Abstract

The Lariang and Karama regions of western Sulawesi, an area of approximately 10 000 km2, were the subject of a field-based investigation with the aim of understanding the Cenozoic evolution of the North Makassar Basin. Western Sulawesi was influenced by the development of the Makassar Straits to the west and the collision of continental, ophiolitic and island-arc fragments to the east. The timing of these events has been the subject of considerable debate and it has been suggested that Neogene collisions in Sulawesi caused inversion in Borneo. A new stratigraphy for the Lariang and Karama regions of western Sulawesi, based on fieldwork, provides new and significant insights into the evolution of the Makassar Straits region. The oldest sediments are non-marine and could be as old as Paleocene; they include coals, sandstones and mudstones. Rifting had started by the Middle Eocene and continued into the Late Eocene. Syn-rift Eocene sediments were deposited in graben and half-graben in both marine and marginal marine environments. The Eocene Makassar Straits rift was highly asymmetrical; the Kalimantan margin was approximately twice the width of the Sulawesi margin. Thermal subsidence had started by the latest Eocene and by the end of the Oligocene most of western Sulawesi was an area of post-rift shelf carbonate and mudstone deposition. This shallow-marine depositional environment persisted throughout the Early Miocene and, in places, until the Middle or Late Miocene. In the Pliocene the character of sedimentation changed significantly. Uplift and erosion was followed by the deposition of coarse clastics derived from an orogenic belt to the east of the study area. The Palaeogene half-graben were inverted, there was localized detachment folding and the overlying Neogene section was folded, faulted and eroded in places. Contractional deformation in western Sulawesi dates from the Pliocene, whereas in eastern Kalimantan it dates from the Early Miocene.

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