Marginate Acritarchs from the Lower Cambrian of the East European Platform: A New Perspective on Their Classification

The classification of Lower Cambrian marginate acritarchs of the East European Platform is revised. Based on a study of extensive material from the type locality in Estonia (Narva-68 Borehole, Lontova
Formation), supplemented by data from the Leningrad Region (Sablino-1 Borehole, Siverskaya Formation), it is shown that the species Leiomarginata simplex, Granomarginata prima, and Annulum squamaceum described in the literature form a continuous range of variability and are probably developmental stages of a single taxon, Granomarginata. Following the emended diagnosis of the genus, an expanded description of its type species G. prima Naumova emend. Raevskaya, Golubkova et Kushim is provided. Separate vesicles (predominant), as well as colonies of 2, 4, 6, and more forms, are found. This taxon is a characteristic representative of the Rovno and Lontova oryctocenoses of the East European Platform and serves as an index taxon for the eponymous regional stages.