--> ABSTRACT: Relationship Between Paleotopographic Surface of Cambrian-Ordovician Knox Group and Oil and Gas Entrapment in Kentucky, by Patrick J. Gooding; #91041 (2010)

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Relationship Between Paleotopographic Surface of Cambrian-Ordovician Knox Group and Oil and Gas Entrapment in Kentucky

Patrick J. Gooding

Cambrian-Ordovician dolostones of the Knox Group constitute one of the largest occurrences of this rock type known in the United States. In Kentucky, the Knox carbonate sequence attains thicknesses of more than 3,500 ft. Mudstone and wackestone are dominant in the upper Knox, with lesser amounts of packstone and grainstone.

The Upper Cambrian to Lower Ordovician carbonate sequences in Kentucky resulted from carbonate sedimentation on a cratonic platform in shallow, low-energy marine environments. Relative structural quiescence existed during this time. The thick sequence of shallow-water carbonates suggests that the rate of deposition generally kept pace with subsidence of the craton. Geologic environments and climatic conditions during this period were similar to those of the Bahamas today. Warm climate, sporadic rainfall, and dry trade winds probably accounted for the net loss of water by evaporation and the resulting hypersaline conditions.

The paleotopographic surface that developed on top of the Knox Group is of considerable economic importance because of potential hydrocarbon entrapment at or near the unconformity. Areas where permeable and porous zones developed on the exposed Knox surface due to erosion and weathering provide reservoir conditions; also, the unconformable surface of the Knox was sealed by an overlapping impermeable formation capable of entrapping hydrocarbons. Because of pressures exerted, hydrocarbons driven by fluids or gas may migrate along the eroded Knox surface laterally and upward onto paleotopographic highs. These conditions increase the probability of finding commercial oil and gas deposits in the Cambrian-Ordovician Knox in Kentucky.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.