Tidal rhythmites in a mixed-energy, macrotidal estuarine channel, Gomso Bay, west coast of Korea

摘要

Well-developed tidal rhythmites are documented from the intertidal point bar of sinuous tidal channel in Gomso Bay, west coast of Korea. Associated with inclined heterolithic stratification, rhythmites constitute the upper part of fining-upward succession formed by the lateral migration of a point bar. Occurring between mean sea-level and mean high water level, rhythmites commonly overlie rhythmic climbing-ripple crosslaminations. Various rhythmicities are registered in laminae thicknesses, which reflect hierarchical tidal cycles ranging from semidiurnal to monthly tidal cycles. Inferred neap–spring tidal cycle (half-synodic) thins upwardly with a proportionately reduced number of preserved laminae in the cycle. Such vertical organization of rhythmites seems to reflect decreased accommodation space through deposition. Tidal rhythmites exhibit longitudinal variation within fluvial–tidal transition with best developed ones formed in a highly meandering tidal channel, where the influence of offshore waves is minimal due to confined channel morphology that is characterized by low energy level in association with high water turbidity. Comparison of spectral peaks between modern and simulated rhythmites further substantiates that tidal rhythmites can serve as a reliable indicator of paleotide, paleoelevation and paleogeography of mixed energy, tide-dominated estuaries.