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The Timing And Causes Of Illite Formation In The Cretaceous Marias River Shale, Disturbed Belt, Montana, Stephen Gerard Osborn
The Timing And Causes Of Illite Formation In The Cretaceous Marias River Shale, Disturbed Belt, Montana, Stephen Gerard Osborn
Geosciences Theses
The clay mineralogy data and K-Ar ages of I/S measured in this study agree with previous work conducted within the Disturbed Belt (Hoffman, 1976) and show that diagenetic I/S formed quickly at several different places in response to thrust sheet burial during the Laramide orogeny. The averages of concordant age values for clay sub-fractions separated from three bentonites of Cretaceous and Jurassic depositional age increase from southeast (53.6 Ma) to northwest (56.7 Ma) along the trend of the Disturbed Belt. This northwestward increase of mean ages of I/S is consistent with a thrust sheet emplacement model for the Disturbed Belt …