Geochemical and Faunal Investigation of Shelf/Slope Environment of North-Central Gulf of Mexico

HEALY-WILLIAMS, N., D. M. TRAINOR, D. F. WILLIAMS, and P. JENKINS, University of South Carolina, Columbia, SC, and A. GARY, Unocal, Brea, CA

The shelf/slope environment of the northern Gulf of Mexico offers a complex pattern of marine and terrestrial derived sediments. We have performed geochemical and faunal investigations on approximately 80 box cores from 30 to 1300 m water depth from the north-central Gulf of Mexico. The geochemical results relate the modern and late Holocene distribution of marine and terrestrial organic carbon to the present day depositional systems of this actively prograding system. Total organic carbon (%TOC) analyses of the surface sediment are used to characterize the distribution of TOC on the Louisiana shelf and slope as a function of distance from the Mississippi delta. Stable carbon isotopic analyses [(13)C/(12)C] of the TOC are used to distinguish marine from terrestrial organic carbon. Hig er amounts of terrestrial organic carbon are associated with the western edge of the Mississippi delta. Marine organic carbon increases seaward of the deltaic system. The percentage of fine-grained (< 63 microns) calcium carbonate also increases seaward of the Mississippi delta as well as with lateral distance along the shelf-slope. Percent CaCO(3) and C(13) of the fine-grained carbonate determinations have been performed in Plio-Pleistocene cores and exploration wells from this region. We use this data to examine how the modern/late Holocene patterns of these variables have changed as a function of continental margin evolution. We have also analyzed the benthic foraminiferal distributions in terms of the sedimentay nature of the box cores. We note increased abundances in certain spec es in relation to deltaic vs nondeltaic environments along with some species altering their depth ranges between the two environments.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)