MESOZOIC AND CAINOZOIC TECTONOSTRATIGRAPHY OF WESTERN ZOCA AND ADJACENT AREAS

Abstract

Increased exploration activity in Area A of the Timor Gap Zone of Cooperation between Australia and Indonesia (ZOCA) has created the need for revision of the existing stratigraphic framework of the region. A chronostratigraphic approach to the analysis of the Mesozoic and Cainozoic succession of Western ZOCA provides a framework for improved stratigraphic prediction. The framework is based on the identification of depositional sequences by the integration of seismic and well data. Genetically related depositional sequences have been grouped into seven 'megasequences' which reflect distinct stages in the tectonic development of the basin.

The Mesozoic and Cainozoic succession in the Northern Bonaparte Basin was deposited in a marginal sag basin that was affected by Triassic to Lower Cretaceous extension related to continental separation along the northwest margin of Australia. Four stages are seen in the evolution of the basin since the end of the Permian. Relative tectonic quiescence during the Triassic preceded two cycles of extension related to continental separation during the Jurassic to Earliest Cretaceous. Continental separation was followed by the development of a Cretaceous/Tertiary passive margin and a subsequent phase of tectonism related to the Miocene/Pliocene collision of the Indo-Australian and Eurasian plates. A tentative correlation has been made between the megasequence framework of Western ZOCA and the geological succession exposed on Timor Island.

The framework forms the basis for a system of common stratigraphic nomenclature for the Timor Gap. The model also assists in understanding the tectono-strati-graphic evolution of the basin and is a foundation for the development of new play concepts that will support continuing exploration activity in the area.