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Hydrocarbon gases in Tertiary and Quaternary sediments offshore Peru; results and comparisons

February 3, 1990

Hydrocarbon gases (methane, ethane, propane, isobutane, «-butane, ethene, and propene) are present in Tertiary and Quaternary shelf, upper-slope, and lower-slope deposits of the Peruvian continental margin. Methane dominates the composition of the hydrocarbon gas at all 10 sites examined during Ocean Drilling Program (ODP) Leg 112. Generation of methane is regulated by the amount of sulfate in pore water. Wherever sulfate concentrations approach or equal zero, methane concentrations increase rapidly, reaching values near 100,000 /tL/L of wet sediment at eight of the 10 sites. Methane at all 10 sites results from methanogenesis, which is inhibited where sulfate is present and microbial reduction of sulfate occurs. Hydrocarbon gases heavier than methane also are present, but at much lower concentrations than methane. These hydrocarbons are thought to result from early thermal and microbial diagenesis, based on relative gas compositions and trends of concentrations with depth. With few exceptions, the results obtained in the shipboard and shore-based laboratories are comparable for methane and ethane in sediments of Leg 112. Reanalyses of canned sediments from ODP Leg 104 and from Deep Sea Drilling Project (DSDP) Legs 76 and 84 show that gas samples can be stored for as long as 8 yr, but the amounts of individual hydrocarbon gases retained vary. Nevertheless, the trends of the data sets with depth are similar for fresh and stored samples.

Publication Year 1990
Title Hydrocarbon gases in Tertiary and Quaternary sediments offshore Peru; results and comparisons
DOI 10.2973/
Authors Keith A. Kvenvolden, Tamara Frank, M. Golan-Bac
Publication Type Article
Publication Subtype Journal Article
Series Title Proceedings of the Ocean Drilling Program: Scientific Results
Index ID 70208306
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center