Abstract

Well-developed rhythmic climbing-ripple cross-lamination (RCRL) was described from estuarine tidal channels in Gomso Bay, west coast of Korea. Associated with upper intertidal point bars of closely spaced meandering channels, RCRL occurs between mean sea level and mean neap high-water level. RCRL is typically less than 40 cm thick, and constitutes the upper part of fining-upward channel-fill successions that are capped by intensely bioturbated mud. RCRL consists of mud-draped climbing-ripple cross-laminae that are continuous along strike direction of the channel for 10–20 m. Climbing patterns are dominantly supercritical and less commonly subcritical. Flood-oriented RCRL is developed in the landward part of the meander bend, while ebb-oriented RCRL is developed in the seaward part. RCRL demonstrates rhythmic change in cross-lamination thickness, which resembles various hierarchical tidal cycles, such as diurnal inequality, synodic neap–spring tidal cycle, and anomalistic tidal cycle. Truncated tidal rhythmicities registered in RCRL and fine-grained textures are consistent with an upper intertidal origin. Common links of RCRL with inclined heterolithic stratification (IHS) and tight meander bends as well as high sedimentation rate is suggestive that RCRL can serve as a diagnostic indicator of active channel migration in the fluvio-estuarine transition. This study highlights the significance of RCRL bearing well-preserved tidal rhythmicities in the reconstruction of paleodepositional environment, paleoelevation in terms of tidal frame, and paleogeography.

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