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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 41 (1991), Pages 276-282

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

Jiasong Fang (1)

ABSTRACT

Examination of thirteen sediment samples from the Gulf of Mexico continental shelf and slope revealed the presence of carbonates which have either high positive (+13.2% vs PDB) or negative carbon isotopic ratios (^dgr13C=-9.7 to -30.7% 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 lead 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 condition leads to the production of 13C-depleted carbon dioxide which precipitates as isotopically light carbonate. Both can co-exist, reflecting different phases of carbonate formation.


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