ABSTRACT

Multifold seismic data tied to wells were used to study basement rocks in the northeast Gulf of Mexico region and to determine the influence of basement structure on the deposition of overlying Jurassic salt and sedimentary rocks. Basement is defined here as all rocks older than Middle Jurassic Louann Salt.

Two large rift basins filled with Middle(?) Triassic-Lower Jurassic redbeds and volcanics occur northeast of the inferred extension of the Bahamas Fracture Zone (BFZ). These features appear to be the offshore extension of the South Georgia rift basin. South of the BFZ are wide areas of dipping intra-basement reflections (monoclines and synclines) truncated by a prominent erosional unconformity marking the top of basement. These rocks may represent Paleozoic sedimentary rocks (encountered in nearby wells) and/or further extensions of the Triassic rift basins.

The basic architecture of the Gulf of Mexico basin formed during the Middle Jurassic when attenuation produced areas of thick and thin transitional crust as South America and Africa began moving away from North America. Thick transition al crust in the northeast Gulf of Mexico is characterized by broad highs (Middle Ground arch, Southern platform, Pensacola arch, and Sarasota arch) and lows (Apalachicola basin and Tampa embayment). Basement structure controlled the distribution and thickness of the Middle Jurassic Louann Salt. Salt was deposited in the Apalachicola basin and lower Tampa embayment but is absent over the basement highs. The updip limit of thick salt and the updip limit of salt tectonics coincide with a basement hingeline in the northern Apalachicola basin. Distribution, thickness, and paleogeography of the three over-lying Upper Jurassic sequences (Norphlet-Smackover, Haynesville, and Cotton Valley) also reflect the configuration of the underlying basement.