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Isotopic Evidence for Petroleum-Derived Carbonates in the Gulf Of Mexico

FANG, JIASONG, Texas A&M University, College Station, TX

Examination of thirteen sediment samples from the Gulf of Mexico continental shelf and slope revealed the presence of carbonates which have both high positive (+13.2(sigma) vs. PDB) or negative carbon isotopic ratios (-9.7 to -30.7(sigma) vs. PDB). Report of anomalously 13C-enriched carbonates in the Gulf of Mexico is noted here for the first time. Combining the observations of the unusual isotopic ratios and organic geochemical analysis has led to the proposed mechanism that bacterial fermentation of petroleum hydrocarbons under anoxic condition produces 13C-rich carbon dioxide which precipitates as the isotopically heavy carbonate, and biodegradation under oxic conditions leads to the production of 13C-depleted carbon dioxide which precipitates as isotopically light carbonate. Both an coexist, reflecting different phases of carbonate formation.


AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)