Publications

The possible occurrence of hydrocarbon deposits in complex paleo subduction zones has recently been advanced in various literature.In this connection it is of interest to compare the out- er-arc ridge of western and eastern Indonesia in order to evaluate the hydrocarbon potentials in the chaotic wedges 111 both areas.The arc-trench system in western lndonesia was formed by subduction of the Indian Ocean oceanic crust beneath the Eurasian continental crust. No significant hydrocarbon occurrence was reported in the accretionary wedge of western lndonesia. The fore-arc basin, west of Sumatra, typically lacks the coarse quartz rich sediqents necessary for clastic reservoir formation. The heatflow and hydrocarbon source rocks are immature.The arc-trench system of eastern Indonesia shows an entirely different character. Two distinct phases can be dis- cerned in the development of the Banda Arc. In an earlier phase, oceanic crust of the Indian-Australian plate was subducted under the Banda oceanic plate, and in a later phase followed by subduction of the Australian continental crust'into the Banda Arc subduction zone.Whereas the oceanic crust dipping in the Sumatra-Java Trench is only covered by relatively thin pelagic sediments, large parts of the shelf and slope qquences of the Arafura Platform are carried passively on top of the Australtian lithospheric plate down into the Taniqhar Trench and Aru Through. The-more consolidated lower part of the sequence has a greater shear strerbgth and consequently little tnaterid from thcse sequences was scraped bff and incolporated in the chaotic wedge. If these older sediments are rich in organic materid, the tectonic processes in the trench and beneath the chaotic wedge in '~ombination with increasing burial depth will enhance the maturity of the organic material. If reservoir rocks exist in front of the chaotic wedge, upslope migration and accumulation must be considered as possible within the faulted blocks in these rocks.Due to the similarity in geological, tectonic and stratigraphic conditions, the oil and gas occurrence in the subduction complex of eastern Sulawesi might be explained in the same way, although the basic problem which has to be solved first is the past geotectonic position of Sulawesi vis a vis the Australian continental crust of the Vogelkop area in Irian Jaya.