Role Of Post Glacial Maximum On Gas Hydrate Dissociation: A Case Study From Eastern Continental Margin Of India

Numerous submarine landslides have been reported in the last two decades due to Gas hydrate dissociation and fluid migration. In various basins across the globe, the dissociation of hydrates into free gas and water has been observed due to a rise in sea surface temperature over the course of the last century. To have an insight into the process, we have studied the effect of temperature variations and the associated impact on gas hydrate dissociation in two gas hydrate provinces in the East Indian Margin of India, namely the Krishna-Godavari (KG) and Cauvery basins. The 3D seismic data of the Krishna Godavari and Cauvery basin has shown occurrences of Bottom Simulating Reflectors (BSR) at ~160 meters below seafloor (mbsf) and ~110 mbsf, respectively. In the Last Glacial Maximum (LGM), the sea surface temperature increased by 3 ºC in the Bay of Bengal and the Indian Ocean. The modelling of the base of the hydrate stability zone (BHSZ) at ~1000m water depth has shown that the BSR is shifted by ~80m in the KG and ~60 m in the Cauvery basin Post LGM. The difference in the shift is due to the Lithology, high sea bottom temperature, Low Geothermal Gradients and less sedimentation rates in the Cauvery basin compared to the KG. The slope angle in both study areas is less than 2 degrees however, we have identified a large slump of ~21sq. km in the KG that occurred due to the gas hydrate dissociation and fluid migration. It appears that there has been no observed slumping in the Cauvery region, possibly due to lower sedimentation rates and lithology. Another reason is that the seismic data is available in limited area i.e., ~20 sq.km in the Cauvery region. However, significant Mass Transport Deposits and mud diapers were observed which might have formed due to the hydrate dissociation beneath the BSR. Hydrate dissociation due to an increase in the bottom water temperatures is also recorded in the carbon isotopes of benthic (Miliolida) foraminifera in the Indian margin. The first ever detected gas flares in the multibeam echo sounder data of the Cauvery basin lends support to our argument that the gas hydrate dissociation is actively occurring in the East Indian margin.