Impact of lithospheric flexure on the evolution of shallow faults in the Timor foreland system

Abstract

Re-evaluation of structural evolution on the Laminaria High (Timor Sea, Australia), shows that lithosphere flexure, associated with the Tertiary collision between the Australian north-west margin and the Banda volcanic arc, is an important mechanism for Neogene fault development and the reactivation of Jurassic structures. 2D elastic models of the lithosphere flexure show that increasing flexural extension is likely to affect the Laminaria High from the Late Miocene onwards. The evaluation of the Neogene fault slip history, based on instantaneous throw estimates, suggests an initiation of faulting during the Late Miocene when the Laminaria High entered the flexed area (forebulge). Increasing fault growth is recorded during the Pliocene and correlates with the Laminaria High reaching the hinge of the forebulge structure. Maximum episodes of fault growth are recorded between the Late Pliocene and Early Pleistocene when the Laminaria High was located near the forebulge hinge or in the slope where curvature and flexural stress are likely to be maximal. NNW extension associated with plate flexure allowed the oblique extensional reactivation of buried reservoir-bounding Jurassic structures. The orientation of the Jurassic structures relative to the flexural extensional front appears as a key factor controlling the type of segment linkage between the reactivated Jurassic faults and the newly developed Neogene faults. Observations from the Laminaria High suggest that with an angle > 20° between σ Hmax and strike orientation of the Jurassic faults, soft-linkage is likely to occur between Jurassic and Neogene segments. An angle < 20° is more likely to trigger hard-linkages between these segments. The development of continuous fault zones results in a higher up-fault migration risk for hydrocarbon leaking from fault-bounded reservoirs.