Tectonic Disposition and Hydrocarbon Potential of 85° East Ridge in Bay of Bengal

Misra, K. S.; Joshi, Vartika
Department of Petroleum Engineering and Earth Sciences, University of Petroleum and Energy Studies, Dehradun, India.

The 85° East Ridge is a very significant geological feature of the Bay of Bengal in the Indian Ocean. The present study has revealed an interesting tectonic evolution and prognosticates a very high hydrocarbon potential in successive wedge-outs on either side, as well as coralline reef complexes capping this ridge. This sinuous feature meanders along the 85° east longitude in the northern part and gently curves towards the southern tip of peninsular India in southern part. This ridge is completely buried under the uninterrupted Tertiary succession and Quaternary Ganga-Brahmaputra submarine fan deposits. Earlier view suggested that this ridge represents a trail left by hotspot on the northerly moving Indian plate. The present study based on interpretation of seismic profiles generated by Pre-Stacking and Depth Migration (PSDM) techniques has suggested that this ridge has originated due to combination of tectonic and related igneous phases. The upward reverse movement along nearly vertical faults is believed to have taken place during Cretaceous igneous activity. The ridge portion is believed to represent felsic phase while extensive mafic volcanics on either side of the ridge represent extrusive phase. The gravity low associated with this ridge is thus believed by the present authors to be due to this density contrast. The central axis of the ridge is incised indicating continuing extensional tectonics. Extrusive phase corresponds with colossal and pulsatory Cretaceous volcanic flows in land areas of peninsular India. In oceanic regions, these volcanics are overlain by an uninterrupted Tertiary sedimentary succession. The intrusive relationship with this succession indicates a Cretaceous-Tertiary event, where Paleocene succession is affected and its wedge-outs are conspicuously seen. The faults located on top of this ridge, form an hour-glass structure, with upward continuing intersectional region. They form several umbrella like growth of coral reef complexes. Interpretation of high resolution satellite gravity data has helped in mapping the southern extension of the 85° East Ridge. Present study has also indicated that this ridge curves around peninsular India along with other oceanic features. The study of sections across the 85° East Ridge from the PSDM seismic profiles and its lateral extension from the satellite gravity data does not support earlier view of its origin due to hotspot.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012