OLD BONES - SVP'S BLOG

From the President: Why SVP Cares About the Grand Staircase

P. David Polly
President, Society of Vertebrate Paleontology
pdpolly@indiana.edu

Two weeks ago I visited Grand Staircase-Escalante National Monument on behalf of SVP. Largely spurred by finds of Late Cretaceous mammals by Jeffery Eaton and Rich Cifelli, the Monument was created in 1996. The proclamation speaks of “world-class paleontological sites” including the “only evidence in our hemisphere of terrestrial vertebrate fauna, including mammals, of the Cenomanian-Santonian ages.” In the intervening 20 years, research there has revolutionized our understanding of Late Cretaceous ecosystems. Now the Trump administration wants to downsize Grand Staircase to expand grazing in a region where annual rainfall averages less than 7 inches and to permit coal mining in one of the least accessible and most fossiliferous places in the country.

Geological overview

The Monument’s bedrock is primarily Mesozoic, from the Lower Triassic Moenkopi Fm. to the Upper Cretaceous Kaiparowits Fm., with a little bit of the Permian Kaibab Limestone exposed in the southwest and north east.

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A geological map and generalized stratigraphic column of Grand Staircase-Escalante National Monument. Numbers mark locations discussed below. Stratigraphic column modified from Doelling (2008), Geologic Map of the Kanab Quadrangle.

Physiographically, the Monument is divided into four regions. The western part is the Grand Staircase proper. An extension of the northern rim of the Grand Canyon, strata there are relatively flat lying and the more indurated units form a series of parallel cliffs that rise like stair treads, each named for its color: Chocolate Cliffs, Vermillion Cliffs, White Cliffs, Gray Cliffs, and Pink Cliffs. The triangular central region is the Kaiparowits Plateau, a high scrub covered area where Upper Cretaceous rocks outcrop. Two remarkable features bound the Plateau. Its western boundary is a monocline known as the Cockscomb where faulted strata tilt almost vertically; the eastern boundary is marked by the Straight Cliffs. To the East of the Kaiparowits is the deeply dissected region of Escalante Canyon, dominantly Jurassic in age. Slot canyons – deeply incised fissures so narrow that you can touch both sides – abound in this area. Even farther east are the Circle Cliffs, a valley-like structure completely enclosed by a wall of inward facing cliffs.

Paleogeographically, the Monument’s sediments are derived from upheavals on the western margin of North America. At the beginning of the Triassic southern Utah looked over the Panthalassic Ocean from the rugged western coast of North America. Orogenies and terrane accretions created new coastal ranges as Pangea’s split pushed North America ever westward, stranding Utah in a large interior basin brimming with the blowing sands that produced the Navajo Sandstone. By the Late Cretaceous, a series of sea level cycles periodically filled that basin with marine water so that the Monument’s views now faced the opposite direction across the western interior seaways.

A trip through time

During my visit I was able to explore most of the easily accessible parts of the Monument. Alan Titus of the Bureau of Land Management, Tom and Colter Hoyt of Boulder, Utah, and Tylor Birthisel of the Natural History Museum of Utah guided me through its geography, history, and paleontology from the bottom to the top of its immense stratigraphic section.

Triassic

The oldest rocks in the Monument demonstrate the devastating effects of the Permo-Triassic extinction. Sharks, conodonts, molluscs, trilobites, corals, and crinoids were abundant in the Late Paleozoic seas as demonstrated by the faunas of the mid-Permian Toroweap Fm. and Kaibab Limestone. Tectonic uplift exposed this area during the Late Permian and earliest Triassic, producing an erosional unconformity leading up to the extinction. The base of the overlying Moenkopi, which represents nearshore marine deposits, contains a strikingly depauperate fauna, including unusual stromatolite-like structures that formed in the absence of grazers, that immediately demonstrates the severity of the extinction.

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Contact between the Permian Kaibab Limestone and overlying Triassic Moenkopi Fm. showing the erosional unconformity and some of the stromatolite-like structures in the extinction-reeling Triassic strata. The type area of the Kaibab Ls. is in the south eastern part of the Monument in Kaibab Gulch at Point 1 on the overview map (photo by P. David Polly, 2017).

By the later Triassic southern Utah was blanketed by massive fluvial systems as orogenies to the west closed it off from the shrinking Panthallasic Ocean. The fossiliferous beds of the Chinle Fm. consist of stream channels, flood plains, lakes, marshes, and river deltas that document that the supercontinent Pangea experienced megamonsoonal climate cycles. The river valleys were stocked with coelacanths, lungfish, ray-finned fish, amphibians, phytosaurs, synapsids, and early archosaurs. Exposures of the Chinle Fm. in the Circle Cliffs area of the Monument contain the largest fossilized forest apart from the one at Petrified Forest National Monument. Thousands of huge trunks of the early conifer Araucarioxylon, some of which are nearly 100 feet long and 3 feet in diameter, are found at the base of a massive conglomerate where they were buried after being transported by the river system. Many of them bear evidence of ancient bark beetle attacks.

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Trunk base of an early conifer
Araucarioxylon tree in the Circle Cliffs area (Point 2 on the overview map) with Colter Hoyt for scale (photo by P. David Polly, 2017).

Jurassic

Utah was enclosed in an arid inland basin by the mid Jurassic, caught in the arid rain shadow of high mountain ranges that were continuing to rise along the western coast of North America. Windswept dunes of a desert much like the Sahara filled the western margin of the basin creating the thick cross-bedded layers of the Navajo Sandstone. These rocks create the landscapes for which the Monument is best known, including narrow mazes of slot canyons cut deep into the sandstone where a hiker can touch both sides as they walk fifty or a hundred feet below the rim. The sparse Jurassic landscape would not have supported the same density of life that was found in the Triassic river systems, but trackways of pterosaurs, lizards, crocodylians, and synapisds are abundant. A skeleton of the early sauropod Seitaad was recovered from the Navajo Sandstone west of Grand Staircase in what is now Bears Ears National Monument.
 

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Utah Highway 12 winding over exposures of the Navajo Sandstone between Escalante and Boulder (Point 3 on the overview map). This view is may be reminiscent of what the Jurassic dune fields themselves might have looked like (photo by P. David Polly, 2017).

 

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Vertically oriented Upper Jurassic rocks in the Cockscomb along Cottonwood Canyon Road (Point 4 on the overview map; photo by P. David Polly, 2017).

 

Having been cut off from the proto-Pacific Ocean by rising western mountains, the seas returned to southern Utah from the east in the later Jurassic and Cretaceous as they filled the interior basins. As sea levels rose and fell, cycles of marine muds, beach dune fields, coal swamps, and river delta systems were deposited at the Grand Staircase. Many of these units are exposed along the western edge of the Kaiparowits. Usually the beds are near horizontal, but in the Cockscomb they are bent and torn in startling ways that sometimes produce vertical slabs arranged in a long line from which the feature gets its name. The paleontology of these units varies with the environment.

Cretaceous

The fauna and flora of the mid-Cretaceous Naturita Fm. (long classified as part of the Dakota Fm.) provides the earliest evidence of the Cretaceous Terrestrial Revolution in the Monument, with abundant angiosperms, including hollies and sycamores, true mammals, lizards, and crocodilians. The area was flooded in the Cenomanian producing the sea-floor muds of the Tropic Shale that are filled with ammonites, bivalves, gastropods, sharks, xiphactin fishes, plesiosaurs, and mosasaurs. A major oceanic anoxic event followed by an extinction is recorded in the Tropic Shale at the Cenomanian-Turonian boundary. During this event, sea surface temperatures near the equator rose to 36°C (96.8°F). The Straight Cliffs formation, which spans the Turonian through Coniacian stages, overlies the Tropic Shale and represents a return to more terrestrial conditions. The coals of the Kaiparowits Plateau are found mostly in the John Henry Member of the Straight Cliffs, which was a swamp faces near the ancient Cretaceous coastline.


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Exposures of the marine Tropic Shale at the Cenomanian-Turonian boundary marked by an extinction driven by a major anoxic event (Point 5 on the overview map; photo by P. David Polly, 2017).


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Coal seams in the John Henry Member of the Straight Cliffs Formation (Point 6 on the overview map). These coals were produced in extensive coastal swamps during the Niobrara cyclothem of the Coniacian and Santonian stages. Deposits of this coal lie underlie the Wahweap and Kaiparowits Formations, deep beneath the surface of the northern Kaiparowits Plateau, and are one of the motivations for breaking up the Monument (photo by P. David Polly, 2017).

The crowning glory of the Monument, both stratigraphically and figuratively, is the Campanian Kaiparowits Fm. The most diverse and abundant Late Cretaceous ecosystem in the world, with the possible exception of the one from the Dinosaur Park Fm. in Alberta, has been found in the Kaiparowits Fm. The diversity of its plants and animals indicate that this mid-latitude community experienced extremely high productivity, enough to support at least six large herbivore species: Utahceratops, Kosmoceratops, Nasutoceratops, Gryposaurus (an extremely large hadrosaur), Parasaurolophus, and another undescribed ceratopsian. Large and small theropods, smaller herbivores, oviraptors, pachycephalosaurs, crocodilians, turtles, and mammals were abundant in the Kaiparowits ecosystem. Not only numerous and diverse, but Kaiparowits finds are often remarkably complete. Hadrosaur skin impressions are common in the fine sand matrix and parasauroloph individuals ranging from young to old demonstrate that their skull crests grew as the animals aged. While I was there, a skeleton of a nearly complete tyrannosaur, Teratophoneus, was airlifted off the Plateau down to the road near Grosvenor Arch after having been discovered and excavated by a collaborative team from the Bureau of Land Management and the Natural History Museum of Utah led by Alan Titus and Taylor Birthisel respectively.

 Above: Video from the Salt Lake Tribune of the airlift of a nearly complete Teratophoneus skeleton from the Kaiparowits Plateau by crews from Bureau of Land Management and the Natural History Museum of Utah (Point 8 on the overview map).

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A 1,200 pound jacket containing part of the tyrannosaur Teratophoneus skeleton being lowered by helicopter into a waiting truck after excavation by a joint Bureau of Land Management and Natural History Museum of Utah crew. (Point 8 on the overview map; photo by P. David Polly, 2017).
 

There is much more, of course, some that I saw and some that I did not. Indeed, Grand Staircase holds a lot that nobody has seen because large parts of the monument have never been systematically surveyed for paleontological resources.
 

Continuing finds

Despite the work already done at Grand Staircase, its potential is only barely tapped. Almost all of the Monument has been assessed to have potential fossil yields that are moderate to high and nowhere in the Monument is the potential for fossils low. In the last ten years more than 25 new taxa have been described, including the dinosaurs Lythronax argestes, Teratophoneus curriei, Utahceratops gettyi, and Diabloceratops eatoni, as well as mammals, crocodylians, squamates, turtles and sharks. More than 35 scientific papers have been published on Monument fossils in the last year alone, most of them by SVP members (click here for a PDF).

After my visit to the Monument, Randall Irmis showed me the material from Grand Staircase housed in the research collections at the Natural History Museum of Utah in Salt Lake. Drawer after drawer contained new taxa that are still in the process of description, including this caiman from the Late Cretaceous.

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A new Late Cretaceous caiman from the Kaiparowits Plateau under study at the Natural History Museum of Utah (photo by P. David Polly, 2017).
 

Why does SVP care?

SVP is dedicated to the study, discovery, interpretation, and preservation of vertebrate fossils. An explicit part of our mission is to “support and encourage the discovery, conservation, and protection of vertebrate fossils and sites”.

Vertebrate fossils are rare – often only a handful of specimens are available to document the growth, variation, and geographic and stratigraphic ranges of any given taxon – and their scientific value is derived from the contextual information that is literally embedded with them in the sites where they are found. Two conditions are therefore crucial for the science of paleontology: (1) that fossils are placed in permanent, accessible repositories so that data derived from them can be amalgamated into any number of research programs; and (2) that sites can be revisited so that prior contextual interpretations can be reassessed and new contextual data can be collected.

SVP’s constitution and bylaws lay out principles aimed at meeting these conditions for healthy science. Our Society has worked to educate legislators and regulators around the world about them. The passage of the US Paleontological Resources Preservation Act in 2009 (PRPA), protection of the Pliocene deposits at Beaumaris, Australia, and the Rother District Council’s Fossil Collecting Code of Conduct are all examples of actions that benefited from input from SVP.

Grand Staircase was established, in large part, to protect paleontological resources and their geological contexts from damage by mining and other activities. By the mid-1990s work by Jeff Eaton, Rich Cifelli, and other SVP members had already established that a unique record of late Mesozoic life, mammalian communities unlike those preserved elsewhere, was preserved on the Kaiparowits Plateau. Eaton and colleagues explained the scientific and aesthetic values of this region to the Department of Interior and to members of Congress. Paleontology was consequently at the forefront when the Monument was established in 1996.

The fact that paleontological resources were part of the Monument’s proclamation give them special status beyond the protections provided by PRPA. The Monument was established under the Antiquities Act, which allows the President to set aside lands owned by the US Federal government when they contain “objects of historic or scientific interest.” Paleontological science therefore takes priority at Grand Staircase over many other potential uses. The Monument has employed a full-time paleontologist since 2000 (Dr. Alan Titus), it allocates funds for internal and collaborative research, and it mandates detailed paleontological surveying.

These resources jump-started the intense research that has transformed our understanding of Mesozoic diversity, ecosystems, and phylogeny in the intervening 20 years. Crews from the Denver Museum, Natural History Museum of Utah, Brigham Young University, the Raymond Alf Museum, the Smithsonian, and many others (not to mention Titus’s own group!) have identified several thousand scientifically important fossil localities and have described new plants, mammals, lizards, crocodylians, phytosaurs, poposaurs, and dinosaurs. The concept of the Cretaceous Terrestrial Revolution is largely underpinned by this work.

That the Monument remains intact is therefore important to SVP. An estimated 10% of our members have conducted research in the Monument or participated in professional field trips to be educated about its paleontology. Reversing Grand Staircase’s monument status would lower the priority of paleontological research, raise the priority of potentially destructive activities such as mining, cut off some funding sources for research, and, in a worst case scenario, open literally thousands of scientifically valuable localities to looting or private collecting. Loss of monument status would likely forfeit the catalysing activities of the monument paleontologist. Other monuments currently under review are also important to paleontological science, notably Bears Ears (also in southern Utah; see Rob Gay’s blog earlier this year) and Gold Butte (in southern Nevada). SVP underscored the scientific reasons for maintaining these monument’s boundaries in the Department of Interior’s consultation earlier this year (see here), and we are currently exploring legal options to ensure they remain intact.

Further reading

Finnegan, M. 2017. “Remarkable dinosaur discoveries under threat with Trump plan to shrink national monument in Utah, scientists say”. Los Angeles Times (27 Oct). [An extended news article on the conflict between politics and science at Grand Staircase by political reporter Michael Finnegan].

Sadler, C. 2016. Where Dinosaurs Roamed: Lost Worlds of Utah’s Grand Staircase. Indiana Uninversity Press: Bloomington, IN. 160 pp. [Sadler’s book is a generously illustrated overview of the Monument’s paleontology, written in an engaging style for a general audience but with enough detail to be of interest to scientific readers].

Titus, A. L. and M. A. Loewen. 2013. At the Top of the Grand Staircase: the Late Cretaceous of Southern Utah. Indiana University Press: Bloomington, IN. 656 pp. [This volume is a compendium of scientific reviews of paleontology and geology of the Kaiparowits Plateau. Work is so fast-paced that some chapters are already out of date only four years after publication. Nevertheless, the book is an excellent entry point into the scientific literature of Grand-Staircase Escalante National Monument].

Posted: 11/6/2017 11:49:56 AM by andyfarkeadmin | with 0 comments
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