Sedimentologic, stratigraphic, and paleoenvironmental study of Paleocene Fort Union Formation in South Cave Hills of Harding County, South Dakota
The Paleocene Fort Union Formation consists of the Ludlow, Cannonball, and Tongue River Members and forms prominent buttes in the Cave Hills, north-central Harding County, South Dakota. Investigations in the North Cave Hills show that cliff-forming Tongue River sandstones are actually the marine Cannonball Member. Field/laboratory studies indicate a similar reinterpretation for the cliff-forming sandstones in the South Cave Hills. These strata include fine to very fine-grained silty/clayey quartz sandstone. Textural analyses indicate the sand grains are subangular to rounded, polished, and of low to moderate sphericity. Sedimentary/biogenic structures indicate a high-energy, mainland beach/nearshore marine depositional environment. The transgressive sequence includes foreshore or littoral, shoreface, and subshoreface or estuarine environments. Foreshore/littoral sediments consist of fine to very fine-grained, moderately well to well-sorted, low-angle wedge planar and wedge trough cross-bedded sandstone. Trace fossils are dominated by Skolithos-like burrows. Marine vertebrate remains include Elasmobrachii sp., Myliobatis sp., and Myledaphus sp. Shoreface deposits are similar to those of the foreshore. Sedimentary structures are dominantly low- and high-angle wedge trough cross-beds. Ophiomorpha burrows occur near the upper contact. Shoreface deposits are separated from the subshoreface deposits by extensively burrowed silty sandstone or an erosional surface. The subshoreface environment produced very fine-grained sandstone interbedded with clay-claystone and clay shale that is very thin to thin bedded with minor amounts of ripple lamination and low-angle cross-stratification. Pseudo-symmetrical and composite ripples; flaser, wavy, and lenticular bedding; and sand-filled trails and burrows are present.
- Research Organization:
- South Dakota School of Mines and Technology, Rapid City
- OSTI ID:
- 6962850
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:8; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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CENOZOIC ERA
DEPOSITION
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
NORTH AMERICA
RESERVOIR ROCK
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEDIMENTATION
SOUTH DAKOTA
STRATIGRAPHY
TERTIARY PERIOD
USA