The stratigraphy and geochronology of the Green River Formation, western United States

The Green River Formation of Wyoming, Colorado and Utah represents one of the world's most studied ancient lake deposits. This dissertation expands the geochonologic and stratigraphic understanding of the Green River Formation by providing a suite of high-resolution 40Ar/39Ar and U-Pb age determinations for interbedded tuff horizons and a detailed stratigraphic analysis of the evaporative Wilkins Peak Member in the southern Bridger subbasin of the Greater Green River Basin.; Electron microprobe analysis, laser incremental heating 40Ar/ 39Ar experiments on biotite and sanidine, and CA-TIMS (annealing and chemical abrasion) treatment of zircons have resulted in several advances in the understanding of the effects of alteration and contamination on biotite 40Ar/39Ar and zircon U-Pb dating. Biotite exhibiting intergrown alteration minerals are shown to be prone to both 40Ar* loss and 39ArK recoil, which are the likely cause of age scatter in total fusion age populations. Zircon from Green River Formation tuff beds commonly contain inherited cores, and are simultaneously affected by Pb loss and the addition of common Pb, both of which are mitigated by the CA-TIMS method. A comparison of U-Pb with 40Ar/39Ar ages for the Analcite tuff indicates a 0.77 +/- 0.30% offset between the two systems. This offset is consistent with other recent comparisons of the two chronometers, and supports suggestions that the 40K decay constant currently in widespread use may be underestimated.; Over 30 new 40Ar/39Ar age determinations for tuff beds in the Green River Formation provide the most highly resolved chronostratigraphic picture of any ancient lake deposit, and permit the synoptic reconstruction of the Eocene landscape in the central Rocky Mountains from 52 through 45 Ma. The resulting regional chronostratigraphy is utilized to establish relative timing between hydrologic inputs and outputs, concurrent volcanism and tectonism, and the evolution of lake type in a series of linked lacustrine and alluvial basins.