2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 129-18
Presentation Time: 9:00 AM-6:30 PM


BUSKIRK, Bret L., Earth and Space Sciences, University of Washington, 802 N 42nd St, Seattle, WA 98103, HUNT, Adrian P., Flying Heritage Collection, 3407 109th Street SW, Everett, WA 98275 and LUCAS, Spencer G., New Mexico Museum of Natural History and Science, 1801 Mountain Road N.W, Albuquerque, NM 87104, bretbus@gmail.com

Bromalites from the Florissant Formation (34.07 ± 0.10 Ma) from the Florissant Fossil Beds National Monument, were analyzed via taxonomic and taphonomic methods to elucidate potential origins and predation dynamics present within the ancient lake system. The Florissant Fm. represents a lacustrine and fluvial depositional system that comprises volcaniclastic shales, mudstones, pumice and ash conglomerates. These sediments contain a highly diverse, excellent and uniquely preserved flora and fauna. Major work has been completed on the paleobotanical, entomological, microvertebrate and invertebrate fossils of the formation, but little work has been done on the bromalites. Preliminary analysis of 25 specimens showed an affinity, based on content, to two major morphotypes, A and B, with an intermediary unresolved morphotype combining the former. Morphotype A--13 specimens with high content of crushed invertebrate shells, ovoid (rarely sinusoidal) in shape and on average 19.68mm by 13.19mm, with little to no groundmass (organic rich). Morphotype B--9 specimens; entirely groundmass, no shells, sinusoidal to kidney shape with few ovoid, on average 14.67mm by 9.5mm, diameter average 4.75mm. Unresolved specimens, 3, contain both shells (small quantity and crushed) and a high quantity of groundmass, irregular to sinusoidal in shape, and on average 17.33mm by 10mm. Due to the shape, size and content of the specimens, the Florisssant bromalites are thought to originate from different biological processes; (Morphotype A: regurgatilites, Morphotype B: coprolites); and the unresolved type as general bromalites. Morphotype A, composed of crushed invertebrate shells; identified as sphaeriids, lymnaeids and planorbids, are generally homogenous in shell type, and rarely show heterogeneity. These differences could reflect additional selective tendencies within the predatory behavior of the lake inhabitants. Likely producers of these bromalites are fish and or shorebirds found within the Florissant Fm., though they may reflect behavior of previously unknown vertebrates. In the comparison of these morphotypes, potential identification of specific consumers and their biologic functions is possible, which helps to elucidate larger trophic structures present within the ecology of the Florissant Lake system.
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