Petrology and depositional significance of Conemaugh marine units in the Appalachian Basin
- Univ. of Iowa, Iowa City, IA (United States). Dept. Geology
The Conemaugh Group contains the last appearance of Pennsylvanian marine units in the Appalachian basin. The marine units range from argillaceous/silty/sandy skeletal limestones to fossiliferous, dark to light gray shales, calcareous siltstones and sandstones. Limestones are present at least locally in all units and are conspicuous in most units. They commonly contain a more abundant and diverse fauna including abundant conodonts, and frequently contain glaucony and phosphorite, indicating long-term slowdown of deposition. They are typically overlain by fossiliferous shales that generally decrease in fossil abundance and diversity upward, locally contain siderite concretions, and coarsen upward to siltstones that lend diffuse upper boundaries to the marine unit. All the marine units appear to represent transgressive-regressive events extensive enough to reach this area from the Midcontinent where marine deposition is more prominent throughout the interval. Initial transgression produced swampy conditions locally permitting formation of coal, which was eventually overwhelmed by marine sediments. At maximum highstand, when clastic supply was reduced, limestones consisting mainly of skeletal debris and containing abundant conodonts were deposited as a condensed interval in which glaucony and phophorite formed slowly in the absence of detrital or carbonate dilution. These limestones are oxygenated shallow-water counterparts to the dark phosphatic, conodont-rich core shale member of the Midcontinent cyclothem. Regression reintroduced clastics readily into the system in the Appalachian basin, greatly diluting skeletal carbonate grains, thus terminating limestone deposition, and decreasing faunal abundance and diversity upward in the overlying detrital part of the marine unit.
- OSTI ID:
- 5805518
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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011000 -- Coal
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58 GEOSCIENCES
580000* -- Geosciences
APPALACHIAN BASIN
CARBONATE ROCKS
CARBONIFEROUS PERIOD
COAL DEPOSITS
DEPOSITION
FOSSILS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
LIMESTONE
MINERAL RESOURCES
PALEONTOLOGY
PALEOZOIC ERA
PETROLOGY
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SHALES
SILTSTONES
STRATIGRAPHY