50. HYDROCARBON GEOCHEMISTRY AND BIOLOGICAL MARKERS IN ORCA AND PIGMY BASIN SEDIMENTS (SITES 618 AND 619)1 A. G. Requejo, Battelle New England Marine Research Laboratory

• Main Authors: Jean K. Whelan, Woods Hole
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Orca
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.594.7396; http://www.deepseadrilling.org/96/volume/dsdp96_50.pdf

The C15+ hydrocarbon geochemistry of sediments from Sites 618 and 619 (Orca and Pigmy basins) has been exam-ined as part of a biogeochemical study of microbial activity and biological markers in Leg 96 sediments. Total hydrocar-bon concentrations (13-78 µg/g dry weight) are elevated in comparison to those reported for Recent sediments from the Gulf of Mexico continental shelf, but there is little evidence that these sediments contain petroleum hydrocarbons origi-nating from seepage. The presence of weathered fossil hydrocarbons is suggested, however, by the unresolved envelope feature observed in gas chromatograms of most sediments and also by the distribution of C27-C29 steranes and triter-panes. Normal alkane distributions are consistent with a predominant input or preservation of terrestrial organic matter in these offshore basins. At Site 619 an enhanced terrestrial contribution below 113 m sub-bottom is indicated by an in-crease in the ratio of odd to even n-alkanes over the range C26 to C30. Pristane/phytane ratios at both sites range be-tween 0.97 and 1.74 which, in conjunction with the occurrence of significant concentrations of perylene (10-500 ng/g dry weight), suggest the prevalence of reducing depositional conditions over the time period covered by the cores. A hy-drocarbon tentatively identified as a C25 multibranched compound similar to those found in Recent sediments was de-tected in most samples.