68-4 Marine benthic ecological shifts in the Late Paleozoic (Kasimovian) Graford Formation

Session: Climate Transitions in the Paleozoic (Posters)

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Abstract:

The Late Paleozoic Ice Age (LPIA) was the longest glacial interval in Earth’s history, characterized by repeated glacial-interglacial cycles recorded in the marine stratigraphic record. This period of icehouse conditions and glacio-eustatic sea level fluctuations is associated with decreased rates of extinction and origination in some marine clades, possibly as a result of fluctuating oceanographic conditions favoring generalist, eurytopic taxa. Though studies on individual clades through this time have been performed, research regarding whole community structure and reorganization through this interval can reveal broader paleoecological trends or lack thereof. The Midland Basin in Texas records abundant material from the peak of LPIA glaciation in the Carboniferous and is therefore an excellent region of study with an expansive geographic and temporal range. Here, we collected bulk samples every 0.5 m from the Missourian/Kasimovian-aged Bridgeport Shale of the Graford Formation. The benthic marine paleocommunity here includes crinoids, echinoids, bryozoans, sponges, and uncommon brachiopods. Sampled material was sieved so that only specimens > 5 mm were utilized for study. Taxa were identified to the genus level and assigned ecological guild categories of; motility, diet, and tiering from the Paleobiology Database. Biovolume estimates were calculated using whole specimen mass and volume which was used to quantitatively assess ecological guild occupation and biomass organization across these paleocommunities through time. Preliminary data indicates an ecological shift through time, with a decrease of lower and upper epifaunal forms: Crinoidea, Rhynchonellata, and Gastropoda along with a concomitant increase in intermediate epifaunal forms, Demospongiae. This class level shift towards a sponge dominated ecosystem may suggest increased rates of total deposition and input of terrigenous sediment. This data can be used to test whether or not palaeoecological stasis is present in marine benthic communities across the peak of the LPIA. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7966

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