Stratigraphic and Structural Development of the Aure Trough and Adjacent Shelf and Slope Areas

Abstract

The Aure Trough is a partially submerged south-southeasterly trending eugeosyncline which comprises the main axial zone of sedimentation in the Cainozoic Papuan Geosyncline. It is bounded to the west by a broad stable miogeosynclinal shelf and slope, and to the east by a narrow unstable shelf.Onshore the trough consists of 10 000 m of deep-water sediments. These extend offshore where the axis of sedimentation coincides with the axis of a present day bathymetric feature, the Moresby Trough. Sediments are folded into north-trending linear anticlines and broad synclines; anticlines are ruptured by thrust faults and offshore by diapiric intrusion of mudstone. The western slope (5000 m of fine marine sediments) and shelf (2500 m of deltaic and shallow marine sediments) are relatively undeformed. Over the eastern shelf, 5000 m of folded fluviatile, deltaic and shallow marine sediments are transitional eastwards to 2000 m of relatively undeformed sub-aerial volcanics. Variations in sedimentary lithologies can be correlated with periods of volcanic activity associated with periods of uplift.The sediments of the Cainozoic Papuan Geosyncline unconformably overlie Mesozoic and Eocene sediments. West of the Aure Trough the Mesozoic and Eocene rocks are weakly deformed shelf sediments derived from the Australian continent; east of the trough they are strongly deformed, metamorphosed and partly volcanogenic. The nature, thickness and extent of these sediments beneath the Aure Trough is not known.The Mesozoic to Eocene sequence accumulated around the margins of the Australian continent in an arcuate geosynclinal basin. Early Cainozoic interaction of the Australian and Pacific plates resulted in deformation of the outer margins of this geosyncline and in the partial emergence of mainland Papua New Guinea. Erosion of this landmass and volcanic activity provided the main source of sediment for the Cainozoic Papuan Geosyncline. Development of the Aure Trough may be related to opening of the Coral Sea Basin in the Eocene; geophysical evidence suggests crustal thinning.Numerous oil and gas seepages have encouraged petroleum exploration throughout the area since 1911. No economic reserves have been located in the Tertiary section, but wells west of the Aure Trough have encountered gas and some oil of probable Mesozoic origin.

The southwest pacific area during the last 90 million years

“…ago (Brown et al, 1975) when flysch ceased to accumulate. The amount of crustal shortening is unknown, but the lack of deformation in the Coral Sea Basin suggests that it was small.…”

Tectonics of the Indonesian region

“…The thick Cenozoic sediments (Papuan Basin, or Aure Trough) beneath the continental shelf at the northwest apex of the Coral Sea presumably overlie oceanic crust. The stratigraphic development of this region, relatively well known from oil-exploration work, has been discussed by Brown, Pieters, andRobinson (1975), Fjelstul, Tallis, andErickson (1969), Harrison (1969), Jenkins and Martin (1969), Laws (1971), O'Brien, Gray, and Gillespie (1961), Oppel (1970), andTallis (1975). Upper Cretaceous and Paleogene strata were deposited transgressively across broadly deformed older materials on the developing eastern Australian shelf.…”

“…In a coastal belt, 10-20 km wide in the sector between 147° and 148° E., Upper Cretaceous (Senonian) through upper Eocene deep-water argillite, shale, siltstone, chert, and limestone are disrupted chaotically and are intercalated with shallow-water Paleocene and Eocene strata and with large and small masses of gabbro, diabase, and basalt ( fig. 133; Brown, 1974Brown, , 1975Davies and Smith, 1971;Glaessner, 1952Glaessner, , 1960Macnab, 1969;O'Brien and others, 1961;Pieters, 1974;Yates and de Ferranti, 1967). Deformation was directed south west ward.…”

“…Volcanic rocks of Miocene and Pliocene age are voluminous as far southeast as about 147° 15' E., beyond which they are less widespread and are little deformed (fig. 134); but dikes and small stocks of mafic and intermediate igneous rocks are abundant (Bain and others, 1972;Brown, 1974Brown, , 1975Pieters, 1974;Yates and de Ferranti, 1967). Dominant compositions throughout are andesite and basalt.…”

Synorogenic alluvial-fan – fan-delta deposition in the Papuan foreland basin: Plio-Pleistocene Era Formation, Papua New Guinea

“…Papua New Guinea is very rugged, outcroppings usually are poor because of intense weathering and dense vegetation, and roads are few. This paper reports on fieldwork and sedimentological investigation of the Pliocene to possibly Pleistocene, siliciclastic upper Orubadi-Era interval exposed on the southwest margin of the Papuan Peninsula ( Figure 1) (Brown et al 1975;Francis et al 1986;Klimchuk 1993). The Orubadi and Era Formations there were deposited in the Aure Trough (Brown et al 1975), which, starting in the Late Miocene, was part of a foreland basin formed from tectonic loading of the Papuan-Aure Fold and Thrust Belt on the Australian craton margin (Pigram et al 1989).…”