Triassic Macrostratigraphy of the Western United States and the Ichnology, Paleoecology, and Paleoenvironments of the Early and Middle Triassic Chugwater Group, Wyoming PDF Download

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Book Description
Triassic deposits of the western United States record an extraordinary period of earth's history that records biotic recovery from the end-Permian extinction, the origin of the modern fauna, and the end-Triassic extinction. Tectonic and climatic variability across this interval influenced the preserved architecture of the stratigraphic record. Using a macrostratigraphic approach the spatiotemporal variability of sedimentary attributes within Triassic deposits of the western US are quantified to test hypotheses of these tectonic and climatic influences. Early Triassic deposition demonstrates significant differences in spatiotemporal distribution of lithology, volume, and rates of accumulation compared to deposits of Late Triassic age. Tectonic signals and links to global carbon¬-Early Triassic sedimentation are explored. Building upon this macrostratigraphic foundation, variability in vertebrate track and body fossil preservation is investigated using a similar macrostratigraphic approach. A significant environmentally linked taphonomic bias, which favors track preservation over body fossils, is demonstrated in two post-extinction recovery intervals, the Early Triassic and Early Jurassic. This study further demonstrates that vertebrate tracks precede the presence of inferred trackmaker body fossils by 2 to 32 million years for 6 of 8 major tetrapod clades. A newly discovered vertebrate and invertebrate `hidden' ichnofauna is described from the Early Triassic Red Peak Formation of the Chugwater Group in central Wyoming. Sedimentology and track associations are suggestive of a hygrophilic invertebrate community found dominantly along riparian and lacustrine margins. Vertebrate tracks of Chelonipus extend the temporal range of testinudes by more than 30 million years supporting observations that tracks appear to precede bone. This discovery demonstrates a diverse paleoecology in the northernmost continental rocks of Early Triassic age in North America. Strontium stable isotope geochemistry of the Alcova Limestone, which immediately overlies the Red Peak Formation in central Wyoming was investigated to test hypotheses of deposition. Global marine strontium signals for the Early Triassic show a distinct pattern and are used to confirm a marine origin for the Alcova Limestone, and were further used to reliably constrain the age of the Alcova Limestone to the Spathian (late-Early Triassic), thus permitting an age assignment to the Red Peak ichnoassemblage.