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Reed, Timothy A.1, Myron J. Cook1, Andrew R. Stephens1, Kim A. Doud1 
(1) Pioneer Natural Resources, Irving, TX

ABSTRACT: The East Breaks Fold Belt: An Anomalous Contractional Regime of the Western Gulf of Mexico

In the East Breaks area of the western Gulf of Mexico, northeast of the Port Isabel Fold Belt, lies a series of northwest-trending folds covering an area of 2700 square miles, referred to herein as the East Breaks Fold Belt. Based on 2D seismic data, previous workers had interpreted these folds as shale and/or salt ridges. However, an analysis of recent 3D seismic reveals that these structures are detached contractional folds commonly bounded by thrusts. 
Structures within the East Breaks Fold Belt formed in a shale-dominated stratigraphy, developed concurrent with sediment deposition, and have a predominant vergence direction toward the southwest. Detachment levels lie with Oligocene shales and deeper salt levels. The fold belt progressively grew in an in-sequence (NE to SW) manner from early Tertiary through Mid-Miocene. 
Like other gravity driven systems in the world, fold belts of the Deep Water Gulf of Mexico (e.g., Port Isabel, Perdido, and Mississippi Fan /Atwater Fold Belts) all have fold axes and thrusts that trend approximately parallel to the strike of the associated growth fault systems. However, folds and thrusts in the East Breaks Fold Belt trend perpendicular to the growth faults which were active as the belt developed. 
The model that best explains the observed relationships is one that involves convergence of slide masses emanating from the arcuate shaped growth fault systems of the Texas coast. As the masses slide downslope toward the focal point of the arc, they impinge on each other, producing a NE-SW compressive stress.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.