Evidence of paleo–cold seep activity from the Bay of Bengal, offshore India

Abstract

We report evidence of paleo–cold seep associated activities, preserved in methane‐derived carbonates in association with chemosynthetic clams (Calyptogena sp.) from a sediment core in the Krishna‐Godavari basin, Bay of Bengal. Visual observations and calculations based on high‐resolution wet bulk density profile of a core collected on board R/V Marion Dufresne (May 2007) show zones of sharp increase in carbonate content (10–55 vol %) within 16–20 meters below seafloor (mbsf). The presence of Calyptogena clam shells, chimneys, shell breccias with high Mg calcite cement, and pyrite within this zone suggest seepage of methane and sulfide‐bearing fluid to the seafloor in the past. Highly depleted carbon isotopic values (δ13C ranges from −41 to −52‰ VPDB) from these carbonates indicate carbon derived via anaerobic oxidation of methane. Extrapolated mean calendar age (∼58.7 ka B.P.) of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the U‐Th based depositional age (46.2 ± 3.7 and 53.0 ± 1.6 ka) of authigenic carbonates sampled from this level, thereby constraining the younger age limit of the carbonate deposition/methane expulsion events. The observed carbonate deposition might have resulted from the flow of methane‐enriched fluids through the fracture network formed because of shale diapirism.

Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

“…2) is representative of the Godavari continental slope (Mazumdar et al, 2009;Ramprasad et al, 2011;Joshi et al, 2014) and is driven by changes in the siliciclastic sedimentation rate as dilution by biogenic carbonates is less than 5 % ). Despite a lower sea level at the time, the flux was relatively small in the early Holocene (∼ 25 g cm −2 kyr −1 ) but began to increase after 6000 years ago (∼ 40 g cm −2 kyr −1 ), as soon as the monsoon started to decline but well before the adoption of Neolithic agriculture and settlement of the savannah zone of the central peninsula (∼ 4500 years ago; Fuller, 2011).…”

Using sediment geochemistry to infer temporal variation of methane flux at a cold seep in the South China Sea

“…Geochemical proxies such as stable carbon isotope records of authigenic carbonates have been applied to evaluate the temporal variation of methane seep, owing to their very negative d 13 C (Peckmann and Thiel, 2004;Han et al, 2004Han et al, , 2008Han et al, , 2013Mazumdar et al, 2009Mazumdar et al, , 2011Bayon et al, 2009aBayon et al, , 2013Bayon et al, , 2015Cr emi ere et al, 2013;Tong et al, 2013;Tribovillard et al, 2013;Feng et al, 2014Feng et al, , 2015a. However, such carbonates are most intense at intermediate flow rates, and usually do not form in low and high flux conditions (Luff and Wallmann, 2003;Karaca et al, 2010).…”

Gas hydrate destabilization and methane release events in the Krishna–Godavari Basin, Bay of Bengal

“…Timings of P 2 and P 3 may correspond to the Dansgaard-Oeschger warming events during the 40-50 ky time window (Kudrass et al, 2001). However, it is difficult to relate the observed small carbon isotope perturbation to episodic destabilization of methane hydrate deposits (Kennett et al, 2000;Kennett et al, 2003) of K-G basin in the absence of corresponding 13 C depletion in benthic foraminifera and other biological/ geochemical evidence (Mazumdar et al, 2009b). Wetland methane emission could also have influenced the depleted carbon isotopic signature.…”

“…Shale tectonics (diapirism) induced deep fault system has been amply demonstrated from the K-G Basin (Mazumdar et al, 2009b;Dewangan et al, 2010;Shankar and Riedel, 2010;Riedel et al, 2010;Choudhury et al,2011). Shale tectonic is driven by the downward movement of thick sediment mass over a deeply buried over pressured shale strata (Damuth, 1994;Wu and Bally, 2000).…”

“…Recently, paleo-cold seepage associated authigenic carbonate and chemosynthetic clam (Calyptogena sp.) shells have been reported from this site (Mazumdar et al, 2009b and and nearby site NGHP-10D (Collett et al, 2008). Based on 14 C and U/Th age dating of foraminiferal tests and authigenic carbonates respectively, a minimum age of 46 to 58 kyr was suggested for the methane expulsion events (Mazumdar et al, 2009).…”