Authigenic carbonates related to gas seepage structures in the Sea of Okhotsk (NE offshore Sakhalin): Results from the Chaos Project

Mineralogical and isotopic analysis of authigenic carbonates from different gas hydrate-bearing seepage structures in the Derugin Basin (Sea of Okhotsk) are presented. The analysis showed the existence of four morphological types of carbonates, with all of them mainly of Mg-calcite. δC values of carbonates generally light owing to the inheritance of carbon from microbial methane. C-enriched samples at the VNIIOkeangeologia structure with δC values of up to +9.3‰ represent carbonate precipitation due to methanogenesis. The calculated equilibrium δO values of carbonates in general correspond to measured values.