Abstract:

Gas seep system is a common phenomenon on the seafloor in the continental shelf and slope. Venting gas is converted partially into CO₂ and H₂S by methane oxidizing archaea and sulfate reducing bacteria in gas seep sites,inducing  seep carbonates precipitation.The most common minerals in seep carbonates are microcrystalline calcite, microcrystalline aragonite and dolomite, and pyrite as well. Cold seep carbonates usually occur as chermoherm, nodule, chimney, hardground, cement and fine vein.Pyrite rim carbonate nodules, corrosion surfaces, inverted stromatactoid cavities, clotted fabrics，and stromatolitic are the most common sedimentary fabrics in seep carbonates. Gas seep carbonates generally are typified by low δ¹³C values, as they inherit the stable isotope signature from their carbon source, ¹³C-depleted methane.Due to the enrichment of ¹⁸O in gas hydrates, anomalously positive δ¹⁸O values in seep carbonates could argue in favour of gas hydrate destabilization at gas seep sites.The pyrite enclosed in the seep carbonates generally shows low ³⁴S values.The ¹³C depleted-lipid biomarkers in cold seep carbonates are believed to reflect in-situ anabolic activity of methane oxidizing archaea and sulfate reducing bacteria

Key words: cold seep carbonate, gas seep system, gas hydrate, microbial process