--> ABSTRACT: Differential Load-Driven Salt and Shale Withdrawal Faults in the Northern Gulf of Mexico, by Barry E. Bradshaw, Joel S. Watkins, Grant Macrae, Jie Zhang; #91020 (1995).

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Differential Load-Driven Salt and Shale Withdrawal Faults in the Northern Gulf of Mexico

Barry E. Bradshaw, Joel S. Watkins, Grant Macrae, Jie Zhang

Shelf-margin growth-fault systems are common structural elements of post-rift strata in the northern Gulf of Mexico. Regional examinations of high-quality seismic data throughout the northern Gulf suggests growth-faults are driven by differential loading of salt or overpressured shale associated with initial gravity spreading or deposition of progradational deltaic wedges. We propose a four stage growth-fault cycle model which uses the multiple level "Roho" type growth-fault system as an end product. A primary withdrawal stage applies to salt and overpressured shale substrates. Primary withdrawal faults are generated by differential loading of these ductile substrates and are accommodated by the emplacement of salt/shale massifs, reactive diapirs, and shortening tructures away from the source of differential loading. A secondary withdrawal stage only occurs in salt basins after the primary withdrawal fault has bottomed out. Overpressured shale does not experience secondary withdrawal due to its tendency to dewater and increase in viscosity with increasing lithostatic pressure. Secondary withdrawal of salt from massifs, pillows, rollers and reactive diapirs generates secondary withdrawal faults and collapse structures (turtle-structures, counter-regional growth-faults), and is accommodated by increased shortening and diapir growth. An allochthonous salt sheet emplacement stage is evident in the deep salt basins from offshore Texas and Louisiana. Continued secondary withdrawal of salt in these offshore salt basins is accommodated by the emplacement of allochthonous salt sheets as overthrusted nappes or collapsed diapirs. Supra-allochthonous "Roho" type growth-fault systems may then be generated in an new phase of primary differential loading.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995