Supplementary material to “One Hundred Million Years of Climatic, Tectonic, and Biotic Evolution in Continental Cores”

Paul E. Olsen, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York

Dennis V. Kent, Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey

John W. Geissman, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque

Citation:
Olsen, P. E., D. V. Kent, and J. W. Geissman (2008), One hundred million years of climatic, tectonic, and biotic evolution in continental cores, Eos Trans. AGU, 89(12), 118. [Full Article (pdf)]

A workshop was convened in November, 2007, in St. George, Utah, to advance planning for the Colorado Plateau Coring Project (CPCP). The vast continental basins of the southwestern United States, particularly well exposed on the Colorado Plateau and its environs, contain one of the richest records of early Mesozoic strata (Fig. 1). This time period was punctuated by two of the major mass extinctions of the Phanerozoic and witnessed the evolutionary appearance of the modern biota and dramatic climate changes on the continents.

Since the mid-19th century, classic studies of these basins, their strata, and their fossils have made this sequence instrumental in framing our context for the early Mesozoic world. Nonetheless, striking ambiguities in temporal resolution, uncertainties in global correlations with other early Mesozoic strata, and major doubts about latitudinal position still hamper testing of the major competing climatic, biotic, and tectonic hypotheses.

A scientific drilling experiment is essential as the most continuous sections in outcrop are either inaccessible in vertical cliffs or are weathered and geochemically altered, making observations and sampling at the appropriate level of detail impossible. Furthermore, the nearly flat-lying sediment layers in combination with facies changes compromise the ability to determine superposition in sections compiled over long geographic traverses.

Forty-five researchers from six countries attended the CPCP workshop and focused their discussion on developing a basic coring plan for the American Southwest venue that would attempt to resolve issues like differentiating global or regional climate trends vs. latitudinal changes in �hot house� Pangea, the response of largely fluvial systems respond to cyclical climate change, the rates and magnitudes of the transition from the Paleozoic to essentially modern terrestrial ecosystems, and how the stratigraphy of the basins reflects the interplay between growth in accommodation space, uplift, and eustatic fluctuations. To tackle these questions, the workshop participants identified five major stratigraphic packages on the Colorado Plateau and environs as key coring targets (Fig. 1): Early to Middle Triassic Moenkopi Formation, Late Triassic Chinle Group, latest Triassic to (?) Middle Jurassic Glen Canyon Group, Middle to (?) Late Jurassic San Rafael Group, and the Late Jurassic Morrison Formation. Specific geographic areas were selected for drilling of three long (~1 km) cores and two shorter cores that will recover the critical Early Mesozoic transitions in the region (Fig. 1).

With the further development of a robust and effective data management system and an education outreach program, the CPCP workshop endorsed development of drilling proposals for submittal to ICDP and US NSF Continental Dynamics in 2008. A smaller ICDP workshop is being planned for mid-2008 in Albuquerque, NM, to crystallize the science groups (PIs) for the CPCP. The CPCP workshop was funded by grants from DOSECC and NSF (Sedimentary Geology and Paleobiology).

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Figure 1. Left, Generalized Colorado Plateau section (Glen Canyon/Kaiparowits Plateau, based on http://jan.ucc.nau.edu/~rcb7/Glen_Can.jpg) with the cored sections recommended by the CPCP workshop participants and a generalized evaporation–precipitation (E-P) curve loosely based on climate sensitive facies. Note that the relative thicknesses of various units are in general different than what is shown in the color section and not the same between different coring areas. Core areas are: PF, Petrified Forest, Arizona; RP, Rock Point, Utah; SG, St. George, Utah; WT, Wards Terrace, Arizona; SRS, San Rafael Swell, Utah. Right, Generalized geological map of the Colorado Plateau (white line) showing Permian and Triassic and Jurassic strata (modified from R. Blakely, http://jan.ucc.nau.edu/~rcb7/Jurassic_erg_graphics.html).