New paleothermometry for mudstone: utilization of calcreous nodules

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More than 100 calcareous nodules from Cretaceous Yezo Group in Hokkaido and Nanaimo Group in Hornby Island, BC, Canada were collected and their occurrences and preservation statuses were described. Classification was also done in the lab based on the color and fossil inclusion observed on their cut and polished surfaces. Carbon and oxygen isotope values from ~20% of the collected samples correspond to the expected values calculated from existing paleothermometry. This data set allowed us to construct criteria for screening nodules for paleothermometry. Two-step screening, i.e. observation during sample collection and observation on cut surfaces, provides simple but efficient method for mudstone paleothermometry using calcareous nodules.