Model for K-bentonite formation: evidence from zoned K-bentonites in the disturbed belt, Montana.

S. P. Altaner, J. Hower, G. Whitney, J. L. Aronson

Research output: Contribution to journalArticlepeer-review

Abstract

Thirty-four K-bentonites from the Upper Cretaceous Marias River formation in the Montana disturbed belt were 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 portion. K/Ar dates of illite/smectite separated from the bed are also zoned, yielding older ages at the contacts than at the centre. 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 100-200oC). Potassium is derived from mineralogical breakdown (probably mica and K-feldspar) in the shale, and migrates by diffusion into the bentonite. (Authors' abstract)-C.N.

Original languageEnglish (US)
Pages (from-to)412-415
Number of pages4
JournalGeology
Volume12
Issue number7
DOIs
StatePublished - Jan 1 1984

ASJC Scopus subject areas

  • Geology

Fingerprint Dive into the research topics of 'Model for K-bentonite formation: evidence from zoned K-bentonites in the disturbed belt, Montana.'. Together they form a unique fingerprint.

Cite this