Remarks on the identification of the Albian/Cenomanian boundary and taxonomic clarification of the planktonic foraminifera index speciesglobotruncanoides, brotzeniandtehamaensis

Abstract

AbstractThe planktonic foraminifera assemblage across the Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage defined at Mont Risou (Haute-Alpes in France) is here restudied to clarify the identification and stratigraphic distribution ofThalmanninella globotruncanoides( =Rotalipora globotruncanoidesSigal, 1948) andPseudothalmanninella tehamaensis( =Rotalipora tehamaensisMarianos & Zingula, 1966) whose appearance levels are primary and secondary criteria for placing the Albian/Cenomanian boundary. Since the ratification of the GSSP in 2002, the identification of the foraminifera index species across the Albian/Cenomanian boundary has been reported to be sometimes difficult either because of their rarity or uncertainty in the taxonomic identifications. We discuss the taxonomic status ofThalmanninella brotzeniSigal 1948, a species regarded for a long time to be a junior synonym ofTh. globotruncanoides, through images of Sigal's type materials deposited at the Musée National d’Histoire Naturelle (Paris), and elucidate the taxonomically important characters that enable unequivocal identification ofTh. brotzeni, Th. globotruncanoidesandPs. tehamaensis. Planktonic foraminifera marker species from Mont Risou are compared with well-preserved specimens from Blake Nose Plateau (ODP 171B, North Western Atlantic Ocean) to verify the reliability and stratigraphic distribution of these marker taxa outside the Mediterranean Tethyan area.