--> --> Abstract: The English Graben: a Seismic Study of the Relationship Between a Proterozoic Rift Segment and Subsequent Paleozoic Structure and Strata, by T. J. Stark, S. H. Rowley, C. K. Steffensen, J. A. Drahovzal, L. E. Schultz, G. W. Bear, and S. Bergman; #90926 (1999)

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STARK, T. JOSHUA, Tulsa, OK; STEPHEN H. ROWLEY, Emet Consulting, Plano, TX; CARL K. STEFFENSEN, Vastar Resources Inc., Houston, TX; JAMES A. DRAHOVZAL, Kentucky Geological Survey, Lexington, KY; and LOUIS E. SCHULTZ, Williams Gas Pipelines Texas Gas, Owensboro, KY; GLENN W. BEAR, Exxon, Houston, TX; STEVE BERGMAN, ARCO EPT, Plano, TX

Abstract: The English Graben: a Seismic Study of the Relationship Between a Proterozoic Rift Segment and Subsequent Paleozoic Structure and Strata

The English Graben is interpreted as a polyphase rift, underlain by Mesoproterozoic strata and filled with Neoproterozoic/Cambrian sediments, forming a portion of the East Continent Rift Complex in areas of Kentucky and Indiana. The western margin of the graben is presently expressed by shallow faults offsetting Paleozoic strata, interpreted to be related to the remobilization of deepseated Proterozoic faults. The eastern margin is defined by the Louisville Accommodation Structure (LAS), a high-relief fault-bounded basement feature expressed in pre-Mount Simon strata by a series of shallow fault systems. The northern extension of this bounding feature is the Mt. Carmel Accommodation Structure (MCAS). Seismic data is interpreted to exhibit flanking pre-Mount Simon basins and complex extensional faulting associated with the MCAS.

Evidence from potential field data indicates deformation of the graben, with several kilometers of transcurrent displacement apparent along the margins of the rift segment. Earthquake epicenters recorded in the area may be localized along these transcurrent systems, responding to current eastwest horizontal maximum principle compressive stress. Hydrocarbon fields occur along the margins of the graben, and appear to be associated with structural remobilization of bounding fault systems.

Both proprietary and published seismic sections demonstrate the existence of a complex structural depocenter with multiple stages of deformation and a depth to crystalline basement exceeding 6100 m. Four borehole penetrations of the pre-Mount Simon sequence in the area of the graben suggest that the depocenter is filled with Neoproterozoic and/or Cambrian strata and underlain by the Mesoproterozoic Middle Run Formation/Centralia Sequence. Variations in stratigraphic thickness and lithology are noted in association with the graben margins, and it is suggested that the epeirogenic remobilization of the rift margins has controlled the Paleozoic structural and stratigraphic development of the area.

AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana