Wave-generated tidal bundles as an indicator of wave-dominated tidal flats

摘要

Detailed observations of the intertidal deposits from two open-coast tidal flats (the Baeksu tidal flat, Korea, and Parksville Bay, Canada) suggest that wave-generated tidal bundles are created by the interaction of tidal currents and waves on the tidal flats. A complete wave bundle is composed of three distinctive rippled intervals: (1) a basal interval consisting of landward-dipping, ripple cross lamination that is formed in response to a combined-flow regime during rising tide; (2) a middle interval with symmetrical buildup of wave-ripple cross lamination that is deposited during high tide when currents are weak and oscillatory motion is dominant; and (3) a top interval having seaward-dipping, ripple cross lamination that is formed as a result of a combined-flow regime during falling tide. The formation of such wave bundles results from the interaction of waves and reversing tidal currents over a single tidal cycle. Therefore, the presence of wave bundles indicates a very specific depositional environment—an area with significant tides, weak tidal currents and considerable wave energy. The finding of such structures may indicate the presence of open-coast tidal flats (i.e., wave-dominated tidal flats) in ancient deposits.