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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


Pub. Id: A117 (1978)

First Page: 303

Last Page: 311

Book Title: SG 7: Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin

Article/Chapter: Orca Basin, Anoxic Depression on the Continental Slope, Northwest Gulf of Mexico: 5. Intraslope Basins

Subject Group: Geologic History and Areal Geology

Spec. Pub. Type: Studies in Geology

Pub. Year: 1978

Author(s): P. K. Trabant (2), B. J. Presley (2)

Abstract:

The Orca basin is an intraslope depression on the continental slope, northwestern Gulf of Mexico, which contains an uncommon anoxic, saline brine. The 400-sq-km basin slopes at angles ranging between 3 and 14° from surrounding water depths of 1,700 to 1,900 m, to over 2,400 m. A 700-j sparker seismic survey shows conformably dipping strata indicative of postdepositional movement, as well as chaotic zones beneath the basin seafloor. The basin appears to be the result of salt tectonism. Sediments from the deep parts of the basin consist of dark anoxic clays with interstitial salinities of 250 ppt. Brine fills the bottom 200 m and provides a seismic-interface reflector at its surface similar to that of the Red Sea. Oxygen values are reduced to zero within the 260-g/kg sa ine brine and temperatures are slightly greater than the directly overlying bottom water. The bulk chemical composition of the brine is similar to that from the Red Sea whereas differences between the two in both heat content and geologic setting indicate different modes of origin.

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