08 December 2009

Structures: Folds and Faults in West Kalimantan, Borneo

In West Kalirnantan, the E-W trending fold system is exemplified by the large synclinal structure that involves the Ketungau Basin sediments. It is a symmetrical fold with dips on both flanks around 30 degree. The situation is quite different in the Melawi Basin to the south, were the folding is asymmetric, with a steeply dipping north limb, and the dips decrease to the south. The fold axes extend NWSE. Similar trending folds have also affected Triassic to Cretaceous sedimentary formations to the west of the Melawi Basin.

In the northern part of Kalimantan, a number of thrust and normal faults have been identified trending E-W. The thrust faults may be associated with Late Cretaceous melange formation and were rejuvanated in the Early Miocene. The normal faults were formed after Oligocene time, probably in the Early Miocene.

There are north-trending faults in West Kalimantan, whose nature is ill defined. In Central Jawa, younger faults intersect the Plio-Pleistocene fold axes nearly perpendicularly.

A set of faults in West Kalimantan trends NE-SW, cutting the Cretaceous sediments and Boyan Melange. They are thought to be strikeslip.
 



2 comments:

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