GEOCHEMICAL AND SEDIMENTOLOGICAL RECORDS OF LACUSTRINE-SPRING INTERACTIONS: A LARGE SPRING MOUND OF THE EOCENE GREEN RIVER FORMATION

An ancient spring system, within the Eocene Green River Formation along White Mountain north of Rock Springs, WY, provides an excellent opportunity to evaluate ancient spring-lake system interactions. Mineralogic distributions provided by XRD Analysis suggest the spring water was fresher than ancient Lake Gosiute. The lower stratigraphic sequence (Tipton time) of spring deposits is predominantly composed of calcimicrite, whereas the upper sequence (Wilkins Peak time) is dolomicrite. Lake deposits adjacent to the Wilkins Peak spring sequence are composed of dolomicrite and orthoclase, which form in hypersaline-alkaline conditions. This suggests that the dolomitization within the Wilkins Peak spring sequence was significantly influenced by the highly evolved magnesium-rich lake waters.

Spring and lake deposit δ¹⁸O values fall within the same range of each other (-10 to -5 per mil); however, differing trends occur within the spring deposits. δ¹⁸O values within the Wilkins Peak spring mound sequence are more positive (-6 to -5 per mil) coinciding with dolomicrite precipitation. More negative δ¹⁸O values from calcimicrite occur in Tipton spring deposits (-10 to -6 per mil). δ¹⁸O values of Wilkins Peak spring deposits reflect the onset of evaporation and closed-basin conditions in the lake, indicating that lake hydrology had a significant impact on spring deposition. δ¹³C values in adjacent Tipton lake deposits range from -1.5 to -0.5 per mil. However, δ¹³C values in contemporary spring deposits are higher, ranging from 0.5 to 2.5 per mil. Higher δ¹³C values from dolomicrite in the spring deposits may have resulted from the influence of highly evolved lake water during closed-basin Wilkins Peak time. In addition, scattered dolomitization in Tipton sequences of the spring deposit suggests that hypersaline-alkaline lake water may have infiltrated and remineralized parts of the Tipton spring strata. XRD and Stable Isotopic Analysis indicate that mineralogic changes in spring deposits mirror basin-wide geochemical trends. This suggests that spring discharge had little regional effect on the chemistry of the lake.