Structural framework of the Clemente-Tomas and Corsair growth fault systems in the Texas continental shelf margin of the Gulf of Mexico basin
Ajiboye, Olabisi A.
In the Texas continental shelf margin, there exist the Clemente-Tomas and the neighboring Corsair growth fault systems, both of which run roughly parallel to the shoreline. The structural and stratigraphic development histories of some parts of these fault systems have not been investigated in detail, even though such knowledge would be crucial in understanding the hydrocarbon migration and trapping mechanisms associated with them. The present study attempts to characterize the structure and stratigraphy of these growth fault systems in the Mustang Island federal lease areas, off Corpus Christi, Texas. It utilizes a time-migrated three-dimensional seismic volume that covers an area of 867mi2 (2245km2), digital well data from 36 wells, wireline logs from 30 boreholes, paleontological reports from 15 boreholes, and velocity survey data from 33 boreholes. In characterizing the stratigraphy five biostratigraphic markers within the Miocene were determined from the paleontological data; Bigenerina ascensionensis (8 Ma), Discorbis 12 (9.11 Ma), Bigenerina humblei (13.4 Ma), Robulus L (16.3Ma) and Marginulina ascensionensis (18Ma). Seismic horizons corresponding to these biostratigraphic markers are tied to the well data, and mapped throughout the study area. Their depths are obtained from the seismic velocity structures at the well tie points. Lithologies of the strata are estimated from the well logs. Fault surfaces are mapped in three dimensions. The detailed mapping enables clear distinction of the two neighboring fault systems. Most of the work is performed on a computer workstation and yields a digital, quantitative model of the regional structure and stratigraphy. The present Study shows that the Clemente-Tomas growth fault detaches into a shaley mobile substrate. Basinward evacuation of the mobile substrate probably initiated the fault movement in the Oligocene. The evacuated shale body developed into a linear, diapiric ridge. By the early Miocene (between 23 to 18 Ma), the shale diapirism was causing the basinward sliding of the overlying sediments, and that initiated the primary Corsair growth fault. This early Corsair faulting process was relatively instantaneous and it led to temporary formation of a semi-starved mini-basin on the downthrown side of this fault. Subsequent depositions on the downthrown side kept the primary Corsair growth fault active though the late Miocene (18 to 8 Ma). By the late Miocene, (Discorbis 12 and Bigenerina ascensionensis) faulting of the Clemente-Tomas slowed down considerably while the Corsair remained active.