The Petrel Sub-Basin System, Timor Sea, Australia: Rift Architecture and Its Control on Structuring Within the Tertiary Sequence, Timor Sea

G. W. O'Brien, J. Blevin, P. Gunn, K. Romine, D. L. Scott, J. B. Willcox, S. Baldwin

Recent deep crustal seismic and high-resolution aeromagnetic acquisition has allowed the Australian Geological Survey Organisation to determine the areal distribution and architecture of the NW-trending Petrel Sub-Basin rift system. The rift, which probably initially developed as an ~80 km wide intra-cratonic rift in the Early Ordovician, with thick salt depocentres developing within restricted environments, was re-rifted in the Late Devonian-Early Carboniferous. Extreme (150-200 km), NE-SW crustal extension produced four massive half-graben of alternating polarity, which were compartmentalised by 25 km wide, ~NE-trending accommodation zones. Within any individual rift segment, one side was characterised by large displacement, planar normal faults, whereas the opposing ma gin had a ramp geometry. The southernmost two rift compartments were located within the Bonaparte Gulf, whereas the two northerly compartments actually defined the proto-Malita and proto-Vulcan Grabens. Post rift subsidence during the Permo-Triassic then led to the deposition of up to 15 km of unstructured section.

Mesozoic structuring in the Timor Sea took place almost exclusively via the reactivation of the Petrel rift (normal and accommodation) faults. Latest Triassic tectonic inversion of the Petrel rift architecture defined the Cartier Trough and the Sahul Platform, and produced large structures such as the Tern and Petrel gas fields. In contrast, extensional reactivation of the rift architecture during the Jurassic produced many grabens which were critical to source rock deposition. Similarly, Mesozoic salt diapirism was restricted to the axis of the Early Ordovician intra-cratonic rift, and was localised by the major Late Devonian rift faults.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995