Sedimentology and stratigraphic development of the upper Nyalau Formation (Early Miocene), Sarawak,Malaysia: A mixed wave- and tide-influenced coastal system |
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| Institution: | 1. Guangdong Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China;3. Laboratory of Ocean and Coast Geology, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China;4. Faculty of Science and Natural Resources, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia;5. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;6. School of Earth, Atmosphere and Environment, Monash University, Melbourne, VIC 3800, Australia;1. Technical Services Division, Department of Mineral and Geoscience Malaysia, Jalan Sultan Azlan Shah, P.O. Box 1015, 30820 Ipoh, Perak, Malaysia;2. Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia;3. Geological Laboratory Division, Orogenic Geo-Sample Facilities and Laboratories (OGFL), Lot 6744, Jalan Tekali 1, Kawasan Perindustrian Tekali, 14(½) Miles, Sungai Tekali, 43100 Hulu Langat, Selangor, Malaysia;4. Department of Mineral and Geoscience Malaysia (Sarawak), Jalan Wan Abdul Rahman, Kenyalang Park, P.O. Box 560, 93712 Kuching, Sarawak, Malaysia |
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| Abstract: | This work presents the first detailed facies analysis of the upper Nyalau Formation exposed around Bintulu, Sarawak, Malaysia. The Lower Miocene Nyalau Formation exposures in NW Sarawak represent one of the closest sedimentological outcrop analogues to the age equivalent, hydrocarbon-bearing, offshore deposits of the Balingian Province. Nine types of facies associations are recognised in the Nyalau Formation, which form elements of larger-scale facies successions. Wave-dominated shoreface facies successions display coarsening upward trends from Offshore, into Lower Shoreface and Upper Shoreface Facies Associations. Fluvio-tidal channel facies successions consist of multi-storey stacks of Fluvial-Dominated, Tide-Influenced and Tide-Dominated Channel Facies Associations interbedded with minor Bay and Mangrove Facies Associations. Estuarine bay facies successions are composed of Tidal Bar and Bay Facies Associations with minor Mangrove Facies Associations. Tide-dominated delta facies successions coarsen upward from an Offshore into the Tidal Bar Facies Association. The Nyalau Formation is interpreted as a mixed wave- and tide-influenced coastal depositional system, with an offshore wave-dominated barrier shoreface being incised by laterally migrating tidal channels and offshore migrating tidal bars. Stratigraphic successions in the Nyalau Formation form repetitive high frequency, regressive–transgressive cycles bounded by flooding surfaces, consisting of a basal coarsening upward, wave-dominated shoreface facies succession (representing a prograding barrier shoreface and/or beach-strandplain) which is sharply overlain by fluvio-tidal channel, estuarine bay or tide-dominated delta facies successions (representing more inshore, tide-influenced coastal depositional environments). An erosion surface separates the underlying wave-dominated facies succession from overlying tidal facies successions in each regressive–transgressive cycle. These erosion surfaces are interpreted as unconformities formed when base level fall resulted in deep incision of barrier shorefaces. Inshore, fluvio-tidal successions above the unconformity display upward increase in marine influence and are interpreted as transgressive incised valley fills. |
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