Print this pageStructure and Evolution of the Kerala Basin, Offshore South-West India
PSDM processed reflection seismic line L-7 acquired by ONGC in 2005-06 is located in the offshore Kerala basin and trends for 570km through the extended continental margin of SW India, to beyond the site of DSDP-219A. It reveals a polyphase rift and post-rift history with syn-tectonic volcanic and sedimentary growth sequences of Late Mesozoic to Palaeocene age and a Tertiary post-rift sequence. Seismic imaging of the pre-Tertiary sequence is generally poor due to the presence of volcanic rocks. Exceptionally well-resolved multiple panels (to depths of 16km or more) of mainly seaward-dipping reflectors in the presumed Mesozoic volcanic rocks are observed. These may have been deposited as growth sequences in major half grabens. Large-scale folds in these sequences can be used to infer the architecture of extended lithosphere and define a system of extensional detachments with ramp-flat trajectory; where the flats and ramps can be correlated with major rheological boundaries within the plate.
The rift and post-rift architecture and history of SW India margin can be correlated with major tectonic events. Separation of India from Madagascar at 93-89Ma and later rifting of Seychelles from India at 65Ma are correlated with growth sequences in the rift system. During post-rift thermal relaxation, rift sequences were overlain unconformably by Eocene and Miocene sediments. A strong angular unconformity at base Oligo-Miocene succession represents a phase of uplift and erosion that coincides with initial impingement of Indian continental lithosphere with SE Asia at 45Ma.
Backstripping of the post-rift sequence using Move2009 software with decompaction and compensation for flexural isostacy validated our interpretation of L-7 and allowed further investigation of the structural evolution. Palinspastic reconstruction of rift architecture has yielded incremental displacement history for major faults (displacements >250m). Rift shoulders appear to have risen above sea level during basin evolution and degradation of volcanic sequences exposed in scarp slopes may explain the “trapwackes” as proximal growth sequences in fault hanging walls. Palinspastic restoration extended to 3D can be used to model the Paleocene paleosurface (bathymetry) and provide a basis for predictive turbidite systems modelling to investigate occurrence and distribution of Paleocene source and reservoir rocks.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil