68-3 Kasimovian (Missourian, Late Pennsylvanian) Foraminifera of the Lake Bridgeport and Wolf Mountain Shales (Canyon Group), North Central Texas

Session: Climate Transitions in the Paleozoic (Posters)

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Abstract:

Strata of the Lake Bridgeport Shale, the basal unit of the Canyon Group, are exposed in two major river valleys of North Central Texas, where they have been variably referred to as the Brownwood Shale (Colorado River Valley) and Lake Bridgeport Shale (Trinity River Valley). In the Brazos River Valley this shaly interval was named the Posideon or Wolf Mountain Shale. This study aims to clarify the stratigraphic position and nomenclature of these units through microfossil analysis. Residue samples from the Lake Bridgeport and Wolf Mountain Shales contain diverse microfossils, including small foraminifers, fusulinids, conodonts, ostracods, and holothurian sclerites. A continuous, well-exposed section of the Lake Bridgeport Shale at the Lake Bridgeport spillway was densely sampled and serves as a reference section for this study. A section referred to as the Wolf Mountain Shale was also closely sampled at Shutin Mountain north of the Brazos River. Preliminary results reveal several foraminiferal species common to both shales, including Orthovertella protea, Earlandia perparva, and Ammobaculites gracilis. Some taxa show distinct distributions for example, Calcitornella heathi is more abundant in the Wolf Mountain Shale compared to the Lake Bridgeport Shale population. Fusulinids are limited to several intervals in the Lake Bridgeport Shale and rare in the Wolf Mountain Shale. During the Late Pennsylvanian, the present-day area of North Central Texas was covered by the Late Pennsylvanian Midcontinent Sea where transgressive and regressive sequences deposited a succession of limestones and shales called cyclothems. Comparing foraminiferal species distributions from both sections will clarify whether the units, which appear to represent regressive phases of a single cyclothem, are indeed distinct.

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

doi: 10.1130/abs/2025AM-10090

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