Controls on peat accumulation in the Permian Vryheid Formation in a part of northern Natal,South Africa |
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| Institution: | 1. Department of Neurology, Stroke Division, Beth Israel Deaconess Medical Center, Boston, MA, United States;2. Harvard Medical School, Boston, MA, United States;3. Department of Biostatistics, Boston University School of Public Health, Boston, MA, United States;4. Department of Neuroscience, MUSC Stroke Center, Medical University of South Carolina, Charleston, SC, United States;5. Department of Neurology, University of Kentucky Medical Center, Lexington, KY, United States;6. Department of Medicine, Division of General Medicine and Primary Care, Beth Israel Deaconess Medical Center, Boston, MA, United States;1. Key Laboratory for Thermal Science and Power Engineering of the Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China;2. Datang International Power Generation co., LTD High Alumina Coal Resources Development and Utilization R&D Center, Ordos 017100, China |
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| Abstract: | The early Permian Vryheid Formation is a fluviodeltaic tongue of sediment deposited on the passive northern margin of an asymmetric, intracontinental linear trough (Karoo basin). In the study area these strata attain a maximum thickness of about 270 m, comprising three informal lithostratigraphic members (Lower zone, Coal zone and Upper zone).The Coal zone is characterized by arkosic, coarse to very coarse, pebbly sandstones and subordinate fines arranged in upward-fining sequences, many of which are coal-capped. These units are interpreted as distal outwash fan deposits.Sedimentation patterns in the Upper and Lower zones are dominated by superimposed upward-coarsening sequences representing repeated wave/fluvially-dominated fan delta progradation.Peat accumulation in the cool, seasonal climate which prevailed during Vryheid Formation sedimentation was slow. Significant peat thicknesses were deposited only in areas of low basin/compaction subsidence in the Coal zone during a period of general stability. Extensive upper delta plain and alluvial plain peats formed on broad platforms created by abandonment of braided channel systems. The thickest peats accumulated in raised swamps where vegetation-stabilized contemporaneous channels promoted a high water table. Peat erosion by later channel activity was slight since channel widening rather than stream-bed erosion prevailed. Coals thin, split and contain more ash near loci of contemporaneous channel activity. Upper delta plain coals were not marine-influenced. Some lower delta plain coals also formed on broad abandoned deltas and are likewise extensive. Rapid compaction subsidence rates attracted channel activity or marine incursions and the seams are thin. Peats also accumulated in restricted emergent interdistributory bays during delta construction. These coals are thin, discontinuous, marine-influenced and contain numerous clastic partings. |
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