Authigenic carbonates in the sediments of Goa offshore basin, western continental margin of India

作者：Kocherla M^*

来源：Current Science, 2012, 102(8): 1205-1211.

• Authigenic carbonates
• euhedral crystals
• methane flux
• sediment core

Euhedral crystals (similar to 1 mm) of authigenic carbonates are identified in 5 m long sediment cores collected from the western continental margin of India in water depths between 2665 and 3070 m. Low-Mg calcite and aragonite are the dominant authigenic minerals while high-Mg calcite, dolomite and siderite occur in minor amounts. Morphological evidences such as euhedral carbonate crystals and slender radiating aragonite crystals suggest that they are formed authigenically in the sediment column. The delta C-13 values of the authigenic carbonates range between 0.63 parts per thousand and -8.12 parts per thousand, and is attributed to the contribution of isotopically light carbon derived from the oxidation of sedimentary organic matter in the surficial sub-oxic Fe reduction and the bacterial sulphate reduction zone during early diagenesis. Mineralogy, morphology and stable carbon isotope signatures of authigenic carbonates and the occurrence of pyrite framboids and octahedral crystals and the evaluation of pore-fluid chemistry are not indicative of enhanced methane flux. They argue against a precipitation of carbonates due to anaerobic oxidation of methane and refute the possible connection of methane gas from the shallow gas-charged sediments to the observed carbonates.

• 出版日期2012-4-25