STRUCTURAL EVOLUTION OF THE NORTHERN BONAPARTE BASEV, NORTHWEST SHELF AUSTRALIA

摘要

The Bonaparte Basin is the northernmost basin on Australia's NW Shelf. The study area lies immediately south of the arc-continent collision in the Timor region. Structural configuration analysis based on time-migrated 3D seismic lines shows three main stages of evolution: (i) Middle Triassic (?) extension produced NNE-SSW trending faults; (ii) Late Jurassic-Early Cretaceous rifting (breakup event) produced E-W to ENE-WSW trending faults; and (iii) Neogene Australia-Banda Arc continental collision in Timor produced NE-SW trending faults. The two Mesozoic events had different extension directions and displacement during Late Jurassic rifting was about half that of the Early Mesozoic extensional phase. Early Mesozoic structures influenced development of the prominent low relief NE-SW trending accommodation zone in the eastern Mesozoic rift graben and also maybe controlled the separation into graben compartments. Australia-Banda Arc continental collision in the Neogene led to the reactivation of the older Mesozoic rift faults, particularly faults that had the largest and longest displacement. As a consequence, conjugate faults developed above narrow horst blocks with hard linkage of older and younger faults in the Cretaceous-Paleocene sequence.Flexure due to Timor loading and also oblique motion along the margin have been proposed as mechanisms responsible for the development of the NE-SW structures with net normal displacement and the reactivation that occurred in the Neogene. Right-stepping en-echelon fault arrays and splay fault development suggest oblique motion during Neogene collision. Neogene reactivation resulted in drowning of car- bonate platform/build-ups near the surface although circular seismic artefacts could indicate hydrocarbon migration/leakage associated with micro-fracture development within fault damage zones.