40Ar/39Ar age and correlation of the nonmarine Two Medicine Formation (Upper Cretaceous), northwestern Montana, U.S.A.
作者： Raymond R Rogers , Carl C Swisher III , John R Horner , None
DOI: 10.1139/E93-090
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摘要: The age of the nonmarine Two Medicine Formation northwestern Montana is currently based upon correlations with K–Ar-dated Western Interior ammonite zones. 40Ar/39Ar dating biotite and plagioclase separated from four bentonites one crystal-rich tuff permits for first time direct determination strata. Biotite a bentonite 10 m below top yield concordant ages 74 Ma, while two approximately 100 m above base formation cluster in around 80 Ma. total duration deposition estimated using these new radio-isotopic via extrapolation an average rock accumulation rate.The facilitate regional correlation dinosaur-dominated paleofauna recovered Formation, help constrain timing Claggett Bearpaw transgressions. support correlatio...
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