Upper Maeotian-Lower Pontian "Transitional Strata" in the Taman Peninsula: stratigraphic position and paleogeographic interpretation

Three sections (Taman, Popov Kamen, and Zheleznyi Rog) of the Upper Maeotian-Lower Pontian sediments of the Taman Peninsula (Eastern Paratethys) have been studied. The sequences represent continuous successions of the Maeotian and Pontian sediments. The transitional Upper Maeotian-Lower Pontian relatively deep-water sediments were formed at the time when Eastern Paratethys was connected with other marine basins. The facies are represented by thin clay layers interbedded with laminated diatomites and contain unusual diatom and nannofossil associations. The small size of coccoliths and the absence of zonal markers indicate that the influx of marine waters took place in the stressed conditions of a restricted basin. Diatom assemblages are more diverse and include the open-marine species Azpeitia aff. komurae and Thalassiosira maruyamica and marine endemics Actinocyclus aff. paradoxus, Rhizosolenia bezrukovii, Hemiaulus sp., Nitzschia miocenica of the tropical Nitzschia miocenica Zone and — the index species of next Thalassiosira convexa Zone appear in these part of the sections. Three stages of the Mediterranean marine invasion are distinguished; during the first one the connection between basins was rather permanent, for the two others its character became pulsing and not stable. The possible duration of the invasion is estimated from 6.4 to 6.1 Ma and belongs to the Early Messinian — to pre-evaporate deposits and lower part of lower evaporate deposits.