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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 958

Last Page: 958

Title: Cretaceous Black Shales in Angola Basin of South Atlantic Ocean: ABSTRACT

Author(s): Philip A. Meyers, Simon C. Brassell, William W. Hay

Article Type: Meeting abstract


Conditions favorable to deposition of black shales in the deep ocean occurred several times during the Cretaceous. Anoxic sediments were laid down in the South Atlantic during two distinct periods, the Aptian-early Albian and the late Albian-Coniacian. At site 530 of DSDP Leg 75 in the Angola Basin, black shales averaging 5.1% and containing up to 16.5% organic carbon were found in a late Albian-Coniacian turbidite sequence. Shipboard analysis shows most of the organic matter to be of marine origin, although several layers contain some terrigenous material. Based upon Rock Eval pyrolysis and the absence of significant amounts of light hydrocarbons, all of this organic matter is classified as immature. Thicknesses of the black shale layers are generally several centimeters or less, and they are separated by fine-grained turbidites containing less than 0.3% organic carbon. These Aptian-Coniacian shales seem to be the result of downslope density flows of shelf-edge sediments rich in organic matter. Preservation of organic matter was a result of rapid burial, not by stagnant basin waters. Furthermore, this mode of preservation appears to be responsible for the Cretaceous black shales throughout the South Atlantic.

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