Short distance variability of trace fossils in submarine slope and proximal basin plain deposits: a case study from the Ceylan Formation (upper Eocene), Gelibolu Peninsula, NW Turkey

The Ceylan Formation (upper Eocene) from the Thrace Basin (Gelibolu Peninsula, NW Turkey), is composed of pelagic shales, marls, clayey limestones, turbiditic sandstone-shale beds and local conglomerates, debris flow mixtites, slumped deposits and silicified tuffites. These deposits, which are about 1000 m thick, generally shallow upwards, show vertical and lateral changes according to their accumulation on different parts of a submarine slope, with a transition to the proximal basin plain. The variability is also expressed in the trace fossil content (33 ichnotaxa, 26 ichnogenera). The fine-grained background sediments are totally bioturbated and they show an ichnofabric with Trichichnus, Chondrites, Planolites and small Thalassinoides. Generally, abundance and diversity of trace fossils increase with frequency of sandstone intercalations, probably because of higher and more variable food content and higher preservational potential. Turbiditic sandstones of the proximal basin plain contain abundant graphoglyptids (Paleodictyon, Helminthorhaphe, Urohelminthoida, Desmograpton, Belorhaphe, Helicolithus). Continuous reworking of background sediments points to a good or moderate oxygenation of pore waters. The trace fossil assemblage of fine-grained pelagic sediments with isolated sandstone beds can be ascribed to the Zoophycos ichnofacies sensu lato, but some ichnotaxa typical of turbiditic sediments (e.g., Ophiomorpha annulata) can be present in isolated sandstone beds. Series of turbiditic sandstones with abundant graphoglyptids are typical of the Paleodictyon ichnosubfacies of the Nereites ichnofacies. Turbiditic series in the upper slope setting contain much fewer graphoglyptids. The absence of graphoglyptids in isolated sandstone beds shows that their occurrence is not only a matter of taphonomy (scouring and casting) but also is related to the presence of more frequent turbidites modifying the substrat