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Bureau Seminar, September 19, 2008

Geometry, origin and significance of coast-perpendicular anticlines in a growth-faulted setting

Angela McDonnell, Martin P. A. Jackson
Bureau of Economic Geology


      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. Using a large (8,500 km2/3,300 mi2), high-quality, 3D seismic survey, we examine Miocene structures trending orthogonal to the extensional Clemente-Tomas fault system and the coastline. This orthogonal trend has received comparatively little attention. The Clemente-Tomas fault is deformed into anticlines and synclines and dip profiles display multiple ramps and flats. The underlying Cretaceous through Eocene succession has a highly irregular geometry reflecting salt pillows, minibasins and salt-stock deflation.

          In this seminar we investigate possible origins for the orthogonal structures including (1) downslope convergent spreading, (2) downslope divergent spreading, (3) differential extension between adjacent growth-fault blocks, and (4) differential sedimentary loading. We also propose a model whereby deep salt structures gave rise to ramps and flats in the master fault. In turn, variation in ramp geometry along strike created the orthogonal ridges and intervening minibasins by the three-dimensional interplay of ramp basins and rollover anticlines.



Department of Geological Sciences
Institute for Geophysics
The University of Texas
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