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Drilling Rationale

Of all the tectonic provinces in the western Cordillera, the Colorado Plateau has the thickest and most well studied Paleozoic and Mesozoic continental sequences as well as some of the most fossiliferous strata. Classic exposures of the Moenkopi Formation (Early and Middle Triassic age), Chinle Group (Late Triassic), and Glen Canyon Group (latest Triassic and Early Jurassic) in the American Southwest contain abundant megafossil plants, palynomorphs, microfossils, marine and non-marine invertebrates, and abundant and classic vertebrates (Lucas, 1998). These deposits represent a diverse suite of depositional environments and ecological niches of tropical Pangea, many of which are not represented in other Pangean basins. Obtaining sufficiently detailed chronostratigraphic and lithologic logs should allow the local response to Milankovitch forcing to be worked out by correlating the fluvial, eolian, and shallow lacustrine Colorado Plateau strata with established cyclicity in the contemporaneous eastern North American Early Mesozoic lacustrine sections. At least locally, deposition seems to have been essentially continuous across the Triassic-Jurassic boundary. Despite the long history of productive work, further progress is impeded by the striking lack of temporal resolution and uncertainties in global correlations with other lower Mesozoic strata, specifically on a global scale, and this deficiency hampers integrating the vast amount of information from the region into the global picture.

Why Core When the Outcrop is so Good?

Although the American Southwest, including the Colorado Plateau, is justifiably famous for spectacular exposures and striking badlands, many of the thickest sections are in the subsurface, and the most continuous outcrops are either in inaccessible vertical cliffs or are heavily weathered, making sampling at the appropriate level of resolution practically impossible, or geochemically altered. In addition, because of the often low dips, the assembly of sections spanning large stratigraphic thicknesses entails long-distance traverses, that because of facies changes, compromise the assumption of superposition. The problems are amply born out by the attempts at compiling long high resolution sections thus far.

A focused coring program in Triassic through Lower Jurassic strata on and east of  the Colorado Plateau would result in a quantum leap in our insight into issues of Pangean chronology, paleogeography, paleoclimate, and biotic evolution that also include those associated with the Triassic-Jurassic boundary.

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