The Turonian - Coniacian boundary in the United States Western Interior

Abstract

The Turonian/Coniacian boundary succession in the United States Western Interior is characterized by the same inoceramid faunas as recognized in Europe, allowing the application of the same zonal scheme in both regions; Mytiloides scupini and Cremnoceramus waltersdorfensis waltersdorfensis zones in the topmost Turonian and Cremnoceramus deformis erectus Zone in the lowermost Coniacian. The correlation with Europe is enhanced, moreover, by a set of boundary events recognized originally in Europe and well represented in the Western Interior: Didymotis I Event and waltersdorfensis Event in the topmost Turonian, and erectus I, II and ?III events in the Lower Coniacian. First "Coniacian" ammonite, Forresteria peruana, appears in the indisputable Turonian, in the zone of M. scupini, and the reference to Forresteria in the boundary definition should be rejected. None of the North American sections, proposed during the Brussels Symposium as the potential boundary stratotypes, i.e. Wagon Mound and Pueblo sections, appears better than the voted section of the Salzgitter-Salder. The Pueblo section is relatively complete but markedly condensed in comparison with the German one, but it may be used as a very convenient reference section for the Turonian/Coniacian boundary in the Western Interior. The Wagon Mound section was mis-interpreted in respect of its biostratigraphical position and is entirely of Late Turonian age.