Abstract: The Palu Koro Shear Zone, a 1000-Kilometer-Long Zone of Middle Miocene Tectonic Activity in Sulawesi and Eastern Borneo

A. D. Scardina, E. A. Haan, K. A. Maher

The middle Miocene was a period of major tectonic activity for Sulawesi and eastern Borneo. Previous workers have documented the effects of the collision of the Sula and Buton microplates on Sulawesi, the uplift of Borneo, and overthrusting onshore and offshore Sabah.

These tectonic events are thought to be related to motion along a regional shear zone that extends 1000 km from the southeastern limb of Sulawesi to the offshore of northern Sabah. Rangin (1989) originally suggested that the collision of the Sula microcontinent was responsible for the compression that lead to the overthrusting onshore Sabah. Here we present additional evidence of the long-range effects of this collision and its control on the basin development and formation of hydrocarbon-bearing structures.

This shear zone is well defined in central Sulawesi by the presence of the Palu Koro fault. Offshore north of Sulawesi the shear zone becomes more diffuse but the location is thought to extend northeast of the Mangkalihat Peninsula along the eastern edge of the Muara basin. The en echelon plunging folds of the Tarakan basin strongly suggest the presence of a shear zone underlying the younger sedimentary fill. In offshore Sabah, the deep regional unconformity, the Sabah ridge zone of wrench tectonics, and the development of a subregional duplex zone in the fore arc all formed during the middle Miocene and are thought to record the final impression of the Sula and Buton microplates on the Sunda craton.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994