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Abstract: Tectonostratigraphic Reconstruction and Lithofacies Distribution of Tertiary Slope Sedimentary Rocks in the Western Mississippi Canyon Area
Andrew E. Hannan, David L. Risch, Abu N. Chowdhury
The distribution of upper Tertiary, sandstone-prone, deep-water sedimentary rocks from the vicinity of Cognac field, Mississippi Canyon (MC) 194, south of Mars field (MC763) is presented based on an integrated sequence stratigraphic analysis of seismic, well log, and biostratigraphic data. Paleo-salt distributions were reconstructed by plotting the changing positions of depocenters on five isopach maps generated from six key sequence boundaries. Depositional trends, projected under allochthonous salt sheets, indicated subsalt prospectivity. Sixteen sequences were interpreted and subdivided into three lowstand depositional units (basin-floor fan, slope fan, and prograding wedge). Thirty isochron/seismic facies maps were made to reveal the stratigraphic pattern through the late Tertiary.
During the early Miocene, a salt-rimmed syncline centered north of Mars field in MC455 accumulated sediments. The salt rim collapsed, creating a middle Miocene turtle structure. Middle-late Miocene sand-rich turbidites bypassed this structure and were deposited to the south around Mars field and beyond. At the same time, another depotrough 30 mi east of Mars field channeled deep-water sands to the MC730 area. A late Miocene-early Pliocene counterregional fault striking parallel to the shelf edge formed as salt evacuated the area on the south side of the Cognac (MC194) and Lena (MC280) fields. This fault trapped the Pliocene reservoir sandstones that produce in these fields. Sedimentation during the late Pliocene-early Pleistocene was very slow (0.2 m/1,000 yr) and characterized by thin, stacked, condensed sections of hemipelagic shale. Since the mid-Pleistocene, the Mississippi River has supplied sediments to the Mississippi Canyon area that have induced salt deformation that has in turn affected recent sedimentation.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
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Copyright © 1999 by The Gulf Coast Association of Geological Societies