Abstract: A section approximately 30 m thick in the uppermost part of the deltaic lower Pleistocene Tursi Sandstone at Rabatana has been analyzed. It contains Bichordites monastiriensis, rare Macaronichnus segregatis, and very rare Rosselia socialis (Bichordites ichnoassemblage) in the lower part, and abundant B. monastiriensis and R. socialis, and rare M. segregatis ( Bichordites-Rosselia ichnoassemblage), in the upper part. Ichnofabric and sedimentologic features indicate upper- to middle-shoreface conditions in the lower part of the section, decreasing in energy up section to lower-shoreface conditions. The Bichordites ichnoassemblage is related to unstable conditions on the sea floor, which favored infaunal colonization by vagile irregular echinoids. The Bichordites-Rosselia ichnoassemblage is related to more stable conditions in a probably deeper and / or protected environment, and to clearer waters in a declining deltaic system. Under such conditions, colonization by sedentary ?terebelloid tracemakers of R. socialis, which fed on the sea floor, was possible. The low trace-fossil diversity is related to intense bioturbation by echinoids, which prevented colonization by other tracemakers, except for the Rosselia tracemakers.

Abstract The Phanerozoic diversity of deep-sea trace fossils, based on 151 flysch formations, displays distinct, non-linear changes through the Phanerozoic, with peaks in the Ordovician-Early Silurian and Early Carboniferous, lowered in the Permian-older Late Jurassic, a peak in the Tithonian-Aptian, lowered in the Albian, and the maximum in the Eocene. The contribution of graphoglyptids in trace fossil assemblages rises gradually up to the end of the Cretaceous, shows a peak in the Palaeocene-Eocene but a depression in the Oligocene. All the changes were probably influenced by competition for food and food supply, bottom water temperatures and oxygenation, and frequency of flysch habitats. There is no clear influence of major biotic crises (Ordovician/Silurian, Cretaceous/Tertiary, Palaeo-cene/Eocene) on the diversity of deep trace fossils, except the Eocene/Oligocene crisis.