Abstract: Salt Geometry and Plio-Pleistocene Evolution of Ewing Bank and Northern Green Canyon, Offshore Louisiana

Mark G. Rowan, Barry C. McBride, Paul Weimer

Interpretation of more than 11,000 km of multifold seismic data and sequential restoration of selected profiles have been used to determine the geometry and evolution of the Ewing Bank/northern Green Canyon area in the Gulf of Mexico basin. The region is characterized by at least three levels of allochthonous, amalgamated salt sheets with irregular map geometries. The upper two levels formed between 1.5-3.4 Ma and prior to 5.5 Ma, respectively, whereas the age of the deepest level is unknown. Individual sheets are composed of salt bodies of widely-varying geometries linked laterally by salt welds, and the various levels are linked vertically to each other by both counter-regional and diapir feeders.

The history of a salt sheet starts with its formation at the sea floor by lateral spreading of salt from source diapirs during a period of slow sedimentation. Because the salt flows into topographic lows, the areal extent of a sheet is constrained by sea-floor highs located over preexisting salt structures. Supra-salt basins are initiated during extension caused by down-dip gravitational spreading/sliding of the salt sheet. Subsequent basin growth is by vertical subsidence into the sheet, with displaced salt moving into flanking diapirs that grow by downbuilding. Once salt welds form, continued clastic input is accommodated by increased down-dip extension and lateral basin growth; this is matched by contractional folding and diapirism near the basinward edge of the sheet. Finally, sal from nature diapirs may form a new salt sheet at the sea floor during another period of slow sedimentation.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994