Field of Science

Sorry Kids, the Dinosaur Museum is Closed...

Today for the first time in decades the University of Wyoming Geological Museum will not open to the public. To save a measly $80,000 a year the university decided to shutter the only place in the area where local children can experience the wonders of the dinosaur paleontology for which the state of Wyoming is famous. Ignoring public outcry, the bureaucrats who should be holding education, research, and outreach, the core values of any learning institution, in esteem have decided to follow through with these cuts, yet the university's sports programs stay pretty much intact? You can read about it more here at ReBecca Hunt-Foster's site.

I also could not help but notice the comment that while the Geological Museum is being closed, the anthropology museum will reopen soon. I have noted repeatedly that geology and paleontology often get the short end of the stick to archaeology and anthropology, and I feel that this may simply be due to the fact that geology and paleontology are fairly foreign topics to the majority of the public. Indeed, as all paleontologists and archaeologists know there is often much confusion between the roles of the two disciplines. Tell someone you are a paleontologist and they will mention all of the arrowheads they have found; mention you are an archaeologist and people will start asking you about dinosaurs. When I entered college expressing a desire to study fossils I was promptly referred to archaeology classes by the councilors and registrars.

Most people (presumably because they are human) seem to have a have a rudimentary knowledge, understanding, and interest in anthropology and archaeology; however, many of these same people do not even know what the study of geology even entails. Much of this I think is a result of the sad state of science education in the United States. I'm not saying that archaeology is lesser to geology and paleontology (I've done all three), I am just trying to understand why this dichotomy exists. Did you know that despite being responsible for some of the greatest geological wonders in the world (Grand Canyon, Zion, Arches, Yellowstone, etc...) there are more archaeologists employed at the Grand Canyon alone than there are geologists and paleontologists (total) in the entire National Park Service? This is mainly because of the need to satisfy law and policy; however, sometimes I wonder if often there is simply a misunderstanding of the fundamental differences between the two disciplines.

I've experienced leadership in institutions that were established for their paleontological resources who not only have little knowledge or interest in paleontology, but cannot even pronounce the word! I often "joke" with my students that because of the plethora of students and lack of positions in paleontology, many of them should train to become administrators and thus provide universities and museums with leadership who understand and appreciate the science. Of course, it is not really a joke, we desperately need this for the good of the profession; however, how many students will want to be a martyr to protect a job that they badly desire but will never get to have?

There are probably more jobs in paleontology now than ever before, mostly because of the wave of interest stemming from a book and movie now rapidly approaching their two decade anniversary. Paleontologists are challenged with keeping our science fresh and engaging and judging by the media we still get regarding new finds, the interest is for the most part still there. Let's hope that events such as what happened in Wyoming aren't indicators of a future trend.

Latest Literature: Triassic redbeds, footprints, and Eshanosaurus

Thanks to Jerry Harris for pointing these out...

Zaghloul, M.N., Critelli, S., Perri, F., Mongelli, G., Perrone, V., Sonnino, M., Tucker, M., Aiello, M., and Ventimiglia, C. 2009. Depositional systems, composition and geochemistry of Triassic rifted-continental margin redbeds of the Internal Rif Chain, Morocco. Sedimentology. doi: 10.1111/j.1365-3091.2009.01080.x.

ABSTRACT: The Middle to Upper Triassic redbeds at the base of the Ghomaride and Internal 'Dorsale Calcaire' Nappes in the Rifian sector of the Maghrebian Chain have been studied for their sedimentological, petrographic, mineralogical and chemical features. Redbeds lie unconformably on a Variscan low-grade metamorphic basement in a 300 m thick, upward fining and thinning megasequence. Successions are composed of predominantly fluvial red sandstones, with many intercalations of quartzose conglomerates in the lower part that pass upwards into fine-grained micaceous siltstones and massive mudstones, with some carbonate and evaporite beds. This suite of sediments suggests that palaeoenvironments evolved from mostly arenaceous alluvial systems (Middle Triassic) to muddy flood and coastal plain deposits. The successions are characterized by local carbonate and evaporite episodes in the Late Triassic. The growth of carbonate platforms is related to the increasing subsidence (Norian-Rhaetian) during the break-up of Pangea and the earliest stages of the Western Tethys opening. Carbonate platforms became widespread in the Sinemurian. Sandstones are quartzose to quartzolithic in composition, testifying a recycled orogenic provenance from low-grade Palaeozoic metasedimentary rocks. Palaeoweathering indices (Chemical Index of Alteration, Chemical Index of Weathering and Plagioclase Index of Alteration) suggest both a K-enrichment during the burial history and a source area that experienced intense weathering and recycling processes. These processes were favoured by seasonal climatic alternations, characterized by hot, episodically humid conditions with a prolonged dry season. These climatic alternations produced illitization of silicate minerals, iron oxidation and quartz-rich red sediments in alluvial systems. The estimated burial temperature for the continental redbeds is in the range of 100 to 160 °C with lithostatic/tectonic loading of ca 4 to 6 km. These redbeds can be considered as regional petrofacies that mark!the onseern Pangea (Middle Triassic) before the opening of the western part of Tethys in the Middle Jurassic. The studied redbeds and the coeval redbeds of many Alpine successions (Betic, Tellian and Apenninic orogens) show a quite similar history; they identify a Mesomediterranean continental block originating from the break-up of Pangea, which then played an important role in the post-Triassic evolution of the Western Mediterranean region.

Gierlinski, G.D. 2009. A preliminary report on new dinosaur tracks from the Triassic, Jurassic and Cretaceous of Poland; pp. 75-90 in Salas, C.A.-P. (ed.), Actas de las IV Jornadas Internacionales sobre Paleontologia de Dinosaurios y su Entorno. Colectivo Arqueológico-Paleontológico de Salas de los Infantes, Burgos.

ABSTRACT: Dinosaur tracks in Poland are mainly recognized in the Lower Jurassic (Hettangian) of the Holy CrossMountains. There are only few finds, so far reported, from the Upper Triassic of the Tatra Mountains and Silesia. Dinosaur footprints in the Upper Jurassic of the Holy Cross Mountains are also little recognized. Field investigations, in 2006 and 2007, revealed new finds of dinosaur footprints in the Upper Triassic (Norian), Lower Jurassic (Pliensbachian) and Upper Jurassic (Oxfordian) of the Holy Cross Mountains (central Poland), and the Upper Cretaceous (Maastrichtian) of the Roztocze region (southeastern Poland). Norian material comprises prosauropod tracks, which came from the coarse-clastic sequences exposed in the Skarszyny outcrops. New Jurassic finds, in the Holy Cross Mountains, are the Pliensbachian sauropod and small theropod footprints from the Smilow sandstone quarry, and the Oxfordian theropod, and small ornithopod tracks from Baltow limestones. Dinosaur footprints, in the Roztocze carbonates, are discovered in the lowermost part of Szopowe quarry on the Mlynarka Mount. The material from Mlynarka Mount resembles Asiatic ichnotaxa, a small didactyl maniraptoran track of Velociraptorichnus, bird-like ichnite similar to Saurexallopus and a large tetradactyl footprint of Macropodosaurus, a form recently supposed of the therizonosauroid origin.

Barrett, P.M. 2009. The affinities of the enigmatic dinosaur Eshanosaurus deguchiianus from the Early Jurassic of Yunnan Province, People's Republic of China. Palaeontology. doi: 10.1111/j.1475-4983.2009.00887.x.

ABSTRACT: Eshanosaurus deguchiianus is based on a single left dentary from the Lower Lufeng Formation (Lower Jurassic) of Yunnan Province, China. It was originally identified as the earliest known member of Therizinosauroidea (Theropoda: Coelurosauria), a conclusion that results in a significant downward range extension for this clade (>65 million years) and for many other major lineages within Coelurosauria. However, this interpretation has been questioned and several authors have proposed that the anatomical features used to refer Eshanosaurus to Therizinosauroidea are more consistent with attribution to a basal sauropodomorph dinosaur. Detailed consideration of the holotype specimen suggests that several features of the dentary and dentition exclude Eshanosaurus from Sauropodomorpha and support its inclusion within Therizinosauroidea. If accepted as an Early Jurassic coelurosaur, Eshanosaurus has important implications for understanding the timing and tempo of early theropod diversification. Moreover, its provenance also suggests that substantial portions of the coelurosaur fossil record may be missing or unsampled. However, the Early Jurassic age of Eshanosaurus requires confirmation if this taxon is to be fully incorporated into broader evolutionary studies.

Bill Mueller and his Field Notes on the Paleontology and Geology of the Dockum Group

I have had this link up on my sidebar since first starting this blog, but I would like to point out Bill Mueller's great Field Notes site to everyone who has not yet visited. Bill is a professional photographer and a staff member at The Museum at Texas Tech University in Lubbock, Texas and for years now he has been detailing his Late Triassic work in the Dockum Group of Texas at his fine arts website. The amount of material he and his field partner Gretchen routinely uncover is nothing short of astounding. I highly recommend his site to anyone interested in ongoing paleontological field work.

The Coelophysis Quarry at Ghost Ranch

I'm back from a couple of days at the Hayden Quarry near Ghost Ranch, New Mexico. As usual it was a great experience with great people and absolutely amazing fossils. My student interns were able to meet quite a few paleontologists including Sterling Nesbitt, Randy Irmis, Nate Smith, Alan Turner, Alex Downs, Mike Getty, and Mark Loewen. Plus they got to get really dirty and find fossils. A great experience for them.

Another perk is that we took some time off to go visit the classic Coelophysis Quarry. For those of you who have never seen it....here it is in all of its glory. The main bone horizon is now a big flat area where the footprints going up end. This is the siltstone member of the Chinle Formation and the sandstone blocks are fallen blocks from the overlying Entrada Sandstone (Jurassic).

This is the famous "Barney-rock" that overlooks the quarry and all workers were always afraid of it possibly coming down on their heads while they were digging.

Here are the interns (Chuck, Adrian, and Rachel) relaxing after the hike up to the quarry and enjoying the view.

We're Off to the Hayden Quarry

Every year I treat my student interns to a weekend working somewhere else in the Chinle Formation with groups from other institutions. For example in 2002 we worked with Sterling Nesbitt in the Moenkopi Formation excavating an excellent skeleton of Arizonasaurus and in 2003 we joined the Yale Peabody Museum crew in Escalante National Monument in Utah and helped with their Poposaurus excavation (also see this link). I feel that it is important to give my students the opportunity to network with other researchers and to see how others work and collect data. This weekend we are headed out to Ghost Ranch, New Mexico to work in the Hayden Quarry (the type locality of Dromomeron romeri and location of a portion of the Dinosaurs Alive IMAX film) with Sterling Nesbitt, Randy Irmis, and others. This is our third summer there and it is always a great experience.

Photos are from past seasons and were lifted from here and here.


Alan Turner preparing his afternoon siesta spot.


Amazing views from the quarry.

Another photo that proves that from the quarry you really can see scenes like the last one.


A bone that I wish that I had found instead of my usual scrap.

Randy protecting his lunch from other ravenous quarry workers.

Limusaurus inextricabilis, a Bizarre Beaked Ceratosaur from the Late Jurassic of China

OK...OK....This post is regarding the Jurassic, and the Late Jurassic specifically, but it is almost Triassic right? Sort of? Still, this is just to cool of a discovery not to mention.

Today's issue of Nature contains an article by Dr. James Clark (George Washington University) and Xu Xing (Chinese Academy of Science's Institute of Vertebrate Paleontology and Paleoanthropology in Beijing) and colleagues titled "A Jurassic ceratosaur from China and its significance fortheropod digit reduction and avian digital homologies". The paper describes a new beaked ceratosaur (yes, beaked ceratosaur) from the Jurassic of China. This new specimen also offers key information regarding the interpretation of digit homology between non- avian and avian dinosaurs.




As Tom Holtz noted to me in an earlier e-mail message....this is a "ceratosaur convergent on Effigia (a Triassic pseudosuchian): Truly weird!". I could not have summed it up any better!

Kudos also to my friend and colleague Sterling Nesbitt and to fellow blogger David Hone who are co-authors on this paper.




The following text is from the Reuters News Release . Photos are from here.

Limusaurus inextricabilis (meaning "mire lizard who could not escape") was found in 159 million-year-old deposits located in the Junggar Basin of Xinjiang, northwestern China. The dinosaur earned its name from the way its skeletons were preserved, stacked on top of each other in fossilized mire pits that were the subject of a 2008 National Geographic film, "Dino Death Trap."

A close examination of the fossil shows that its upper and lower jaws were toothless, demonstrating that the dinosaur possessed a fully developed beak. Its lack of teeth, short arms without sharp claws and possession of gizzard stones suggest that it was a plant-eater, though it is related to carnivorous dinosaurs.

The newly discovered dinosaur's hand is unusual and provides surprising new insights into a long-standing controversy over which fingers are present in living birds, which are theropod dinosaur descendants. The hands of theropod dinosaurs suggest that the outer two fingers were lost during the course of evolution and the inner three remained. Conversely, embryos of living birds suggest that birds have lost one finger from the outside and one from the inside of the hand.

Unlike all other theropods, the hand of Limusaurus strongly reduced the first finger and increased the size of the second. Drs. Clark and Xu and their co-authors argue that Limusaurus' hand represents a transitional condition in which the inner finger was lost and the other fingers took on the shape of the fingers next to them. The three fingers of most advanced theropods are the second, third and fourth fingers -- the same ones indicated by bird embryos -- contrary to the traditional interpretation that they were the first, second and third.

Limusaurus is the first ceratosaur known from East Asia and one of the most primitive members of the group. Ceratosaurs are a diverse group of theropods that often bear crests or horns on their heads, and many have unusual, knobbyfingers lacking sharp claws.The fossil beds in China that produced Limusaurus have previously yielded skeletons of a variety of dinosaurs and contemporary animals described by Drs.Clark and Xu and their colleagues. These include the oldest tyrannosaur, Guanlong wucaii; the oldest horned dinosaur, Yinlong downsi; a new stegosaur, Jiangjunosaurus junggarensis; and the running crocodile relative, Junggarsuchus sloani.

REFERENCE

Xing Xu et al, 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459:940. doi:10.1038/nature08124

Route 66 and its Influence on Triassic Paleontology of the American Southwest

Route 66; the "mother road"; Bobby Troupe singing "get your kicks"... Anyone who has worked with me knows that I have a keen interest in this historic highway. Part of this stems from living in Northern Arizona for more than a decade, twice within a block of this road. Although officially decommissioned in 1985, Route 66 nostalgia is alive and well in these areas and the road still forms the basis of the many towns and cities it passed through. Furthermore, its scars can still be seen across the landscape in the form of abandoned roadbeds, bridges, roadcuts, and debris, including abandoned structures. In its heyday more than a million cars a year travelled its length from Chicago, Illinois to Los Angeles, California.



However, my infatuation with Route 66 stems from more than just searching out abandoned sections as something to do to pass the time while driving across Arizona. This is the road that past paleontologists used when conducting much of the early work in the Triassic rocks of Arizona and New Mexico. Charles Camp's field notes from the 1920s discuss travelling the route and stopping at historic places including Ed's Camp. When Camp mentions camping near the roadbridge across "Little Carrizo" Wash (also known as the Little Lithodendron Wash) we can revisit that camp as the bridge still exists.

Sam Welles did not care to see the Meteor Crater one more time so he had his team drop him off at the intersection of Route 66 and the old Meteor Crater road so he could prospect the Moenkopi Formation. This paid dividends as he discovered the prolific Middle Triassic Meteor Crater Quarry. The Holbrook Quarry was another productive quarry in the Moenkopi right along Route 66.

Petrified Forest National Park is the only National Park that contains a section of Route 66 and until it was replaced by Interstate 40 in the late 1950s was an important marker for paleontologists and geologists working in the park and surrounding area. For example many of Maurice "Spade" Cooley's Chinle geological sections were measured along Route 66 and it would be impossible to relocate them without knowing the old alignments of the road.

Ned Colbert also travelled extensively up and down Route 66 while doing his southwest U.S. work and prominently mentions sites such as Rimmy Jims in his notes.

Last week we were examining outcrops of the Chinle Formation north of Joseph City, Arizona and I had the opportunity to stop at a classic Route 66 stop, Ella's Frontier. Below is a photo of me standing outside of the now abandoned log structure. You can find a picture of this trading post in its heyday here.


The next picture is looking east up old Route 66 from in front of Ella's. The old Howdy Hank's trading post is on the left (with its well-known mural of the cowboy and horse barely visible), and an old campground is on the right side of the road.


I find it absolutely fascinating to trace the footsteps of earlier paleontologists such as Colbert, Welles, Camp, etc... and fortunately Route 66 still allows me to do this. Furthermore, as this was the main route travelled by these workers while conducting fieldwork, it had a major influence on which outcrops were prospected (accessiblity is important) adding to our knowledge of Triassic paleontology in the southwest.

Introducing Dromomeron gregorii a New Lagerpetid Dinosauromorph from the Lower Chinle Formation of Arizona and Dockum Group of Texas

The new issue (June 2009) of the Journal of Vertebrate Paleontology features an article by Sterling Nesbitt, Randy Irmis, and colleagues featuring new data on the Late Triassic North American lagerpetid dinosauromorphs first mentioned by Irmis et al. (2007). This new data includes:

1) A complete decription of the hindlimb material of Dromomeron romeri Irmis et al. 2007.

2) A description of a second species of Dromomeron, D. gregorii.

3) A phylogenetic analysis of basal dinosauromorphs.

4) A detailed discussion of ontogenetic changes in the femur of Dromomeron, which has implications for the phylogeny of early dinosaurs. Specifically that a well-developed anterior trochanter and trochanteric shelf is developed from a low rugosity as femoral size increases. Thus the lack of a trochanteric shelf in some dinosauromorph specimens (e.g., D. romeri and Lagerpeton) may simply indicate immaturity of the specimen rather than a taxonomic or phylogenetic distinction.

Note that Lagerpetidae is formally diagnosed in this paper as a converted clade name to include both species of Dromomeron and Lagerpeton chanarensis.

Also note that lagerpetids now are know from the basal Chinle Formation of Arizona, the upper Chinle of west-central New Mexico, and the lower and middle Dockum Group of Texas. These animals were much more diverse and widespread than previously believed. However, I'm still waiting to recover one in the Petrified Forest. They should be present along with our "silesaurid", Chindesaurus bryansmalli, and coelophysoid theropods.

Here is the abstract from the new paper:

Nesbitt, S.J., Irmis, R.B., Parker, W.G., Smith, N.D., Turner, A.H., and T. Rowe. 2009. Hindlimb osteology and description of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29:498-516.

ABSTRACT—The recent discovery of early dinosauromorphs from North America demonstrates that they were contemporaries with dinosaurs and other basal archosaurs during a substantial portion of the Late Triassic Period. Hindlimb material (femora, tibiae, a fibula, astragalocalcanea, and phalanges) of Dromomeron romeri, a non-dinosauriform dinosauromorph from the Petrified Forest Member of the Chinle Formation from north-central New Mexico, is described. A new species of Dromomeron from the lower portion of the Chinle Formation (eastern Arizona) and Dockum Group (northern Texas) is also described, based on several disarticulated femora and tibiae. D. romeri, Lagerpeton, and the new taxon form the sister group to all other dinosauromorphs and demonstrate that this clade, Lagerpetidae, persisted well into the Norian. Lagerpetidae is supported by several synapomorphies: femoral head hook-shaped in medial and lateral views; ventral emargination on the anterolateral side of the femoral head; an enlarged posteromedial tuber of the proximal end of the femur; femoral crista tibiofibularis larger than the medial condyle; anteromedial corner of the distal end of the femur forms 90 degree or acute (>90 degree) angle; and a posterior ascending process of the astragalus. An ontogenetic series of the femur of Dromomeron indicates that some character states previously used in phylogenetic analyses of early dinosaurs may be ontogenetically variable.

REFERENCES

Irmis, R. B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science
317:358–361.

University of Wyoming Geology Museum in Trouble

Just in case you have not heard the Geology Museum at the University of Wyoming is slated to be closed and the two staff members let go. You can read more on this here and here and if you are outraged please sign the petition, or even better write a letter to the board of trustees and let them know you are tired of academia being squandered for sports programs and higher administrative salaries.

New Paper on Archosaurian Locomotion Evolution

Livingston, V.J., Bonnan, M.F., Elsey, R.M., Sandrik, J.L., and D.R. Wilhite.2009. Differential limb scaling in the american alligator (Alligator mississippiensis) and its implications for archosaur locomotor evolution. The Anatomical Record 292:787-797. doi 10.1002/ar.20912

Abstract- Bipedalism evolved multiple times within archosaurs, and relatively shorter forelimbs characterize both crocodyliforms and nonavian dinosaurs. Analysis of a comprehensive ontogenetic sequence of specimens (embryo to adult) of the sauropodomorph Massospondylus has shown that bipedal limb proportions result from negative forelimb allometry. We ask, is negative forelimb allometry a pattern basal to archosaurs, amplified in certain taxa to produce bipedalism? Given the phylogenetic position of extant crocodylians and their relatively shorter forelimb, we tested the hypothesis that prevalent negative forelimb allometry is present in Alligator mississippiensis from a sample of wild specimens from embryonic to adult sizes. Long bone lengths (humerus, radius, ulna, femur, tibia, fibula, third metapodials) were measured with their epiphyseal cartilage intact at all sizes. Our results show an overall isometric pattern for most elements regressed on femur length, humerus length, or total limb length. However, negative allometry was prevalent for the ulna, and the third metapodials scale with positive allometry embryonically. These data suggest that the general forelimb proportions in relation to the hindlimb do not change significantly with increasing size in A. mississippiensis. The negative allometry of the ulna and embryonicaly positive allometry of the third metapodials appears to be related to maintaining the functional integrity of the limbs. We show that this pattern is different from that of the sauropodomorph Massospondylus, and we suggest that if bipedalism in archosaurs is tied, in part, to negative forearm allometry, it was either secondarily lost through isometric scaling, or never developed in the ancestor of A. mississippiensis.

Special Issue on Transitional Fossils in the Journal Evolution: Education and Outreach

This was already announced on the Vertebrate Paleontology Listserver; however, for those of you who do not subscribe:

The new issue of the open access journal "Evolution: Education and Outreach" is now available online here. This is a special issue on transitional fossils an contains articles from a number of specialists on a the origins of variety of animal groups as well as articles on evolution and systematics.

And of course as open access it is all freely available.

Enjoy

Mottled Horizons in the Basal Portion of the Chinle Formation

Strongly mottled sedimentary horizons are very common in the basal members of the Chinle Formation. The most prominent are the Temple Butte Member (Robeck, 1956) in the San Rafael Swell of Utah, and the "mottled strata" of Stewart et al. (1972). The "mottled strata" represent a zone of alteration, believed to have resulted from extreme pedogenesis (soil formation), found in the base of the Chinle Formation and sometimes in the top of the underlying Moenkopi Formation (Stewart et al., 1972; Dubiel, 1989).

According to Stewart et al. (1972) this mottled coloration is "striking and unmistakable" and consists of various rock types (mainly siltstone and sandstone, but also conglomerate and even some igneous rocks) that contain intricately mottled reddish purple, pale reddish brown, and light greenish gray. These strata are generally 5 to 25 feet thick, overly the Moenkopi Formation or the Shinarump Member of the Chinle Formation, and outcrops are discontinuous, occurring only locally. Despite stating that these strata are not really mappable at the 1:24000 scale, Heckert and Lucas (2003) provided a formal name, the Zuni Mountains Formation; however, this terminology has not been accepted by any other Chinle worker, and Zeigler et al. (2008) argued that it did not form a valid lithostratigraphic unit.

I still have yet to find this "distinctive" horizon in outcrop and through in many places the lateral muddy facies of the Shinarump (normally a conglomerate) is mottled. However, this unit contains many petrified logs, a charateristic of the Shinarump (Stewart et al., 1972). I have visited places where other authors (e.g., Heckert and Lucas, 2003) have stated the unit to be present (e.g., Six Mile Canyon, New Mexico; Placerias Quarry, Arizona) but the "mottled" rocks here are not the well developed horizon described by Stewart et al. (1972). Zeigler et al. (2008) found the same thing to be true for proposed outcrops of "mottled strata" in the Chama Basin of New Mexico.

Stewart et al. (1972) briefly mention a second mottled horizon near the top of the Mesa Redondo Member near St. Johns, Arizona. Jeff Martz and I have repeatedly found this horizon at roughly the same stratigraphic interval near St. Johns, near Concho (west of St. Johns), and even in the Petrified Forest National Park.

Earlier today, I did a brief reconnaissance of an outcrop of Chinle Formation rocks near the Tunnel Overlook (find map here) at Canyon De Chelly National Monument in northeastern Arizona. The majority of the monument consists of deep canyons carved into the Permian De Chelly Sandstone; however, several paleovalleys filled with Chinle sediments are scoured into the De Chelly Sandstone and thick outcrops of Chinle strata occur in the nearby city of Chinle (hence the name of the Formation).

This outcrop is of interest as it rests within one of these paleovalleys and thus represents basal Chinle strata. Would I find the "mottled strata" here? From the picture below it can be seen that the base of the outcrop consists of a chocolate brown siltstone horizon (unit 1) filling the paleovalley in the sandstone. Although hard to tell from this limited outcrop, this unit is similar to Moenkopi sediments. Above this is a layer of mottled yellow and gray siltstone and sandy siltstone (unit 2) capped by a resistant brown cross-stratified sandstone lens (unit 3). Above this is gray, non-mottled, siltstone (unit 4) and above this is a very hard strongly mottled unit (unit 5) very similar to the upper mottled unit found near St. Johns and Concho. The medial sandstone lens could possibly represent the Shinarump. See photos below.

View of Chinle Formation section exposed near Tunnel Overlook in Canyon De Chelly.

Units 2 and 3. Is Unit 2 the "Mottled Strata"?

Unit 5.

Close-up of mottling in Unit 5.

Unfortunately I only had a few minutes here, enough time to snap a few photos, but will definitely return in the near future for a more detailed investigation. I need to search laterally for the base of the section to find the Shinarump, and see if the basal brown unit is really the Moenkopi. The significance of these mottled units is unclear; however, if they truly are correlatable, they will be extremely important in sorting out the nomenclatural mess an correlations of the basal Chinle Formation.

REFERENCES

Dubiel, R. F. 1989. Depositional and climatic setting of the Upper Triassic Chinle Formation, Colorado Plateau; pp. 171-187 in Lucas, S.G., and A.P. Hunt (eds.), Dawn of the Dinosaurs in the American Southwest, University of New Mexico Press, Albuquerque.

Heckert, A. B., and S.G. Lucas. 2003. Triassic stratigraphy in the Zuni Mountains, west-central New Mexico. New Mexico Geological Society Guidebook 54:245-262.

Stewart, J.H., Poole, F.G. and Wilson, R.F. 1972. Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata in the Colorado Plateau region: U.S. Geological Survey Professional Paper, 690, 336 p.

Zeigler, K. E., Kelley, S., and J. W. Geissman. 2008. Revisions to stratigraphic nomenclature of the Upper Triassic Chinle Group in New Mexico: New insights from geologic mapping, sedimentology, and magnetostratigraphic/paleomagnetic data. Rocky Mountain Geology 43:121-141.

The Central Atlantic Magmatic Province and its Connection with the Triassic/Jurassic Extinction

The Central Atlantic magmatic province (CAMP) is a large igneous province formed during the breakup of Pangaea during the Mesozoic era. Rifting of North America from Europe and Africa (i.e., the open of the present day Atlantic Ocean) occurred during the Latest Triassic and or/ Earliest Jurassic and resulted in the emplacement of at least 10 million square kilometers of basalt in eastern North America, South America, Northern Africa, and Europe, the largest known igneous province in area of extent.




The CAMP is of significance because of its possible relationship with the Triassic/Jurassic boundary and thus a contributor to the Triassic/Jurassic extinction event. However, the exact timing of the event and whether or not it was a factor in extinction is highly debated with one group of workers arguing for it as a cause and another group denying this. Interestingly, support for or against the CAMP being a cause for the TR/J extinction depends on where the rocks are studied and dated. In Morocco the age of lava flows appears to coincide with the TR/J boundary (e.g., Marzoli et al., 2004, 2008; Verati et al., 2007), whereas in North America the flows appear to be too young (e.g., Whiteside et al, 2007, 2008).

A recent paper by Jourdan et al. (2009) provides new dates of CAMP deposits from North America and again argues for a causal effect on the end Triassic extinction (see the full abstract below), thus this issue is far from resolved.

You can read more on the CAMP at these websites:

http://en.wikipedia.org/wiki/Central_Atlantic_Magmatic_Province

http://www.auburn.edu/academic/science_math/res_area/geology/camp/

Jourdan, F., Marzoli A., Bertrand, H., S. Cirilli, S., Tanner, L.H., Kontak, D.J.,
McHone, G, Renne, P.R., and G. Bellieni. 2009. 40Ar/39Ar ages of CAMP in North America: Implications for the Triassic–Jurassic boundary and the 40K decay constant bias. Lithos 110:167-180. doi:10.1016/j.lithos.2008.12.011


ABSTRACT - The Central Atlantic magmatic province (CAMP) is one of the largest igneous provinces on Earth (greater than 10 million square km), spanning four continents. Recent high-precision 40Ar/39Ar dating of mineral separates has provided important constraints on the age, duration, and geodynamic history of CAMP. Yet the North American CAMP is strikingly under-represented in this dating effort.

Here we present 13 new statistically robust plateau, mini-plateau and isochron ages obtained on plagioclase and sericite separates from lava flows from the Fundy (n=10; Nova Scotia, Canada), Hartford and Deerfield (n=3; U.S.A.) basins. Ages mostly range from 198.6±1.1 to 201.0±1.4 Ma (2σ), with 1 date substantially younger at 190.6±1.0 Ma. Careful statistical regression shows that ages from the upper (199.7.0±1.5 Ma) and bottom (200.1±0.9 Ma) units of the lava pile in the Fundy basin are statistically indistinguishable, confirming a short duration of emplacement (≪1.6 Ma; ≤1 Ma). Three ages obtained on the Hartford (198.6±2.0 Ma and 199.8±1.1 Ma) and Deerfield (199.3±1.2 Ma) basins were measured on sericite from the upper lava flow units. We interpret these dates as reflecting syn-emplacement hydrothermal activity within these units. Collectively, CAMP ages gathered so far suggest a short duration of the main magmatic activity (2–3 Ma), but also suggest the possibility of a temporal migration of the active magmatic centers from north to south. Such a migration challenges a plume model that would postulate a radial outward migration of the magmatism and is more compatible with other models, such as the supercontinent global warming hypothesis. When compared to the age of the Triassic–Jurassic boundary, the filtered CAMP age database suggests that the onset of the magmatic activity precedes the limit by at least few hundred thousand years, thereby suggesting a causal relationship between CAMP and the end of Triassic mass extinction.

An age at 191 Ma possibly suggests a minor CAMP late tailing activity (190–194 Ma) which has been observed already for dykes and sills in Africa and Brazil. We speculate that, if genuine, this late activity can be due to a major extensional event, possibly heralding the oceanization process at ~190 Ma. Comparison between high quality U/Pb and 40Ar/39Ar ages of pegmatite lenses from the North Mountain basalts confirms a ~1% bias between the two chronometers. This discrepancy is likely attributed to the miscalibration of the 40K decay constants, in particular the electron capture branch.

REFERENCES

Marzoli, A., Bertrand, H., Knight, K.B., Cirilli, S., Buratti, N., Vérati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., and G. Bellieni. 2004. Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis. Geology 32:973–976. doi: 10.1130/G20652.1

Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Nomade, S., Renne, P.R., Verati, C., Youbi, N., Martini, R., and G. Bellieni. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Comment. Palaeogeography, Palaeoclimatology, Palaeoecology 262, 189–193. doi:10.1016/j.palaeo.2008.01.016

Verati, C., Rapaille, C., Féraud, G., Marzoli, A., Bertrand, H., and N. Youbi. 2007. Timing the Tr–J boundary: further constraints on duration and age of the CAMP volcanism recorded in Morocco and Portugal. Palaeogeography Palaeoclimatology Palaeoecology 246. doi:10.1016/j.palaeo.2006.06.033

Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2007. Synchrony between the Central Atlantic magmatic province and the Triassic-Jurassic mass-extinction event? Palaeogeography, Palaeoclimatology, Palaeoecology 244:345-367. doi:10.1016/j.palaeo.2006.06.035

Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., and M. Et-Touhami. 2008. Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Reply to Marzoli et al. Palaeogeography,Palaeoclimatology, Palaeoecology 262, 194–198. doi:10.1016/j.palaeo.2008.02.010

Graphic is from here.