Depositional and diagenetic records in the siderite concretions of the Llewellyn Formation from the anthracite field, PA
- Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Geology Bryn Mawr College, PA (United States)
The Llewellyn Formation is the major coal-bearing Pennsylvanian-age formation in the anthracite fields of eastern Pennsylvania. It comprises thick sandstones, mudstones, and anthracite-grade coals deposited on alluvial plains. In the abandoned Bear Valley Strip Mine of Shamokin, abundant siderite concretions with cm to m diameter are exposed along the bedding planes of folded beds. These concretions show structural elongation and flattening attributed to deformation during the Alleghenian orogeny. The prolific septarian cracks and abundant pyrite suggest early concretion growth, perhaps within the top 100 meters of sediment. In addition to the siderite, carbonate phases such as ankerite, calcite and dolomite occur in trace quantities in the concretions. Quartz and feldspars are abundant in the shales. Illite, kaolinite and chlorite occur in comparable quantities in both. Kerogen concentrates from the concretions contain yellow to light brown tissues, spores and reticulate pollen and spores. In contrast, those from shales comprise dark brown to black charred organic debris only. The difference in thermal alteration indices indicates that the organic matter in the concretions was preserved despite the high deformation temperatures (>200C) undergone by both the shales and concretions. This suggests that the early cementation may have completely sealed off the organic matter from chemical attack by volatiles. The data so far collected suggests that the clastic mineralogy and plant remains preserved in the concretions can be used to reconstruct the depositional history for the Llewellyn Formation, whereas the abundance of iron in the cement and its absence in the surrounding shales may be used to evaluate the rapid changes in pore water chemistry during diagenesis.
- OSTI ID:
- 5934708
- Report Number(s):
- CONF-9303211-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CONCRETIONS
DEPOSITION
DIAGENESIS
MINERALOGY
GEOLOGIC FORMATIONS
PENNSYLVANIA
ANTHRACITE
CARBONIFEROUS PERIOD
DEFORMATION
GEOLOGIC HISTORY
SHALES
SIDERITE
BLACK COAL
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CARBONATE MINERALS
CARBONATES
COAL
DEVELOPED COUNTRIES
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
IRON CARBONATES
IRON COMPOUNDS
IRON ORES
MATERIALS
MINERALS
NORTH AMERICA
ORES
OXYGEN COMPOUNDS
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
TRANSITION ELEMENT COMPOUNDS
USA
580000* - Geosciences