DETAILED SEDIMENTOLOGICAL ANALYSIS OF THE LATAH FORMATION FROM CORE 5, CHENEY, WA

The Latah Formation, located in Eastern Washington, is a sedimentary unit of Miocene age overlying granitic basement, and interfingered and overlain by Columbia River Flood Basalts. The Latah Formation is interpreted to represent a largely lacustrine paleoenvironment. It is comprised predominantly of fine-grained sediments. The Latah Formation contains an important and unique fossil record that provides insight into the paleoenvironment and climate of Miocene Eastern Washington. While much work has been done examining the fossil biota and a broad understanding of the geologic events that led to the Latah Formation’s deposition has been explored, little work has been done in examining the depositional history on a small scale.

Here we present a detailed analysis of a drill core (Core 5) from a well near Cheney, WA in Spokane County. Core 5 contains three intervals of the Latah Formation exposed between interfingerings of the Grand Ronde flows and overlain by the Wanapun flows of the Columbia River Basalts. The Latah Formation is dominated by weakly-indurated mudstones and siltstones, and has varying concentrations of organic carbon (fossil plant fragments). Decimeter-scale analyses of the Latah Formation reveal at least eight distinct sedimentary facies representing multiple depositional energies and environments. This data will be compared to local outcrops where similar Latah Formation intervals are exposed to examine the lateral continuity of these facies within the local depositional basin. This detailed interpretation of the sedimentary history will allow for a more complete picture of that past depositional environment of the Cheney area in the Miocene.