GSA Connects 2022 meeting in Denver, Colorado

Paper No. 260-4
Presentation Time: 2:25 PM

ICHNOLOGY OF THE BRIGHT ANGEL FORMATION, GRAND CANYON, ARIZONA: INDICATORS FOR MIDDLE CAMBRIAN PALEOECOLOGY


MILLER, Anne, Department of Interior, National Park Service, Flagstaff, AZ 86001

The Cambrian Explosion is the major animal diversification event yielding the roots of all modern animal phyla. Famed Lagerstätten like the Burgess Shale and Chengjiang inform the anatomical details of this diversification event with ongoing research. A complementary record of preserved living environments, as opposed to transported environments, exists in the well-preserved and highly diverse trace fossil record of the Middle Cambrian Bright Angel Formation (BAF) of Grand Canyon National Park. The Bright Angel paleoenvironment was a shallow sea on a low-gradient shelf influenced by terrestrial rivers and localized tidal processes. This complex shoreline allowed opportunities for various ecological niches to support the progression of faunal behavior as seen in the ichnological record. The project aims to compare the known faunal diversity of, e.g., the contemporaneous Burgess Shale, to the ichnodiversity of the BAF to better characterize localized paleoecology and ichnofacies of the Middle Cambrian. Fifteen stratigraphic sections, with their corresponding bioturbation index, were measured in the BAF at eleven localities in eastern and western Grand Canyon. Bioturbation is generally high and ranges throughout the heterolithic sandstone and shale facies of the BAF. Fifteen ichnogenera and three ichnospecies were identified throughout these sections. Ichnogenera were quantified by counting their stratigraphic occurrence at each measured section. Predominance of Teichichcnus, Palaeophycus, Diplocraterion, and Arenicolites indicate faunal abundance of annelid and priapulid worms or other vermiform burrowing types. These worms have been identified in the Burgess Shale and Chengjiang Lagerstätten, but their preserved record is very limited relative to arthropods. The BAF contains few body fossils, most of which are trilobites, and lacks any record of soft-bodied fauna thus far. Combining the record of interpreted tracemakers with the body fossil record in the BAF provides opportunities to correlate tracemaker abundance despite the preservational biases of the BAF. The BAF ichnology record also provides insights into faunal behavioral evolution during the final stages of the Cambrian Explosion.