Stratigraphic Distribution and Mineralogic Correlation of the Green River Formation, Green River and Washakie Basins, Wyoming, U.S.A.

Abstract

The Green River Formation of Wyoming represents a complex sequence of lacustrine, fluvial, and playa strata deposited in and associated with Eocene Lake Gosiute. Detailed mineralogical and organic analysis of 10 cores from the Green River Basin identified correlatable stratigraphic intervals that can be used to interpret the geochemical and sedimentologic history of Lake Gosiute. More than 30 minerals were identified in this study, with graphic correlations and geostatistical evaluations defining 16 major minerals and oil yields, as defined by modified Fischer assay. These relations could be used to define distinct correlatable stratigraphic intervals that, when used in conjunction with known chronostratigraphic volcaniclastic units, could be used to interpret major influences upon the depositional history of Lake Gosiute. The four principal influences upon mineralogical stratigraphy of Lake Gosiute were determined to be (1) deposition and preservation of organic matter, (2) volcaniclastics, (3) periods of evaporation and concentration, and (4) influxes of fresh water accompanied by increased transported detrital material. Climatic variation both on broad and seasonal scales is interpreted to have influenced the mineral suite. The changes among these members have been alternatively interpreted as recording changes in lake-water hydrology, not necessarily related to climate changes (Carroll and Bohacs, 1999; Pietras et al., 2003). Wet periods in the history of Lake Gosiute (Tipton and Laney members) were associated with increased organic production and a related mineral suite, whereas dry periods (Wilkins Peak Member) resulted in decreased organic production and the genesis of a prolific suite of saline and evaporite minerals. This systematic investigation of the distribution, chemical composition, and structure of the minerals in these sediments supported a playa-lake depositional model for the members covered by this study for genesis of the Green River Formation in Lake Gosiute.