Part 2. Younger Pacifics arcs and the eastern marginal seas: Structure of the Loyalty Basin

Abstract

Seismic reflection, bathymetric and magnetic profiles across the Loyalty Basin and Ridge show the geological or sedimentary Loyalty Basin to be a restricted feature within the morphological basin. The basin contains a thick accumulation of sediment which in the centre exceeds a two-way reflection time of 4 sec., and thickens northwards. Three main sedimentary formations are recognised which rest on a basement which is correlated with the layer of about 5.9 km/sec velocity of the seismic refraction profile of Shor et al. (1971). The axes of sedimentation of these main sedimentary units and the respective areas of provenance vary between the different formations, with both the New Caledonia and Loyalty Ridges acting as important source areas at various time through the depositional history, giving three main phases of morphological and sedimentological history prior to the present time. Although only pelagic sedimentation is currently taking place within the Loyalty Basin, the large thickness of sediment within the basin implies a considerable amount of terrigenous and volcanoclastic sedimentation during earlier deposition.