Ostracod assemblages from the uppermost Pliensbachian and Lower Toarcian of the Traras Mountains (Tlemcen Domain, north Algeria)

Abstract

This work presents a taxonomic study of the Upper Pliensbachian-Lower Toarcian ostracods from the Traras Mountains situated in northwestern of Algeria. The ostracod fauna comprises 8 families, 11 genera and 20 species. Important changes in the composition of the ostracod assemblages have been recorded related to the Pliensbachian-Toarcian boundary and the Polymorphum-Levisoni zonal boundary (the biotic crisis related to the Toarcian Oceanic Anoxic Event). This turnover is denoted by the uppermost Pliensbachian assemblages dominated by the families Healdiidae and Cytherellidae to the upper part of Levisoni Zone with the assemblages dominated by the families Protocytheridae and Polycopidae. Ten species of ostracods are recognised for the first time from the Lower Toarcian of the North Gondwana palaeomargin (Bairdia kempfi, Bairdiacypris dorisae, B. triangularis, Ektyphocythere bizoni, Ogmoconcha convexa, Paracypris sp. and Polycope cincinnata). The comparison with other regions (intrafamilial comparison and qualitative comparison) reveals close relationships between the location of the basins and their taxonomic compositions.