189-7 Faunal Census and Biostratigraphy of a Bioherm from the Fort Payne Formation (Lower Mississippian), Clay County, Tennessee

Session: Paleontology, Paleoecology/Taphonomy (Posters)

Presenting Author:

Authors:

Abstract:

A roadcut along Tennessee Highway 52 exposes a bioherm at the base of the Fort Payne Formation in Clay County, Tennessee (36.5344, -85.4992). The bioherm is approximately 20 meters high and 140 meters long, comprised primarily of a gray-green shale divided into two distinct units separated by a complex of carbonate beds. The lower shale unit has three prominent crests, ranging in thickness from approximately 1 meter to 4 meters at the highest crest. Overlying this unit, a complex of several carbonate beds pinches and swells, measuring up to 7 meters at the thickest point and thinning laterally to approximately 7 cm.

A faunal census focusing on the lower shale unit has documented a diverse fauna that includes articulate brachiopods, sponge spicules, cryptostome bryozoans, fenestrate bryozoans, crinoids, and trilobites. We collected 41 samples at 25 cm intervals from nine sites along the outcrop, identifying a total of 492 individual organisms. Poor preservation within the bioherm limited taxonomic resolution beyond phylum. However, 17 brachiopod genera have been identified with Composita and Leiorhynchus being the most abundant. Bryozoan diversity is relatively low, represented by only 4 genera. Additionally, we have recovered 3 trilobite pygidia, all belonging to the same species of Australosutura.

Examination of the carbonate beds primarily targeted microfossils, resulting in the recovery of several conodont elements. Although many of the recovered S- and M-elements remain difficult to assign taxonomically, we have successfully identified one specimen of Gnathodus texanus.

Stratigraphically, the Fort Payne bioherm overlies a condensed Kinderhookian-aged unit known as the Maury Shale, which is in sharp contact with the Devonian-aged Chattanooga Shale. Previous authors have inferred this bioherm to be deposited during the Early to Middle Mississippian (Osagean). However, biostratigraphic confirmation has until now been lacking. The presence of G. texanus supports an Osagean depositional age. As this period follows a major mass extinction, our faunal census provides critical insights into ecological recovery and enhances our understanding of regional biostratigraphy during this geological period.

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

doi: 10.1130/abs/2025AM-8052

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