Evolution of Cenozoic Inversion Structures, East Java Sea, Indonesia

Peter A. Emmet and Albert W. Bally

A detailed structural and stratigraphic study of a deep water (>200 m) sub-basin in the East Java Sea utilized 2-D seismic and well log data in the vicinity of four Amoco wildcats drilled in the early 1980's. A pelitic basement was deformed in an accretionary prism during the Cretaceous and uplifted and peneplained during the early Tertiary. Extensional half-grabens trending ENE with respect to present geography formed in the Sunda back-arc during the middle Eocene to early Oligocene. The basin-bounding faults are highly listric and are inferred to sole into a sub- horizontal detachment at a depth of less than 10 km. The location and orientation of the extensional structures was strongly controlled by preexisting thrusts and shaly bedding planes within basement. Isochron maps show Eocene rifting to be localized in a few deep basins, and Oligocene rifting to be more broadly distributed in shallower basins.

Inversion began during the early Miocene as listric basin-bounding faults were reactivated in a compressional mode and graben-filling sediments were displaced towards adjacent horst blocks. Most inversions trend ENE with respect to present geography and have grown in bathyal water depths by differential subsidence due to tectonic loading of paleo- horst blocks. Inversion progressed throughout the Miocene and culminated in the development of a regional basement-involved inversion high (eastern extension of Kangean high) which was uplifted and truncated in the latest Miocene. Despite regional compression which continues today at a deep structural level, small-displacement domino-style normal faults are ubiquitous at a shallow structural level and apparently form on the flanks of the groving inversions by a gravity sliding mechanism.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California