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

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Mazumdar, A., Dewangan, P., Joaeo, H. M., Peketi, A., Khosla, V. R., Kocherla, M., Badesab, F. K., Joshi, R. K., Roxanne, P., Ramamurty, P. B., Karisiddaiah, S. M., Patil, D. J., Dayal, A. M., Ramprasad, T., Hawkesworth, C. J., Avanzinelli, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 2009
• Subjects: methane hydrate; cold seep; authigenic carbonate; Bay of Bengal; AMO; chemosynthetic community; Methane hydrate
• Online Access: https://archimer.ifremer.fr/doc/00218/32911/31414.pdf; https://doi.org/10.1029/2008GC002337; https://archimer.ifremer.fr/doc/00218/32911/

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 (delta(13)C ranges from -41 to -52% VPDB) from these carbonates indicate carbon derived via anaerobic oxidation of methane. Extrapolated mean calendar age (similar to 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.