Cenomanian planktonic foraminifera, bioevents and biozonation - A brief review

Cenomanian planktonic foraminifera are important tools for biostratigraphic correlation and calibration to the standard geological timescale. However, their utility is hampered by ambiguity in age calibration, in turn relating to issues of taxonomic identity, potential misidentification, and uncertainty in calibration through association with other fossil groups and proxies such as carbon isotopes. A review of taxonomic and calibration issues suggests that a simple scheme for low to mid latitudes reminiscent of long-established standards is robust. This recognises biozones from oldest to youngest: Thalmanninella globotruncanoides Interval Zone (interval from the First Appearance Datum of Thalmanninella globotruncanoides to the First Appearance Datum of Thalmanninella greenhornensis; lower Cenomanian); Thalmanninella greenhornensis Interval Zone (interval from First Appearance Datum of Thalmanninella greenhornensis to First Appearance Datum of Rotalipora cushmani; approximately middle Cenomanian); Rotalipora cushmani Total Range Zone (interval comprising the total range of R. cushmani; upper Cenomanian); Whiteinella archaeocretacea Interval Zone (interval from Last Appearance Datum of R. cushmani to First Appearance Datum of Helvetoglobotruncana helvetica; uppermost Cenomanian - lowermost Turonian). Such a scheme allows for unambiguous correlation and age calibration.