Calcareous nannofossil biostratigraphy of the Coniacian/Santonian boundary interval in Romania and comparison with other European regions

Abstract

The Upper Coniacian–Lower Santonian marine sediments of two sections in the Romanian Carpathians were investigated for their calcareous nannofossil content. These sections were previously dated based on macro- and microfaunal assemblages. The first occurrence (FO) of the inoceramid species Platyceramus undulatoplicatus, the primary marker for the Coniacian/Santonian boundary interval, was not identified. The boundary was identified based on the FOs of the ammonite genus Texanites and of the planktonic foraminifer Dicarinella asymetrica. In terms of the nannofossils, the Coniacian/Santonian boundary in the Romanian Carpathians falls within the UC11c (equivalent to CC16) Nannofossil Zone, between the FO of Lucianorhabdus cayeuxii and the last occurrence (LO) of Lithastrinus septenarius. The succession of the nannofloral events identified in the Romanian Carpathians (the FO of Lithastrinus grillii followed by the FO of Lucianorhabdus cayeuxii and by an increased abundance of holococcoliths and Micula concava) is similar to that recorded in the Olazagutia section of northern Spain. A comparison of the nannofossil biostratigraphy focused on the Coniacian/Santonian boundary interval in other European regions, mainly in low to middle-latitudes, is also presented.