--> Abstract: Geometry, Origin and Significance of Coast-Perpendicular Anticlines in a Growth-Faulted Setting, by Angela McDonnell and Martin P. Jackson; #90078 (2008)

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Geometry, Origin and Significance of Coast-Perpendicular Anticlines in a Growth-Faulted Setting

Angela McDonnell and Martin P. Jackson
Bureau of Economic Geology, Austin, TX

Growth faults parallel to the coastline of the northeastern Gulf of Mexico have been well studied as one of the world’s classic extensional provinces. Even so, a striking and important facet of this down-to-basin fault system has received comparatively little attention. Using a large (8,500 km2/3,300 mi2), high-quality, 3D seismic survey, we examine Miocene structures trending orthogonal to the extensional fault system. The hangingwall succession of the master growth faults is folded into an orthogonal train of anticlines, typically spaced 6 miles apart and converging seaward. The anticlines are cored by Oligocene shale in the footwall of the growth faults. In the anticlinal crests, extensional grabens or half-grabens are also perpendicular to the master faults. Locally, these grabens are replaced by thrusts having coast-parallel vergence. Between the orthogonal anticlines, synclines focus synkinematic sediments, which overlie prekinematic strata, locally separated by onlap surfaces. Our study evaluates various origins for these orthogonal structures, which include (a) differential loading of a mobile substrate (salt, shale) by prograding lobes, (b) downslope convergent slip of hangingwall strata, or (c) strike-slip between adjacent growth-fault blocks slipping basinward at different rates. These orthogonal structures are large enough that their pattern is only revealed by 3D seismic data of considerable coast-parallel extent. Thus, their importance may have been underappreciated in the past. Plays cluster along the orthogonal anticlines in the study area. Hence, if analogous structures are present elsewhere, they may also have exploration significance.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas