Provenance of the Cretaceous–Eocene Rajang Group submarine fan,Sarawak, Malaysia from light and heavy mineral assemblages and U-Pb zircon geochronology |
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| Institution: | 1. SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, UK;2. Minerals and Geoscience Department Malaysia (JMG) Sarawak, Jalan Wan Abdul Rahman, Kenyalang Park, P.O. Box 560, 93712 Kuching, Sarawak, Malaysia;3. Getech Group plc, Leeds LS8 2LJ, UK;1. SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, UK;2. Minerals and Geoscience Department Malaysia (JMG) Sarawak, Jalan Wan Abdul Rahman, Kenyalang Park, P.O. Box, 560 93712 Kuching, Sarawak, Malaysia;3. Research School of Earth Sciences, The Australian National University, Canberra 2601, Australia;4. Department of Earth Sciences, University College London, London, WC1H 0BT, UK;1. Centre for Tectonics, Resources and Exploration (TRaX), Department of Earth Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia;2. PTTEP, EnCo, Soi 11, GGS, Vibhavadi Rangsit Road, Chatuchak, Bangkok 10900, Thailand;3. Department of Geological Sciences, Chiang Mai University, 239 Huay Kaew Road, Chiang Mai 50200, Thailand;4. Department of Geology, Ghent University, Krijgslaan 281.S8, WE13, Ghent 9000, Belgium;5. Basin Analysis and Structural Evolution Special Task Force for Activating Research (BASE STAR), Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand;6. School of Earth and Planetary Science, John de Laeter Centre, TIGeR, Curtin University, Perth, Western Australia 6102, Australia |
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| Abstract: | The Rajang Group sediments in central Borneo form a very thick deep-water sequence which was deposited in one of the world's largest ancient submarine fans. In Sarawak, the Lupar and Belaga Formations form the Rajang Group, characterised by turbidites and large debris flows, deposited in an interval of at least 30 Ma between the Late Cretaceous (Maastrichtian) and late Middle Eocene. Borneo is one of the few places in SE Asia where sediments of this age are preserved. Heavy mineral assemblages and detrital zircon U-Pb dating permit the Rajang Group to be divided into three units. The Schwaner Mountains area in SW Borneo, and West Borneo and the Malay Tin Belt were the main source regions and the contribution from these source areas varied with time. Unit 1, of Late Cretaceous to Early Eocene age, is characterised by zircon-tourmaline-dominated heavy mineral assemblages derived from both source areas. Unit 2, of Early to Middle Eocene age, has zircon-dominated heavy mineral assemblages, abundant Cretaceous zircons and few Precambrian zircons derived primarily from the Schwaner Mountains. Unit 3, of Middle Eocene age, has zircon-tourmaline-dominated heavy mineral assemblages derived from both sources and reworked sedimentary rocks. There was limited contemporaneous magmatism during deposition of the Rajang Group inconsistent with a subduction arc setting. We suggest the Rajang Group was deposited north of the shelf edge formed by the Lupar Line which was a significant strike-slip fault. |
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