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Clay minerals of the Green River Formation (Eocene) of Wyoming

Published online by Cambridge University Press:  09 July 2018

R. W. Tank
R. W. Tank*
Affiliation:
Lawrence University, Appleton, Wisconsin, U.S.A.
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Abstract

X-ray analyses indicate that illite, smectite, loughlinite (Na20.3Mg0.6SiO2.8H2O) and chlorite are present in the < 2 μm fraction of the lacustrine Green River Formation (Eocene) of Wyoming. Material amorphous to X-rays and random mixed-layer structures are present in subordinate amounts. Individual crystals vary from pure, well-ordered structures to poorly crystallized forms.

Illite is ubiquitous, occurring in all the samples studied. It is generally associated with other clay minerals but frequently occurs as the only clay mineral found in the 'oil shales'. Smectite is present in all three members of the Green River Formation, but its presence frequently shows an inverse relationship to both analcime and loughlinite. Loughlinite is restricted to the saline facies of the Wilkins Peak Member. Chlorite occurs only in the silty and sandy beds of the Tipton Shale Member. The distribution of random mixed-layer structures and amorphous material is irregular. Several independent lines of evidence favour an in situ origin for many of the clay minerals reported in this investigation.

The 'oil shales', which are in most cases varved, kerogenous, dolomitic marls, have a variable clay mineral composition. There is a marked tendency, however, for illite to be the dominant or the only clay mineral present. Apparently the geochemical conditions favouring the accumulation of the oil shales also favoured in situ generation of illite.

Type
Research Article
Information
Clay Minerals , Volume 9 , Issue 3 , July 1972 , pp. 297 - 308
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1972

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