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Abstract: Tectonostratigraphic Reconstruction and Lithofacies Distribution of Tertiary Slope Sediments in Western Mississippi Canyon Area

Andrew E. Hannan, David L. Risch, Abu N. Chowdhury

The distribution of late Tertiary, sand-prone, deep-water sediments from the vicinity of Cognac field, Mississippi Canyon (MC) 194, to south of the 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 were projected under allochthonous salt sheets and 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 to the east of the 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 sands that produce in these fields. Sedimentation during the late Pliocene-early Pleistocene was very slow (0.2 m/1000 yr), and is characte ized by thin, stacked, condensed sections of hemipelagic mud. 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.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994