Cyclothems in the Shelburn Formation (Middle and Upper Pennsylvanian) of southwestern Indiana

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5012084

King, N R ^[1]

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1. Univ. of Southern Indiana, Evansville, IN (United States). Dept. of Geosciences

The lower part of the Shelburn Formation (upper Desmoinesian -- below the West Franklin Limestone Member) in the subsurface of southwestern Indiana includes an incised paleovalley system. A core from Posey County, Indiana through the valley-fill sediments penetrated four lithologic cycles (cyclothems) in 12 meters of strata. In ascending order, each cyclothem includes: (1) dark-colored shale with marine fossils; (2) greenish-gray shale with siderite granules and concretions; (3) bioturbated or rooted shale or mudstone; and (4) (in two of the four cyclothems), coal or shale with thin lenses of coal. The shales of unit no. 1 were deposited during sea-level highstands, and overlying units in each cyclothem were deposited during infilling of the flooded paleovalleys (estuaries ). Rooted zones and other exposure features in unit no. 3 suggest that sea-level lowstands alternated with highstands. The highstand shale of the second cyclothem is highly radioactive, and is the only paleovalley bed that can be traced beyond the limits of the paleovalley system. It apparently represents a major highstand of sea level. Otherwise, paleovalleys provided the accommodation space necessary for deposition and preservation of these units. Cyclothems of greater geographic extent and thickness occur both above and below the paleovalley system. These include a widespread radioactive shale, prominent limestone bed, or well-developed coal, alone or in combination. Existence of more than one order of cyclothem complicates regional correlation of maximum highstand units and exposure surfaces. The fortuitous preservation of minor cyclothems only in paleovalleys suggests that the smallest-scale sea-level cycles during the Pennsylvanian have left little or no stratigraphic record in this area.

• OSTI ID: 5012084
• Report Number(s): CONF-9303210--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:3
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBONIFEROUS PERIOD
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGY
INDIANA
LITHOLOGY
NORTH AMERICA
PALEOZOIC ERA
PETROLOGY
ROCKS
SEDIMENTARY ROCKS
SHALES
STRATIGRAPHY
USA