Autogenic occurrence of Glossifungites Ichnofacies: Examples from wave-dominated, macrotidal flats, southwestern coast of Korea

Abstract

Firmground muds are frequently exposed on the high-tide beach face in the zone of maximum wave energy on the wave-dominated tidal flats along the southwestern coast of Korea. The firmground muds typically display open, unlined burrows, dominated by incipient Psilonichnus and Thalassinoides that cross-cut the earlier-formed softground suites, which comprise Skolithos, Arenicolites and Monocraterion. Modern faunal distributions confirm that these ichnogenera are constructed in sediments of different consistency at the time of colonization as a result of autogenic swash-bar migration. By considering the migration-rate of the intertidal swash bars, it can be shown that the mud only needs to be buried as little as 0.5 m for a few years to produce the firmground muds. These numbers for burial depth and duration are much less than is commonly realized. The results of this research, combined with previous studies, suggest that the Glossifungites Ichnofacies is environmentally wide-ranging from tide-dominated to wave-dominated settings. This study also confirms that the Glossifungites Ichnofacies is mainly associated with erosion in marginal-marine settings and can thereby be deployed as a stratigraphic indicator of hiatal surfaces. However, the stratigraphic importance of Glossifungites-demarcated discontinuities must be assessed carefully to determine whether or not allogenic or autogenic processes contributed to their emplacement.