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 Kamci ja Group in the Stara Planina Mts., especially in the distal and meso-dista l flysch of the Sini Vir Formation (Pliensbachian - Lower Toarcian). A much less diverse ichnoassemblage occurs in the overlying proximal flysch of th e Balaban Formation (Upper Toarcian), and in dark shales with rare turbidit es and olistoliths of the uppermost Kotel Formation (Aalenian-Middle Bathon ian). Generally, there is no increase in ichnodiversity in the Lower Jurass ic in compared to the Upper Palaeozoic, but ichnodiversity is distinctly lo wer than in the Upper Cretaceous-Tertiary.