Biostratigraphy of the Cretaceous deposits in the Western Transylvanides from Ampoi Valley (Southern Apuseni Mountains, Romania)

The present study is an approach of the issues related to the biostratigraphy of the Western Transylvanides. The research provided exact age data for the Feneş Formation, Valea lui Paul Formation, Bozeş Formation and Râmeţi Formation. The age of the formations was established based on the calcareous nannoplankton assemblages in Barremian-Campanian range. The lithological features together with the new age data allowed us to modify the boundaries between formations; accordingly the knowledge on the structure of South Apuseni Mountains required changes, too. The new data also imply the modification of the existent geological maps of the region. Based on the identified calcareous nannoplankton assemblages, the following zones were defined: CC6 – Late Barremian, CC9 – Lower Cenomanian, CC14 – Late Coniacian and CC17, CC18, and CC19 for Campanian