Publications

Collision between an Australian continental promontory, the Sula Spur, and the SE Asian margin North Sulawesi volcanic arc began in the Early Miocene. Over the past century, poorly-dated Neogene sediments that unconformably overlie pre-Neogene rocks were assigned to the Celebes Molasse, and were commonly interpreted as the result of this collision. The Celebes Molasse was often considered to be of similar age and lithology across Sulawesi. However, new data from fieldwork and laboratory work with mineralogical, palaeontological and zircon geochronological analyses in this project have shown that Celebes Molasse sediments have significant variations in timing of deposition and composition. We present a revised Neogene stratigraphy for Sulawesi based on these new observations and synthesis of previous studies including some offshore data from wells providing, for the first time, a detailed picture of the island’s Late Cenozoic evolution. Regionally, the Neogene stratigraphy of Sulawesi can be divided into Lower Miocene, Middle to Upper Miocene, Pliocene, and Lower and Upper Pleistocene mega-sequences that are separated by five regional unconformities at (1) Early Miocene (c. 23Ma), (2) Middle Miocene (c. 15Ma), (3) Latest Miocene-Earliest Pliocene (c. 6-5.3Ma), (4) Early (c. 1.8 Ma), and (5) Middle Pleistocene (c. 1 Ma). A Middle Pliocene unconformity was observed in some areas of northern Sulawesi and separates Lower and Upper Pliocene sequences. Ten palaeogeographic maps are presented for intervals from the Early Miocene to Pleistocene at 20, 15, 10, 8, 6, 5, 4, 3, 2, and 1 Ma to give a better understanding of the complex geology and new insights into the similarities and differences between different formations included in the Celebes Molasse. The Neogene sediments were deposited in various depositional environments from terrestrial to deep marine and reflect hinterland-to-basin sediment-routing systems. This study also reveals the importance of extension-related uplift and subsidence in the Neogene following the Early Miocene collision.