On the timing and causes of illite formation and remagnetization in the Cretaceous Marias River Shale, Disturbed Belt, Montana

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 i...

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Bibliographic Details
Published in:	Journal of geochemical exploration Vol. 89; no. 1; pp. 92 - 95
Main Authors:	Elliott, W. Crawford, Osborn, Stephen G., O'Brien, Vanessa J., Elmore, R. Douglas, Engel, Michael H., Wampler, J. Marion
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 01-04-2006
Subjects:	Chemical Remanent Magnetization Illite K–Ar Northwestern Montana Chemical Remanent Magnetization K–Ar Northwestern Montana Illite
Online Access:	Get full text
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Summary:	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.
ISSN:	0375-6742 1879-1689
DOI:	10.1016/j.gexplo.2005.11.033