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.