Marine seismic profiling and shallow marine sand resistivity investigations in Jervis Bay, NSW, Australia

Abstract

A marine continuous seismic (CSP) profiling study and a resistivity study of vibrocore samples of shallow marine sands were undertaken in Jervis Bay, NSW, Australia, to characterise the seabed. The CSP study also included Crookhaven Bight, adjacent to Jervis Bay facing northeast to the ocean. The results of the CSP studies show variable geological conditions below the seabed, indicating very dense sands and variably weathered sandstones. The bedrock surface was also highly irregular in places suggesting cyclic erosional pulses under rapidly falling sea levels at various times in the past. Bedrock was found to form the seafloor in some locations and deeply incised paleochannels extending to -62 m below sea level in the Crookhaven Bight and bay entrance areas. The sampled sands had very low magnetic susceptibilities, thus corroborating the visual impression of low clay content. However, a variety of grainsizes, grainshapes, colours and cohesions were noted. These factors, together with variations in inferred porosity, gave rise to a range of resistivities, which, when temperature corrected, plotted with some scatter about an appropriate Archie Equation curve. Resistivity values recorded ranged from ~ 1.0 to 0.8 O m (20°C) for the samples obtained from 11 sites.