Some bathymetric and geotectonic features of the eastern part of the Indian Ocean

Abstract

Tectonic relations of the mainland of Western Australia are reflected seawards by the topography of both continental shelf and adjacent deep ocean floor respectively. The basic pattern of the mainland is controlled by the early Pre-Cambrian “grain” (fracture and folding trends). The continental shelf is narrow and rocky where these ancient orogenic lines cross it, amd they appear to continue oceanwards in elevations of the deep-sea floor. On the other hand, the Palaeozoic-Mesozoic-tertiary basins (paraliageosynclines) of the mainland (up to 20,000 feet deep) are matched on the shelf by wide sandy, and atoll-rimmed embayments; and seawards again by oceanic basins approaching 3,000 fathoms in depth. Crustal character of the main eastern Indian Ocean suggests a thalasso-craton (here defined as primary oceanic crust), but these marginal intermediate ridges and basins suggests a common evolution with the continent. Formal names have been given to sectors of the West Australian shelf and the deep-sea floor in the eastern part of the Indian Ocean.