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GEOREF RECORD

Model for K-bentonite formation; evidence from zoned K-bentonites in the Disturbed Belt, Montana

Stephen P. Altaner, John Hower, Gene Whitney and James L. Aronson
Model for K-bentonite formation; evidence from zoned K-bentonites in the Disturbed Belt, Montana
Geology (Boulder) (July 1984) 12 (7): 412-415

Abstract

Thirty-four K-bentonites from the Marias River Formation (Upper Cretaceous) studied in detail. A 2.5-m-thick K-bentonite is zoned mineralogically and chemically, the upper and lower contacts of the bed being more illitic and K-rich than the middle of the bentonite. K/Ar dates of illite/smectite separated from the bed are also zoned, yielding older ages at the contacts than at the center. A model for the formation of K-bentonites enclosed by K-rich shale is presented in which K-bentonites form from smectite bentonites during a thermal event (T = 100-200 degrees C). Potassium is derived from mineralogic breakdown (probably mica and K-feldpsar) in the shale, and migrates by diffusion into the bentonite.--Modified journal abstract.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 12
Serial Issue: 7
Title: Model for K-bentonite formation; evidence from zoned K-bentonites in the Disturbed Belt, Montana
Affiliation: Univ. Ill., Dep. Geol., Urbana, IL, United States
Pages: 412-415
Published: 198407
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 27
Accession Number: 1984-039136
Categories: Igneous and metamorphic petrologyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N47°00'00" - N48°00'00", W113°30'00" - W111°00'00"
Secondary Affiliation: U. S. Geol. Surv., USA, United StatesCase West. Reserve Univ., USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 1984
Program Name: USGSOPNon-USGS publications with USGS authors
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