Integrated geophysical analysis along a transect southeast of Sri Lanka, Bay of Bengal
Maria Ana Desa*, M.V. Ramana
CSIR National Institute of Oceanography Panaji, Goa, India Pincode: 403004 Mobile: 9860188272 E-mail: firstname.lastname@example.org
Integrated analysis of high quality magnetic, gravity, bathymetry and multichannel seismic reflection data along a 1300 km long transect between the DSDP218/IODP1455 and ODP718 sites reveals the structure and evolutionary history of the underlying sedimentary load and basement. The smooth southward increasing bathymetry is pierced by several topographic highs of varying dimensions. Gravity does not mimic the bathymetry in general, and is low over the inferred deep basement. Magnetic anomalies depict significant variation along the transect, with chron A34 identified at its either end.
Multichannel seismic reflection data reveal sediment thickness up to 3 s TWT, but minimal over the topographic highs. Deep drilling facilitated the identification of major horizons in the sedimentary record such as the Pleistocene, Pliocene and Miocene unconformities. The steep topographic highs are basement outcrops, and the truncation of sediments against these highs indicates that they may have emplaced along with the surrounding oceanic crust. Intense deformation of the sediments and basement is seen towards south, resulting in smaller broader topographic highs.
Integration of these data sets suggest that the transect is underlain by Early to Late Cretaceous crust. The basement highs lying at the southern end of the NW-SE trending fracture zones may have formed as the spreading center rotated clockwise during the Middle Cretaceous period. The arcuate gravity low is due to the presence of a deep and old basement, overlain by thick sediments. A prominent step in the basement coinciding with an abrupt change in magnetic anomaly pattern probably indicates the concurrent presence of oceanic crust of different ages, as a consequence of the Middle Cretaceous major plate reorganization.