Development of Tertiary West Papuan Basin: ABSTRACT

Abstract

Marine-seismic studies and wildcat drilling in the Gulf of Papua have provided a comprehensive insight into the geology of the West Papuan basin. The basin is integrated closely in the west with a downwarped but structurally rigid segment of the Australian shield, and in the south with the Coral Sea hydrographic basin. It incorporates arcuate geosynclinal development eastward and northward beyond the continental margin. The pre-Tertiary history is obscure. Middle Jurassic-Cretaceous clastic sediments overlie granite of the continental shield on the west. Eastward, the record is interrupted by a thick cover of Tertiary strata, and then possibly may be represented in outcrop by a metamorphic series of indeterminate age. The Tertiary basin developed in three distinct phases, the first commencing in early Eocene. Marine seas transgressed a peneplaned and tilted Mesozoic land surface from east to west. A remarkably uniform wedge of shoal limestone and chert was deposited. Regression and erosion occurred in late Eocene time. Late Oligocene oceanic crustal upwarp created an eastern volcanic rim to the basin. Typical orthogeosynclinal deposition followed in early Miocene time, with reef, shoal, and pelagic limestone formed marginal to the stable western (continental) shelf, and with prolific volcanism associated with the eastern (oceanic) flank. Mudstone-graywacke sediments were deposited in a narrow intermediate eugeosyncline. Middle Miocene regional uplift and orogenesis of the Central Mountain geanticlinal belt resulted in the development of an inmmense southeasterly prograding system, which rapidly buried the early Miocene sequence. This phase probably still is actively prograding southward into the Coral Sea basin. End_of_Article - Last_Page 745------------