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Book Chapter

Growth Fault—Upper Continental Slope

By
J.B. Wanslow
J.B. Wanslow
Tenneco Oil Company
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Published:
January 01, 1983

Abstract

Line A is located on the upper continental slope of offshore Louisiana, Gulf of Mexico (index, Figure 1). Water depth along the section ranges from about 442 m (1,450 ft) on the northwest end to greater than 914 m (3,000 ft) at the deepest point of the surface basin near shotpoint 27. The line is oriented approximately N 63 W.

To illustrate structural features present on the line, four seismic horizons were carried across the entire section (see interpreted seismic section). The particular horizons chosen were selected because of their lateral continuity. Correlation across fault A is based on correlation of recognizable seismic stratigraphic zones as well as similar character of major reflectors. Correlation across fault B is based on obvious seismic character correlation. A geologic cross section was also constructed. It should be noted that while vertical exaggeration visually is about 2:1 on the seismic sections, no vertical exaggeration is present on the cross section (that is, the horizontal and vertical scales are the same). Velocity effects of the water were also removed in constructing the cross section.

The major structural feature illustrated is fault A, a large growth (syndepositional) fault. Throw increases from less than 518 m (1,700 ft) at horizon 1, to nearly 1,829 m (6,000 ft) at horizon 4 (see cross section). Evidence that the fault is still active is indicated by its effect on the sea floor, where an increase in slope (which should probably be interpreted as a slumped fault scarp) produces an elevation change of some 183 m (600 ft) in about 1 mi (1,609 m). Downthrown to fault A is a large structural syncline, bounded on the southeast by a salt uplift occurring past the end of the section. Upthrown to fault A, a broad, subtle doming is apparent between shotpoints 9 and 18. Although occurring at all levels, its strongest expression is at horizon 2, where its crest occurs near shotpoint 14. At the northwest end of line A, a recent fault, B, breaches the sea floor between shotpoints 1 and 2. B is associated with another fault which merges with it near horizon 1. Genetically, B is probably related to the deep uplift occurring beneath it, which produces an obvious doming as shallow as horizon 1 upthrown to B.

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Contents

AAPG Studies in Geology

Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces

A. W. Bally
A. W. Bally
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American Association of Petroleum Geologists
Volume
15
ISBN electronic:
9781629810188
Publication date:
January 01, 1983

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