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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 914

Last Page: 915

Title: Source Rock Potential of Basinal Carbonate Muds, Bahamas: ABSTRACT

Author(s): P. D. Crevello, J. W. Patton, G. K. Guennel

Article Type: Meeting abstract


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Some carbonate muds deposited in intraplatform basins of the Bahamas contain sufficient organic matter to be considered potential source rocks. The sediments are Holocene to late Pliocene and immature.

Total organic carbon (TOC) values range between 0.1 and 2.58% for the basinal sediments of Tongue of the Ocean and Exuma Sound, though averaging 1.0% in the Tongue versus 0.33% for Exuma Sound. The difference appears to be related to the sedimentation rates of the basins, estimated to be 10 to 200 mm/103 years for Tongue of the Ocean and 4 to 50 mm/103 years for Exuma Sound.

In Tongue of the Ocean we have correlated cyclic variations in TOC with fluctuations of sea level. High sea levels are recorded by aragonite-rich basinal muds (peri-platform ooze) with an average TOC of 0.7% and an abundance of organic-rich turbidite muds with TOC averaging 1.21%. Peri-platform ooze deposited during low sea levels is calcitic, contains few turbidites, and generally is organic lean--0.1 to 0.3% TOC. Of the organic matter, ^dgrC13 suggests different sources for the organics deposited in the turbidite muds (-13.9 to -16.4% PDB) and the peri-platform ooze (-17.4 to -26.13% PDB). Cyclic variation in organic content in the Tongue is portrayed in the color of the muds: green muds have high TOC, while brown and white muds are leaner. Cyclic variation in sediment co or also occurs in Exuma Sound and Columbus Basin. Basin depth does not seem to influence the TOC: Columbus Basin, the deepest, appears to be as rich in organics as the Tongue (shallowest). No clearcut correlation with kerogen types is seen at present.

Gas chromatographic analysis of organic matter evolved from samples heated only to 350°C demonstrated that the material evolved was not simply vaporized, but represented the thermal cracking of relatively heat-sensitive material. Mass spectral pyrolysis experiments on some samples suggests the presence of amino acids or proteins.

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Copyright 1997 American Association of Petroleum Geologists