Sedimentological and ichnological characteristics on macrotidal Baeksu tidal shoreface, southwestern coast of Korea

Abstract

Integrated sedimentologic and ichnologic studies along the Baeksu coast of southwestern Korea have revealed that despite the macrotidal conditions, the morphologic characteristics and preserved deposits of the intertidal flats show strong similarities to those commonly reported from wave-dominated shorefaces. Morphologically, a beachface is developed near the high-tide level, which is backed by the high-tide mud flat and fronted by the extensive intertidal shoreface (sensu Dashtgard et al., 2021), where wave-formed swash bars are present. Although sedimentation is strongly influenced by seasonal winds and waves, the preserved deposits conspicuously comprise abundant storm beds that consist mainly of wave-rippled and hummocky cross-stratified sands, because summer muds are typically ephemeral. The storm beds, which are predominant and thick near the low-tide line, become thinner in a landward direction, due to the progressive dissipation of wave-energy by bottom friction. Such physical processes, exerted on tidal-shoreface sedimentation, are also reflected in the ichnofacies distribution, showing that distal expressions of the Skolithos Ichnofacies characterize the lower intertidal zone and are replaced landward by proximal expressions of the Cruziana Ichnofacies. Except for the low-BI beachface (BI 0–1), the intensities of bioturbation generally increase in a landward direction (BI 0–1 to BI 3–4), in correspondence with the physical-energy distribution.The study area reveals that the sedimentological and ichnological characteristics commonly employed to recognize wave-dominated shoreface settings (even including high-wave-energy tidal-shoreface counterparts) apparently show a reverse trend within the intertidal shoreface, probably overlying the normal-trend, subtidal shoreface. Although these findings have not been broadly tested, we, however, believe that these features are representative of the low-energy end of the full spectrum of wave-dominated coastal settings.