Distribution, paleodrainage, and paleoclimate of the Miocene Columbia River Basalt Group and associated sedimentary interbeds in the Clearwater Embayment of West-Central Idaho and southeastern Washington

Chemostratigraphic and chronostratigraphic correlation of X-ray fluorescence (XRF) whole rock geochemical analyses of flows of the Columbia River Basalt Group (CRBG) facilitated the identification of the distribution of these flows within the Clearwater Embayment. These analyses also identified an andesite flow in the Downey Gulch Member of the Grande Ronde Basalt and a fused tuff in the Deer Creek 1 stratigraphic section. The correlation of CRBG flows permitted the chronostratigraphic correlations and paleodrainage reconstructions of intercalated sedimentary intervals.; Compositional layering identified by XRF analyses and internal structures observed in flows with Wilbur Creek Member (Tw), Lapwai flow (Tl), and Asotin Member (Ta) chemistries suggest inflation as the mechanism for emplacement. Compositional layering and emplacement by an inflation mechanism of the Tw, Tl, and Ta flows suggests that the three chemistries were emplaced during a single eruptive event.; Miocene sedimentary successions intercalated with CRBG flows preserve a record of the depositional and erosional settings that characterized the Clearwater Embayment between and during emplacement of the flows. The sedimentary interbeds in the embayment are composed of unconsolidated to moderately consolidated, interstratified sand, silt, clay, and gravel. Spatial distribution of sedimentary facies, grain size, and internal sedimentary structures suggest that these interbeds were deposited primarily in fluvial and lacustrine systems.; Nine pedogenic carbonate samples from three late Miocene paleosol intervals and one modern soil were analyzed for stable carbon (delta13C) and oxygen (delta18O) isotopic compositions. The delta 13C values of late Miocene carbonates show no major difference from the modern pedogenic carbonates most likely due to the lack of change of vegetation types from the late Miocene through the modern. The delta18O values of modern pedogenic carbonates show a decrease of ∼1.5-4‰ from delta18O values of the later late Miocene pedogenic carbonates. The decrease in delta18O values between the modern and later late Miocene carbonates suggests the climate became cooler and more arid since the late Miocene. The cooling and drying climate could have been the result of global climate change, uplift of the Cascade Range, uplift of the Blue Mountains or a combination of all of these factors.