Reducing microenvironments promote incorporation of magnesium ions into authigenic carbonate forming at methane seeps: Constraints for dolomite formation

In part composed of Mg calcite and dolomite with a nearly continuous spectrum MgCO3 contents, carbonates forming at marine methane seeps are ideal candidates to study the formation early diagenetic surface conditions. Laboratory experiments, modelling co-variation mineralogical geochemical attributes seep suggest that sulphide – locally released from sulphate-driven anaerobic oxidation drives catalytic seeps. Direct comparison concentration dissolved content carbonate could test this hypothesis. Although during precipitation cannot be determined, sedimentary fabrics probably had an effect on local concentration. Carbonates seabed Shenhu seepage area South China Sea reveal longitudinal, winding branched width 400 700 ?m, interpreted represent burrows piercing semi-consolidated sediment. The abandoned were infilled fine-grained sediment, which was subsequently cemented by microcrystalline calcite. degree cation ordering in burrow infills host sediment is similar, indicating virtually coeval formation. Mg/Ca mole ratios minerals lower than surrounding matrix. Similarly, ?13Ccarbonate values tend higher for (from ?41 ?33‰) matrix ?43 ?38‰), suggesting stronger seawater influence pore waters burrows. More reducing microenvironments supposedly came along concentrations sulphide, allowed more Mg2+ ions enter crystal lattice led distribution contents ?13C authigenic reinforces hypothesis release key factor