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Monday, February 6, 2017

Comparative Trilobite Taphonomy from the Near-shore to Outer Shelf Settings, Latest Early Cambrian of the Southern Great Basin

Speaker: John Foster, PhD

The latest early Cambrian is a time of moderate species turnover in the early Paleozoic. Olenelloid trilobites, exemplified by spiny genera such as Olenelllus, Bristolia, and Nephrolenellus, dominate the time but then disappear just before the middle Cambrian. These trilobites are abundant in Cambrian deposits of the Great Basin and comprise a dataset with which to study conditions on the shallow shelf of what was then the north coast of our continent. Analysis of a sample of more than 2600 fossil specimens from across a near-shore to deep-water transect of the Cambrian passive margin wedge of southwestern Laurentia shows patterns within the distribution of material from shallow, proximal settings to those farther offshore. The results suggest that sedimentation and burial rates decreased from near-shore to deep-water settings, that diversity was high in all but the deepest settings, and that scavenging may have been more responsible for fragmentation of trilobite sclerites than current-derived mechanical breakage.

About the Speaker John Foster is the director of the Museum of Moab and first worked in Cambrian rocks of the Mojave Desert as an undergraduate. He has since had a number of day jobs that kept him in the Mesozoic, although his mind was even then often in the Cambrian seas. His current position follows short stints of school or work at the South Dakota School of Mines, University of Colorado, Denver Museum of Natural History (at the time), Utah Geological Survey, University of Wyoming, and Museum of Western Colorado. He is glad that although the Moab area lacks Cambrian rocks except in the sub-surface, he is at least a little closer to the House Range and Pioche area. He is author of Cambrian Ocean World: Ancient Sea Life of North America and Jurassic West: The Dinosaurs of the Morrison Formation and Their World.