The petroleum potential of the Indonesian Banda Arc
Consultant, Guildford, United Kingdom.
The Banda forearc is the zone of collision between the northwest passive margin of Australia and the Banda island arc subduction system. Structurally the collision complex is a fold and thrust belt corresponding essentially to the telescoped outer edge of the Australian continental margin. Near-surface structures are complex within a thin-skinned foldbelt, but deeper structural levels involve continental basement, producing large and structurally simple inversion anticlines. Numerous oil and gas seeps attest to an active petroleum system, with oils typed geochemically to Late Triassic restricted marine shales. Potential reservoir rocks include Late Triassic-Middle Jurassic shallow marine sandstones equivalent to the Malita and Plover Formations of the Northwest Shelf, and sealed by thick shales of Early-Middle Jurassic age. These shales (the Wai Luli Formation in Timor) also provide the primary detachment level for the thin-skinned foldbelt, and thus separate tectonic complexity above from simple structuring beneath. The large and structurally simple inversion anticlines are exposed onshore in the interior of Timor island and are increasingly imaged by seismic in the offshore collision complex; but in the current absence of onshore seismic data the locations of subsurface inversion anticlines can be inferred from such features as surface doming of Quaternary reef terraces; on Bouguer gravity anomalies; and on the presence of oil and gas seeps around the margins of the structures, and gas seeps and mud volcanoes over the crests. Simple inversion anticlines (both inferred in the subsurface and seen at exposure) are up to several tens of kilometres long and multi-kilometres wide, and are sufficiently large to potentially contain giant hydrocarbon accumulations.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012