animas River's east side. They called it Animas City (not to be confused with the later-named suburb of Durango) and built the first Baker's Bridge of logs across the narrow gorge.
|Charles Baker's bridge of logs across the Animas River (c. 1898 photograph)|
From The San Juan Highway by Frederic B. Wildfang
Unfortunately, the prospectors found little placer gold. Deterred by hostile Utes, extreme winter hardship and the Civil War looming, the group disbanded. Charles went back east to join the Confederate forces and achieved the rank of captain. Charles returned after the war only to be killed by Utes while preparing to lead a party into the Grand Canyon. So the story goes.
The 1870's witnessed a rush for gold in the San Juan Mountains upstream in Baker’s Park, where rich lodes were discovered. Through the 1890's, silver reigned as the predominant metal. Legend has it that Charles' cache of gold is buried somewhere in the hills around Baker's Bridge. The following memorial at the bridge recalls his trials and tribulations. The contemporary concrete bridge was built in the 1930's.
|Memorial to Captain Charles H. Baker framed in Bakers Bridge granite|
Erected by the State Historical Society of Colorado
THE GRANDEST GREAT UNCONFORMITY
Discussions of the Great Unconformity invariably begin or end with mention of the spectacular display within the Inner Gorge of the Grand Canyon in northern Arizona. The contact exists between 1.7 billion year-old Early Proterozoic Vishnu Schist and overlying 525 million year-old Cambrian Tapeats Sandstone - 1.2 billion years of missing time. In Annals of the Former World, Pulitzer Prize-winning author John McPhee states, "More time is absent than is represented. If a gap of five hundred million years were the right five hundred million years, it could erase the Grand Canyon."
|The Great Unconformity within the Grand Canyon's Inner Gorge|
The time gap within the contact is 1.2 billion years, more time than it took to form all of the canyon's layers.
John Wesley Powell, Civil War general, geologist, explorer and head of the U.S. Geological Survey, documented the Great Unconformity during his first trip through the Grand Canyon in 1869, but at the time couldn't have fully appreciated its enormity and age. We know a great deal more about the events associated with it, yet since its recognition the Great Unconformity has remained something of an enigma. Scientists enjoy torturing themselves with questions about how it formed and what happened during the long interval geologically and biologically.
The passage of time is recorded in the rock record with deposition that might seem to occur without interruption, layer upon layer in a continuous sequence. But our dynamic planet forms new layers of rock at its surface with fits and starts, while older ones are inexorably worn away, and later redeposited upon. As a result, a hiatus or interruption within the rock record is the norm and is measured by missing time. Time isn't really missing; the anticipated rock layers are.
Gaps in the rock record are called "unconformities" and represent rock layers that either never formed or were eroded away. The "interruption" in the depositional sequence brings strata into contact of different ages. Many are long-term gaps - tens of millions to hundreds of millions of years. The vastness of the Great Unconformity qualifies it as a unique geological entity, but as we shall see, not just because of its size.
Knowing how the gap in the rock record formed may provide important clues about crustal activity or movement such as uplift, erosion and subsidence. Thus, the "time gap" can be of tremendous geological value...even biological value!
THOSE THAT CAME BEFORE AND LOOKED INTO THE ABYSS OF TIME
Horizontal strata resting atop the eroded edges of inclined strata was recognized in the early 1700’s as an indication that a significant period of erosion and non-deposition had occurred before the younger formation came to bury the older formation. In 1788, James Hutton of Scotland, the "Father of Modern Geology," looked into the abyss of time at the angular contact at Siccar Point along the northeast coast of Scotland, arguably one of the most important geological sites in the world. He described it as “a beautiful picture of a junction washed bare by the sea” and envisioned the process as an endless succession of deposition “with no vestige of a beginning, no prospect of an end,” a famous phrase in geology.
The contact gave evidence to Hutton that deep burial of an erosion surface had occurred after prolonged erosion. His vision was limited to the realization that uplift had raised the land and was unable to see the mountains that had once existed. It wasn’t until 1805 that Prof. Robert Jameson of Edinburgh University called the surface separating two discordant formations an “unconformity.” Since then, American geologists expanded upon the entity, adding new definitions and interpretations.
THREE FLAVORS OF UNCONFORMITIES
Geologists categorize an unconformity based on the strata that embrace the contact above and below. Disconformities are found between horizontal sedimentary layers. Angular unconformities are between underlying metamorphosed, tilted and uplifted strata and overlying horizontal strata. Nonconformities are between younger, overlying sedimentary rock and older, underlying igneous or metamorphic rocks. At Baker's Bridge, igneous and metamorphic rocks below the Great Unconformity and sedimentary rocks above identify the contact as "nonconformable."
|The three types of temporal stratigraphic gaps|
SO WHERE IN COLORADO IS BAKER'S BRIDGE?
Baker's Bridge resides in southwest Colorado in the southern foothills of the San Juan Mountains, whose area embraces about 12,000 square miles, the combined size of Massachusetts and Connecticut. The San Juans are a high and rugged range of the Southern Rocky Mountain province that geologist and author Donald L. Baars refers to as the "American Alps."
Replete with alpine crags, glacially carved valleys and deep canyons, many of the peaks in the central San Juan's exceed 13,000 feet, and a few exceed 14,000. Composed of erosion-resistant granitic and quartzitic rocks, the range falls within the Colorado Mineral Belt, an area with abundant ore deposits, notably gold, that played an integral role in the region's settlement history. The San Juan Mountains contain numerous sub-ranges such as the Needles, the Grenadiers and the La Platas.
The San Juan Mountains possess an extremely complex history, beyond the purview of this post to elucidate. Simply stated, they are the erosional remnant of a large composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time, about 30-35 million years ago, in Colorado and adjacent parts of New Mexico. Notice Baker's Bridge (red dot) in the foothills.
THE SAN JUAN MOUNTAIN'S RELATIONSHIP TO THE COLORADO PLATEAU
Beginning in the latest Jurassic, subduction of the oceanic Farallon plate beneath the North American plate was responsible for east-directed compression that added crust to western North America. With ongoing subduction, compression wrinkled the Rockies skyward and uplifted the Colorado Plateau en masse, a physiographic province with minimal deformation and a handful of small volcanic intrusions in the region of the Four Corners.
Triggered by a change in the geometrics and speed of Farallon descent into the mantle during the Tertiary, extension followed compression. Still intact internally, the Colorado Plateau's surrounding regions were extensively faulted, intruded by pluton-forming magma and covered by volcanic deposits. The outcome on the landscape was the formation of the Basin and Range province and the generation of voluminous lava on three sides of the Colorado Plateau, one of which was within the San Juan Volcanic Field on the east.
Today, the eastern boundary of the Colorado Plateau (wide black line) makes a curious skirt to the west to exclude the uplifted igneous and metamorphic rocks of the San Juan Volcanic Field (red). In Plateau Magazine (Volume 6, 2007), geologist and author Wayne Ranney states, "It is interesting to note that these volcanic deposits were erupted upon and rest on a Plateau-like surface; prior to 30 million years ago, the area of the present-day San Juan Mountains could have been considered a part of the Colorado Plateau.
If it wasn't for late Cretaceous plutonic and late Tertiary volcanic activity that typifies the region, the San Juans would likely be included within the Plateau's eastern boundary. If you know the Colorado Plateau's Precambrian basement and its Paleozoic through Mesozoic stratigraphy, the rock units at Baker's Bridge will be fairly familiar. Later in this post, we'll briefly tap into that knowledge base for our discussion of the Great Unconformity at Baker's Bridge, in particular the strata that formed above the unconformity. First, let's visit the river that flows through Baker's Bridge.
"THE RIVER OF LOST SOULS"
Perhaps prophetic, Spanish explorers in the mid-1700's named the river El Rio de las Animas Perdidas. Its 126-mile descent headwaters at an elevation of 11,120 feet in the mining ghost town of Animas Forks, over forty canyon-cut, river-miles upstream from Baker's Bridge in the heart of the San Juans. Fed by a host of tributaries, the Animas watershed drains much of the southwestern San Juans.
LAS ANIMAS CAÑON
As the Animas courses south towards Baker's Bridge, its gradient varies from moderate to steep, slicing through narrow, forested canyons carved into the San Juan's erosion-resistant granites and quartzites. The Baker's Bridge granite is exposed for a few miles above the bridge within Animas Canyon.
Sadly, the upper reaches of the Animas are contaminated by toxic heavy metals of lead, cadmium, copper, manganese, zinc and iron that discharge from the countless mines and tailings (waste) piles in Baker's Park, legacies of the gold and silver that lured the hordes of prospectors and miners beginning in the last quarter of the nineteenth century. The degradation in water quality has adversely impacted all forms of aquatic wildlife, although further downstream, particularly below Baker's Bridge, its quality is greatly improved through dilution from inflow of high quality tributaries.
A CHANGE IN GEOMORPHOLOGY BELOW BAKER'S BRIDGE
At an elevation of 6,761 feet, Baker's Bridge (red arrow below) lies at the juncture of a profound change in the topography owing to the presence (or absence) of the locale's Precambrian crystalline basement. Above the bridge into the mountains, the Animas Canyon confines a swift Animas River within its narrow, resistant walls.
At Baker's Bridge, where our photo of the Great Unconformity is well displayed, the Precambrian basement is in contact with the overlying Paleozoic strata. Just below Baker's Bridge where the Animas Gorge ends, the eponymous granite dives into the subsurface buried under alluvium and Paleozoic rocks.
Looking north, Baker's Bridge (red arrow) lies at the head of wide Animas Valley and floodplain and at the bottom of narrow Animas Canyon. The Great Unconformity is exposed at Baker's Bridge and for a few miles upriver. The change in terrain is at Baker's Bridge is synonymous with its granite entering the subsurface.
Within and around Animas Valley, yellow and tan colors designate Quaternary Pleistocene and Holocene glacial, alluvial and colluvial deposits, and turquoises and shades of purple designate Paleozoic bedrock. Immediately above Baker's Bridge, the bedrock (taupe) is Paleoproterozoic Baker's Bridge Granite and Irving Formation. See references below for the on-line location of this map.
Shaded relief map of the Hermosa quadrangle with geology and topography overlay|
Modified from the Geologic Map of the Hermosa Quadrangle, La Plata County, Colorado, 2003
THE ANIMAS RIVER VALLEY BETWEEN BAKER'S BRIDGE AND DURANGO
During the Pleistocene, the San Juan Mountains experienced 15 or more glacial advances that blanketed the region with a 1,900 square mile ice-field. The high cirques became ice-free at least 15,000 years ago with the peaks of some remaining above ice. The forty mile-long Animas glacier, one of the longest in the Southern Rockies, scoured out Animas Valley, evidenced by lateral moraines over 1,000 feet above the valley floor.
Today, the U-shaped valley floor is flat, having been filled with Pleistocene glacial outwash and moraines, and Holocene alluvium (stream deposits) and colluvium (slope deposits). The valley is continually being modified by mass wasting with landslides, mudflows, debris flows and creep, and periodic Animas flooding from voluminous winter snowmelt and summer monsoons.
The valley's walls are formed from 16,000 feet of limestone, shale and sandstone sedimentary beds of Mesozoic and Paleozoic-age. At the mouth of the Animas Valley (map below) near Durango, we ascend the Mesozoic column beginning with the Late Triassic Chinle Formation at the base of Animas City Mountain (photo below) and progress through the Middle Jurassic San Rafael Group beginning with the Entrada Sandstone. The slope-forming Late Jurassic Morrison Formation follows with a resistant cap of the Late Cretaceous Dakota Sandstone.
MOUTH OF THE LOWER ANIMAS VALLEY
We’re standing on a glacial moraine facing the mouth of the lower Animas Valley looking north across the Animas River and floodplain. Baker’s Bridge is 12 miles upvalley in the foothills of the San Juans. The valley's U-shape was scoured by the forty mile-long, Pleistocene Animas glacier that originated within the San Juan Mountains. Withdrawing late during the Pinedale glaciation, its sediments accumulated in Glacial Lake Durango, a proglacial lake that formed in a deeply scoured basin cut into bedrock. The valley's flat floor is filled with lake sediments, glacial till, and Holocene alluvium and colluvium.
Within this expanse of the lower Animas Valley, the Ariver has become a very low energy system of oxbows and vegetation-rich, abandoned cutoffs on its flood plain. Durango, to the south behind us, is built on late Cretaceous sedimentary rock, principally the Mancos Shale, with a veneer of Animas River gravels. Higher portions of Durango are built on glacial outwash, terraces and moraines generated from the recent 18,-25,000 year old Wisconsin glacial event and others earlier such as the Pinedale.
PALEOZOIC HERMOSA CLIFFS FRAME BAKER'S BRIDGE
At Baker’s Bridge, down-section in the upper Animas Valley, an early to middle Paleozoic assemblage is revealed, Cambrian(?) through Pennsylvanian. This photo was taken from atop an elongate ridge of Leadville Limestone (a Redwall equivalent) and a patchy, paleosol-veneer of reddish Molas Formation. Underlying it is Devonian Ouray Limestone that forms the cliff above the Great Unconformity at Baker's Bridge nearby.
Looking to the northwest, Middle Pennsylvanian Hermosa Group cliffs (the type-section) dramatically rise with forested, lower slopes in the Paradox Formation. Recall that although we are positioned outside the physiographic boundary of the Colorado Plateau, the stratigraphy is Paleozoic-Mesozoic syn-depositional and concordant. The entire display is beautifully exposed throughout the Animas Valley.
|Hermosa cliffs above Baker's Bridge|
HOW DID THE CONTIGUOUS STRATIGRAPHY OF THE GREAT UNCONFORMITY FORM AT BAKER'S BRIDGE?
The Great Unconformity is the expression of geological events that occurred globally; that is, conditions existed worldwide to promote the development of this massive gap in time. At Baker's Bridge, the stratigraphy embracing the unconformity is an outcome of regional tectonic controls, in many respects, a microcosm of the global event.
Acquisition of Proterozoic crust...
The Southwest's oldest rocks, its crystalline basement, formed in a flotsam and jetsam of tectonic collisions of juvenile volcanic arcs and marine basins during the Early to Middle Proterozoic. In succession, first the Mojave, then the Yavapai (1.8-1.7 Ga), and finally the Mazatzal (1.7-1.65 Ga) provinces collided with pre-2.5 billion year old rocks of the Archean Wyoming Province of the Canadian Shield, a portion of the craton or ancient nucleus of the nascent North American continent to the north.
Using Southeast Asia as a modern analogue, the Southwest may have appeared something like this during the Early to Middle Proterozoic. The region of Baker's Bridge (encircled) received crust largely from Yavapai tectonic derivatives.
Once accreted, the Yavapai basement in the region of Baker's Bridge and the future San Juan Mountains were twice metamorphosed during the Middle Proterozoic. The first epsiode was part of a mountain-building event called the Boulder Creek orogeny (1.72 to 1.667 Gma) in which Twilight Gneiss metamorphosed from andesite and the Irving Formation from basalt. By 1.5 Gma, the eroded Boulder Creek Mountains were covered by marine sediments of the Uncompahgre Formation.
The emplacement of the Baker's Bridge granite...
During the second, milder metamorphic episode of the Silver Plume orogeny (~1.5 Gma), magma intruded the Twilight and Irving metamorphic rocks with felsic plutons of both Baker' Bridge and Tenmile granites (part of the statewide Routt Plutonic Suite), and metamorphosed the Uncompahgre sediments into quartzites, slate, phyllites and schist. These Precambrian rocks can be found in the various sub-ranges of the San Juan's.
Rifting to drifting to exposure and weathering...
In the late Middle Proterozoic (1.4 to 1.0 Ga), the supercontinent of Rodinia finally assembled with the Grenville orogeny that united the majority of the world's landmasses and built a transglobal Grenville mountain chain. Following Rodinia's break-up in the latest Proterozoic, its crust distributed globally with the drifting apart of its continental siblings. Once exposed, the basement rock experienced extensive weathering over a prolonged period. The eroded Precambrian crust, both Archean and Proterozoic, is the foundation on which the Great Unconformity formed.
The remnants of Rodinia's Archean and Proterozoic crustal core are distributed throughout the globe after the continents reassembled at the end of the Paleozoic into the supercontinent of Pangaea, and then redistributed upon its fragmentation.
Great floods of the Phanerozoic...
On the short term, the level of the sea rises and falls, whether lunar orbitally-induced or regionally weather-related. Sea level also possesses a long-term oscillation that typically lasts hundreds of millions of years, related to celestial parameters (that trigger glaciation cycles) and planetary tectonic events (that change the holding capacity of ocean basins).
Six times in the Phanerozoic, the level of the sea substantially rose and fell, flooding low-lying regions of the continents globally. With each landward advance (transgression) and withdrawal (regression), the seas deposited continental-scale, unconformity-bounded, sedimentary sequences. Centered on the Cambrian, the earliest was the Sauk sequence from the latest Proterozoic through the early Ordovician.
The Sauk transgression-regression...
At its peak, the Sauk flooded the low-lying, weathered Precambrian margins of the drifted paleo-continents and their cratonic interiors from the latest Proterozoic and into the beginning of the Paleozoic for 50 million years or so. In North America, the continent was blanketed largely with a sequence of well-sorted sandstones and clastic carbonates (excluding topographic highs such as the NE-SW-trending Transcontinental Arch that extended into Arizona and parts of the raised Canadian Shield well to the north).
The birth of the Great Unconformity...
The siliciclastic, near-shore Ignacio Formation (the Grand Canyon's Tapeats equivalent) was the first sedimentary rock deposited in the region of Baker's Bridge and the future San Juan Mountains. Voila! With covering of the Precambrian basement by the Cambrian transgressive-regressive sequence, the Great Unconformity had formed.
The Great Unconformity, so well exposed in the Grand Canyon and on grand display at Baker's Bridge, can be traced across Laurentia (here) and found globally on Rodinia's tectonically dispersed landmasses - including Gondwana (largely the Southern Hemisheric continents), Baltica, Avalonia and Siberia. That makes the Great Unconformity "the most widely recognized and distinctive stratigraphic surface in the rock record" (Peters and Gaines, 2012). Geologists can't resist touching it and pausing for reflection!
WHAT HAPPENED DURING THE GREAT UNCONFORMITY?
The Late Proterozoic and the time of the Great Unconformity was a turning point in the development of "the modern earth system" (Shields-Zhou, 2011). Its half-billion or so years were enough time to allow for a total re-invention of earth's geosphere, atmosphere, hydrosphere and biosphere.
Geologically, it accommodated a complete reorganization of the Earth’s tectonic plates, the uplift and erosion of vast mountain ranges to sea level, a rifting apart of the supercontinent of Rodinia into smaller continental fragments and their drifting throughout the globe. Biologically, it was enough time to evolve completely new and diverse lifeforms, and accommodate their radiation.
The two are thought to be related in that the geological processes that resulted in the formation of the Great Unconformity provided the impetus for the burst of biological diversity of the Cambrian Explosion of multi-cellular animal life. There are many competing theories that are highly controversial and lack a consensus of opinion. That said, let's attempt to assimilate them into one apologetically simplistic scenario. It's a rather unlikely tale of a fragmenting supercontinent, a dimly lit planet that became entombed in glacial ice, a hothouse heat wave, an oceanic geochemical infusion and an explosion of multi-cellular animal life within the sea.
LATE PROTEROZOIC WEATHER REPORT
During the Great Unconformity, the breakup of Rodinia (900-750 Ma) occurred largely during the Tonian Period (Greek meaning “to stretch”) early in the Late Proterozoic. In the Cryogenian (Greek for "cold" and "birth") Period (850-635 Ma) in the mid-Late Proterozoic, our planet experienced two intense and widespread glaciations that were notably equatorial in locale - as opposed to more familiar high latitude Phanerozoic glaciations such as those of the Pleistocene.
These were the Sturtian (715-680 Ma) and Marinoan (680-635 Ma) glaciations. A third Cryogenian glaciation, the Gaskier or Varanger, was less extreme, likely short-lived and not global in extent.
A COSMIC BALL OF ICE
The ice ages prevailed with such intensity that the surface oceans in the tropics froze. The event has been anointed with the colorful and description of “Snowball Earth” (Kirschvink coined the term in 1992, and Hoffman presented the hypothesis in 1998). It’s a bold and imaginative theory that remains speculative and controversial, yet very attractive since it successfully explains the geological findings regarding the glaciations (e.g. equatorial glacial tillites and diamictites, banded iron formations, post-glacial marine “cap” carbonates, carbon isotopic anomalies, etc.).
These events – Rodinia's assembly, break-up and the ensuing glaciation - preceded the recognition of multicellular animal life during the Ediacaran Period (named for the type-section at the Ediacara Hills of Australia), the final time period of the Proterozoic.
TRIGGERS OF THE DEEP FREEZE
What are the causes of extreme climate deterioration, that is, the prolonged cooling that led to equatorial snowball glaciations? Proposed explanations include extraterrestrial triggers such as galactic cosmic rays driving cloudiness, the dimmer young sun (solar luminosity 83-94% of present-day values) and high planetary obliquity (> 54º of axial tilt) that resulted in a colder low-latitudinal climate than at the poles. Terrestrial triggers include methane degassing from anoxic oceans (boosting the hydrologic cycle) and tectonic influences.
The latter trigger - tectonics - relates epochs of glaciation to a reduction in the partial pressure of atmospheric CO2 caused by supercontinental break-up. It’s an attractive model. Here’s how it works.
FRAGMENTATION AND ATMOSPHERIC pCO2…
Rodinia fragmented apart a good 70 million years before the first snowball event. Although Rodinia may have stretched from pole to pole, its paleo-orientation and that of its rifted constituents was likely, largely equatorial, at least initially. Its fragmentation generated intense magmatic activity within the Laurentian magmatic province. It also opened many seaways as the severed continental blocks drifted apart, which in turn increased precipitation and temperature along newly rifted margins, largely in a low-latitudinal locale.
The continental runoff increased weathering, particularly of silicates on freshly generated basaltic surfaces, and hence atmospheric consumption (q.v. long-term carbon cycle). The “drawdown” (reduction) of CO2, a greenhouse gas, resulted in long-term climate cooling, trending toward an icehouse. As ice accumulated equatorially, a “runaway ice-albedo”
(reflective ice reduced solar absorption leading to more cooling; Budyko, 1968) drove the earth into a snowball glaciation. Thus, supercontinental break-up is thought to have had a profoundly cooling effect at low latitudes during the Late Proterozoic and to have been the main trigger in reducing atmospheric CO2.
WHAT AWAKENED THE EARTH FROM ITS CRYOGENIC SLUMBER?
The Snowball Earth hypothesis also postulates that millions of years of glaciation ended when sufficient volumes of volcanically-derived CO2 emissions accumulated within the atmosphere. Degassing overcame the effect of the runaway albedo climate, which collapsed weathering and allowed the planet to transition from an icehouse to a greenhouse world that melted the ice and liberated the planet from its snowball state.
A geochemical infusion of weathering products...
During the Great Unconformity, continental exposure and chemical weathering of silicate materials effected seawater chemistry and global bio-geochemical cycling in the atmosphere and the oceans. The weathered-runoff was delivered to rivers and oceans in massive quantities conducive to the evolution of new forms of life, in particular, Ediacara-type fauna that flourished as a prelude to more diverse forms of the Phanerozoic world.
The final stages of the Great Unconformity are thought to have acted as a “geological trigger” by infusing the oceans with continental weathering products including carbonates, calcium, potassium, sodium, magnesium and iron (Peters and Gaines, 2012). That had profound implications for ocean chemistry at the time that complex life was proliferating and initiated a biochemical response seen in the Cambrian Explosion.
Lifeforms that existed before and after the Precambrian-Cambrian boundary differed immensely. During the Ediacaran Period lifeforms were plant-like, suspension-feeding metazoans (multi-cellular) that lacked the morphological capacity (form and structure) for locomotion and were non-biomineralized (without hard calcified tissues like shells and bones).
They are generally viewed as the oldest unequivocal animals and passive inhabitants of their ecosystem, tethered to a cyanobacterial microbial mat on the ocean floor. By and large, the Ediacara fauna became extinct by the end of the Ediacaran Period, although proponents of Burgess-type ancestral relationships believe some lifeforms persisted into the Cambrian.
BURGESS SHALE-TYPE FAUNA
Following the Ediacaran-Cambrian boundary, new lifeforms were distinguished by the emergence and rapid diversification of more complex multicellular animals, by their acquisition of biomineralized skeletons (phosphate and carbonate salts of calcium), and by their innovative body plans with movable, muscular body parts.
With new bodies came new lifestyles - possessing the ability to bioturbinate the substrate (rework the sediments by burrowing), move vertically through the water column and exploit new habitats. Predation had begun across the threshold of the gap in time, and along with it, the ability of prey to protect themselves and escape from capture. Things have never been the same. This period is referred to as the Cambrian Explosion of life because of the seemingly abrupt timing of the biological event. Evolutionary biologists single the Cambrian Explosion as the event that generated all the phyla that have persisted to the present.
WE SEE THE GREAT UNCONFORMITY IN A NEW LIGHT
Alas, we have come to perceive the Great Unconformity as more than just a gap in time but as “a unique physical, environmental boundary condition” (Peters and Gaines, Nature, 2012). Reflecting on the dramatic transition from Ediacaran to Burgess-style lifeforms across the Great Unconformity, Robert R. Gaines (personal communication, 2012) believes the "geological circumstances surrounding its formation led to the Cambrian Explosion."
Analyses of seawater chemistries “provide support evidence for changes in tectonic activity and enhanced (and extensive Late Proterozoic) continental weathering during the formation of the Great Unconformity” (Peters and Gaines). The chemical infusion that was delivered to the sea – with minerals such as calcium that rose precipitously – has been proposed as a mechanism for the origin of biomineralization of animals during the Cambrian Explosion that evolved in Cryogenian to Ediacaran time.
LET'S RETURN TO BAKER'S BRIDGE FOR A FINAL LOOK AT THE CONTACT
Now that we have an enlightened geological and biological perspective of the events that occured during and surrounding the Great Unconformity, let's take one last look at the contact at Baker's Bridge. The Ignacio Formation, the stratum anticipated to cap the Great Unconformity, appears absent at Baker's Bridge.
Geologists have found it difficult to distinguish between the sandstones of the McCracken from the underlying Ignacio. Petrographic analyses at Baker's Bridge has found that the sandstone overlying the Great Unconformity is more similar to the Devonian McCracken Sandstone Member of the Elbert Formation rather than the Cambrian Ignacio Formation, which contacts the granite elsewhere regionally. The following paleo-map depicts the widespread Devonian through the Mississippi-age Kaskaskia transgression (on the sequence map above) that deposited Redwall limestones in northern Arizona, and Elbert and Leadville Formations in the region of Baker's Bridge in Colorado.
The McCracken-Ignacio age-uncertainty has persisted in the literature for over a hundred years, much to the surprise and even disappointment of some Plateau geologists that expect the Tapeats or its regional equivalent overlying the Great Unconformity. The problem has been with the precise dating of the Ignacio, which has been difficult since it's regionally depauperate (greatly diminished or devoid of ecosystem fossils). In the strata above the Ignacio, trace burrows, and brachiopod and fish remains are plentiful in the Elbert and overyling Leadville, which does allow reliable dating.
I asked the question "What stratum overlies Baker's Bridge granite at Baker's Bridge?" to Dr. David Gonzales, Professor and Chair in the Department of Geosciences at Fort Lewis College in Durango). He responded, "Unfortunately, there is not a definitive answer (personal communication, 2013). He continued, "The Ignacio Formation at Baker's Bridge is somewhat unique on a regional level. In a number of locations, Devonian limestone lies directly on Proterozoic rocks. So, clearly, depending on what area you are in, there is both Cambrian(?) and Devonian rock units on the Proterozoic. Unless more fossils are found, I am not sure the issue will be easily resolved."
A thesis interpretation (Maurer, 2012) of the strata-conundrum attributes Ignacio's absence at Baker's Bridge to its deposition mostly as estuarine within an incised valley sequence. Thus, it was not deposited at Baker's Bridge but located elsewhere regionally. With the return of the sea, the landward advance of the Kaskaskia transgression left McCracken marine sediments upon Bakers Bridge granite at Baker's Bridge.
The Ignacio question at Baker's Bridge is surprising to geologists that anticipate its presence. But technically - recalling our definition of the Great Unconformity - the overlying strata can very greatly both regionally and even globally contingent on the circumstances of deposition.
PLEISTOCENE GLACIAL AND HOLOCENE POST-GLACIAL PROCESSES LEAVE THEIR MARKS
Back at the bridge, glacial and fluvial erosion have stripped the sedimentary cover from the granite, and allowed the Animas River to carve a channel through the Animas Gorge. Notice the smooth glacial polish and multiple, parallel glacial striations produced by the Animas Glacier moving downvalley some 18,000 years ago. Once exposed, repetitive freeze-thaw cycles have also taken their toll on the granite as it began to exfoliate at the surface into gently curved slabs.
VERY INFORMATIVE PRINTED RESOURCES
Ancient Landscapes of the Colorado Plateau by Ron Blakey and Wayne Ranney,
Plateau: The Land and People of the Colorado Plateau, Vol. 6, Nos. 1 and 2, 2009.
Snowball Earth by Paul F. Hoffman and Daniel P. Schrag, Scientific American, 1999.
The American Alps by Donald L. Baars, 1992.
The Garden of Ediacara by Mark A.S. McMenamin, 1998.
The Geology of the American Southwest by W. Scott Baldridge, 2004.
The Roadside Geology of Colorado by Halka Chronic and Felicie Williams, 2002.
The Western San Juan Mountains by Rob Blair, 1996.
Wonderful Life by Stephen Jay Gould, 1989.
VERY INFORMATIVE ON-LINE RESOURCES
Geologic Bedrock Map of the Hermosa Quadrangle, Colorado Geological Survey, 2003.
Reinterpretation of the Ignacio and Elbert Formations by Joshua T. Maurer, 2012.
Petrologic Evolution of the San Juan Volcanic Field by Peter W. Lipman et al, 1978.
Formation of the Great Unconformity as a Trigger for the Cambrian Explosion by Shanon E. Peters and Robert R. Gaines, Nature, 2012.
whither it is a slight insult to the gods to climb and pry into their secrets,
and try their effect on our humanity.
Only daring and insolent men, perchance, go there.
Simple races, as savages, do not climb mountains,
their tops are sacred and mysterious tracts never visited by them.
Pamola is always angry with those who climb to the summit of Ktaadn.”
We're facing east from Baxter Peak at 5,269 feet, the penultimate summit of Katahdin's five peaks and the highest point in the State of Maine. The afternoon sun is casting long October shadows into the semi-circular abyss of glacial ice-gouged South Basin. A vertiginous 2,000 foot headwall of erosion-resistant Katahdin granite rises to the top of Pamola Peak across the cirque. To the right of Pamola and running to the summit on which we're standing is a daring traverse called the Knife Edge. It's a two-foot wide boulder-scramble on the apex of a glacial arête that is both famous and revered throughout the northeast. Textbook glacial tarns, hummocky moraines and serpentine eskers lie on a heavily forested, boulder-strewn outwash plain across the valley floor. Welcome to Katahdin!
MANY GEOLOGICAL QUESTIONS
Pronounced "kuh-TAH-din", it's a Penobscot word of Maine Native Americans that means "the greatest mountain", so the need for "Mount" is redundant. Katahdin and its features harbor geological secrets of their past that have plagued geologists for over a century.
What is the tectonic relationship of Katahdin to the Appalachian Mountain chain along North America’s eastern margin? By what tectonic design did Katahdin's granitic core emplace? How did did Katahdin come to be positioned within a middle Paleozoic “sea” of metasedimentary rock?
The granites of Katahdin and the rhyolites of nearby Traveler Mountain exhibit a remarkable chemical homogeneity and time of emplacement. In fact, a contact exists where one intrudes the other. Is there a geological association between Katahdin and Traveler Mountain? By what process did Katahdin’s subterranean magma chamber become "the greatest mountain" towering above the others in the region?
|Great Basin by American landscape oil painter Frederic Edwin Church (1826-1900), 1852.|
Penobscot mythology exalts Pamola - part moose and part eagle - as the prisoner-taking spirit of thunder and supreme protector of “K’taadn.” Our fervent hope on this near-freezing Columbus Day weekend, the last of the hiking season in Baxter State Park of Maine, was that the mysterious winged deity would hold mountain storms, lightning strikes and high winds at bay, and repress his anger long enough for us to ascend his granite fortress, observe its geology - and return safely.
About 90 miles upstream from Penobscot Bay in mid-coastal Maine, the Penobscot River divides into a West and East Branch. Between the two branches is the edifice of Katahdin in north-central Maine, near its geographical center at: 45º 54’ 16.07” N, 68º 55’ 18.75” W. If you plug the co-ordinates into Google Earth, it will take you there.
Bangor is 75 miles to the southeast, and Boston is another 225. Nova Scotia and the Bay of Fundy are a good 200 miles to the east, and the Canadian border is 60 miles to the northwest towards Quebec.
WHAT IS KATAHDIN?
Using the simplest definition possible, Katahdin is a steep and tall mountain composed of a large mass of granite that has weathered to the surface over time. Its granite core formed within a cooled magma chamber or batholith below the earth's surface. It's also a pluton - an encompassing term that includes other intrusive (also called plutonic and means formed into older rock below ground) igneous bodies such as stocks, dikes and sills.
When molten magma reaches the surface, it may extrude and flow as lava, or in the case of Katahdin, violently eject outward under tremendous pressure. Small particles of ash blasted aloft and settled on the landscape in the form of a rock called welded tuff when solidified. Rhyolite is the extrusive counterpart of its parent intrusive granite. Thus, rhyolite-tuff describes its chemical composition and genesis-rock, Katahdin granite.
These volcanic events are the result of tectonic plate convergence on the earth's surface, a process that forms continents, closes intervening ocean basins and builds lofty mountain ranges. The tectonic collision that created the magma chamber of Katahdin also built the Appalachian Mountain chain. Of course, this is a basic interpretation. In order to better understand the topography, we must gain an appreciation for the geologic processes that have shaped the region and the east coast of North America for that matter.
The footpath of the Appalachian Trail from Springer Mountain in Georgia to Mount Katahdin in Maine |
follows the strike of the Appalachian orogen.
Map from n2backpacking.com
Katahdin is the undisputed centerpiece of Baxter State Park - an over 200,000-acre preserve of mountains and valleys generously established by donations of land beginning in 1931 from Percival P. Baxter, a two-time governor of Maine. To protect the area from logging, he personally purchased the land from logging companies and deeded it to the state.
The stipulation was that it remains “forever…in the natural wild state…as a sanctuary for wild beasts and birds that no roads or ways…be constructed therein or thereon.” In Governor Baxter's own words:
Buildings crumble, monuments decay and wealth vanishes,
but Katahdin in all its glory forever shall remain the mountain of the people of Maine."
SETTING THE LANDSCAPE FOR THE EMPLACEMENT OF KATAHDIN
Recording a billion years of orogenesis, the once Himalayan-comparable Appalachian orogen extends 2,000 miles from Georgia to Maine and as far as Newfoundland, Canada with buried components beneath the Atlantic and Gulf coastal plains, and the Atlantic continental shelf. Named by the Spanish in the 1500’s for a Native American tribe – the Apalachis - it is an eroded, accretionary orogen and represents the site of long-vanished ocean basins consumed in a collision of a mosaic of terranes with Laurentia - the core of ancestral North America.
Traditional descriptions of the evolution of New England and its Northern Appalachian section include a succession of Paleozoic tectonic events: the Penobscottian, Taconic, Salinic, Acadian and Alleghanian orogenies. The landscapes that these mountain-building events created are manifested by a geological zonation across the strike of the orogen in the direction of their tectonic migration onto and across Laurentia (below).
Unravelling the tectonic history of Laurentia's eastern plate margin has been an arduous and complicated work in progress. That said, let's briefly summarize the orogenic events in order to put Katahdin's regional emplacement into perspective (red dot).
THE FRAGMENTATION OF RODINIA - A GOOD STARTING POINT
In the earliest Paleozoic, the fragmented Late Proterozoic supercontinent of Rodinia is represented largely by the megacontinents of equatorial Laurentia, South Hemispheric Gondwana and the micro-continent of Baltica - all sharing the waters of the Iapetus Sea. This was a pivotal interval in the Earth’s history – a time of worldwide orogeny, proposed "snowball" glaciations, rapid continental growth, profound changes in ocean geochemistry, and an explosion of biological activity and early animal radiation (Visit here).
Rodinia's rifted continental elements would re-assemble in succession throughout the Paleozoic and eventually form the supercontinent of Pangaea, create the Appalachian Mountain chain and emplace Katahdin in the process.
THE PENOBSCOTTIAN OROGENY
The Pebobscottian orogeny is in part coeval (time equivalent) with the early phases of the Taconic orogeny (below). It was caused by a collision between the Penobscot arc and the terrane of Ganderia, a widely misunderstood microterrane situated in the periphery of Gondwana across the Iapetus Ocean. It involved back-arc ophiolites that were obducted onto the Gander margin. The composite terrane trends northeast from Northern New Hampshire, across west-central Maine and into New Brunswick, Canada. This subduction-obduction tectonic event occured in the Late Cambrian to Early Ordovician and preceded the Taconic orogeny, whose arc rocks locally overlie it.
THE TACONIC OROGENY
After some 150 million years following Rodinia's fragmentation, the world's continental plates began to converge in the early Paleozoic, driven by the incremental closure of their interposed ocean basins. The first was the Late Ordovician Taconic orogeny from Newfoundland to New York. It involved Laurentia’s collision with an island arc complex upon closure of the intervening Western Iapetus Ocean.
The Taconic allochthon that formed signifies the earliest recognition of the Northern Appalachian Mountains in western New England and southeastern New York State, while a massive clastic wedge was shed westward into a developing foreland in New York, Pennsylvania and beyond called the Queenston delta.
This was the beginning of the replacement of the open seas of the Western Iapetus off the coast of Rodinia with "exotic" continental crust, a process that would end in the northeast with the formation of New England, Maine and the emplacement of Katahdin.
THE SALINIC OROGENY
The tectonic history of New England during the Paleozoic has been dominated by discussions of island arcs, exotic terranes and compressional events. Recently, an event of crustal extension has been elucidated - the Salinic orogeny. Replete with sedimentation and a mafic intrusive complex, it developed within elements of the Taconic event in central New England to the west during the Silurian. It includes deep-water strata of four basins, two of which are relevant to our discussion of Katahdin: the Connecticut Valley-Gaspe synclinorium and the Central Maine trough in New England and eastern Quebec.
A boundary within the basins implies a change in the depositional setting from an intercontinental backarc extensional setting to a foreland basin as the Acadian wedge approached from the east (black arrow). Other tectonic models have been proposed, but regardless of the process, the Salinic involved rifting or crustal divergence followed by Acadian deformation and metamorphism.
On the "Regional Geologic Map" above (red dot) and the map below (red circle), note Katahdin within the Piscataquis magmatic (volcanic) belt AND within the CVG and Central Maine basins. Outboard in the direction of the Acadian front to the southeast (diagram below is a rotated perspective) lies Avalon's coastal volcanic belt "proper" of the orogen.
THE ACADIAN OROGENY
The third event to shape northeastern Laurentia was the Middle Devonian Acadian orogeny with the closure of the Eastern Iapetus Ocean. It involved the collision of Avalonia – a peri-Gondwanan, rifted terrane - with Laurentia's east margin. It too built a large clastic wedge and foreland called the Catskill delta. In reality, the accretion of the Avalon arc involved several composite subduction zones. The details of its superterranes and geometries of the Acadian event are only partially understood and beyond the scope of this post.
The Acadian orogeny finalized the northern Appalachians from the Canadian Maritimes into New England (and the central and southern Appalachians into the Carolinas), and penetrated into, deformed and imprinted the previous Taconic orogen and its foreland. In Maine, it formed the state's highest mountains in a belt that runs from the New Hampshire border on the west through Katahdin and beyond to the northeast, a distance of 150 miles. In New Hampshire, the range continues through the White Mountains to Mount Monadnock in the southwest part of the state. Thus, the Maine Appalachians are mostly Devonian in age - initially Taconic but deformed and elevated in the Acadian orogeny.
Katahdin emplaced during the Acadian orogeny as deformation migrated from the southeast to the northwest. What's more, its curious locus of emplacement relevant to the Acadian subduction zone was within the flysch and molasse of the Acadian foreland, which will be investigated on our climb of Katahdin.
THE ALLEGHANIAN OROGENY
Lastly, the Pennsylvanian-Permian Alleghanian orogeny (Ouachita orogen in southern and eastern Mexico, and Hercynian-Variscan in southern Europe) finalized the Central and Southern Appalachians and overprinted the Acadian orogen by deforming and metamorphosing parts of New England.
The Acadian involved a largely translational, highly oblique, continent-continent collision that closed the Rheic Ocean, sutured western Gondwana to Laurussia (Laurentia and Baltica), completed a Wilson cycle (here), produced the Appalachian Mountain chain and finalized the formation of Pangaea. The multi-phasic, Taconic through Alleghanian, Paleozoic-spanning event is summarily called the Appalachian orogeny.
|Katahdin from the east|
Katahdin looms large from all directions, here from the east outside of nearby Millinocket.
High Dynamic Range photo contributed by resident Mainer FL Doyle III (fldoyle.com)
|Google Earth View of Katahdin Looking South|
The trailhead is at Katahdin Stream campground, elevation 1,075 feet. It follows the stream on a persistent upslope built on talus through a mixed boreal forest of hardwoods such as white birch and red maple, and evergreens such as balsam fir, red-black spruce, hemlock and white cedar. The ground flora was rich in mosses, ferns, bunchberry and hobblebush. This is an alpine temperature ecosystem of great diversity.
Virtually all of the granite bedrock is related to the time of Katahdin's emplacement - Early, possibly some Middle, Devonian age, although a small region in the park’s southwest corner is Late Devonian. Older Cambrian and Silurian rocks surround the park within the aforementioned basins, attributable to the tectonic and emplacement regime of the Katahdin pluton, of which less than half is within Baxter State Park.
A SHIMMERING LAKE-MIRAGE
The cold October night created a temperature inversion in the valleys around Katahdin. Looking like a large lake off to the west, trapped cold air created a thick foggy blanket that quickly burned off in the sun. Still near freezing, we immediately began shedding layers as the pitch and our efforts increased.
|Temperature Inversion Fog|
Picturesque Katahdin Falls, at an elevation of about 1,600 feet, spills over a wall of Katahdin granite. The bedrock is homogeneously granitic on the Katahdin pluton, so the knickpoint didn't form on strata of varying lithologies with differing erosion-resistance typical of a sedimentary rock-dominated terrain. Instead, the falls is a consequence of the varying glacial landscape and mass-wasting that was rendered to the region after 12,000 years of erosion. At this elevation, the forest is predominantly red-black spruce and balsam fir that provides a veneer of aromatic and spongy, orange-brown needles everywhere.
The calmness bequeathed here is in contrast to the arduous climb that awaits above.
EVERGREENS OF THE NORTH WOODS
The boreal forests of Baxter State Park began to develop about 12,000 years ago with the regression of the Laurentide ice sheet. The land retained its tundra ecology for at least 1,000 years as the first human inhabitants left evidence of their presence. As the climate gradually warmed, it had a profound effect on the resident animal population. Northern forests of spruce and fir support relatively little herbaceous vegetation, offering little subsistence for gregarious herbivores like musk ox and caribou that gradually drifted northward out of the region.
Today, 8,000 or so years later, the forests of northern Maine changed from boreal to spruce and fir-dominated. The regional soil is generally poorly to moderately drained over compressed glacial till or areas of shallow soil clinging to the bedrock. A great many of the forests have been harvested for logging, but Baxter is a "gem in the woods" - literally.
GAINING ELEVATION AND INSIGHT
Upon gaining altitude, the terrain began to unfold. It was even more clear that Katahdin is situated in an extensive forest of the Maine Wilderness. The stands and bands of bright-orange Sugar Maples in the valleys are growing on alluvially-enriched soils generated by huge glacial meltwater channels from the Pleistocene. As we progressed upslope, the soil-till-talus mix gave way to talus-dominated, and ultimately bedrock sprinkled with weather-fractured blocks of granite. The mosaic of hardwoods and softwoods is evident with the change in autumnal color.
The mountains immediately off to the west of Katahdin have names such as Squaws Bosom, Tabletop, Barren, The Owl and the Brothers. Every one is cored with intrusive granite of the Katahdin pluton. That's not the case north of Katahdin where Traveler Mountain is composed of bluish-gray extrusive rhyolite, yet it's part of the same pluton, or better stated, volcanic complex - a hint at the co-magmatic regime of Katahdin. By the way, Traveler got its name from the early explorers that boated down the East Branch of the Penobscot River since the mountain seemed to travel with them.
Macrolichens of New England|
A foliose (leafy) and a fruticose (shrubby) lichen - two of the main types - germinate on a hardwood branch. Exposed rocks, particularly at higher elevations, are covered with the third lichen-type - crustose (crusty).
SILURIAN BASINS IMPRINTED BY THE ADVANCING DEVONIAN OROGEN
To the west, beyond the composite of summits of the Katahdin pluton and those of the Piscataquis belt, lies the aforementioned sedimentary, Salinic basin of the Connecticut Valley-Gaspe synclinorium. The extensional trough formed in the Middle Silurian within previously-accreted magmatic arcs of the Taconic orogeny (the Shelburne Falls and Bronson Hills arcs) that separated them. The sediments that accumulated within the trough were overlain by those derived from the foreland of the encroaching Acadian orogen.
With the convergence of the Avalon terrane in Late Silurian to Middle Devonian time upon Laurentia’s eastern margin and the trough, the Acadian front and foreland basin migrated northwestward across Maine, adjacent areas of New England, and New Brunswick and eastern Quebec of Canada. With the orogen's advance, it overrode and deformed the earlier Taconic-modified margin and inundated its migrating Acadian foreland basin with clastic successions of Devonian flysch and molasse and blanketed some of the deep-water Silurian sequences that accumulated within the synclinorium.
The landscape we see today records these Silurian and Devonian sedimentary deposits and retains the barely perceptible, synclinal geomorphology of the extensional tectonic regime. But by what tectonic design did Katahdin and the Piscataquis volcanics emplace?
THE EMPLACEMENT OF THE KATAHDIN PLUTON
Volcanic rocks within the Acadian orogen occur in two broad belts: a Coastal belt that erupted into the basement of the Avalon terrane and a second belt of Silurian-Devonian volcanic rocks – called the Piscataquis magmatic (or volcanic) belt within the foreland of New England (and the Tobique volcanic belt in Canada).
Plutonic activity in this part of the orogen was produced by Acadian deformation and falls within a narrow range of the Emsian age of the Devonian (400-410 Ma.). The actual deformation front was south of the Katahdin pluton - placing it within the foreland basin, a location of emplacement that departs from the conventional tectonic norm.
KATAHDIN AND TRAVELER ARE CO-MAGMATIC
In addition, the ash-flows of Traveler rhyolite on Traveler Mountain to the north of Katahdin AND Katahdin itself are regarded as the volcanic and plutonic parts of the SAME igneous complex. In fact, the granite intrudes the rhyolite (on the north ridge of Wassataquoik Mountain and on the southern slope of South Traveler Mountain both to the north of Katahdin). The rhyolite-granite contact has been Zircon dated at 406.9 ± 0.4 Ma, which sets the maximum age for the granite.
The emplacement of the Katahdin pluton likely occurred at shallow depths because of the presence of the granophyric phase of granite and because the granite intruded its cover-carapace of rhyolite. Violent, successive eruptions at the surface spewed thick volcanic ash that flowed over the region preserved in the welded tuff of Traveler Mountain. If the carapace of Traveler rhyolite that once covered the likely caldera of Katahdin (formed when the volcano's magma chamber collapsed within itself), then the Katahdin volcanic complex would qualify as among the largest volcanic features known in the world (Hon, 1976). One can only imagine what this place was like during the Early Devonian!
Dating and geologic mapping have arrived at the conclusion that the upper parts of the Katahdin pluton are close to the roof of the magma chamber of the Katahdin granite and that the roof or carapace slopes north toward Traveler Mountain. We will see this in the phases of granite that crops out at various elevations on our climb. Where's the ash that we assume once covered Katahdin? It eroded away in the roughly 400 hundred million years since it blanketed the region, at a rate estimated at 20-100 feet per million years (Judson and Ritter, 1964). What's left of the ash comprises the rhyolite-tuff in the region of Traveler Mountain to Katahdin's north, all that's left of Katahdin's carapace.
EMPLACEMENT PROFILE FROM HINTERLAND TO FORELAND
An Emsian-age transect (below) through the orogen in the Katahdin area shows the plutons emplaced into already-deformed Devonian rocks at a depth of 6.5 km. At this time, Katahdin is envisioned to entertain both "volcanism at the surface and plutonism at depth." (Bradley and Tucker, 2001). Emsian magmatism originated within and beneath the orogen BUT were extruded across the deformation front into the foreland. According to Bradley and Turner, "Although these younger plutons are commonly referred to as "Acadian," they postdated the documented cratonward advance of the deformation front and so cannot be linked to Acadian plate convergence."
The calc-alkaline, subduction-related granites likely possess a mantle component. The magmatism "cannot be solely a consequence of collision-induced thickening of continental crust" (Bradley and Tucker). One interpretation of the Katahdin-Traveler system is that mafic magma, generated deep within the mantle, ascended perhaps 20 miles from the surface beneath the crust (diagram below). Heat from the ponded magma partially melted the crust, generating a granitic magma. As the magma continued its buoyant ascent, it cooled and crystallized, accumulating gases within the upper chamber. The gas-rich magma escaped to the surface in a series of violent eruptions generating the
successive ash flows of the Traveler rhyolite.
Cross section through the Acadian Deformation Front during Early Emsian Time in the Katahdin Region|
From Bradley and Tucker, 2001.
The volume of rhyolite that was produced is estimated to have been 80 cubic miles
compared to less than 1/10th of a cubic mile in the devastating 1980 eruption of Mount St. Helens. Typically, large extravasations of rhyolite lead to caldera formation with a rapid evacuation or pressure release within the magma chamber. It's likely that Katadin experienced some caldera formation, since some components of the Traveler rhyolite (Black Cat Member) demonstrate compaction foliation and faulting. Clearly though, the caldera-like geomorphology of Katahdin is the product of erosion following its exhumation.
THE SPUR SECTION OF THE HUNT TRAIL
Unfortunately, I have no photos taken from within the Spur - a hundred feet or so of near-vertical, jointed granite. I admit that I was more concerned with safety than photography. However, I borrowed this photo from the web to illustrate my point.
"What am I doing up here?"|
Jsdangelo.com nicely sums up the Spur
ON TOP OF THE SPUR
Leo and Will rejoice from the top of the Spur. Notice the Katahdin granite is now pinkish and blanketed by a black and yellow-iridescent lichen, largely Lecidea geographica. Eight distinct lichen habitats of almost 300 species have been found on Katahdin from its subalpine forests through the krummholz to the exposed alpine tundra at the summit. Lichens are sensitive to elevation, climate and air pollution. Bryophytes (liverworts and mosses) are also abundant - over 200 species.
In the distance, the chain of post-Pleistocene lakes are within the Maine Wilderness Area. In the lowlands, orange Sugar Maples are sharply demarcated against evergreens that are thriving on nutrient-rich alluvium deposited during glacial melt.
Atop the Spur|
Leo and Will rejoice at the top of the Spur.
At about 3,850 feet, we're entering the Gateway - a ridge of boulder-strewn bedrock that leads to the flat plateau of the Tableland. Having negotiated the Spur we expected to have a glimpse of the summit but were surprised by the size of the Gateway. We were amused by descending climbers who exclaimed, "You're almost there!" - when in reality, there's another 4 miles to the penultimate summit of Katahdin!
We're clearly above the treeline. At this elevation, growing conditions have become increasingly severe with scarce nutrients, poorly drained, thin residual soils, wind, exposure and prolonged cold. Mineral soils have given way to organic soils. Most
herbaceous plants and tall trees can't tolerate these conditions. This is the sub-arctic krummholz or "crooked-wood" zone, dominated by tangled and stunted balsam fir, many in close stands that are almost impenetrable. The krummholz transitions to the alpine zone once on the Tableland.
At first glance, the plantscape appears uniform, but close observation shows a mosaic of
mosses, lichens and dwarf shrubs of fir, juniper and spruce. Microclimates and flora vary with the topography - expanses of bare bedrock, areas with thin soil and sheltered depressions out of the wind. You can tell the prevailing direction of the wind by the distorted shrubs that draw to the left.
TWO MAIN PHASES OF KATAHDIN GRANITE
Katahdin's granite occurs in two phases. The variety that forms the core and most of the pluton is the granitic phase. Largely light gray and homogenous, its an equigranular (uniform), medium-grained granite. Compositionally, the granite is 33% quartz, 33% alkali feldspar, 25% plagioclase, 5-10% biotite and accessory minerals.
As one ascends Katahdin, a gradual transition occurs from the light gray granitic phase at lower elevations, through mottled white and pink to salmon, and finally to brick red of the granophyric phase near the top of the pluton. The red comes from grains of hematite (iron oxide) contained within crystals of alkali feldspar. The color change is accompanied by higher percentages of fine-grained quartz and alkali feldspar that surround larger crystals with interlocking crystals. The geometric patterns one sees are typical of porphyritic igneous rocks and also contain small vugs (cavities).
The coarser-grained granitic phase is thought to have cooled more slowly allowing for crystal growth, being closer to the interior of the magma chamber, than the granophyric phase, that cooled more rapidly being closer to the colder bordering rock. Water-rich gas bubbles near the roof of the chamber were trapped by the rapidly cooling granophyric phases.
The Two Phases of Granite within the Katahdin Pluton - Granitic and Granophyric|
In these specimens photographed on Katahdin, one can readily identify white feldspars,
black biotites and gray quartz.
WEATHERING OF THE GRANITE
Parallel sets of through-going planar cracks or joints that develop in the granite fuel the mass wasting process that sends boulders downslope. It will eventually level Katahdin to a peneplain - the fate of all mountains in time. On the Tableland and scattered across Katadin's summit, the bedrock is broken into scattered boulders on the summit.
The body of granite can also form joints from contractional cooling and from the strain induced by continent-deforming tectonic processes. Exfoliation or sheet joints are found on steep planar surfaces such as found on the walls of glacial cirques. They are formed more recently by unloading as the weight of the overburden is removed by erosion and the melting of glacial ice. Once formed, granite sheets can be further truncated by erosion as freeze-thaw cycles and gravity pry off the surface and fill the floor with talus debris.
Transitioning from the Granitic to Granophyric Phase of the Katahdin Granite on the Gateway|
White blazes of paint and small cairns mark the trail. Notice the blanket of black and green lichens that cover the granite and its increasingly salmon color.
Halfway up the Gateway|
Massive boulders litter the bedrock of the Gateway. "Almost on the plateau!"
Off to the right are Mount Coe and South Brother. The lowlands to the left (west),
blanketed in colorful hardwoods, drape away from the Katahdin pluton onto till-covered Early Devonian, Ordovician and Silurian sedimentary rocks.
|Will clears the Spur onto the flat of the Tableland|
The southern region of the Katahdin massif is a broad, open, treeless, weather-exposed, gradually sloping plateau to the peaks that lie on the edge of the cliff-rimmed basins. Weathered blocks of bedrock were strewn everywhere, virtually coated with iridescent green-yellow lichen illuminated by the sun.
The plants of this arctic zone at this altitude have evolved to tolerate the extreme environmental conditions. Grow low is the dominant survival tactic, but everything from shallow root systems to desiccation-resistant leaves contribute to their ability to thrive in this fragile habitat. Although alpine grasses exist, most herbaceous grass can't survive at this elevation and are mostly sedges. Lichens and mosses are also found in abundance. Climbing a high peak such as this is equivalent to traveling north to the arctic in terms of both the flora and fauna encountered. Many of the plants here are rare or endangered, and are protected by a cobble-lined trail to prevent trampling.
View to the northwest from the Tableland|
The sign welcomes hikers to the Tableland.
From the same location in the above photo on the Tableland, we're facing north. The peaks of Katahdin's summit appear to be nothing more than a long trek that ends on a plateau, which is what it is. But looks are deceiving in that the east face, which we can't yet see from here, is sculpted beyond anything imaginable. Also blocked from view, rhyolite-built, co-magmatic Traveler Mountain is 13 miles due north beyond Katahdin. We're nearing the top of the magma chamber that is Katahdin!
|From the Tableland, we're looking due north across a deep ravine that is the Katahdin Stream watershed. The flat-appearing, bare summit to the far right is Hamlin Peak, one of five that comprises Katahdin.|
Looking down from the Tableland to the Gateway, here's a last look at the tabular
landscape to the west. The "cloud factory" on Katahdin's south slope is still highly productive as the cool rising valley air meets the warmer air aloft. Our climb that began just above freezing is now a balmy 60 degrees.
Several theories have been offered to explain the origin of the broad upland surface of the Tableland including erosional peneplanation and bevelling by glacio-peneplanation. The Tableland consists of resistant granophyric granite identical to that of Katahdin's summit. This resistant caprock in many ways is analagous to a sandstone overlying an erodable shale. Thus, the granophyre "holds up" or protects Katahdin. Once removed, rapid slope retreat occurs and decline into the hills and lowlands of the granitic phase around the pluton.
THE NORTHWEST PLATEAU AND BASIN
From the same perspective looking due north (below), we're viewing Hamlin Peak (4,751 feet) to the right across the Northwest Plateau and Basin at the summit of Katahdin. Typical of glaciated terrain in the north, notice the glacial plucking on the south, leeward outcrop of granite. Viewed from the west, the plateau has a roche moutonnee or "sheep-back" configuration with a gently sloping, north face. Our view of Traveler Mountain is blocked by Hamlin peak. To the right are Fort Mountain and North Brother. Our destination of Baxter Peak is to the right (out of view) about 1.4 miles.
We're near Thoreau Spring. Whether or not he actually reached this area is unknown. It is known from his journal that he never reached the summit of Katahdin, having been determined by bad weather. The Tableland is notorious for high winds and pelting rain and snow.
In 1924, Governor Baxter lost his Republican party's nomination to Owen Brewster. While in office, Governor Brewster climbed and erected a plaque at the site of the spring as the first "sitting" governor to climb the edifice. Called Governor's Spring, he used photos of his climb to promote his proposal to convert the region to a national park. Baxter defeated the proposal and in 1933 purchased the first parcel of land of what would eventually become Baxter State Park. Of course the Governor's Spring plaque was replaced with one that reads Thoreau Spring - whether or not he was actually there. So the story goes.
A SPECTACULAR DISPLAY FROM ATOP BAXTER
After 5 hours of climbing, our efforts were rewarded with an unmatched view from the east side of Katahdin. Everything in sight is a compendium of a billion years of geological evolution - Rodinia's fragmentation, Paleozoic plate convergence, the closure of two oceans, Acadian deformation, Katahdin emplacement, the rifting apart of Pangaea, hundreds of millions of years of landscape erosion and exhumation, and finally, Pleistocene glaciation.
Facing northeast from Baxter Peak, the glacial tarn of Chimney Pond lies 2,775 feet at the foot of the ice-carved, semi-circular cirque of South Basin - formed by erosion of an alpine glacier. With the cessation of glaciation, erosion has continued the process of excavation via mass-wasting and repetitive freeze-thaw cycles. Further out on the forest floor of glacial outwash and till, North and South Basins, also tarns, have been impounded by the Basin Ponds end moraine. In the middle distance, North and South Turner Mountains are separated by a glacial U-shaped valley. Rhyolite-composed Traveler Mountain, the co-magmatic partner of Katahdin, is in the clouds at the extreme left.
Photographic documentation of our ascent to the summit of Katahdin! We're standing on weathered blocks of granite, although bedrock crops out just below the summit. On the far side of the sign is a 2,000 foot drop off to the valley below.
|Well done, Will!|
Leo and Will's turn in front of the lens!
|This photo says it all.|
This tablet on the summit of Mount Katahdin was placed on March 16,1932 to record the "gift and conveyance" of nine square miles of land to the State of Maine by former Governor Percival P. Baxter, made upon the express condition that the tract "forever be left in the natural wild state."
Notice the salmon color of the granite. It is estimated that the roof of the pluton was only a few hundred feet above this spot. Also, observe the weather fractured cobbles, boulders and grus (coarse-grained sand and gravel resulting from the granular disintegration of the granite from mechanical and chemical weathering) that cover the summit. Even lichens contribute to the insidious dissintegration of the granite by secreting organic acids.
THE KNIFE EDGE
The Knife Edge Trail (blue paint blazes) traverses the apex of a serrated arête that runs the mile or so between Baxter and Pamola Peaks. The north side of the ridge is formed by the glacial cirque of South Basin, while the south side, which likely was sculpted by the Laurentide ice sheet, doesn't bear the classical cirqued-features of alpine glaciation. The south side of the arête may be a greater victim of mass wasting and frost-shattering. Therefore, calling it an arête, which technically requires carving from alpine glaciers on both sides, may not be totally correct.
That said, nothing detracts from the massivity of the ridge and the focus climbers must maintain while negotiating its exposed sections that are merely two feet wide in some areas and plummet some 2,000 feet in either direction. This is probably the most spectacular mountain trail in the East. High winds can be unpredictable and extremely menacing here. The Baxter State Park website posts the warning "Not for the faint of heart!"
This photo faces east from Baxter and illustrates how the Knife Edge curves to meet Pamola Peak. If you click on the image to enlarge it, you'll see numerous hikers balancing their way across it.
|The Knife Edge|
From the same perch on Baxter Peak, we're looking south into the "cloud factory" of Katahdin's south face that we experienced earlier on the Gateway and the Tableland, which slopes off to the right. The Knife Edge begins off to the left. Notice the extent of weather-pulverized rock that litters the summit that completely blankets the bedrock.
|South-facing view from Baxter Peak|
The Knife Edge is rather blunted in this early section and covered by large boulders of Katahdin granite. At the far left in the sun, heavily-jointed, granophyric Katahdin bedrock is exposed at the top of South Basin's headwall and throughout most of the arête. Again, notice the climbers for scale. I counted 11 in the photo.
|The Knife Edge as it strikes east from Baxter Peak|
THE LAURENTIDE ICE SHEET
The Pleistocene epoch began in North America about 2.58 million years ago - traditionally referred to as the first of the Quaternary Period. Over this relatively short span of time geologically, the landscape of North America in Canada and the United States was dramatically altered by at least four phases of glaciation by an up to two-mile thick, slow-moving ice sheet called the Laurentide. Driven by vacillations in the climate, a multitude of glacial advances and regressions (glacial and interglacial episodes) occurred, the most recent of which is the Wisconsinan that extended to about 38 degrees latitude.
Extent of Pleistocene glaciation at 18,000 years ago.|
Note the depth of the continental ice sheet in meters. Katahdin is at the red dot.
Modified from A. McIntyre, CLIMAP Project, Lamont-Doherty Earth Observatory, 1981.
THE ICE AGE IN MAINE AND THE SCULPTING OF THE MODERN LANDSCAPE
Following Katahdin's emplacement in the Early Devonian, hundreds of millions of years of erosion worked to remove nearly two miles of overburden that buried the pluton. Looking back about 10 million years, we would likely see that the general features of the landscape in Baxter State Park were likely already fashioned. Once exhumed, Pleistocene glaciers began to sculpt Katahdin's modern landscape out of its granite.
The Laurentide ice sheet flowed southeast across Maine and terminated at Georges Bank (a submerged area of the sea floor between Cape Cod and Nova Scotia) at a time when the level of the seas was 300 feet below present during glacial maximum. The oceans reached their modern level about 3,000 years ago and of course are on the rise - this being an inetrglacial epoch of warming called the Holocene - the most recent time frame of the Quaternary.
Enough water was held in continental ice sheets during the Pleistocene to lower sea level worldwide by about 150 meters. When deglaciation and the ice age finally ended about 12,000 years ago, the ice sheet left the landscape of Katahdin and the surrounding lowlands with a distinctive array of erosional and depositional landforms in what is a textbook study in glaciomorphology. Few places in the northeastern United states offer a chance to see these features in such an unspoiled setting. Some 400 million years of surface erosion and post-glacial isostatic rebound have allowed the landscape to assume its present attitude almost a mile above sea level.
North view of the Basin Ponds and the Basin Ponds moraine|
The Google Earth vertical exaggeration is greatly increased in order to visualize the Basin Ponds moraine that impounds three tarns at the foot of Great and South basins.
THE ENIGMA OF THE BASIN PONDS MORAINE
Perhaps the most puzzling question concerning Katahdin’s glacial history was whether there was cirque glaciation on Katahdin following the retreat of the continental ice sheet of late Wisconsinan time or perhaps even whether alpine glaciation preceded the arrival of the ice sheet. A second question is whether Katahdin was a nunatak (an Inuit word) with its summit remaining isolated from glaciation.
Glacial erratics found on Katahdin in addition to polished bedrock and striations indicate that Katahdin was in fact once covered by the last advance of the Laurentide ice sheet during Late Wisconsinan glaciation between about 25,000 and 12,-13,000 years ago (Davis, 1989). That disproves the hypothesis that Katahdin remained a nunatak during continental glacial advance (at least during the late Wisconsinan glacial maximum). On the other hand, arguements against the nunatak explain why the serrate topography such as the Kinfe Edge appears so fresh. The controversy that remains is whether the alpine glaciers persisted in the cirques after the ice sheet retreated to the north.
|I photographed this quartz-veined metamorphic rock high on the slopes of the Hunt Trail of west Katahdin. This small erratic is a confirmation of the glaciers that once covered at least a portion of Katahdin.|
In the past, many (including Caldwell, 1959) felt the cirques and arêtes were too fresh to have been ice sheet overridden and therefore shaped by alpine glaciers. More recently, it has been suggested that the continental ice sheet covered Katahdin but post-glacial mass wasting controlled by vertical jointing of the bedrock shaped the cirques and arêtes (Davis).
Two scenarios are being entertained today. Caldwell envisions a "two-glacier" history - ice sheet followed by alpine glaciers. He interpreted the Basin Ponds moraine to be a medial moraine between alpine glaciers flowing from the east-side cirques and a tongue of the ice sheet flowing between Katahdin and the Turner Mountains to the east. Davis, on the other hand, hypothesized the continental ice sheet was the final glacial activity on Katahdin and interpreted the Basin Ponds moraine to be a recessional-lateral moraine of the waning ice sheet between Katahdin and the Turner Mountains. Clearly, the Basin Ponds moraine is the most controversial glacial feature in Baxter State Park.
A TREK ACROSS THE SADDLE
As we descended from Baxter Peak across the Tableland, the Saddle Trail can be seen below winding along on the low-lying, flat-topped ridge called the Saddle. The Saddle Trail traces the rim of the Great Basin before abruptly heading down the cirque on a precariously steep and loose rock slide from an avalanche that occurred during the winter of 1898-1899. Avalanche scars are common on Katahdin's steep slopes such as the Y-shaped one in the photo. Rockfalls are common as well on the cirque walls, weakened by joints and freeze-thaw action.
Coming off the rubble-covered Tableland from Baxter Peak, the Saddle Trail dips into the Saddle.
The surface leading to the Saddle is literally covered with weather-pulverized cobbles of granite with larger boulders peppered here and there.
|Weathered and frost-shattered granite literally painted with lichen on the Saddle|
Bright yellow-green and black lichens on the red granophyric phase of Katahdin granite were a feast for the eyes.
We're looking back at Baxter Peak from the beginning of the Saddle, as we entered the densely packed and stunted trees of the krummholz zone. There are almost 50 people celebrating their ascent on the summit of Baxter, but you'd never know it from here. One group opened a bottle of champagne to toast their accomplishment.
|Glancing back at Baxter Peak, once we cometh, from within the krummholz|
The Saddle Trail strikes a rock-hopping path through the krummholz on large boulders of weathered granite. That's Will in the green shirt picking his way down. The landscape pitches to the right in the direction of the cirques.
|Krummholz zone of the Saddle|
DESCENDING THE SADDLE TRAIL
The first portion of the Saddle Trail is appropriately called the Slide on the start of Great Basin's headwall. The going is slow on thin, steep ledges and loose slide material. Cathedral Ridge and Trail are in the middle distance - an arête that separates Great Basin from South Basin. The three knobs on the trail are the "cathedrals" formed by the erosion of porphyritic granite that has been sectioned by vertical joints. Triangular-shaped Chimney Pond is at the base of South Basin at the foot of the headwall that rises to Pamola Peak in the clouds. As one progresses downslope, the red granophyric phase of granite gradually transitions back to the light gray granitic phase, the reverse of what we saw on our west side ascent.
By way of review, every feature in immediate view is composed of intrusive, Devonian-age Katahdin granite with the exception of the more easily eroded sedimentary rocks of the lowlands. The volcano's carapace of extrusive tuff-rhyolite has been eroded away in the process of its exhumation with the exception of Traveler Mountain.
Surprisingly, the majority of the granites in Maine don't form mountains. The multi-phasic structure of the Katahdin granite - the granophyric phase in particular - is responsible for building the high mountain edifice, or better stated, preventing its erosion. Finally, glaciers of the Pleistocene are responsible for the extreme topography, and its erosional and depositional features and landforms.
For another perspective of South Basin, here's a Google Earth view from the middle of the Saddle Trail, which we descended in the above photo. The caldera-like morphology of Katahdin is a consequence of glacial erosion, mass wasting and freeze-thaw action, although some calderic collapse was a likely occurence during Katahdin's post-emplacement history. The U-shaped bowl of South Basin is framed by the arêtes of Keep Ridge on the left and Cathedral Ridge on the right - created by the action of alpine glaciers excavating both sides of the ridges. At the top of the headwall, the Knife Edge runs from Pamola to Baxter Peak.
THE UPPER AND LOWER BASIN PONDS AND MORAINE
In the distance (below), Upper and Lower Basin Ponds are dammed by the Basin Ponds moraine just beyond them - the puzzling feature that we discussed. The moraine stretches nearly three miles and has as much as 50 feet of relief. Its largely consists of granite in all sizes, some up to 20 feet across. It's noteworthy that Davis (mentioned earlier) found that 10-44% of its rocks were non-granitic - in keeping with his only an ice-sheet-conclusion. Davis further pointed out that the ridge of the moraine is convex westward - a curvature opposite to what one would expect from alpine glaciers that might have originated from the west on Katahdin. What's your interpretation? No Biblical Flood theories please.
The ephemeral Dry Pond in the foreground is water-filled. Beyond, Whidden and Sandy Stream Ponds are almost hidden in the forest before the slopes of South Turner Mountain.
Subglacial sediment transport as debris-rich ice were deposited as meltout till, but other depositional landforms exist as well in Baxter State Park. While a large drumlin-field exists in southern Maine, the Katahdin esker system consists of a sinuous, branching network of poorly-sorted sand, gravel and boulders that stretches 150 km from its source near the entrance to Baxter State Park just south of Katahdin to its terminus at Pineo Ridge near the Maine coast. These glacio-depositional landforms were left in the wake of the receding ice sheet.
Eskers are constructed by subglacial streams and rivers flowing within ice-walled tunnels along the glacier bed. Their resemblance to long-abandoned railway embankments led Maine old timers to humorously refer to them as "Indian railroads." In fact, some rural roads in the area are built along the crest of an esker.
The Basin Ponds, Dry Pond and the Basin Ponds moraine|
The setting sun on the opposite side of Katahdin is casting long shadows across the valley.
Perched on a thin ledge of the Saddle Trail, the view was unmatched. That's Katahdin Lake in the middle distance. The Canadian border between eastern Maine and the province of New Brunswick lies 55 miles due east, and Nova Scotia and the Bay of Fundy is another 160 miles.
For the record, the Bay of Fundy lies in a rift valley called the Fundy Basin. The rift began to form when Pangaea began to break up in the Late Triassic. The formation of the Atlantic Ocean placed Katahdin and the entire Appalachian Mountain range within reach of the sea along North America's east coast.
|View from the Saddle Trail of the glacial valley at the merging of the foot of the cirques|
Vertical-jointed granite on the knobs of Cathedral Trail stand out in profile. Beyond, Pamola has briefly emerged from the clouds. The notch to the right of the peak is the ridge-crest manifestation of the Chimney, a northwest-trending fault zone of highly fractured rocks that continues to the foot of the cirque as a steep, narrow gully or couloir. The Chimney is a popular challenge for technical climbers heading to the Knife Edge.
|Pamola Peak and the Cathedral Ridge in profile from Saddle Trail|
From the Ranger Cabin at Chimney Pond, the impressive semi-circular headwall of South Basin dominates the frame. The sun was very low on the horizon on the far side of Katahdin. You can make out curtains of granite that are exfoliating from the headwall.
Eight or nine recognizable cirques surround Katahdin with the exception of its south flank. The three largest are on the east side of the mountain. Why are the east-facing cirques larger than the others? One explanation is that prevailing northwest winds blow snow to the largely sun-sheltered east-side cirques. A similar prevailing climate during the Pleistocene would have encouraged the cirque-size disparity.
|The sheer headwall of South Basin|
From the water-filled Dry Pond seen from above, we're looking back at the base of the Cathedral and Great Basin beyond. Wet Pond is an ephemeral tarn that is subject to the whim of precipitation from the watershed of South Basin. Outwash deposits from meltwater streams blanket the region as do erratics of all shapes and sizes.
|A not-so-dry Dry Pond|
BAXTER PARK RANGER TO THE RESCUE
Pamola, the bad-tempered, winged deity of Katahdin, was good to us. Our west-to-east traverse was a resounding success and an invigorating experience in terms of the geology and the fun we had. Our 10-mile expedition took 11 hours to complete. The only problem was that our car was over 20 miles away on the opposite side of the mountain. Having arrived in the valley and forest wilderness after dark, we more fully appreciated why the gate attendant asked if everyone was carrying a flashlight. Fortunately for us, it was a brilliant full moon, and we didn't even need one.
Our plan to hitch to our car was totally unsuccessful in that virtually none were leaving the Roaring Brook campground. Fortuitously, a conversation we struck up with a Search and Rescue Ranger on the trail resulted in him radioing ahead to the Park Ranger, unbeknownst to us, who picked us up on the forest road and gave us a lift back to our car.
That's Leo and Will in the back of the Ranger's pickup. Thank you Baxter Park Rangers and Governor Percival Baxter for making it all happen. What a great day!
Henry David Thoreau
WHAT'S IN A NAME?
The Romans called their settlement on the south bank of the Seine River Lutetia Parisiorum or Lutetia of the Parisi, after the Gallic people who settled in the area in the third century BC. Lutetia (Lutece in French) is thought to have been derived from a Celtic root-word luteuo- meaning "marsh" or "swamp." Lutum is also the Latin word for "mud."
The settlement also lent its name to the Lutetian Age of the Eocene Epoch that occurred 41.3 to 47.8 million years ago. It was a time when the Paris Basin was invaded by a shallow, warm tropical sea from the north of Europe, one of many marine cycles that have flooded the region. It was also a time of marine sedimentation and the evolution of a carbonate platform, when Lutetian gypsums and limestones formed. Its rocks would eventually help to construct the buildings, monuments and churches of the city of Paris.
The official international reference point (GSSP) for the Lutetian is located in the limestone strata of the quarries below the streets of Paris at a water-well that bears the name Bain de pieds des carriers or the Quarrymen's Footbath. The descent to the footbath cuts through the Lower Lutetian limestone allowing the age's precise identification. We'll visit the footbath on post Part II, when we investigate the subterranean catacombs of Paris.
MOULIN DE LA GALETTE - THE MILL OF GALETTE
Perched high above Paris on "La Butte" of Montmartre stands a windmill called le Moulin de la Galette or the Mill of Galette. More precisely a cluster of windmills than any one in particular, it was built in 1717. The name is derived from a “galette” - a flat crusty tart baked by the Debray family, the mill’s nineteenth century owners and millers. Along with le Moulin de Radet down the street and Moulin a Poivre nearby, they were the last of perhaps thirty (the numbers vary in the literature) that once dominated the heights of Montmartre, a once pastoral village dotted with vineyards on the northern outskirts of Paris and now a heavily touristed, upscale residential district of the city.
The windmill was also known as the Blute-Fin - from the French verb “bluter” which means to sift flour. In addition to grinding corn and grains, and crushing grapes and flowers, many of the mills crushed gypsum into a fine powder for the making of plaster of Paris.
The Mill of Montmartre|
In the first quarter of the nineteenth century, bucolic Montmartre
was a picturesque Paris suburb of windmills and vineyards.
Georges Michel, oil on canvas, ca. 1820
Moulin de la Galette and Moulin de Radet on Rue Lepic near the end of the nineteenth century|
According to French history, four Debray family men were involved in defending Montmartre and Paris against the invading Cossacks in 1814. Three were killed with one being quartered and nailed to the blades of the windmill. So the legend goes. The surviving fourth transformed the windmill into the Blute-Fin. The family is buried in the butte's small cemetery with small red windmills marking their graves, a fitting memorial to their nationalistic pride.
As we shall see, the Impressionist artists turned their attention to the windmills of Montmartre, joining the tradition of a cadre of great masters in celebrating an iconic image of Bohemian Paris. Today, the windmill stands as a French national monument with a great story to tell - one where history, politics, philosophy, art and even geology come together.
|Moulin de Radet, a few doors down Rue Lepic from Moulin de la Galette|
THE GYPSUM OF MONTMARTRE
The country village of Montmartre arose on a 420-foot butte above Paris, which served to isolate it from Paris - for a time. Its core contained extensive deposits of layered gypsum - "gypse" in French - derived during the Lutetian Age that played into the history of the region. The word gypsum is a contraction of two Greek words, "ge" for earth and "epsun" meaning to concoct. The soft mineral was sought after throughout Europe and across the Atlantic in the 18th and 19th centuries. For it was gypsum that was processed into plaster of Paris.
Entrance to a quarry at the foot of Montmartre in 1832|
|Cathedral-like vault in a Montmartre gypsum quarry with wooden shorings to prevent collapse|
When approaching Paris from a distance or seen from the Eiffel Tower in the photo below, one of the most conspicuous buildings is the gleaming travertine of the Basilica of Sacre Cour, dedicated to the Sacred Heart of Jesus on the penultimate summit of Montmartre. Built between 1875 and 1914, the absence of large surrounding structures isn't because developers desired to maintain the butte's rustic ambiance. It's because the undermined, gypsum terrain is unsuitable to withstand the weight. To overcome the obstacle, the travertine of Sacre Cour required specially deep foundations during its construction to secure it from collapse. An intergral part of Paris today, it takes some imagination to envision the butte of Montmartre only 175 years ago as a hilltop village.
FROM MINE TO MARKET
After removal from the quarries, gypsum was heated in kilns at 300º F to drive off water and brought up the road on wagons pulled by donkeys or oxen to the mills for grinding. Romantic and colorful images of the early mining and milling days of Montmartre were created by a cadre of Impressionist artists that gravitated to the area not only to paint but to take up residence. They document the pastoral nature of Montmartre, its windmills on the heights and the quarries below.
Early Windmills and Montmartre Quarry|
Artist and source unknown
Montmartre the Quarry and Windmills|
Vincent van Gogh, oil on canvas, 1886
After milling, the calcined ground gypsum was bagged and sent downhill by wagon on its way to global markets via the River Seine. At the foot of Montmartre, it passed through the Barriere Blanche or White Barrier, a gate built for the collection of taxes for goods such as plaster coming into the city of Paris and named for the white powder that spilled from the wagons on the facades of buildings and the roadway.
Bagged plaster loaded onto wagons|
Museum of Fine Arts in Bordeaux
Later, the gate became the Place Blanche or White Plaza. Even the Paris Metro train station is called Blanche. Francophiles will recognize the plaza as the location of the Moulin de la Galette-inspired Moulin Rouge or Red Mill. The faux-mill was a fashionable cabaret that opened at the foot of the Montmartre hill in the red-light district in the late nineteenth century and home of the anatomy-revealing can-can dance. And nearby at the top of the Rue Lepic on Montmartre, the historic Moulin de la Galette is still open for business as a restaurant.
At the Moulin Rouge, the Dance|
Henri de Toulouse-Latrec, oil on canvas, 1880
The impact of geology on the evolution of Parisian history acted in both subtle and obvious ways - the butte location of Montmartre (which has also served as a strategic military location), its gypsum-grinding windmills, and the establishment of Montmartre's artistic heritage based on its geographic and political location and isolation.
PLASTER OF PARIS, FRANCE
When water is re-added to heat-calcined gypsum, it forms a hard setting paste - a calcium sulphate hemi-hydrate or plaster of Paris. Amongst its many desirable properties, the compound is a non-combustible, natural fire retardant and insulator that absorbs heat and only releases water vapor in a fire. It was not only used on building facades but as a stone mortar by the Romans in the first century. It was also a sculpting material and used for decorative architectural purposes on tiles and frescoes dating back as far as the ancient Egyptians and Mesopotamian cultures.
Paris escaped devastating urban fires since the late Middle Ages, in part because of plaster on interior and exterior walls. One year after the Great Fire of London in 1666, French King Louis XIV decreed that timber-framed structures were to be covered with plaster. That put Montmartre and its gypsum deposits on the map. But it was Louis-Napoleon Bonaparte, later to become Emperor Napoleon III and the nephew of Napoleon Bonaparte, that took the city of Paris and Montmartre in a completely different direction, a path that would end gypsum mining and radically change the urban landscape.
|In this 1820 view of the butte of Montmartre, urbanization has already begun, yet the gypsum quarries, both open and underground, were still present. Off to the left you can make out two windmills. Mining would change under the reign of Napoleon III.|
QUEST TO BUILD A MODERN METROPOLIS OUT OF A MEDIEVAL CITY
In 1848, Louis-Napoleon arrived in Paris from London at forty years of age. After a family exile of thirty-three years, he brought back his architectural experience of Europe's grand cities and envisioned the same for Paris. After becoming the first president of France in 1853, Napoleon and his appointed Prefect of the Seine, Georges-Eugene Haussmann, initiated a seventeen year plan of radical demolition and extensive reconstruction of the city of Paris. Napoleon's quest to build a modern European French capitol had begun, and its buildings and monuments would rise out of the limestone buried beneath the city.
The "Old" Paris of crowded, dangerous, filthy, disease-infested, narrow labyrinthine streets was razed and transformed into a modern "New" Paris of broadly radiating boulevards, elegant parks, public buildings, private palaces, apartment complexes, ornate fountains, decorated bridges, reliable water, sewer systems, facade-standardized buildings, railroads, gas street lamps and even public urinals for men - essentially the modern Paris of today.
THE GEOGRAPHIC ISOLATION OF LA BUTTE DE MONTMARTRE
Reminiscent of Greenwich Village, a former bohemian haven and now upper-class neighborhood in New York City, Montmartre's autonomy as a country village has survived, in part, by virtue of its isolated geography having been a train ride or one hour walk from center Paris up the heights, as well as having escaped Haussmann's radical renovation.
Montmartre was outside the Mur des Fermiers generaux (the Wall of the Farmers-General), a 28 km long, physical and fiscal barrier that surrounded Paris built by King Louis XVI between 1784 and 1791. Rather than acting as a defensive barrier against invasion, unpopular entry tolls were extracted and duties were levied on goods entering the city (called "octroi") at various point along the wall. The wall contained 47 gates and 16 tollhouses, many with architectural merit. Interestingly, some portions of the wall still exist as an elevated roadway and four tollhouses remain. We'll enter one in my Post II at the Barriere d'Enfer on the Left Bank and descend into the limestone quarries beneath the streets of Paris.
WORKING CLASS EXODUS
Unable or unwilling to pay the entry taxes and displaced by Haussmann's city-wide renovation, thousands of the less well-healed working class of laborers, farmers, seamstresses, milliners, students and artists departed from Paris. Outside the customs barriers and the taxman's reach, Montmartre's quiet streets and low rents made it a melting pot for free-thinking bohemians, dissident politicians and the young avant-garde.
As for the fourteen windmills on the hill, they had less to grind. The gypsum quarries closed in 1860, the same year that Montmartre was annexed to Paris with the destruction of its walled enclosure. Today, Montmartre is within the 18th arrondissement - Paris's clockwise spiral of municipal districts - yet still retains its medieval, narrow maze of streets in contrast to the "new" Paris in the flats below the butte.
A TALE OF TWO CITIES - ONE A MODERN NEW METROPOLIS AND THE OTHER A STRONGHOLD OF CREATIVITY AND FREE-THINKING
As for the Moulin de la Galette, it was repurposed by the Debray family into a "guinguette," after a sour local white wine called "ginguet". Guinguettes were colorful, outdoor, raucous establishments for eating, drinking, laughing and enjoying life and nightlife. It was where bourgeois (middle class) patrons from Paris could rub elbows with prostitutes. It was where dancing was allowed where you could touch your partner!
Furthermore, it had an even greater impact as a place where Paris's displaced intellectuals, artists, writers, poets, musicians, sculptors and architects gathered. Impressionist paintings of carefree Parisians enjoying Montmartre - by artists such as Renoir, van Gogh, Degas, Picasso, Modigliani, Utrillo, Toulouse-Lautrec and others - documented the evolution of the two cities - and even their geological histories! Let's return to the quarries of Paris.
LES GYPSE ET CALCAIRE DES CARRIERES DE PARIS - THE GYPSUM AND LIMESTONE QUARRIES OF PARIS
Sedimentary deposits of gypsum were generally located in the north and northeast quarters of Paris, mainly in the neighborhoods of Montmartre, Buttes-Chaumont, Charonne and Menilmontant. Gypsum is present in South Paris across the river but in thinner deposits. On the map (below) of the "Old Quarries of Paris," the two main quarries of gypsum (green shaded) are identified by arrows in the villages of Montmartre on the left and Belleville on the right, both on the Right Bank (north side) of the River Seine.
The Lutetian-age gypsum that was quarried in Paris's northern tier was called ludium gypsum in strata separate and above that of limestone in the southern tier called lutetian limestone. Before the initiation of limestone formation, 50 million years ago, deformation elevated the southern portion of the Paris Basin. The sea repeatedly transgressed and regressed over the region forming carbonate banks. Once elevated, a crustal fold confined sea water to lagunas that formed evaporites of gypsum in layers. The geological fold - called the Ypresian fold - acted as a dam on the upper plateau south of Paris. The contemporary result was high concentrations of gypsum in the subsurface and limestone to the south near the surface (20 to 30 m).
ANCIENNES CARRIERES DE PARIS - OLD QUARRIES OF PARIS
Across the River Seine from Montmartre that slices Paris into its two famous banks, the Left Bank was open-pit mined for its "coarse" limestone (calcaire grossier) since Gallo-Roman times. In the 17th and 18th centuries, mining went underground. That practice honeycombed the depths of Paris even more than Montmartre with miles of subterranean (souterraines) quarries. As with gypsum, the deposits of limestone and their quarries have affected the historical, political, cultural and creative evolution of the city of Paris. What is the Paris Basin, and how did it form?
LE BASSIN DE PARIS - THE PARIS BASIN
More than just the immediate lowland around its namesake, the Paris Basin covers a vast portion of northern France – over 140,000 square kilometers - and measures 500 by 300 km. The basin extends northwestward below the English Channel into the London Basin and connects to the Belgium Basin to the north - summarily referred to as the Anglo-Paris Basin.
Simplified Geologic Map of Europe Showing the Main Orogenic Systems and Sedimentary Basins|
From Geology of Europe by Franz Neubauer
The 776 km Seine River and its tributaries drain the basin and slice Paris into its two famous banks – Left and Right for south and north. The basin recharges along its eastern border and discharges to the English Channel’s seafloor at Le Havre, Normandy.
ORIGIN AND EVOLUTION OF THE PARIS BASIN
Geologically, the Paris Basin is an intracratonic (intraplate) sedimentary trough of flat valleys and low plateaus built on a collapsed Variscan collisional belt. The depocenter resides on an extended continental shelf (epicontinental) of the Eurasian plate that has been periodically invaded by marine high seas. It's built on a Cadomian-Variscan crystalline foundation surrounded by crystalline highs of late Paleozoic age and came into existence during a period of rifting in Permo-Triassic times.
The basin's tectono-sedimentary history is complex with several aspects that are poorly understood and strongly debated. For clarity (I hope), I divided the events into stages: (1) Acquisition of Cadomian basement; (2) Avalonia-type terranes accrete to Laurentia; (3) Cadomia-type terranes accrete to Laurussia; (4) Variscan orogeny forms a Gondwana Europe within Pangaea; (5) Post-Variscan extension creates epicontinental depocenters; (6) Pangaea rifts apart sending peri-Gondwanan terranes across the Atlantic; (7) Global high seas repeatedly flood epicontinental Europe; (8) Alpine Orogeny shapes and confines the basins.
(1) Acquisition of Cadomian basement rocks
The break-up of the supercontinent of Rodinia in the latest Proterozoic to Early Cambrian (ca. 0.75 Ga) resulted in the formation of three large mega-continents, and numerous smaller landmasses and microterranes. The big three were: Laurentia and Baltica located equatorially and massive Gondwana sprawling australly. An elongate assemblage of island-arc, microterranes of Rodinian ancestry became attached to the northern margin of West Gondwana during the Cadomian orogeny. The ribbon of amalgamated terranes is also called a superterrane, with each component named for its ultimate tectonic-destination on the continents of North America and Europe.
Facing the newly opened Iapetus Ocean (more so as Baltica drifts to the north), the “peri-Gondwanan” terranes are categorized as largely Avalonian-type and Cadomian-type, which designates their future accretionary locale after separating, rifting and drifting from Gondwana. One author's interpretation (below) adds the Serindia-type terrane for regions of North China. The Cadomian terranes eventually formed a portion of western Europe's basement carrying its earlier Rodinia rocks in transit. Typical of tectonic processes, plate collisions transport, reimprint and rework their crust.
(2) Avalon-type terranes accrete to Laurentia
Although this stage is not germane to the formation of the Paris Basin, an explanation would be incomplete without commenting on the destiny of the Avalonia terrane. Throughout Paleozoic time in what's called the "supercontinental cycle," the Gondwana-derived basement blocks sequentially reassembled to form the supercontinent of Pangaea. During the Acadian-Caledonian orogeny (Ordovician to Early Devonian), the Avalonian-type terranes rifted from Gondawana, drifted across the Iapetus Ocean as it closed, and accreted to eastern Laurentia (early or proto-North America). Following the Silurian closure of the Iapetus Ocean, mountains were built from northeastern Laurentia into Scandinavia and parts of north-central Europe. The black outline of the modern continents can be differentiated on the map. At this time, the Cadomia-type terranes remained attached to Gondwana.
Jumping ahead, when Pangaea later fragmented apart (just as Rodinia previously did), the Avalonia terranes would separate between North America and Europe across the Atlantic Ocean. As a result, we occasionally use the terms of West Avalonia (for the Canadian Maritimes and down the east coast of North America) and East Avalonia (for southern Britain and the Brabant Massif into parts of northern Germany). When new landmasses (and even ocean basins) form and reform, geologists use new names to identify them in time - similar to new countries that are renamed by their new political leaders.
(3) Cadomia-type terranes accrete to Laurussia - France's basement!
By the Permian, the main mass of Gondwana collided with Laurussia (Laurentia + Baltica + Avalonia) in the Ouachita-Alleghenian-Variscan orogeny and assembled the supercontinent of Pangaea. The resulting mountain belt was the largest collisional orogen of the Paleozoic. In Europe, it produced a suture from Germany (Mid-German Crystalline zone) through southern Britain (Lizard ophiolite) through France to southern Iberia (Pulo do Lobo unit). Hence, the Rheic suture separates the Cadomian terranes of western and central Europe from the terranes derived from East Avalonia in Britain.
The closure of the intervening Rheic Ocean (recall that the Iapetus Ocean closed with the Avalonia collision!) brought the Cadomian-type terranes of Gondwana into contact with Laurussia (red arrow) during the Variscan orogeny (formerly Hercynian). The Variscan and Alleghenian orogenies were contemporaneous and more-or-less physically contiguous. The collision of a Gondwana-derived Europe was forming on Laurussian soil! France was never before so close to French Canada!
(4) Variscan orogeny forms a Gondwana Europe within Pangaea
The Variscan orogeny is building a Gondwana European basement within Pangaea. Its formation left Variscan orogenic remnants and a montage of Cadomian terranes in France and central Europe. As with East Avalonia in southern Britain, Europe's Cadomian basement ended up across the Atlantic when Pangaea fragmented apart.
|A European Collage of Amalgamated Gondwana-derived, Avalonia and Cadomia-type Terranes|
This map demonstrates the complex accretion history of Europe. For reference, Paris is at the red dot.
Modified from Ballevre et al, 2008.
(5) Post-Variscan extension creates epicontinental depocenters
Following the Permian consolidation of Pangaea, the supercontinent began to fragment apart. The re-activation of pre-exisiting Variscan compressional faults formed new, extensional back-arc rifts in late Permian through Triassic times. In the Triassic, extension led to the opening of oceanic marginal basins. This allowed the development of numerous European sedimentary basins including the Paris Basin in Gondwana Europe. Europe has not yet formed and will not be called as such, geologically, until Pangaea fragments aparts and sends parts of the Avalonia terrane and the entirety of the Cadomia terrane across the Atlantic Ocean.
(6) Pangaea rifts apart sending peri-Gondwanan terranes across the Atlantic
As Pangaea's break up progressed, the Eurasian-North American plates drifted apart sending East Avalonia and the Cadomian terranes across the Atlantic. Beginning in the Permian and while in tectonic-transport, crustal extension continued across Europe with the establishment of a broad, open shelf that occupied much of southern Germany, the North Sea and the Paris Basin. The subsidence of the basins created accommodation space that became the site of sedimentation as the sea level of global high seas repeatedly and episodically fluctuated. Most of the Paris Basin became emergent near the end of Jurassic time, a relict appendage of the large Triassic German basin.
Paris within the Paris Basin Surrounded by Remnants of the Variscan Orogen|
From CNAM / MNHN: SGF "The Parisian basement: quarries, underground projects and the Grand Paris"
by J.-P. Gely, 2013
(7) Global high seas repeatedly flood epicontinental Europe
The opening of the Atlantic Ocean, beginning in the Cenozoic, had a profound affect on the neighboring North America and Eurasian plates. The main process was a general extensional stretching that produced numerous marginal basins and grabens. Large quantities of clastic materials were deposited in repeated transgression-regressions of the sea within the many depocenters that trended pre-existing structural directions.
In France within the Paris Basin, during the Late Triassic, siliciclastics were deposited; Jurassic Liassic-time organic-rich black shales, Dogger carbonates and Malm-time clays. The return of the sea in Cretaceous time deposited chalk. Basin sedimentation continued into the Tertiary. With particular interest to this post is the Lutetian age of the Eocene (Tertiaire on the map below and diagram below) with a shallow-water environment conducive to the formation of limestone and evaporite deposits of gypsum.
|Simplified Map of France and the Paris Basin|
In addition to creating Alpine mountain plate across Europe and into Asia, it regionally caused northwest-southeast compression of the Paris Basin and formed anticlines along genetically-related, basement fault systems. The widespread uplift inverted many basins and served to isolate the Paris Basin. The uplift also profoundly effected the fluvial systems with drainage lines occurring along structural elements. Cretaceous and Tertiary deformation and erosion have exhumed Mesozoic sediments and the underlying basement.
Main Stages of the Tectono-Sedimentary Evolution of the Paris Basin|
From Baccaletto, 2010.
THE PARK OF BUTTES-CHAUMONT - A GREEN SPACE UNLIKE ANY OTHER
We have one more important gypsum-mining area to discuss located about two miles east of the Montmartre quarries. Like Montmartre, the quarry is inactive and unrecognizable. Inaugurated in 1867 and coinciding with the opening of the World's Fair in Paris, les Parc des Buttes-Chaumont occupies the site between the villages of Belleville and La Villette (right arrow above on the "Ancient Quarries of Paris" map) in the 19th arrondissement.
Butte is French for “mound,” and Chaumont is a 9th century contraction of “chauve” meaning bald and “mont” meaning mount. The "Bald Mount" acquired its name from its lack of vegetation due to an abundance of clay and gypsum in the soil.
|View of Park of Buttes-Chaumont from the promenade looking north toward the lake and the temple. The residential quarter of La Villette is in the background.|
In spite of its most austere beginnings, today the park is a major local attraction replete with a rocky island topped by a romantic shrine in the middle of a picturesque artificial lake. Evocative of the Alps, it occupies 25 hectares and is the fifth largest park in Paris. Its grounds are overflowing with ornamental trees, waterbirds, and within the lake, an abundance of fish. From a bleak gypsum quarry to an iconic urban park, the history of its metamorphosis is beyond anything imaginable.
The Temple of Sibylle in the Park of the Buttes-Chaumont|
A tonemapped, High Dynamic Range Photo
A LUNAR LANDSCAPE WITH A SINISTER AND MOST PUTRID REPUTATION
The area of the park, being just outside the limits of the toll barrier wall, was mined for gypsum for centuries as was the Butte Montmartre. It was close to the site of the Gibet of Montfaucon, a notorious and malodorous place where 80 condemned men and women could be executed at the gallows simultaneously and their bodies left to dangle on display as a deterrent to crime well after their executions. Later, the desolate quarry became a public waste refuse and sewage dump, and even an abattoir (slaughterhouse) for horses where the remains were left to decompose. The quarry also had an unsavory reputation for harboring thieves and as a shelter for the destitute. It took a tremendous imagination to envision a park on this impoverished site.
|The quarry photographed by Henri le Secq in 1863 showed a desolate, pockmarked lunar-landscape sandwiched between the villages of Belleville and La Villette.|
The site "spread infectious emanations not only to the neighboring areas, but, following the direction of the wind, over the entire city" (Alphand). Amazingly, this most desolate wasteland was transformed into a spectacular garden park as part of the new Paris of the Second Empire.
Left: Gibet de Montfaucon, 1811. Right: 1811 Rendering horses
From an article by Francois Choay in the Urban Park magazine, 29, 1975.
"A DELICIOUS OASIS" (GUIDE DU PROMENEUR, 1867)
This not so promising site, to say the least, was envisioned by Napoleon III as a romantic garden showcase befitting a capital. Chosen and conceived by his prefect, Baron Haussmann, it was to be the site of a park for the recreation and pleasure of the rapidly growing population of the 19th and 20th arrondissement - the working class of the petit bourgeoisie. Jean-Charles Adolphe Alphand was the chosen landscape engineer to personally execute the remarkable transformation.
A plan of the Parc des Buttes-Chaumont|
Note the promenades, belvedere, restaurants, artificial lake, central island and its rotunda. A railroad (left) was constructed to bring in soil and supplies. The grotto is at the top center.
When Napolean III became emperor in 1852, Paris had only four public parks, all in the center of the city. His vision changed parks such as the Buttes-Chaumont that were not longer the preserve of aristocratic or royal landowners but were open to the public at large. Through their collaboration, what resulted was one of the crowning achievements of the Second Empire as part of the radical renovation that swept through Paris.
|The quarry cliffs likely photographed by Charles Marville around 1865. The key features of the park are beginning to emerge -the gorge-spanning brick bridge and a section of the quarry above what is to be the lake.|
GLAMOUR FROM DECAY
Beginning in 1864, two years were spent in terracing the land. Railroad tracks were laid to bring in 200,000 cubic meters of topsoil. A thousand workers renovated the landscape, digging a lake and contouring the grounds with rambling lawns, gently sloping hillsides, splendid vistas and shaded strolling paths.
|The plan of the park created by Alphand and photographed by Marville. Again, notice the promenades, the carefully landscaped terrain, a restaurant, the supply railroad, the lake, island and temple at the summit.|
NATURE TECHNOLOGICALLY REINVENTED FOR THE PETITE BOURGEOISIE
Explosives were used to sculpt the gypsum buttes and former quarry into a small mountain 50 meters high on a rocky island surrounded by cliffs. In a corner of the park, a spacious grotto was fashioned with a cathedral-like vault remniscent of the interiors of gypsum quarries seen at Montmartre. Its ceiling was decorated with artifical stalactites. Even a hydraulically-pumped waterfall cascaded into a stepping-stone lined pool that flowed out of the grottoes second opening. And everywhere, mosses and vines hung on its walls.
|Outside view of the grotto from the walking path|
View of the inside of the grotto with its contrived waterfall, reflecting pool and faux stalactites
|The ceiling of the grotto with its faux stalactites and skylight. No bats in this place!|
|Even the stone railings that line the paths of the park are faux bois or fake wood intricately stylized with cut branches, bark, leaves and knots, all cast in recently-perfected concrete almost 150 years ago.|
|The Roman temple at the top of the promontory was modelled after the Temple of Vesta in Tivoli, Italy|
Two bridges reach the center island - a 63 meter-long, red metal suspension bridge by Gustave Eiffel, the designer of the Eiffel Tower, and a twelve meter-long masonry bridge, known as the "suicide bridge." Unnoticed by most passersby, the alternating layers of gypsum, marl and sandstone are on display on the excavated quarry-flanks of the mountain.
It comes as no surprise, certainly amongst geologists who are acutely aware of these things, that geology has a profound affect on the evolution of civilizations, cultures and societies. We have seen on our brief visit to Paris, in a small corner of the Paris Basin, how geography and its mineral deposits of gypsum have shaped the history of politics, philosophy and art within the city and around the world.
In my next post "Geological Legacies of the Paris Basin - Part II", we will see the affect that deposits of limestone had on the city of Paris. We'll also descend into the dimly-lit catacombs beneath the streets and explore the infamous ossuaries where 6,000,000 exhumed skeletons from the eighteenth century are both interred and on display.
After returning from Paris, my wife and I drove from Boston to New York City and experienced a most fitting conclusion to our trip abroad. We visited the Metropolitan Museum of Art to see their final exhibition of "Charles Marville: Photographer of Paris." His nineteenth century photographs (425 of them) document the radical transition from the medieval streets of "Old Paris" that led to the broad boulevards and grand public structures of the "New Paris", the one we recognize today. His photos of the gypsum quarries of the Right Bank were incredible.
1. European Geography in a Global Context from the Vendian to the End of the Paleozoic by Cocks and Torsvik, 2006.
2. Growth and Demise of the Jurassic Carbonate Platform in the Intracratonic Basin Paris by Benjamin Brigaud et al, 2013.
3. Impressionism - 50 Paintings You Should Know by Ines Janet Engelman, 2010.
4. Le Lutetien: Une Periode Charniere de L'histoire du Bassin Parisien by Par Jean-Pierre Gely, 2009 (on-line on French).
5. Meso-Cenozoic Geodynnamic Evolution of the Paris Basin: 3D Stratigraphic Constraints by Francois Guillocheau et al, 2000.
6. Middle Lutetian Climate in the Paris Basin: Implications for a Marine Hotspot of Paleodiversity by D. Huyghe et al, 2012 (on-line).
7. Neoproterozoic-Early Cambrian Evolution of Peri-Gondwanan Terranes: Implications for Laurentia-Gondwana Connections by Murphy et al, 2003.
8. Overview of the Subsurface Structural Pattern of the Paris Basin by Baccaletto et al, 2010.
9. Paleography of Europe, DVD Collection, Ron Blakey, Colorado Plateau Geosystems, Arizona, USA.
10. Paleozoic Evolution of the Pre-Variscan Terranes: From Gondwana to the Variscan Collision by Stampfli et al, 2002.
11. Paleozoic History of the Armorican Massif by Michel Ballevre et al, 2008.
12. Paris Basin (Chapter 32) by Alain Perrodon and Julien Zabek, undated.
13. Paris Reborn - Napoleon III, Baron Haussmann and the Quest to Build a Modern City, by Stephane Kirkland, 2013.
14. The Formation of Pangaea by G.M. Stampfli et al, 2013.
15. The Rheic Ocean: Origin, Evolution, and Significance by R. Damian Nance, 2008 (on-line).
16. Urban Design and Civic Spaces: Nature at the Parc des Buttes-Chaumont in Paris by Ulf Strohmayer, 2006 (on-line).
17. Vincent van Gogh - Moulin de la Galette by Simon C. Dickinson, 1023 (on-line).
its squares, its dead ends, its arteries, and its circulation”
Les Miserables, Victor Hugo, 1862
For a discussion of the tectonic evolution of the Paris Basin, its Lutetian stratigraphy and the gypsum deposits of the Right Bank, please visit my previous post entitled "Geological Legacies of the Paris Basin: Part I - Plaster of Paris, the Windmills of Montmartre, the Park of Buttes-Chaumont and a New Artistic Creativity"here.
PARIS SOUTERRAIN - PARIS UNDERGROUND
Stroll the narrow cobbled streets and broad boulevards on the Left Bank of the old French capital. Enjoy Paris’s beautiful storefronts, its exquisite monuments, museums, parks and stunning architecture. Languish in a sidewalk café or dine in a fashionably chic bistro. For the casual observer, it’s impossible to imagine what lies underfoot – 20 to 25 meters below street level.
Paris is a city of layers – both above ground and below. Its underground has many new additions, while others are vestiges of the past, often lost and forgotten. Some are accessible to the public, and others have been sealed for an eternity.
There are Roman Empire foundations and more recent wartime shelters, medieval basements and mysterious church crypts, musty wine cellars and shadowy mushroom farms, subterranean shopping malls and modern multi-level car parks. Factor in 1,305 miles of storm drains and sewers, 133 miles of Métro and RER railway tunnels, and countless miles of utility lines and pipes for water, gas, electricity and telephone. Standing on the streets of Paris, you'd never suspect what exists below you unless you looked at a map of the underground that mirrors the landscape above.
|Modified from the Atlas du Paris Souterrain– a highly-recommended source of information!|
The city of Paris occupies a tiny portion of the extensive Paris Basin – a 140,000 square kilometer shallow epicontinental trough of flat valleys and low plateaus in the north of France. On a larger scale, the depocenter of the Anglo-Paris Basin that spans the English Channel into Great Britain resides on the continental shelf of the Eurasian plate. Its foundation is a Late Proterozoic Cadomian-late Paleozoic Variscan crystalline basement. Please visit my post Part I for the Paris Basin’s juicy tectonic details here.
|Paris (red dot) within the extensive Anglo-Paris Basin on a |
Jurassic through Neogene Surficial Geology Map
The basin’s strata were deposited in a multitude of Tertiary age transgressions and regressions of tropical seas that flooded the epicontinent of Western Europe. Formed in a mixed environment of marine, coastal, lagoonal and freshwater conditions, deposition was followed by compaction, cementation and eventual lithification.
|Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.|
The sedimentary rocks that formed - during the Eocene epoch in particular - built the city of Paris: Bartonian age gypsums (gypse) for plaster of Paris on the Right Bank (north side of the river Seine) and Lutetian age limestones (calcaire grossier), chalks (craie) for lime-based cements and paints, clays (argile) for tiles and bricks, and sand (sable) for masonry on the Left Bank (south of the river). The deposits on each side of the river Seine are between two low plateaus, Montmartre and Montparnasse. Both banks were exploited from under the city, as Paris grew and expanded on the surface.
ANTICLINE OF MEUDON
Fortuitously for Paris’s architectural future, the axis of the Tertiary age anticline of Meudon (red dotted line below) passes south of the city. The flexure allowed for the excavation of Paris’s geological bounty of gypsum from the Right Bank and deeper, coarse limestone from the Left.
|Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013|
The geologic transect (black line above) extends across the basin from north to south and is represented cross-sectionally below. Note the availability of Lutetian limestone (calcaire grossier) south of the Seine on the Left Bank and gypsum (gypse) north of the Seine on the Right Bank in Montmartre. The vertical scale across the basin is greatly exaggerated making Montmartre appear like the Matterhorn.
|Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013|
TWO MAJOR EXPLOITATION ZONES OF PARIS
Thus, gypsum has been extracted in the hills of Paris on the Right Bank from Menilmontant, Montmartre and Buttes-Chaumont areas of the 18th, 19th and 20th arrondisements, respectively. Limestone was mined under the small Parisian hills of Montparnasse, Montsouris, Montrouge, the Butte aux Cailles and the Colline de Chaillot, largely on the Left Bank.
|Topographical Considerations of Paris|
Modified from Arch.ttu.edu
ANCIENNES CARRIÈRES DE PARIS - ANCIENT MINES OF PARIS
The areas of Right Bank gypsum (green clusters) and largely Left Bank limestone (red) exploitation can be seen highlighted on this old Paris map of 1908. The direction of flow of the River Seine is shown in black arrows.
By 53-52 BC, the Romans had conquered Gaul (roughly France and Belgium) and the Celtic Iron Age tribes living in the region. Within the Paris Basin, that included the Parisii, living on the banks of the river Seine. The Romans called their settlement on the hills south of the river Lutetia Parisiorum or Lutece in French. The name was derived from a Parisii word meaning marsh or swamp. In turn, geologists borrowed the name for the Lutetian age - a division of the Eocene epoch of the Cenozoic Era- the time in which the limestone called “Paris Stone” formed – 47.8 to 41.3 million years ago.
The Romans in the 1st century and the early Parisians through the end of the 12th century acquired coarse limestone for structures in the most instinctive of ways – from above ground where it was most convenient. It was removed from open quarries (carrières à ciel ouvert) where it had been exposed by erosion such as the region of the Seine’s ancestral tributary, the Bievre (see above). The technique was primitive, but the rock was readily available and had existing natural fractures that facilitated its extraction.
By the end of the 12th century, medieval Paris had become a medium-size, walled city with a population of 25,000 surrounded by countryside of farms and vineyards. The extraction of surface limestone was gradually replaced by underground workings to satisfy the sharply increased needs for building construction such as Notre-Dame Cathedral, the Louvre Palace and the ramparts of the city.
|Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013|
The first mining method employed the “room and pillar” technique, called piliers tournes. After a horizontal tunnel was excavated, perpendicular and then parallel tunnels were added (right diagram). The result was a maze of interconnecting passageways with the weight of the ceiling supported by a grid of massive columns of untouched, solid limestone. It helped to prevent collapse of the undermined roof, but a significant portion of usable excavated material was lost.
|Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013|
In the 16th century, the mining method of hagues et bourrages was employed that was economically productive and structurally sound. Instead of tunneling horizontally into the exploited table of limestone, miners would extract stone progressively outward from a central point. When the ceiling became sufficiently unsupported, a line of stacked piliers a bras was erected from the floor to the ceiling. When extraction continued outward, a second line of stone columns was added, which were then transformed into walls or hagues as the space in between was backfilled with waste rubble or bourrage.
The first underground limestone quarries were located in Paris's suburbs (faubourgs) on the Left Bank. As the city continued to grow, new underground quarries with interconnecting galleries were developed on the city’s expanding periphery. Old abandoned quarries fell into oblivion and were gradually built over.
Formation and Evolution of Subsidence |
A fontis is a cavity that develops when the roof of a subterranean gallery caves in.
A cloche is the rounded top of the rubble pile.
Modified from Daniel Munier and from M. Vire
When the largest collapse occurred in 1774, a wave of panic spread through Paris. A giant sinkhole catastrophically swallowed a busy Parisian neighborhood including roads, buildings, houses, horses, carriages, oxcarts and throngs of people along Rue d’Enfer (now called Boulevard Saint Michel near Avenue Denfert-Rochereau). Appropriately, enfer is the French word for “hell,” and the gaping hole in the earth became known as the “mouth of hell.” The quarries that built the city of Paris were literally threatening to destroy it - neighborhood by neighborhood.
How ironic! The limestone that went into the construction of Notre-Dame, the Palais-Royal and the mansions of the Marais on the surface of Paris actually had come from the quarries beneath Rue d’Enfer – now taking revenge upon the city.
gypsum for plaster, limestone for walls, green clay for bricks and tiles.”
In response to the fear of collapse, King Louis XVI designated a commission to investigate the state of the Parisian underground on April 4, 1777. It was called the Inspection Unit for Quarries Below Paris and Surrounding Plains. The head of the newly minted office - appointed by the King by chance of fate only a few hours before the collapse - was an architect named Charles-Axel Guillaumot, who held the position of General Inspectorate of the Quarries (IGC) until his death in 1807 - in French, Inspection Générale des Carrières.
Author Graham Robb
In order to safeguard public roads and of course the King’s properties, Guillaumot erected pillars from the quarry floors to their ceilings, “retrospectively-created foundations for the edifices built on the surface” (Gilles Thomas). The result was that every undercut surface street was doubled by a gallery that followed the same layout. In a sense, Paris became a mirrored city with one above ground and the other below. This allowed the evolution of subsidence voids to be monitored and shored up as needed. The same can be said of the modern city of Paris with its underground double. Here's an example from the 13th arrondissemont.
It was necessary to render them accessible; to this effect,
a gallery wide enough to allow passage of construction materials was left under
and within the public way; at the gallery’s farthest point, another wall was built.
Perpendicular galleries were dug here and there to enable communication between
both sides of the public way and to allow movement from one gallery to the next.”
(Memoirs on the Work Ordered in Quarries in Paris and Adjacent Plains, 1804)
Another peril was threatening the city – an insidious one that had become equally intolerable and every bit as dangerous. Paris’s cemeteries had become horrifically overcrowded. The earliest burial grounds were on the southern out-skirts of the Roman-era city on the Left Bank - outside the city! By the 4th century, burials had moved to the Right Bank on filled-in marshland - within the city. In particular was the property of the Saints Innocents church in 1130 - named after the biblical narrative of the "Massacre of the Innocents" by Herod the Great, the Roman-appointed King of the Jews.
Map of Paris in 1550|
The Cemetery of Saint-Innocents is circled for reference. Click for a larger view.
Modified from OldMapsofParis.com in the Public Domain
Turgot-Berez Map Plan of Paris in 1739|
Modified from geographicus.com/blog/rare-and-antique-maps/antique-map-of-the-week-the-turgot-bretez-plan-of-paris
A close up of the charnel house shows the skulls stacked in the upper tiers, while rotting corpses literally littered the burying grounds. Now lost but recorded in manuscripts, a mural of Danse Macabre or the Dance of Death was painted on the south wall within an alcove of the charnel house. Represented in many languages and countries, the theme dates from 1424-24. No matter one’s station in life, the universality of death depicted in the “dance” is an artistic genre of late-medieval allegory. It was meant to remind people of life’s fragility and the vainness of the glories of their earthly lives. One might think that a view of the burial grounds was likely all that was needed!
for that precise reason, simple head and leg wounds become lethal in that hospital.
Nothing proves my point so well as the tally of patients who perish miserably each year
in the Paris Hôtel-Dieu…a fifth of the patients succumb; a frightful tally
treated only with the greatest indifference.”
Nothing was done to remedy the intolerable situation until King Louis XV initiated an investigation in 1763. His successor, King Louis XVI, in his first year on the throne in 1775, issued an edict to move the deceased out of the city. The church resisted the notion, which profited from burial fees. Business was good! To reduce the number of burials, the price was increased, something only the wealthy could afford.
Mine consolidations were still under way and included the addition of a network of interconnecting subterranean passageways for access. With the cemeteries closed, Police Prefect Lieutenant-General Alexandre Lenoir supported an idea of moving the dead to the newly renovated corridors to be used as an underground sepulcher. The idea became law in 1785. Saints-Innocents was to be evacuated and converted into the public square that has remained to this day, Place Joachim-du-Bellay – more on that story later in this post.
|The location of the Plains of Montrouge outside the walls of the city of Paris|
On April 7, 1786, the grounds of the former quarries of the Tombe-Issoire under the Plain of Montrouge (the burial site of a legendary giant named Issoire slain by William the monk) were sanctified in the presence of the church abbots, the architects of the project and Charles-Axel Guillaumot. On November 16th, Monseigneur Leclerc de Juigne and Archbishop of Paris ordered:
entailing the turning of the soil to a depth of five feet and the sieving of earth,
with any remaining corpses or bones to be transported and buried
in the new underground cemetery of the Montrouge Plain.”
Cited in Les Catacombes, etude historique, 1861
The first transfers of bones from Saints-Innocents to the Catacombs lasted 15 months and continued with the populations of Saint-Étienne-des-Grès, Saint-Eustache, Saint-Landry, Sainte-Croix-de-la-Bretonneries, Saint-Julien-des-Ménétriers and so forth. Continuing to 1814, every cemetery, church ground, crypt and tomb of Paris was nocturnally emptied of its human remains. In total, over six million Parisians were withdrawn and transported to their new “haven of peace” beneath the Plains of Montrouge. The exact number is impossible to determine. The estimate is based on the number of burials up to the year 1860 when the contents of the last graves were transferred to the ossuary.
The Catacombs of Paris lie some 20 meters beneath the south Paris suburb of Montrouge. The town bears little resemblance to the former bucolic royal hunting ground on the Plain of Montrouge. In fact, one must look hard to identify buildings of “old” pre-Haussmann Paris, but they’re there. In fact, you arrive beneath one if you take the Paris Métro at Denfert-Rochereau station, and you must enter one in order to descend into the Catacombs!