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OBC 5-A: Overthrusting in a Deep-Water Carbonate Terrane

J.A. Austin, Jr.
J.A. Austin, Jr.
University of Texas at Austin, Institute for Geophysics
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January 01, 1983


The geology of the Bahamas has been studied for decades. We know that steady subsidence since the Jurassic and the associated continuous upbuilding of carbonate banks have resulted in a thick (more than 5 km; 3.1 mi) sequence of shallow-water limestones and evaporites overlying postulated rift basins filled with terrigenous clastics and volcanics (Dietz et al, 1970; Meyerhoff and Hatten, 1974; Sheridan, 1974; Tator and Hatfield, 1975; Case and Holcombe, 1980; Sheridan et al, 1981). However, the complete sedimentary section was never sampled and seismic reflection profiles collected over the banks are characterized by poor penetration and persistent ringing caused by competent shallow sediments.

Consequently, a continuing controversy exists as to whether the Bahamas are underlain by continental or oceanic crust. Based on a variety of evidence, Uchupi et al (1971) hypothesized that the northwestern Bahamas are an extension of the North American continent, while the southeastern Bahamas rests on oceanic crust with structural trends controlled by Atlantic fracture zones. In contrast, Mullins and Lynts (1977) postulated that the Bahamas are completely underlain by rifted continental crust which was originally part of Africa but became attached to the North American plate when the modern Atlantic began to develop. Gravity surveys in the region do suggest the presence of fairly low-density (continental) rocks (Talwani et al, 1960), and magnetics data also support a continental origin in that anomaly trends are continuous with those of peninsular Florida (Klitgord et al, in press). However, major difficulties arise in computing accurate layer thicknesses and velocities for the Bahamas because of the similar acoustic properties of basement rocks and well-lithified flat-bedded carbonates. For example, Ball et al (1971) used seismic refraction techniques to estimate an average crustal thickness of 23.5 km (14.6 mi) for the Bahamas, whereas Rayleigh wave dispersion studies suggest an oceanic-type crust perhaps only 14 km (8.7 mi) thick (Sheridan, 1972).

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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
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Publication date:
January 01, 1983




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