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.

Geochemical record of methane seepage in authigenic carbonates and surrounding host sediments: A case study from the South China Sea

“…Numerous studies attempted to employ various indicators in marine sediments to reveal past seepage events and recognize the SMTZ, including barium (Ba) anomalies (e.g. Torres et al, 1996;Dickens, 2001;Snyder et al, 2007;Vanneste et al, 2013), authigenic carbonate and its carbon isotope composition (Nöthen and Kasten, 2011;Lim et al, 2011;Peketi et al, 2012Peketi et al, , 2015Chen et al, 2015), and content of pyrite and its sulfur isotope composition (Pu et al, 2007;Lim et al, 2011;Peketi et al, 2012Peketi et al, , 2015Borowski et al, 2013;Lin et al, 2016a,b,c). In particular, increasing studies have used 34 S-enriched sulfide minerals in sediments for the identification of AOM-related processes and the SMTZs (Pu et al, 2007;Peketi et al, 2012;Borowski et al, 2013;Lin et al, 2016c).…”

Dolomite genesis in bioturbated marine zones of an early-middle Miocene coastal mud volcano outcrop (Kuwait)

“…Mud volcanoes belong to cold seep systems where the discharged fluids are transformed to authigenic carbonates because of microbial oxidation of methane and other hydrocarbons 47 . Dolomite formation in marine coastal hydrocarbon seeping environments is well-documented in the literature from different geographic locations including Barbados Accretionary Prism 48 , northern South China Sea 49 , Gulf of Mexico 50 , Eastern Mediterranean Sea 51 , south east Caspian Basin 52 , and Kuroshima Knoll in Japan 53 .…”