Characteristics of the organic material in Green River Formation shale suggest that this material was derived mainly from algae that grew in Eocene lakes. The basin depressions were formed by the uplifting of the Rocky Mountains. Large quantities of soluble salts flowed into these basins from the mountain streams, increasing the salinity of the lakes until they became chemically stratified. In the upper, relatively freshwater section of the lakes, abundant quantities of microscopic algae and other biota grew. The lower section of the lakes became highly reducing and stagnant because of lack of seasonal oxidative turnovers, thus providing ideal conditions for the accumulation and preservation of the organic debris.

Precipitation of mineral carbonates and silicates from the highly saline waters provided most of the minerals that were co-deposited with the organic matter. The characteristics of the lake water varied considerably and significantly effected the composition of both the inorganic and organic constituents of the Green River shale.

Sixty to seventy-five samples from each of three basins of the Green River Formation were analyzed for changes in the organic constituents. Considerable variations in the organic components of the soluble bitumens and of the insoluble kerogens were evident. Some of these variations appeared to be related to depth of burial and some to source material or the environment of the lake water. Compositional differences were related to lithologic differences in the sediments of the three basins.

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