Palaeoenvironmental and palaeobiologic changes across the Barremian/Aptian boundary interval in the Tethys Realm, Mexico and Romania

Upper Barremian–lower Aptian rock sequences in northeast Mexico and the South Carpathians of Romania display palaeoenvironmental and palaeobiologic similarities. The upper Barremian deposits in both areas studied accumulated in shallow marine environments. A latest Barremian transgression was recorded only in Romania, where it is characterized by the prevalence of marly sequences that include mixed Tethyan and Boreal floras and faunas. In both study areas, late Barremian shallow-marine carbonate platforms were succeeded by deep-marine facies in the early Aptian. This was probably related to the early Aptian global sea-level rise. The Barremian/Aptian boundary in both areas is indicated approximately by the first occurrence of the foraminifer species Palorbitolina lenticularis, a bioevent that is coincident with the acme of the foraminifer group Orbitolina. In the early Aptian, Tethyan faunas and floras characteristic of the late Barremian were replaced by cosmopolitan assemblages, an event coincident with the first appearance in Romania of the ammonite genus Deshayesites.