Environments of Sedimentation and Controls on Diagenesis of the Creede Fm., Colorado

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The sedimentary and volcaniclastic rocks of the Oligocene Creede Formation will be investigated in order to assess the range and evolution of intracaldera sedimentary environments, and the controls on diagenesis and alteration in an intracaldera setting. The Creede Formation was chosen for this study because of the extensive exposures of relatively underformed intracaldera sedimentary rocks associated with a large resurgent caldera, the well known volcanic stratigraphy and chronology of the Creede area, and the opportunity to test and contribute to the well-studied Creede hydrothermal model. In contrast to previous studies of intracaldera sedimentary rocks, this study will focus on evaluating the basin-wide field relationships among sedimentary, primary pyroclastic, and hydrothermal rocks, as well as authigenic mineral chemistry and distribution. These data will be used to: 1) develop an understanding of depositional processes and sediment distribution patterns occurring in an intracaldera basin; and 2) assess the relative controls of the depositional environment, hydrothermal activity, organic carbon distribution, and basin hydrology on the diagenesis of the volcaniclastic rocks. The results of this project will provide a working model for sedimentary deposition and diagenesis in an intracaldera setting, as well as allow an assessment of the role the Creede Formation sediments may have played in the evolution of the Creed hydrothermal system. In general, the results will contribute to our understanding of caldera evolution and hydrothermal systems associated with calderas, and provide valuable baseline data for evaluation of other intracaldera sedimentary sequences.