Trace fossils from the normal delta deposits in the third member of the Shahejie Formation in the Dongpu depression and their significance

The trace fossils from the third member of the Palaeogene Shahejie Formation in the Dongpu depression are divided, on the basis of core observation and trace fossil identification, into 10 genera and 15 species, including Skolithos vertivalis, Skolithos linearis, Skolithos isp. and Palaeophycus tubularis, Palaeophycus isp., Planolites montanus, Planolites beverlegensis, Planolites isp., Mermoides isp., Taenidium isp., Teichichnus isp., Helminthoidichnites tenuis, Helminthopsis isp., Beaconites isp., and Thalassinoides isp. According to lithology, sedimentary structures, and the types and distribution of the trace fossils, the normal delta front subfacies and prodelta subfacies are separated in the third member of the Palaeogene Shahejie Formation. Two trace fossil assemblages are also recognized, including the Palaeophycus-Planolites and Planolites-Helminthoidichnites trace fossil assemblages which have reflected different sedimentary environments and water depths in the study area.