ABSTRACT: Structures and Tectonics of the Sunda and Asri Basins
Coward, Mike1, Dave Carter2,
and Andy Wight2
(1) Ries-Coward Associates Limited, Reading, United Kingdom
(2) YPF Indonesia Limited, Jakarta, Indonesia
The Sunda Basin offshore N Java can be divided into three separate sub-basins with differing structural style and different fault polarities, separated by wide transfer zones. The adjacent Asri Basin appears symmetrical with no major faults, though the early basin-forming faults dip to the E. The structural history involves NW/SE extension with minor pulses of NE/SW shortening. NE/SW trending normal faults are cut by or merge into a conjugate set of shear zones trending approximately ENE/WSW and WNW/ESE. The shortening is accommodated by these shears, together with some reverse oblique movement up the earlier normal faults. Oligocene shales and mudstones acted as decoupling zones during later pulses of extension, so that structures in the basement became soft-linked to structures in the upper part of the sediment fill.
The stratigraphy involves a lower sequence of non-marine Paleogene sediments, reaching a maximum thickness of c 2500 m in the Sunda Basin. They are overlain by thick Neogene late-rift to post-rift sediments. During the first 10-20 Ma of subsidence the basin was filled with terrestrial sediments. Rotated fault blocks indicate that the area had been extended by a factor of c 2-3 before the basin submerged below sea level, suggesting that the land surface may have been at c 3 km above sea level prior to subsidence. The Sumatra-Java landmass therefore formed a high plateau prior to extrusion and extension. The structures formed in response to spreading of the initially thick crust along the length of an actively convergent plate margin.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia