Paleomagnetism of Eocene volcanic tuffs from Laramide foreland basins: Implications for the Geomagnetic Polarity Time Scale

Volcanic tuff samples were collected from twenty-nine tuff horizons in Laramide foreland basins and measured for their paleomagnetism. The results were combined with high precision radiometric ages of the same tuffs to evaluate eight competing calibration models for the Eocene part of the Geomagnetic Polarity Time Scale (GPTS) by comparing the measured polarity to that predicted by each age model. Of the eight models, the New Willwood model is tentatively favored and recommended as the best alternative yet available to the current GPTS calibration. It not only removes an ongoing chronostratigraphic discrepancy in the Greater Green River Basin, but also provides a new temporal framework to which regional chronostratigraphic data are correlated most coherently. This new calibration model implies a shorter duration for the early Eocene and the Early Eocene Climatic Optimum and also suggests that rates of seafloor spreading were more variable than traditionally modeled in the GPTS.