GREINERT, JENS, ERWIN SUESS, GEOMAR Research Center, Kiel; ALEXANDER DERKACHEV, ANATOLIY OBZHIROV, Pacific Oceanological Institute, Vladivostok; BORIS BARANOV, Institute of Oceanology, Moscow; and GISELA WINCKLER, Institut for Umweltphysik, Universitat Heidelberg

Abstract: Gas Venting, Biota and Carbonate Mineralization Along the Sakhalin Shear Zone, Sea of Okhotsk

Submarine gas emissions off eastern Sakhalin Island are persistent trough time and confined to tectonically controlled locations along shear zones. On the slope (400-800 m depth) gas plumes were documented by high methane concentrations and lately by acoustic imaging of "flares" in the water column. We documented for the first time by video-observation and sampling spectacular manifestations of active venting. These include large fields of Thyasirid bivalve Conchocele sp. and other symbiotic benthic fauna. Their burrows, dwellings, and bioturbate structures churn up the seafloor and structures are preserved via carbonate cementation. In addition tubular concretions, encrustations, and glendonites (pseudomorphs after ikaite CaCO₃.6 H₂O) attest to the intense material turnover at these vent sites.

The activity is fueled by methane and sulfide oxidation and subsequent carbonate precipitation. Pore waters are supersaturated up to 60-times with respect to calcite and aragonite. They contain high metabolites and H2S and show complete removal of interstitial sulfate as shallow as <50 cm below seafloor. One of the pore water characteristics which supports methane oxidation as the dominant vent reaction, is the high C:N remineralization ratio of 106:<0.2. This together with methane in sediments and carbon isotopes of solid phases, the dissolved carbonate pool, and methane help identify the cold vent activity at the Sakhalin shear zone.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California