Abstract

Mesozoic sediments are very important for hydrocarbon potential all over the world. The Saurashtra basin of India has wide-spread Mesozoic sediments hidden below the Deccan Traps. To image the Mesozoic sediments and delineate the sub-surface geological structures along with the basement configuration of the Saurashtra basin, we have used long-offset seismic data and residual-Bouguer gravity data along the NW-SE trending 180 km long JodiaAnsador profile. The refraction and reflection traveltime data have been used for ray-trace inversion to obtain the shallow P-wave velocity model (VP) along the profile. The VP model has been derived down to a depth of 10 km show the presence of 0.5-1.0 km thick low-velocity-layer (LVL) Mesozoic sediments (4.2 km/s) hidden below the 1.0-1.5 km thick high-velocity-layer (HVL) Deccan Traps of velocity varying from 4.8-5.2 km/s. Below the LVL Mesozoic layer, another HVL (5.4-5.5 km/s) is present considered as Mesozoic volcanics with thickness variations of 0.5-1.6 km and pinching-out towards Ansador. The basement (5.8-6.0 km/s) is undulated having thickness variation of 2.5-3.5 km forming horst and graben structures along the profile. Below the basement, relatively high-velocity (6.5 km/s) layer has been delineated, which may be attributed to mid-crustal rocks constrained to a maximum 10 km depth using long-offset seismic reflection data. The velocity model obtained is corroborated by the corresponding density model derived from inversion of residual Bouguergravity data along the same profile. This indicate complex geological and tectonic setup of the basin due to the Late Cretaceous Deccan volcanism and out-pouring of wide-spread tholeiitic lavas/basalts.