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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 962

Last Page: 963

Title: Anatomy of Modern Open-Ocean Windward Carbonate Slope: Northern Little Bahama Bank: ABSTRACT

Author(s): Henry T. Mullins, H. M. Van Buren, R. A. Davis

Article Type: Meeting abstract


The modern carbonate slopes in the northern Bahamas are classified as windward or leeward types along open oceans, open seaways, or closed seaways.

Morphologically the open-ocean windward carbonate slope,

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north of Little Bahama Bank, can be divided into upper and lower slopes. The upper slope is relatively steep (2 to 4°) and heavily dissected by numerous, roughly evenly spaced submarine canyons or gullies that display 50 to 100 m of relief. The seismic facies of this upper slope consists of parallel to subparallel reflectors. Core data indicate that most sediments on this upper slope, including those immediately adjacent to shallow-water reefs, are fine-grained periplatform oozes. Core data combined with 3.5 kHz PDR profiles reveal a gradual downslope decrease in the amount of submarine cementation. Where cementation is not an important factor, submarine sliding begins, probably due to overloading.

In contrast, the lower slope is a broad, smooth, relatively gentle (~ 1°) region with few canyons. The seismic facies here consists of chaotic/discordant to wavy, subparallel reflectors. Core data indicate a dominance of coarse-grained debris flow and turbidity current deposits, interlayered with minor pelagic sediments. Most of the coarse detritus in these sediment gravity flows was derived from the upper slope. Pelagic sedimentation, incipient submarine cementation, and mass movements interact to produce very coarse-grained material on the lower slope from initially fine-grained upper slope sediments. Numerous unlithified deep-water coral mounds are also present on the lower slope.

The morphology and sedimentary/seismic facies relations of this carbonate slope indicate sedimentation from a line source rather than a point source. In contrast to submarine fan development from a point source, base of slope sedimentation along a line source produces a broad apron of coarse sediment, gravity flow deposits on the lower slope paralleling the shelf/slope break. In terms of hydrocarbon exploration the lower slope sediment gravity flow facies appears to have the greatest potential as a reservoir.

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