SEISMIC STRATIGRAPHY AND GEOLOGIC HISTORY OF JURASSIC ROCKS, NORTHEASTERN GULF-OF-MEXICO

A grid of two-dimensional seismic data tied to exploration wells defin es four Jurassic sequences in the northeastern Gulf of Mexico. These s equences correlate with well-known northern Gulf of Mexico basin strat igraphic units: the Louann Salt (L sequence), Norphlet and Smackover f ormations (N-S sequence), Haynesville Formation (H sequence), and Cott on Valley Group (C sequence). The Jurassic section overlies a basement surface characterized by broad highs (Middle Ground arch and Southern platform) and lows (Apalachicola basin and Tampa embayment). This bas ement structure controlled the distribution, thickness, and paleogeogr aphy of all the Jurassic sequences, but its influence became progressi vely less pronounced as sediment filled the basin. The Jurassic geolog ic history of the region is developed from an interpretation of these sequences. Well control documents the presence of Louann Salt in the A palachicola basin, whereas in the Tampa embayment the interval is inte rpreted only from seismic data. Salt movement on the West Florida Shel f began early, during Norphlet; Smackover deposition, and slowed drama tically by the end of Haynesville deposition. Smackover paleo geograph y includes progradation of a carbonate shelf in the Apalachicola basin and the Tampa embayment, as well as development of carbonate buildups updip of basement hingelines, over basement highs, and above early sa lt structures. In the Apalachicola basin, Haynesville elastic sediment ation updip was coeval with carbonate deposition downdip, and a locali zed carbonate shelf margin developed to the southwest. Haynesville cla stic sedimentation may have prevailed in the Tampa embayment, where ob lique clinoforms represent shelf margin progradation. During depositio n of the Cotton Valley sequence, the northeastern Gulf of Mexico was c haracterized by delta-plain and delta-platform sedimentation with seis mically defined shelf margin progradation only in the Tampa embayment. Jurassic sedimentation culminated with progradation of the Knowles Li mestone.