Signatures of Changing Eruptive Style, and Bias in the Sedimentary Record of Volcanism, Challis Volcanic Field, Idaho

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This project is a three-year study of reworked volcaniclastic deposits in the Eocene Challis volcanic field in central Idaho. The project focuses on two major goals. The first is identification of changes in sedimentation style and pattern that result from different types of volcanic eruptions. The second goal is analysis of bias in the sedimentary record of volcanism. Deposits of the Challis volcanic field represent a long period of volcanic activity (51 to 40 million years ago) characterized by an initial period of predominantly non-explosive intermediate volcanism followed by caldera-forming volcanism. The sedimentary system associated with this volcanism comprises high - and low - sinuosity streams, lakes (claystone - tuff and turbidite components), and debris - flow aprons deposited by lahars. The study will identify the signal of different eruption types in a diverse assemblage of depositional environments. The study will also identify which environments are most sensitive to perturbation by eruption and therefore, contain the best record of volcanic activity. The study is field - oriented, combining lithostratigraphy, tephra fingerprinting, and petrofacies stratigraphy to produce the detailed correlation framework needed to achieve the projects goals. These methods require measurement of detailed stratigraphic sections, sandstone, diamictite, and conglomerate petrology, and chemical analyses of fallout tuffs in the sections.