Systematics of Middle Eocene Marine Mollusca and their assemblages from the Kocacay Formation in the Cankiri-Corum Basin, Turkiye

Molluscs are significant indicators for paleoenvironmental reconstructions in time and space. During the Eocene period, morphological characteristics of various mollusc assemblages are a clue to paleoenvironmental interpretations. The cankm-corum Paleogene basin in the central Anatolia includes thick beds of marine carbonate rocks with numerous Gastropoda and Bivalvia. Thirty-five species of gastropods and twenty-six species of bivalves were determined from the middle Eocene (Lutetian-?Bartonian) limestone and marly levels of the Kocacay Formation. In the studied areas, four Abundance Biozones namely Ostrea roncaensis, Velates perversus, Miltha gigantean and Pycnodonte gigantica and three Community Biozones, Ostrea roncaensis-Campanile incomptum, Pycnodonte gigantic-Crassatella gigantica, Amaurellina spirata-Globularia sigaretina have been identified. During the middle Eocene time, mollusc fauna indicates deltaic to shallow marine paleoenvironments in the northern part of the basin (Bayat, corum), lagoon in the western part (Sulakyurt, Kmkkale) and the centre of the basin (Sungurlu, corum) and shallow marine conditions in the southern part (cicekdagi, Kirsehir). The described fauna is endemic to the Mesogen or Tethys geography, spreading from the Iberian Peninsula in the west to the island of Java in the east and from Crimea in the north to Central Africa in the south.