Ichnological features of a marine transgression: Middle Miocene rocky shores of Tarragona, Spain

Bioerosion traces from six rocky shore localities in the Miocene Tarragona basin are described. The bioerosion affects Jurassic and Miocene carbonate substrates. The ichnotaxa include borings produced by bivalves (Gastrochaen olites and Phryxichnus), sponges (Entobia), annelids (Maeandropolydora) and sipunculids (Trypanites). Phryxichnus is recorded for the first time in th e Miocene. Trace fossil assemblages, although slightly different among loca lities, can be tipified as a Gastrochaenolites-Entobia assemblage which is typical of Neogene rocky shores and belongs to the Entobia Ichnofacies whic h characterizes littoral rockground environments since the Jurassic. Boring s affect both the rocky substrate and the associated conglomeratic deposits . The assemblages found on wave-cut platforms are composite assemblages res ulting from the overprinting of successive ichnocenoses that replace each o ther during a transgression. The assemblages found in the conglomerates rep resent less mature communities due to clast instability produced by physica l disturbance characteristic of a littoral environment. The rocky shores de scribed in this paper were originated during a single transgressive event t hat took place during the Langhian-Serravalian (Middle Miocene) and the sur face that can be drawn correlating the sites constitutes the base of the Ta rragona Depositional Sequence. (C) Editions scientifiques et medicales Else vier SAS.