Late Cenozoic palaeogeography of Sulawesi, Indonesia

Abstract

Sulawesi has a remarkable biodiversity, an unusually rich endemic fauna, and is the largest island in Wallacea, just west of the Wallace Line. Alfred Russel Wallace himself suggested it could perhaps be the most remarkable island on the globe because of its peculiar fauna. It was home to extinct fossil fauna such as dwarf proboscideans, records significant Pleistocene faunal turnover, and evidence of early human occupation suggests an important role in hominid migration through the Sunda-Sahul region. Information on Neogene palaeogeography is essential for understanding biogeographic patterns, biodiversity and faunal changes. New palaeogeographic maps reflecting recent work on Sulawesi's complex geology and changes in tectonic interpretations are presented for intervals from the Early Miocene to Pleistocene, at 20, 15, 10, 8, 6, 5, 4, 3, 2, and 1Ma. Additional maps illustrate the effects of glacially-driven sea level change in the last 1Myr. They are based on a field-based investigation of sedimentary rocks in Sulawesi, accompanied by palaeontological, petrological and heavy mineral studies and U-Pb dating of detrital zircons, to date and determine depositional environments. The new results have been supplemented by re-evaluation of previous studies, including reports from oil company wells and seismic lines. Igneous rocks provided ages, indications of surface environment of eruptions, and location of magmatic activity. For most of the Neogene from the Early Miocene Sulawesi was a shallow marine area with a number of small islands, surrounded by relatively deep marine areas. Deep inter-arm bays began to form in the Late Miocene and the islands became larger. The most significant palaeogeographic change began in the Pliocene with an increase in the area and elevation of land accompanied by major subsidence of the inter-arm bays. The separate islands gradually coalesced in the Pleistocene to form the distinctive K-shaped island known today.