On the timing and causes of illite formation and remagnetization in the Cretaceous Marias River Shale, Disturbed Belt, Montana |
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Authors: | W. Crawford Elliott Stephen G. Osborn Vanessa J. O'Brien R. Douglas Elmore Michael H. Engel J. Marion Wampler |
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Affiliation: | aDepartment of Geology, Georgia State University, Atlanta, GA 30303, United States;bSchool of Geology and Geophysics, The University of Oklahoma, Norman, OK 73019-0628, United States;cSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, United States |
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Abstract: | In this study, we test a burial model for diagenetic illite and whether illitization is related to the acquisition of a chemical remanent magnetization (CRM). A prefolding, reversed polarity, secondary magnetization is found in carbonate concretions in diagenetically altered Upper Cretaceous rocks in the disturbed belt of Montana. Stratigraphically equivalent unaltered rocks to the east do not contain the magnetization. The magnetization could be a CRM or a thermoviscous remagnetization. The pole position is generally consistent with the Early Tertiary K–Ar ages of diagenetic illite–smectite formed under thrust loading, but it is not constrained well enough for a precise age comparison. If this magnetization is a CRM, it could be related to illitization. Alternatively, if the prefolding CRM had been acquired prior to thrust loading then the magnetization is not related to illitization. Geochemical studies are currently underway to test if the magnetization could be related to fluid alteration. |
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Keywords: | K– Ar Illite Chemical Remanent Magnetization Northwestern Montana |
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