ABSTRACT: Comparisons in the Structural and Stratigraphic Evolution of the Vulcan Graben and Basins in the Eastern Timor Sea and Ramifications for Hydrocarbon Exploration

BOTTEN, PETER ROBERT, JACK ROSSER, and JOHN GORTER, Petroz, Perth, Western Australia

Recent acquisition of good-quality seismic data in the eastern Timor Sea, along with detailed analysis of well data in this area, have shown important differences between the structural evolution of the Vulcan Graben and the Sahul and Malita basins and given further resolution to the timing and nature of rift system development of the Jurassic and Cretaceous breakup of the Australian northwest continental margin.

Late Jurassic rifting in the Vulcan Graben was initiated in the late Callovian, imprinting a northeast to southwest tectonic grain. Further rifting took place in the Kimmeridgian with faults trending east-northeast to west-southwest. The present-day structural architecture is dominated by these trends. These rifting phases control distribution

of reservoir and source rocks and have considerable impact on play potential in the area.

In the eastern Timor Sea, Late Triassic to Early Jurassic northwesterly trending depocenters, including the Sahul and Flamingo synclines, were formed during a period of abundant normal faulting, mimicking Permian-Triassic trends of the Petrel Subbasin. The Malita Basin developed in a northeast-southwest-trending sag basin in the Late Jurassic period. There is little evidence for rifting in either the Callovian or Kimmeridgian period. Lack of faulting during this time is in direct contrast to the Vulcan Graben and has important ramifications on the distribution of primary reservoir and source rock intervals. Abundant northeast to southwest normal faulting of Albian-Aptian age is present throughout the eastern Timor Sea. Reactivation of normal faulting on the margins of the Malita Basin during the Late Cretaceous and Tertiary periods has led to accumulation of thick sedimentary sequences during this time.

The thickness of the Upper Cretaceous and Tertiary section is critical to the timing of hydrocarbon generation from potential Jurassic source rocks in the eastern Timor Sea. This is not the case in the Vulcan Graben area where this section is less than half the thickness seen in the Malita Basin.

Understanding the differences in structural and stratigraphic evolution between the Vulcan Graben and basins in the eastern Timor Sea is fundamental to developing exploration programs to explore the area. Depositional models for the Jurassic and Cretaceous intervals, based on the observed tectonic history in the eastern Timor Sea, will provide a basis for petroleum exploration, including prediction of reservoir, seal, and source rocks.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)