ABSTRACT: Geometries and kinematics of inversion tectonics, West Natuna Sea Basin, Indonesia

The West Natuna Sea Basin, Indonesia is an inverted intracratonic rift basin within the Sundaland microplate, bordered by the Indo-Australian Plate to the south and west, by the Eurasian plate to the north and to the east by a collage of microplates that form the eastern Indonesia archipelago. The West Natuna Sea Basin consists of dominantly NE-SW trending grabens and half-grabens that underwent NW-SE extension in the Oligocene and were subsequently inverted in the Late Oligocene through the Mid-Miocene. NW-SE trending transverse graben systems occur in the north and north-western parts of the West Natuna Sea Basin. Large, asymmetric anticlines are formed in the hangingwalls of reactivated planar, domino-style extensional faults. Back-limb dips are gentle whereas the fold front limbs are steep to possibly overturned. Syn-rift strata form characteristic harpoon structures in the inversion anticlines whereas syn-inversion strata display growth geometries on both the back-limbs and front-limbs of the inversion anticlines. Unconformities and onlap structures separate phases of inversion. The post-inversion sequence in some structures overlies the crests of the anticlines and in others is deformed by continued inversion almost to the present day.

Regional and detailed seismic lines were depth converted, interpreted and progressively restored using computer section balancing programs. Amounts of extension, inversion and uplift were calculated for structures within the West Natuna Sea basin. Key structural styles are illustrated and compared with numerical and physical models of inverted fault systems.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia