Orbital timescale for the Cenomanian-Turonian boundary stratotype and OAE II, central Colorado, USA

Previous time scales for the Cenomanian-Turonian boundary (CTB) interval containing Oceanic Anoxic Event II (OAE II) vary by a factor of three. In this paper we present a new orbital time scale for the CTB stratotype established independently of radio- metric, biostratigraphic, or geochemical data sets, update revisions of CTB biostratigraphic zonation, and provide a new detailed car- bon isotopic record for the CTB study interval. The orbital time scale allows an independent assessment of basal biozone ages rel- ative to the new CTB date of 93.55 Ma (GTS04). The fc07;13Corg data document the abrupt onset of OAE II, significant variability in fc07;13Corg values, and values enriched to almost fc08;22‰. These new data underscore the difficulty in defining OAE II termination. Us- ing the new isotope curve and time scale, estimates of OAE II duration can be determined and exported to other sites based on integration of well-established chemostratigraphic and biostrati- graphic datums. The new data will allow more accurate calcula- tions of biogeochemical and paleobiologic rates across the CTB.