Type of Document Master's Thesis Author Osborn, Stephen Gerard URN etd-04252006-151625 Title The Timing and Causes of Illite Formation in the Cretaceous Marias River Shale, Disturbed Belt, Montana Degree Master of Science Department Geology Advisory Committee
Advisor Name Title Dr. Crawford Elliott Committee Chair Dr. J. Marion Wampler Committee Member Dr. R. Dougles Elmore Committee Member Dr. Seth Rose Committee Member Keywords
- Chemical remanent magnetization
- Disturbed Belt
- Montana
- K-Ar
- illite
Date of Defense 2006-04-13 Availability unrestricted Abstract 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 (Mudge and Earhart, 1980). The rate of the eastward advancement of the Lewis Thrust Sheet derived from the concordant K-Ar dates of I/S was about 1 cm/year in the Marias River area. The absence of the 2M1 illite polytype in most bentonitic shales does not permit the derivation of the age of diagenetic I/S by Illite Age Analysis and yet constrains the estimate of maximum burial temperature to 250°C.Files
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access osborn_stephen_g_200605_ms.pdf 5.89 Mb 00:27:14 00:14:00 00:12:15 00:06:07 00:00:31