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Mineralogy and Geology of the Green River Formation of Colorado, Utah, and Wyoming: Abstract
The Green River formation of Eocene age outcrops over many thousand square miles in each of the three states, Wyoming, Colorado, and Utah, and underlies similar large areas. It contains the world's largest known accumulation of hydrocarbons as oil shale, and the world's greatest deposits of sodium carbonate minerals, mined to produce soda ash, a basic industrial commodity. Both the hydrocarbons, if converted into marketable fuels, and the soda ash, could fill the nation's needs for centuries to come. At present besides the soda ash, produced in two large mines in Wyoming, gilsonite, a solid hydrocarbon is mined for gasoline production in Utah, and oil and gas are produced in all three states.
The geological history of the formation, essentially a lacustrine deposit in a basin cut off from the sea for millions of years, appears to be unique. Conditions of sedimentation included formation of thousands of feet of rich oil shale, apparently from a lake whose upper waters supported teeming animal and vegetable life, but whose bottom waters were depleted of oxygen and high in hydrogen sulphide. Tremendous quantities of sodium compounds, mostly carbonates, accumulated in the bottom waters or underlying muds with significant boron and barium.
The Green River formation contains an extraordinary variety of authigenic minerals, many found nowhere else in the world, and containing such elements as uranium, niobium, rare-earths, zirconium, and titanium, not normally found in lacustrine sediments. There are likewise many minerals, here formed at temperatures not thought to exceed 200°C, such as pyroxenes, amphiboles, biotite, and feldspars, which ordinarily are formed only under relatively high temperature magmatic or metamorphic conditions.
Recent work has made known extensive apatite deposits, a new type (non-marine) of bedded phosphate, which carries significant uranium. Also the thick series of oil shales in Colorado appear to be vertically zoned mineralogically, a new development in sedimentary petrology.
Acknowledgments and Associated Footnotes
1 USGS, Washington
Copyright © 2006 by the Tulsa Geological Society