Publications

The key structural event and the primary control on hydrocarbon prospectivity in western Indonesia is a major phase of rifting that occurred during the Paleogene. In southeastern Sundaland (Java, SE Kalimantan and the eastern Java Sea) Paleogene grabens are oriented predominantly NNE-SSW at the present day, markedly oblique to present and inferred palaeo-plate boundaries. Existing regional plate tectonic reconstructions for the Paleogene do not adequately account for this major phase of rifting. Eastern Java is a Gondwanan-affinity terrane (Smyth et al., 2005, 2007) which together with SE Kalimantan and the eastern Java Sea comprises a coherent continental fragment (the East Java Terrane) which based on the JavaSPAN deep seismic survey shows convincing correlation to the Arafura margin in eastern Indonesia (Granath et al., 2010). The East Java Terrane was already attached to western Sundaland prior to the Paleogene regional rifting, and has been interpreted as detaching from Australia during the Late Jurassic-Early Cretaceous, and colliding with western Sundaland during the mid Cretaceous. However, regional seismic data and onshore geology fail to demonstrate convincingly a Cretaceous collisional suture between southeastern and western Sundaland: the usually quoted ‘Meratus suture’ is volumetrically insufficient to represent an entire arc-continent collision complex. A contemporaneous phase of major rifting is also interpreted in Timor (eastern Indonesian geological region) during the Paleogene. Palaeomagnetic data from eastern Indonesia may furthermore suggest that during the later Mesozoic and Paleogene Australia was located substantially further north than has usually been interpreted. An alternative ‘working hypothesis’ might suggest that northern Gondwanaland/Australia lay immediately south of Sundaland during the Triassic, but began to separate as Australia moved southward during the Jurassic, with the opening of the Indian Ocean. Gondwanan terranes on the southern margin of Sundaland (East Java, Woyla, West Burma) may be continental fragments ‘left behind’ as Australia moved southward. However, the Mesozoic Indian Ocean may have opened essentially about a pole of rotation located in the region of present-day eastern Indonesia, so that eastern Sundaland (the East Java Terrane) remained located within the Banda Embayment until final separation by rifting in the Paleogene.