K-bentonites and graptolite biostratigraphy in the Middle Ordovician of New York State and Quebec: a new chronostratigraphic model

Published correlations of the extensive set of altered volcanic ash beds (K-bentonites) present in the upper Middle Ordovician rocks of New York State imply that the lower Climacograptus (Diplacanthograptus spiniferus Zone, the entire Orthograptus ruedemanni Zone, and the upper Corynoides americanus Zone are coeval. Precise new information on the ranges of graptolite and conodont species and the position of zonal boundaries within key Mohawk Valley sections together with new data on the occurrence of K-bentonites provide the foundation for an alternative, integrated chronostratigraphic model for the Middle Ordovician of the Mohawk Valley and the St. Lawrence Lowland of Quebec. -from Authors