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ABSTRACT: New Paleogeographic Maps for the Coral Sea and Darai Megasequences, Papua New Guinea, Enhanced by Geological Icons

CARMAN, GEORGE J, Earth Sciences Department, Monash University, Clayton, Australia, and Austin Oil N.L., South Melbourne, Victoria, Australia

The Coral Sea syn-rift and post rift, and Darai back-arc sequences are most continuously exposed at the Aure scarp in eastern Papua. Biostratigraphic correlations to 40 well and outcrop localities permits the construction of seven paleogeographic maps and their readability is enhanced by geological icons illustrating paleophysiographic elements.

Pillowed olivine basalt at the Aure scarp overlying Gondwana shelfal sediments are the oldest record of the onset (K-Ar = 87 m.y.), and the most northern locality, yet known for the Coral Sea Rift on the northeastern Australian plate margin. Late Cretaceous syn-rift coarse clastics occur adjacent to the Aure fault, (the Pale Sandstone) and the Bogoro fault (Barune Sandstone) whereas bioturbated littoral sediments occur at Menyamya within a northwest-trending rift. Seismically defined wedges of sediments, possibly offset by transverse faults, in the Gulf of Papua and farther south, are also interpreted as Coral Sea sequences. Upper Cretaceous sediments are absent on the western rift-shoulder highs (e.g., Wana Swell) and overprinting in the Owen Stanley metamorphics obscures the eastern margin.

Post-rift Paleogene carbonate lithotypes define a northwest trending bathyal environment (Moresby Deep) flanked by neritic limestones. Facies belts in the Darai back-arc sequence continue to reflect the rift geometry during the early Miocene. A western biohermal shelf (Fly Platform) with a shelf edge reefs (Borabi reef trend) and off-platform pinnacle reefs (e.g., Uramu, Pasca, Pandora) are mirrored by a 100 km carbonate belt (including reefs) about 200 km east of the Pasca/Pandora reefs and probably fringing the Maramuni arc. Middle Miocene craton/arc collision introduced volcaniclastics and stifled the reef growth.

During the late Miocene, syntectonic processes (Talama Volcanics and cannibalistic reworking of thrust anticlines in the Aure Trough) accompanied passive foreland sedimentation farther west. Southwest propagation of a fold and thrust belt in the Pliocene led to the present physiography characterized by topographic forms closely resembling geological structure.

 

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)