Biostratigraphy and Inoceramus survival across the Cenomanian–Turonian (Cretaceous) boundary in the Ram River section, Alberta, Canada

Authors

  • Ireneusz Walaszczyk Faculty of Geology, University of Warsaw, Al. Żwirki i Wigury 93, PL-02-089 Warszawa
  • A. Guy Plint Department of Earth Sciences, The University of Western Ontario, London, Ontario, N6A 5B7
  • William J. Kennedy Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW and Department of Earth Sciences, South Parks Road, Oxford OX1 3AN

Keywords:

Cenomanian–Turonian boundary, Mytiloides, Ammonites, Inoceramus survival, Biostratigraphy, Western Interior Basin, Canada.

Abstract

The biostratigraphy of the uppermost Cenomanian – Lower Turonian succession in the lower part of the Blackstone Formation exposed in the Ram River (Alberta, Canada), is interpreted in terms of the standard inoceramid/ ammonite zonation of the interval. Four successive inoceramid zones are recognized, those of Inoceramus pictus, Mytiloides puebloensis, M. kossmati, and M. mytiloides, as established in the stratotype section at Pueblo, Colorado. Their correlation to Pueblo is confirmed by ammonite data.The mid-Early Turonian zone of M. kossmati yielded an assemblage of Inoceramus, with species showing close affinity to the latest Cenomanian lineages. This multi-species sample proves the survival of Inoceramus lineages into the otherwise Mytiloides-dominated Early Turonian, and indicates that their disappearance from the record of the North American Western Interior was not because of their extinction. It is suggested that the apparent lack of Inoceramus in Lower Turonian strata is due to an extremely low population abundance in the Early Turonian sea.

Downloads

Published

2016-12-23