Selective colonization after storm events in a delta environment: applied ichnology from the early Miocene of Taiwan

The sedimentological and palaeoecological interpretation of early Miocene age shallow marine deposits from one of the most emblematic geological areas of Taiwan-Yehliu peninsula is not easy to approach in detail, and several contrasting proposals can be found in the literature. The present ichnological study helps to corroborate a delta environment as the most likely palaeoenvironmental setting, and to recognize the different sub-environments and hydrodynamic processes involved. The distal delta front displays the greatest trace fossil diversity, assigned to the Cruziana ichnofacies, including Ophiomorpha, Phycosiphon, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Thalassinoides and vertical equilibrium adjustment structures. The delta front records predominantly vertical traces attributable to the Skolithos ichnofacies. Amalgamated shell beds (most likely related to storm events) show concentrations of broken bivalve shells. After storm a selective colonization is interpreted, firstly by bioerosive tracemakers during times of decreasing sedimentation rate, followed by a dominance of trophic generalists such as those producing Ophiomorpha during post-storm sedimentation.