COMPLEX MODIFIED THRUST SYSTEMS ALONG THE SOUTHERN MARGIN OF EAST TIMOR

Abstract

Seismic structural interpretation of data across three basins along the southern coast of East Timor (the Suai, Beaco and Aliambata basins) reveals a complex deformation history dominated by intense thrust deformation within the thick (>3 km) Plio-Pleistocene sequence.

Our interpreted deformation sequence of the clay-dominated rocks includes a series of south-directed, low-angle thrusts creating extensive thrust piles, and in places, antiformal stacks. These thickened piles exhibit later modification by crestal collapse. Rapid thickening destabilised the growing thrust packages, and caused regional-scale slumping of material into the Timor Trough to the south. The slumping disrupted thrust fronts and caused significant offset at the sea floor. Finally, shale injection and diapirism along the slump faults re-elevated some of the hanging-walls of the slumps.

Oil and gas seeps, which occur mainly in southern East Timor, follow structural trends parallel to those offshore. Although sourced from proposed Triassic source rocks, uplift, exposure and subsequent leakage from these seeps probably occurred within the last 2 Ma, and possibly even later, co-eval with Plio-Pleistocene deformation. The proximity of oil seeps to fold and thrust deformation raises the possibility that additional Triassic or other Mesozoic section may occur at various structural levels within the deformed sedimentary wedge.