Bathymetric and seismic reflection profiles totalling about 2800 km, and covering about 110 000 km2 of the Argo Abyssal plain, have been analysed. The early emplacement of oceanic crust and volcanic edifices (Late Jurassic and Early Cretaceous) was followed by cooling, and marked subsidence until the Miocene. The principal structural features have been identified as the right-laterally sheared Wombat Graben in the south, the N-S trending Joey Rise in the west, the parallel sediment-filled Joey Graben to its east, a NW-trending eastward tilted and subsided volcanic massif to its east, a NW-trending linear volcanic massif on the old oceanic plate farther east, the deformed and uplifted sediments and basement in the north, and the central basin with 1.2 km thick sediments. The Joey, Wombat and Kivi Grabens are newly identified. The N- S trending Joey Graben is 400-450 km long, parallel to and east of the Joey Rise, and it is filled with up to 1 km of sediment. Beneath it, the mantle has been identified at depths of 12-15 km and deepening westward. The other two grabens form moats hundreds of metres deep, at the foot of the Australian margin in the south. The right-lateral displacements in the axis of the Wombat Graben reflect the initial shearing and rifting of the thinned crust. The widespread faulting in the basement, and the persistence of some faults upward into sediments as young as early Miocene, indicate that tectonism was marked until then. The eastern and northern parts of the abyssal plain have been uplifted as they came within the peripheral fore-bulge south of the Sunda Trench. Five sequences (A-E) overlie the oceanic crust and they have been correlated with the lithology of ODP Site 765 and DSDP Site 261. They probably represent Plio-Pleistocene, upper Miocene-lower Pliocene, middle Miocene, upper Oligocene-lower Miocene and uppermost Jurassic to Lower Cretaceous strata, respectively. The depositional trends in the Mesozoic and Miocene sediments are controlled by basement structure. Isopach maps of the Mesozoic and Cainozoic sediments reveal that their maximum thicknesses are about 0.6-0.8 km and 0.2-0.4 km, respectively, with the bulk of the sediments (calcareous turbidites and claystone) laid down in the Early Cretaceous and the middle Miocene to Pliocene. During the Oligocen e to early Miocene period (37-16 Ma), a remarkable geologic event led to non-deposition or erosion of sediments.
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