WU, SHENGYU, and A. W. BALLY, Rice University, Department of Geology and Geophysics, Houston, TX

ABSTRACT: Salt Tectonics and its Influence on Meso-Cenozoic Tectonics of the North-Eastern Gulf of Mexico

The mid-Jurassic salt was deposited on a relatively smooth regional unconformity. The salt diminishes basinward to the south along a generally E-W trending transitional-oceanic crust boundary. Four-episodes of

Meso-Cenozoic tectonics can be summarized:

1. From its mid-Jurassic deposition to the mid-Cretaceous, salt was deformed constantly by sediment loading. As a result, peripheral fault systems, salt domes, anticlines, massifs, rollers and local growth structures were formed. The majority of the salt was pushed in front under the sediment load and concentrated near the present shelf to slope. Some salt formed small scale allochthonous salt bodies.

2. During a significant period of sediment starvation, between mid-Cretaceous (Turonian) and mid-Oligocene time, previously formed salt structures were stabilized.

3.From mid-Oligocene to early mid-Miocene time, salt structures were buried and reactivated by rapid sediment loading. By middle mid-Miocene, large diapiric salt ridges, walls and stocks formed due to increased sediment load. The lateral displacement caused by growing salt structures driven by buoyancy force, combined with gravity gliding, pushed the Mesozoic-mid-Miocene section down-slope over autochthonous salt toward the basinward edge of the Jurassic salt basin. The compressional strains, not accommodated by the salt withdrawal basins, were transmitted to and concentrated along the basinward edge of the Jurassic salt basin. The Mississippi Fan Foldbelt thus formed along the E-W trending basinward edge of the salt basin as a result of these concentrated compressional strains. The l test shortening in the Mississippi Fan Foldbelt ceased by the late Miocene as the salt walls and stocks had made their way up through the overburden and began to emplace in the less dense sediments to form allochthonous salt structures. During and after the formation of the Mississippi Fan Foldbelt, up-dip from the foldbelt, large withdrawal basins along with regional, counter-regional and local growth fault systems were formed as massive salt withdrawal from below the Meso-Cenozoic overburden. Massive allochthonous salt structures have been forming since mid-Miocene time.

4. During late Miocene to present time, large scale asymmetric allochthonous salt sheets continue to form and advance down-slope due to gravity spreading and sediment loading. Part of the Mississippi Fan Foldbelt lies under the advancing allochthonous salt sheet. Structures such as salt withdrawal basins, basinward and landward dipping growth faults, local folds and reverse faults and secondary allochthonous salt structures have been forming on top of the allochthonous salt sheets. Extensive salt welds exist on the Jurassic salt bed as well as on the allochthonous salt sheets.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.