Geochemical and magnetic signals for the mud volcano-induced methane seepage in the core sediments of Shenhu area, northern South China Sea

Abstract

The Shenhu Area of the northern South China Sea (SCS) has been regarded as a promising area for gas hydrate exploration. In this research, the petrography and stable isotopic composition of authigenic carbonates within a core of shallow sediment from Site 08CF7 in the Shenhu area have been studied. Based on the results of grain sizes, magnetic susceptibility, carbonate contents, textural characteristics, the age constrains of the core and the tectonic setting of the study area, it can be inferred that the core may represent the subsurface sediment in a mud volcano area within the gas hydrate system. Core sediments below 188 cm in the core may be associated with the in situ mud volcano activity. The authigenic carbonates (calcite, aragonite and dolomite) in fine size fraction below 188 cm indicate the mud volcano-induced methane seepage and anaerobic oxidation of methane (AOM), and their carbon source was mainly biogenic methane. In addition, the variation in magnetic susceptibility corresponds with in situ mud volcano sediments and associated methane seepage. These signals provide new methods of identifying AOM and application prospect for the exploration of seepage gas hydrates in SCS.