Отправлено: 14.02.17 06:00. Заголовок: METHANE-RELATED CARBONATE CEMENTS IN POCKMARKS OF THE NORTH SEA

METHANE-RELATED CARBONATE CEMENTS IN POCKMARKS OF THE NORTH SEA
MARTIN HOVLAND
Statoil
P.O. Box 300
N-4001 Stavanger, Norway
MICHAEL R. TALBOT
Geological Deparlment A
University of Bergen
N-5014 Bergen, Norway
HENNING QVALE
Institute for Energy Technology
P.O. Box 40
N-2007 Kjeller, Norway
SNORRE OLAUSSEN
AND
LARS AASBERG
Statoil
P.O. Box 300
N-4001 Stavanger, Norway
ABSTRACT: Some pockmarks on the Norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds
attractive to a variety of benthonic organisms. Detailed examination of a sandstone sample from a pockmark in Norwegian Block
25/7 in the North Sea has revealed the presence of Mg calcite and aragonite cements, some of the latter forming botryoids. All
cement types are characterized by extremely light carbon isotopic compositions, with a mean 5t3C value of -56.1%o PDB, which
shows that the cements contain carbonate produced by oxidation of bingenic methane. Oxidation occurred in both the oxic and
anoxic diagenetie zones. Trace amounts of interstitial methane (mean 6~3C = -40.8%¢) and higher hydrocarbon gases (up to C0 with
a C,/Co ratio of 0.855--0.874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic
gas.