Delineation of Trap and Subtrappean Mesozoic Sediments in Saurashtra Peninsula, India

Abstract

Mapping of sediments beneath volcanic Traps is a highly challenging task. Here we report on the analysis of wide-angle seismic data from Trap-covered Saurashtra peninsula to address this problem. Traveltime modelling of mainly seismic refraction and some reflection phases yields basement configuration, trap and subtrappean sediment thicknesses along the Jodia-Ansador (NW-SE) profile in Saurashtra peninsula. Travel-time skip and amplitude decay in seismic refraction data indicate the presence of low-velocity sediments beneath the Traps. The result reveals two layers with Deccan Traps (4.85-5.0 km s-1) followed by Mesozoic sediments above the basement (5.8-6.1 km s-1). Using the lower bound velocity (3.2 km s-1), sediment thickness varies between 800 and 1500 m. Based on upper bound velocity (4.3 km s-1), we find both the sediment thickness and basement depth increase by 600-700 m. The thickness of sediments is more in the northwest and decreases gradually in the southeast, suggesting that the northwestern part of the profile is an important zone for hydrocarbon exploration in the Saurashtra peninsula. With the lower bound velocity of Mesozoics, we find that the basement (5.8-6.1 km s-1) is deep (~2100 m) in the northwest and shallows up near Atkot to ~1.0 km depth, and then deepens further southeast, showing the basement upwarped. The overall velocity and boundary uncertainties are of the order of ±0.15 km s-1 and ± 0.15 km respectively.