SHOUP, ROBERT C., Shell Deepwater Development Inc., New Orleans, LA, and JOHN F. KARLO, Shell Technology Co., Houston,TX
Abstract: Classification of Syndepositional Structural Systems, Northern Gulf of Mexico
There are three primary types of syndepositional growth-fault systems observed in the northern Gulf of Mexico: shale-based detachment fault systems, salt-withdrawal mini-basin systems, and salt-based detachment (Roho) systems.These systems consist of large scale structural complexes comprised of a number of different, yet related components. The components are smaller scale structures, which occur within the system in an orderly and repetitive pattern.
Shale-based detachment fault systems are strike-linear gravity slides. Characteristically they exhibit a highly listric master expanding fault, a rollover anticline, a planar synthetic fault, a syncline, a planar antithetic fault, and a horst block. Compressional toe folds may be visible, but are usually obscured by younger systems.The listric faults share a common sole plane most often a locally thick transgressive shale.
Salt-withdrawal mini-basin systems consist of large (12-20 miles), elliptical withdrawal basins. They consist of a deep turtle structure, a syncline, and a series of subsidiary faults and diapirs that outline the basin's margin. In the slope region, tabular salt may obscure all or part of the underlying mini-basin.
Salt-based detachment faults or Roho are combination gravity slide and salt evacuation structures. Deposition of upper slope and/or outer shelf sediments onto a salt wing initiates formation of a series of highly listric down to basin faults. Rohos generally exhibit a series of nested, horseshoe-shaped listric faults that sole into evacuated salt. These faults grade laterally into strike slip fault zones and dip-oriented salt diapirs.
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