Relationships between benthic communities and sedimentary environments in the Pennsylvanian Finis Shale near Jacksboro, Texas
- Univ. of Texas, Arlington, TX (United States). Dept. of Geology
In a new complete exposure near Jacksboro, unweathered and highly fossiliferous Finis Shale overlies greenish laminated shales with mudcracks, and has a transgressive sandstone at the base. Five or more superimposed fossil assemblages can be distinguished. The basal sandstone is overlain by a thin red mudstone with calcareous concretions and abundant Myalina shells (very shallow water), followed by a thin sandy mudstone bed that contains abundant shell fragments and fusulinids. Then follows a black to dark-gray shale unit with abundant conularids, brachiopods, fossil seed pods and wood fragments (pyritic preservation). Modern analogs suggest that the latter might have been reworked from mangrove soils in the course of transgression. The next higher unit is a thin, highly fossiliferous horizon of light gray shale with phosphatic nodules and abundant evidence of erosion and reworking (disarticulated and broken brachiopod shells, epibionts on nodules). The uppermost unit is a dark gray shale with a brachiopod and bivalve dwarf fauna at the bottom, changing upwards into an assemblage where in contrast very large specimens are conspicuous in addition to rugose corals and soft bottom sponges. Faunal and sedimentological characteristics such as degree of bioturbation, population density, dwarf faunas, shell morphology (e.g. thin vs massive shells and spine development in brachiopods), and faunal assemblages reflect a complex interplay of oxygen levels, food supply, strength of bottom currents, turbidity, and substrate properties (firm vs soft). Careful examination of these characteristics allows detailed reconstruction of living conditions and depositional environments of a Pennsylvanian core shale.
- OSTI ID:
- 6002338
- Report Number(s):
- CONF-9303212--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:1; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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