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https://hdl.handle.net/2142/19429
Description
Title
White River Group diagenesis
Author(s)
Lander, Robert Hal
Issue Date
1991
Doctoral Committee Chair(s)
Hay, Richard L.
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Hydrology
Agriculture, Soil Science
Geochemistry
Language
eng
Abstract
The geochemical characteristics of paleofluids in the White River Group played a vital role in controlling zeolitic alteration as well as the formation of calcretes. The White River Group is a terrestrially deposited sequence of mid-Tertiary age in the northern Rocky Mountains and Great Plains of North America.
"Calcretes are planar accumulations of fine-grained calcite that range from 10 cm to 2 m in thickness and are laterally persistent over distances up to tens of kilometers. Calcretes probably formed near the groundwater table shortly after burial in response to the mixing of fluids derived from soils with alkaline groundwaters. This interpretation can account for the apparently contradictory evidence for derivation of calcium and carbonate species from soils but lack of soil calcrete morphology. In addition, it is consistent with the large degree of buffering of calcite $\delta\sp{13}$C and $\delta\sp{18}$O compositions, the magnitude of calcium mass fluxes, the lack of direct association of pedoturbation and calcite cementation, and the similarity of White River Group calcretes to other ""groundwater"" calcretes."
While many localities have been unaffected by zeolitic alteration, extensive zeolite deposits occur in the northern Great Plains as well as in two localities in Wyoming. Zeolitization in the Wyoming localities resulted from hydrologic systems centered around groundwater discharge zones. In the clay-rich facies of the northern Great Plains, zeolite formed due to high fluid residence times.
Compared to glass-rich portions, altered tuffs in the Douglas, WY area show decreases in porosity on the order of 2 to 4 times (from 40 to 12%) and in permeability of 4 to 5 orders of magnitude (from 35 to 10$\sp{-4}$ md). Mass flux into altered tuffs is indicated by an increase in bulk rock density from 1.3 g/cm$\sp3$ for glassy tuff to 1.7 and 2.0 g/cm$\sp3$, respectively, for its zeolitic and siliceous counterparts. Silica largely accounts for the density increase by mass/volume increases of 9% and 32% in zeolitic and silceous zones, respectively.
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