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Factors Controlling the Morphodynamics of Macrotidal Channels in Korea: Implications on the Facies and Stratigraphic Architecture of Inclined Heterolithic Stratification (IHS) formed in the Tidal-Fluvial Transition


Extensive Korean tidal flats are heavily incised by dendritic intertidal channels of various sizes ranging from 10-600 m in width and 1-10 m in depth. The channels migrate actively in response to monsoon-driven discharge fluctuation as well as strong tidal currents. Channel migration is pronounced during summertime monsoonal high-discharge events, which triggered downstream translation of meander bend, meander-bend cutoff and subsequent infilling of abandoned channels. Point-bar geometry alternates between a concave-up profile in summertime and a convex-up profile during the rest of year. Such seasonal morphodynamic responses are linked with the intensity and the timing of precipitation. Heavy precipitation during low tides results in severe rill erosion on the exposed channel bank, creating a concave-up point-bar geometry. Overall ebb-dominance in the channels produces ebbwardly dipping inclined heterolithic stratification (IHS). Sinuous channel planform and mutually evasive tidal current facilitate preferential preservation of bedforms formed by subordinate (flood) current, giving rise to counterintuitive relationship between ebb-oriented IHS and flood-oriented bedforms. The relationship tends to be less distinct toward either tide-dominated area with straight channel or river-dominated area with weak flood current, and deeper part in the channel where flow is confined. Rain-induced rill erosion and wind-induced waves further complicate the IHS architecture especially in the distal location by generating bank-normal and bank-parallel discontinuity, respectively. Present study suggests that climate-driven high-discharge events control the IHS architecture regardless of tidal range and relative position in the tidal-fluvial transition. Careful examination of the IHS architecture may hint at the depositional setting in terms of tidal frame (intertidal versus subtidal), climate regime (monsoonal versus non-monsoonal) and relative position (proximal versus distal).