Miocene structure of Mustang Island, Mustang Island East Addition and part of Matagorda Island, Outer Continental Shelf areas, Gulf of Mexico

Abstract

Understanding the Miocene structure of Mustang Island and the neighboring areas in the northwestern Gulf of Mexico helps to increase knowledge of the geology and hence contribute to petroleum exploration and production in the area. Interpretation of about 1465 miles of multifold, migrated seismic reflection data, integrated with 35 well log data, served to detail the Miocene structure and its evolution. Early Miocene sedimentation resulted in differential loading of mobile substrates of shale. This caused movement of the shale basinward. Further loading caused overlying sediments to yield, forming the Clemente-Tomas fault. This is a listric, down to the basin growth fault, lying on the seaward flanks of a shale ridge. Rollover anticlines characterize the hangingwall blocks of this fault especially in the southwestern part of the study area. These rollover anticlines could be potential hydrocarbon traps. Rapid sedimentation during the Middle Miocene was responsible for the formation of the contemporaneous growth faults of the Corsair-Wanda system. The Corsair fault is an extensive, listric, mostly concave up growth fault that diagonally runs through the area along a southwest-northeast trend. A salt withdrawal syncline separates the Wanda from the Corsair fault. This suggests that the Corsair formed as a result of primary salt withdrawal. Planar rotation of hangingwall blocks of the Corsair fault formed structural highs that are able to accumulate hydrocarbons. Continued sedimentation during the Middle-Upper Miocene caused the underlying salt to undergo secondary withdrawal. This withdrawal caused the overlying sediments to collapse into a half-turtle anticline upon which the Wanda fault appears to detach. The half-turtle anticlines and a series of horsts could be prospective zones of hydrocarbon accumulation. The Wanda fault zone appears to lie along the landward limit of salt deposition in this part of the Gulf of Mexico. The only salt diapir in the area lies immediately basinward of the Wanda fault.