STRUCTURAL STYLES OF THE OFFSHORE WEST SULAWESI FOLD BELT, NORTH MAKASSAR STRAITS, INDONESIA

摘要

The offshore part of the West Sulawesi Fold Belt (WSFB), in the eastern part of the North Makassar Straits, has not been studied in detail until recently because there were few seismic data. New 2D seismic surveys cover most of the North Makassar Straits and permit detailed study of the offshore fold belt. On the basis of new data the area can be divided into three parts: the Southern Structural Province (SSP), Central Structural Province (CSP) and Northern Structural Province (NSP). These provinces are controlled by basement structures and differ in the amount and character of Cenozoic sediment. In the CSP, there is a topographic high (Central High), onlap of sediments from Kalimantan, little sediment building out from West Sulawesi, and the fold-thrust belt extends only a short distance offshore. The Central High separates the SSP and NSP which extend west into deep water. The ,SSP contains a wedge of sediment which tapers gently to the west and contains well-developed thrust propagation folds with a thin-skinned tectonic style. The NSP has a much steeper western front to the sediment wedge, and reflectors within it are chaotic and incoherent, so that the folding and thrusting is less clear. The character of the two wedges suggests that the SSP is sandier; whereas the NSP is mud-rich and may be dominated by mud diapirism. The different deformation styles in the NSP and SSP are influenced not only by the presence of existing structures such as the Central High, and decollement layers, but also by sediment thickness and type. The Palu-Lariang region is the likely source of sediments in the NSP; whereas the Karama-Kalosi region is probably the source for the SSP. Deformation is propagating west from onshore Western Sulawesi andrnbegan in the Pliocene. We suggest the North Makassar Straits are underlain by thinned continental crust.