High-resolution seismic reflection profiling in conjunction with detailed bathymetry on the southwestern continental margin of India revealed that the continental shelf is characterized by smooth/or undulatory seafloor up to about 100 m water depth between Quilon and Trivandrum. However, the shelf widens in the southwest off Cape Comorin. The shelf break occurs at about 100 m off Quilon-Trivandrum, while it lies at about 250 m south off Cape Comorin. Beyond those depths the continental slope is marked by steep gradients and isolated topographic highs. Seismic profiles showed a sub-bottom penetration of 50-200 ms (twtt) on the shelf and 800-1000 ms twtt on the continental slope and in the adjoining deep-sea region. Seismic profiles revealed the presence of bright, high amplitude seismic reflections 15 ms below seafloor (bsf) and distinct velocity pull-down structures or gas sags 190 ms bsf at about 200 m water depth suggesting gassy sediments/ gas-bearing sands. The seismic profiles also indicated the presence of bottom simulating reflections (BSRs) at about 240-340 ms twtt bsf between 1160 and 1825 m water depths revealing the occurrence of gas hydrates off Cape Comorin. This study complements the findings reported earlier on the western continental margin of India (Veerayya et.al., 1998), north of the present study region. A plot of sub-bottom depth of BSR horizons versus seafloor depth clearly reveals the close affinity between the presently studied BSRs and the world-wide occurrences particularly in the Gulf of Mexico, off Panama and Costa Rica. It is surmised that rapid sedimentation and organic carbon-rich sediments coupled with optimal lithostatic and hydrostatic pressures favored the formation of gas hydrates along the margin. Concerted efforts aimed at understanding geological, geophysical, bio-geochemical and physical oceanographic aspects, and in situ measurements using state-of the-art techniques for gas hydrate exploration along the margin are being made which in turn helps to identify and quantify the potential gas hydrate resources along the continental margins of India.

References:

Veerayya, M., Karisiddaiah, S.M., Vora, K.H., Wagle, B.G. & Almeida, F. 1998, Detection of gas-charged sediments and gas hydrate horizons along the western continental margin of India, In: Henriet J.P.& Mienert, J. (eds). Gas Hydrates: Relevance to World Margin Stability and Climate Change. Geol. Soc. London, Spl. Publ. 137: 239-253.