The sediments of the Argo Abyssal Plain and adjacent areas, northeast Indian Ocean

A series of geophysical traverses by the Atlantis II across the Argo Abyssal Plain, together with coring at a number of selected localities has provided new information on sedimentary and tectonic processes in this region of the northeast Indian Ocean. Isopach maps prepared from the seismic profiles show that sediment thicknesses crudely parallel the bathymetry. The presence of some diapirs in the Argo Abyssal Plain was indicated. It was not possible to say from the present program whether the probable diapirs are salt or mud-cored. A diverse group of cores were obtained from a variety of sites including siliceous clays from below the CCD, calcareous oozes from above the CCD, calcareous clays (showing evidence of abundant sulphate reduction) from a fore-arc basin site, and manganese nodules from an abyssal site. In addition, hyaloclastites from the Joey Rise area (north of the Exmouth Plateau), suggest that the Joey Rise, and possibly also the Roo Rise, are underlain by basaltic material. A sample of basalt was also recovered from the outer part of the Exmouth Plateau.