CPCP : Colorado Plateau Coring Project – 100 Million Years of Early Mesozoic Climatic , Tectonic , and Biotic Evolution of an Epicontinental Basin Complex

Early Mesozoic epicontinental basins of western North America contain a spectacular record of the climatic and tectonic development of northwestern Pangea as well as what is arguably the world’s richest and most-studied Triassic-Jurassic continental biota. The Colorado Plateau and its environs (Fig. 1) expose the textbook example of these layered sedimentary records (Fig. 2). Intensely studied since the mid-nineteenth century, the basins, their strata, and their fossils have stimulated hypotheses on the development of the Early Mesozoic world as reflected in the international literature. Despite this long history of research, the lack of numerical time calibration, the presence of major uncertainties in global correlations, and an absence of entire suites of environmental proxies still loom large and prevent integration of this immense environmental repository into a useful global picture. Practically insurmountable obstacles to outcrop sampling require a scientific drilling experiment to recover key sedimentary sections that will transform our understanding of the Early Mesozoic world.


Introduction
Early Mesozoic epicontinental basins of western North America contain a spectacular record of the climatic and tectonic development of northwestern Pangea as well as what is arguably the world's richest and most-studied Triassic-Jurassic continental biota.The Colorado Plateau and its environs (Fig. 1) expose the textbook example of these layered sedimentary records (Fig. 2).Intensely studied since the mid-nineteenth century, the basins, their strata, and their fossils have stimulated hypotheses on the development of the Early Mesozoic world as reflected in the international literature.Despite this long history of research, the lack of Despite this long history of research, the lack of espite this long history of research, the lack of numerical time calibration, the presence of major uncertainties in global correlations, and an absence of entire suites of environmental proxies still loom large and prevent integration of this immense environmental repository into a useful global picture.Practically insurmountable obstacles to outcrop sampling require a scientific drilling experiment to recover key sedimentary sections that will transform our understanding of the Early Mesozoic world.Olsen et al., 1999), section "Western Equatorial Pangea" (http://www.ldeo.columbia.edu/~polsen/nbcp/westpangea.html).Forty-five researchers from six countries attended the inaugural CPCP planning workshop held 13-16 November 2007, in St. George, Utah.The main goal was to develop a community consensus science plan for the CPCP (http:// www.ldeo.columbia.edu/~polsen/cpcp/CPCP_home_page.html).The participants represented disciplines ranging from geochronology and physical stratigraphy through vertebrate paleontology and paleobotany.A plenary session with speak-plenary session with speak-lenary session with speakers highlighting the major science issues, precedents, and geoinformatics priorities was followed by thematic breakout by thematic breakout thematic breakout groups.These included Stratigraphy, Geochronology and Magnetostratigraphy, Climate and Environments, Paleontology and Biotic Change, and Geoinformatics and Core-log Outcrop Integration.A half-day field trip was made Outcrop Integration.A half-day field trip was made utcrop Integration.A half-day field trip was made Integration.A half-day field trip was made ntegration.A half-day field trip was made to the St. George Dinosaur Discovery Site at Johnson Farm (http://www.sgcity.org/dinotrax/)and Warner Valley outcrops of Triassic-Jurassic strata (Fig. 3), and was followed by a plenary synthesis session.As developed by consensus at the workshop, the goal of the CPCP is to transform our understanding of the interplay between major biotic transitions, global climate change, plate position, and tectonics over 100 Ma of Earth histories (Fig. 2).2) Development of the highest-resolution magnetic polarity stratigraphy for Early Triassic through Late Jurassic strata to facilitate detailed regional and global correlation.3) Determination of how paleoclimates are expressed through time in the sedimentary record of western Pangea.4) Identification of the precise stratigraphic position of major global biotic transitions (i.e., Permo-Triassic, Triassic-Jurassic, and Toarcian) 5) Refinement of lithostratigraphic and biostratigraphic correlations, considering regional unconformities and their possible relationship to eustacy and tectonics (c.f., Bachmann and Kozur, 2004).6) Development of a chemostratigraphic (δ 13 C, cuticular CO 2 proxy, Nd, Sr, clays, etc.) reference sections.7) Improvement of U-Pb zircon provenance stratigraphy and geochronology of ash beds.8) Establishment of links among the temporal evolution of the Colorado Plateau sedimentary record, rifting of Pangea opening of the Atlantic Ocean, and emplacement of basalt provinces (Fig. 2).

Coring Plans
Given these overall goals, the workshop reached several conclusions that dictated the coring plan.

1) Early Triassic through Late Jurassic Formations including the Morrison
Formation should be cored in order to cover the full range of climatic milieus represented by these rocks.Collectively, the group defined a three-tiered coring plan consisting of (1) three relatively thick (~1 km) synoptic intervals that together would yield an overlapping stratigraphic framework for the entire Jurassic and Triassic section, (2) two thinner (<500 m) cored sections that would tie to critical outcrop areas or to expanded critical intervals, and (3) a number of short sections to address more specific problems or provide regional coverage to the other five cores that are the nexus of the project.
2) Superposition is paramount.Evaluation of the critical Early Mesozoic transitions is required of all Early Mesozoic is required of all Early Mesozoic required of all Early Mesozoic d of all Early Mesozoic of all Early Mesozoic units in clear superposition.The five major stratigraphic units identified as major coring targets reflect, from oldest to youngest: arid (Moenkopi)�� humid to semiarid (Chinle)�� very arid (Glen Canyon and San Rafael)�� and return to semiarid and humid (Morrison) (Figs. 2 and 4).These climate transi-4).These climate transi-4).These climate transitions have been explained in several ways-translation of the North American plate from equatorial to mid-latitudes through zonal climate belts (Dickinson, 2005�� Kent and Muttoni, 2003�� Kent and Tauxe, 2004)�� large scale changes in �� large scale changes in large scale changes in the climate system involving changes in the non-zonal components of the climate system, particularly the monsoon (Kutzbach and Gallimore, 1989�� Parrish, 1995�� Rowe et al., 2007)�� or fluctuations in greenhouse gases like CO �� or fluctuations in greenhouse gases like CO or fluctuations in greenhouse gases like CO 2 (e.g., (e.g., McElwain et al., 1999�� Kürschner, 2001).These fundamentally different hypotheses remain untested because the temporal evolution of major boundary conditions, most notably latitude, has not been resolved to a useful level of precision (Tauxe andKent, 2004�� Tan et al., 2007).
3) Internal time calibration needed.Correlation of the Plateau sequence is presently based on low-resolution non-marine biostratigraphic approaches, and it does not pro-, and it does not pro-and it does not pro-it does not pro-does not provide clear biogeographic patterns or determination of the rates of biotic change in these very fossiliferous sequences.None of the major intervals of biotic change (Permo-Triassic�� Triassic-Jurassic�� or Toarcian) are located with precision in this succession.A combination of polarity stratigraphy along with geochronologic dates from ash deposits and dispersed grains will allow global correlations, including: 1) Triassic and Early Jurassic reference sections (Szurlies, 2007)�� 2) the astronomically calibrated polarity time scale (Kent and Olsen, 1999, 2008�� Olsen and Kent, 1999�� Hounslow et al., 2004�� Kemp and Coe, 2007)�� 3) the Germanic basin (Bachmann and Kozur, 2004)�� 4) fully marine Tethyan sections (Muttoni et al., 2005�� Channell et al., 2003�� Gallet et al., 2007)  and 6) possibly, the marine magnetic anomaly M-sequence (Channell et al., 1995�� Sager et al., 1998).4) Minimize hiatuses.Acquiring as much stratigraphic scope as possible through the more continuous units and testing any paleomagnetic reversal sequences across geography by designing stratigraphic overlap between cores will help overcome significant unconformities and possible smaller and cryptic hiatuses.The thickest sections, least likely to be affected by rampant hiatuses, are not confined to a single area in the Colorado Plateau because of lateral shifts in the basin's depocenters.Several cores will be necessary to get the most favorable sections of each of the units.However, the thick sections proposed for coring are far from comparable surface outcrops, and thus, subsidiary sections more , and thus, subsidiary sections more and thus, subsidiary sections more , subsidiary sections more subsidiary sections more proximal to sources of the surface data must be cored as well.The goal is to provide a long enough section with unambiguous ties to the outcrop and sufficient stratigraphic scope to correlate with the main, long cores.5) Thick eolianite successions should be avoided while key limestone and eolianite tongues must be intersected for age control by lateral correlation to outcrop.
Using these five principles above, three areas identified s above, three areas identified above, three areas identified , three areas identified three areas identified for long (~1 km) cores are, from the uppermost stratigraphic interval downward (Figs. 1 and 2 plausibly made by a large theropod dinosaur similar to Dilophosaurus from the lower Kayenta Formation; [B] small theropod dinosaur footprints of the "Grallator" and "Anchisauripus" types (~10-15 cm long each).The importance of these fossil assemblages is that they document the terrestrial assemblages just after the Triassic-Jurassic extinction event that surprisingly is overwhelmingly dominated by carnivores.
Although the American Southwest, including the Colorado Plateau, is famous for spectacular exposures in striking badlands, the thickest sections of key time intervals are often projected from the subsurface.The most continuous sections in outcrop are often exposed as inaccessible vertical cliffs or are heavily weathered and geochemically altered, precluding research at the appropriate level of detail.Because of low bedding dips, the assembly of sections spanning large stratigraphic thicknesses requires long-distance traverses that often compromise the essential assumption of superposition because of facies changes.The problems are amply revealed by repeated attempts in the literature at compiling long, high-resolution sections that describe the succession in any specific area.Long, continuously cored intervals tied to outcrop in key areas are required for further substantial progress.
Opportunities and problems of working only with outcrops present themselves in examples of superb near-100% outcrops, especially of muddy facies (Fig. 4).Mudstones are often bentonitic and with a partial volcanic source, which means there are datable ashes; however, it also means that the outcrop surfaces present horrendous sampling problems where freshness and physical integrity are at a premium as for geochemistry or paleomagnetics.Two examples include the Late Jurassic Morrison Formation (Fig. 4A and 4B) and the Late Triassic Chinle Group (Fig. 4C and 4D).   it is a natural is a natural complement to the Chinle section in the Tuba City area.The workshop concluded that the geophysical logs of the core holes and cores will be critical in tying cores to outcrop (Szurlies et al., 2003(Szurlies et al., ). et al., 2003))., 2003).

Ne�t Steps
The CPCP workshop endorsed aiming full drilling proposals to ICDP and U.S. .S. S. .National Science Foundation (NSF) Continental Dynamics.In preparation for this, there will be an international CPCP for this, there will be an international CPCP this, there will be an international CPCP , there will be an international CPCP there will be an international CPCP proposal planning workshop in Albuquerque, N.M., to be advertised in the near future.

Figure Credits
To bring our insight into this critical time in Earth history to a new level, we developed the concept of the Colorado Plateau Coring Project (CPCP), an effort to recover continuous core spanning the early Mesozoic (Triassic-Jurassic) section of the Colorado Plateau and adjacent areas.The original basis for this was outlined at the 1999 International Continental Scientific Drilling Program (ICDP) and U.S. National Science Foundation (NSF) funded International Workshop for a Climatic, Biotic, and Tectonic, Pole-to-Pole Coring Transect of Triassic-Jurassic Pangea (http://www.ldeo.columbia.edu/~polsen/nbcp/pangeafinalreport.html, Broad questions that could be profitably addressed in the Colorado Plateau venue include the following: what are the the following: what are the : what are the global or regional climate trends vs. plate position changes in "hot house" Pangea�� how do largely fluvial systems respond to cyclical climate�� what are the rates and magnitudes of the transition from the Paleozoic to essentially modern terrestrial ecosystems�� and how does the stratigraphy reflect the interplay between growth in accommodation, uplift, and eustatic fluctuations?Based on these questions, the workshop identified eight goals attainable by coring of key eight goals attainable by coring of key goals attainable by coring of key Triassic/Jurassic sections: 1) Establishment of paleogeographic boundary conditions, particularly changes in paleolatitude.

Figure 2 .
Figure 2. Details are given to the right.
Figure 3. Examples of dinosaur tracks at the St. George Discovery Site at Johnson Farm in the lower Whitmore Point Member of the Moenave Formation: [A] Example of natural cast of Eubrontes giganteus (~35 cm long),plausibly made by a large theropod dinosaur similar to Dilophosaurus from the lower Kayenta Formation; [B] small theropod dinosaur footprints of the "Grallator" and "Anchisauripus" types (~10-15 cm long each).The importance of these fossil assemblages is that they document the terrestrial assemblages just after the Triassic-Jurassic extinction event that surprisingly is overwhelmingly dominated by carnivores.
Fig. 4A, Brushy Basin Member of the Morrison Formation west of Green River, Utah (from http://en.wikipedia.org/wiki/Morrison_Formation);Fig. 4B, typical "popcorn" surface of bentonitic mudstone of the Brushy Basin Member of the Morrison Formation west of Green River, Utah (same source as 4A); Fig. 4C, "popcorn" surface of the Chinle Group near Bluewater Creek, NM (Stop 1 of Lucas et al., 2007), with fragmentary weathered metoposaur amphibian dermal bones; and Fig. 4D, outcrops of bentonitic Painted Desert Member of the Petrified Forest Formation of the Chinle Group in Petrified Forest National Park with the U-Pb dated Black Forest Bed(Riggs et al., 2003) outcropping as the white bed in foreground.

Figure 4 .
Figure 4. Details are given below.