VARIABILITY OF PALEOGENE SOURCE FACIES OF CIRCUM-SUNDALAND BASINS, WESTERN INDONESIA: TECTONIC, SEDIMENTARY AND GEOCHEMICAL CONSTRAINTS - IMPLICATIONS FOR OIL CHARACTERISTIC

摘要

Tertiary basins encircling Sundaland (circum- Sundaland Basins) of Western Indonesia (North Sumatra, Central Sumatra, South Sumatra, Sunda- Asri, West Java, East Java, Barito, Kutei, West Natuna, East Natuna, South Makassar, West-South Sulawesi Basins) were formed in the Mid-Eocene to Early Oligocene. The basins were formed mostly as tectonic responses due to collision of India to Eurasia, they were formed by: (1) trans-tensional rifting induced by regional post-collision tectonic escape or (2) back arc rifting induced by roll-back movement due to slower rate of Eocene subduction. Thick intervals of Paleogene sediments were deposited in early, middle, and late phases of rifting, as well as early phase of post-rifting of the basins, covering depositional environments ranging from nonmarine, lacustrine, fluvio-deltaic, paralic, marginal- to shallow marine facies. These sediments are important hydrocarbon source rocks in the basins. Few wells or no well penetrated these sources, causing precise interpretation of the source facies is impossible due to the absence of samples for biostratigraphic analyses. However, interpretation of the source facies can be assessed by detailed examination of biomarkers of oils generated from these sources (geochemical inversion). Varied biomarkers are encountered, revealing the variability of their source facies. Characteristic of oils generated are various caused by their various source facies, but the facies variability of each basin is typical and predictable, systematically expressing its tectonic and sedimentary settings on and around the Sundaland.