Isotopic Organic Carbon Composition of Recent Continental Derived Clastic Sediments of Eastern Gulf Coast, Gulf of Mexico: GEOLOGICAL NOTES

Abstract

The isotopic composition of organic C from 3 environments was compared: from continental-derived clastic sediments, from brackish-water sediments, and from open marine environments in southern Mississippi and Alabama, Biloxi Bay and Mississippi Sound, and the upper Gulf of Mexico. The per mil deviations from the C 13 C 12 ratio of a standard was an average of -26.2% for river sediments as contrasted with -19 to -21% for open marine. For sediments of Biloxi Bay and Mississippi Sound, lagoonal and channel environments, a systematic variation from river to open marine values was observed. A mixing of land- and marine-plant-derived organic materials which differ in isotopic composition is probably responsible for the systematic variation observed in sediments from river, through lagoonal to open marine environments. Other processes may complement the mixing process in producing the observed variation.