Lower and Middle Jurassic flysch trace fossils from the eastern Stara Planina Mountains, Bulgaria: A contribution to the evolution of mesozoic ichnodiversity

The most diverse Lower-Middle Jurassic flysch trace fossil assemblage known so far (Nereites ichnofacies with 15 ichnogenera) occurs in the Luda Kamcija Group in the Stara Planina Mts., especially in the distal and meso-distal flysch of the Sini Vir Formation (Pliensbachian - Lower Toarcian). A much less diverse ichnoassemblage occurs in the overlying proximal flysch of the Balaban Formation (Upper Toarcian), and in dark shales with rare turbidites and olistoliths of the uppermost Kotel Formation (Aalenian-Middle Bathonian). Generally, there is no increase in ichnodiversity in the Lower Jurassic in compared to the Upper Palaeozoic, but ichnodiversity is distinctly lower than in the Upper Cretaceous-Tertiary.