Post-Oligocene Seismic Stratigraphy and Structure, Northern High Island Area, Gulf of Mexico

James J. Chodzko, Joel S. Watkins

The structure and stratigraphy of the northern High Island area was studied using 2,300 mi of seismic reflection data integrated with 54 paleontologic reports and logs from 37 wells.

Normal faults, depotroughs, shale or salt masses, and shallow salt diapirs dominate the structural style of the area. Major faults tend to be located downdip from deep, low-relief shale or salt masses and updip from sedimentary troughs. These faults are commonly listric, down-to-the-basin, and syndepositional. However, considerable variability exists in the amount of expansion and rotation of downthrown blocks, fault-plane curvature and dip angle, depth of basal detachment, and fault spacing. Several basinward-dipping postdepositional faults as well as landward-dipping antithetic and counterregional faults are observed. Only six shallow (< 2 sec two-way traveltime) salt diapirs are located in the area. The lack of shallow diapirism suggests that the "mother salt" is thin or absent nder much of this area. The High Island Ridge, a broad structural high, extends across the southern part of the study area.

Post-Oligocene deposits can be divided into six sequences, roughly bounded by major eustatic events. During the Miocene, the shelf edge prograded basinward from near the present shoreline to the vicinity of the High Island Ridge. Paleo-shelf edges coincide with the major growth-fault trends, isochron maxima, increased regional dip, and the outer neritic-to-upper bathyal paleoecology zone. Hummocky [mass transport deposits(?)] and high-amplitude continuous reflectors [turbidite facies(?)] are frequently observed downdip from the paleoshelf breaks.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.