Abstract

Through the integration of well data, offshore seismic, published literature, and newly acquired surface geologic data, new insights into the geologic history of the eastern portion of Timor Island have been gained. These data reveal a geologic history somewhat different from previously published interpretations. Regional balanced and restored cross sections illustrate this history.

From latest Permian through earliest Cretaceous, the area experienced rifting. Shallow water sediments were initially deposited, but the region quickly subsided to bathyal depths by Triassic time. From Early Cretaceous to Early Eocene, the area was a passive margin undergoing thermal subsidence wherein deep water carbonates and shales were deposited. In mid-Eocene the area experienced thrusting as the Australian continent initially collided with a subduction zone. This produced both basement-involved and detached folds and thrusts. Large, far-traveled thrust sheets composed of ophiolites and continental crystalline basement were emplaced over Mesozoic sediments at this time. This induced generation of hydrocarbons from lean Triassic shales beneath the large thrust sheets and established shallow water conditions once more. Sediments eroded from these thrust sheets were deposited in a proposed foredeep basin to the south.

From Late Eocene to Late Miocene, Timor was a tectonically quiescent area undergoing slow subsidence and shallow water carbonate deposition. A second pulse of thrusting occurred from latest Miocene to present day. Pre-existing onshore structures were reactivated and uplifted over 1000 meters as new thrust sheets developed offshore along the leading southern edge of the belt. The offshore thrust sheets were buried by thick, shaly Plio-Pleistocene sediments as they developed.

Areas with the highest hydrocarbon potential lie within and immediately adjacent to the thick, offshore Plio-Pleistocene sub-basins, which may have experienced more recent hydrocarbon generation. However, the lack of data and poor seismic imaging make this potential very high risk and uncertain.