Polyphase erosion of subaerial omission surfaces in the Late Dinantian of Anglesey, North Wales |
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| Authors: | GORDON WALKDENs JERRY DAVIES† |
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| Institution: | Department of Geology, University of Aberdeen, Aberdeen AB9 1AS;Institute of Geological Sciences, Bryn Eithyn Hall, Aberystwyth, Dyfed SY23 4BY |
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| Abstract: | The Lower Carboniferous of Anglesey consists of bioclastic carbonates and subsidiary terrigenous siliciclastics built as a cyclic succession against the northern flank of the contemporary Welsh landmass. Cycle boundaries are marked by subaerial erosive features that are unlike the normal Late Dinantian palaeokarst association, and one such surface, at Red Wharf Bay, shows remarkable evidence of polyphase erosion indicating at least three distinct periods of karstification and one of fluvial channelling. Each erosive period was succeeded by an interval of lithification during which newly arrived siliciclastic sediment was stabilized. Diagenetic textures in the underlying limestones reveal no evidence of this complex surface history, and seen in cathodoluminescence the earliest pore filling cements evidently post-date the entire emergent episode. The karsts occupy positions adjacent to channels and are attributable to overbank flooding rather than atmospheric weathering. Autocyclic mechanisms may be responsible for the polyphase development but the overall control of sedimentary cyclicity is considered to have been eustatic. |
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