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

通过对渐新统Creede组沉积岩和火山碎屑岩的研究，探讨了裂孔内沉积环境的范围和演化，以及裂孔内环境对成岩和蚀变的控制作用。之所以选择Creede组作为研究对象，是因为这里有大量相对不成熟的破火山口内沉积岩，这些沉积岩与一个大型的再生破火山口有关，还有Creede地区众所周知的火山地层学和年代学，而且有机会测试和促进已经得到充分研究的Creede热液模型。与以往的孔内沉积岩研究相比，本研究将重点评价沉积岩、原生火山碎屑岩和热液岩在全盆地范围内的相互关系，以及自生矿物的化学和分布。这些数据将用于：1)了解裂谷内盆地的沉积过程和沉积分布模式；2)评价沉积环境、热液活动、有机碳分布和盆地水文对火山碎屑岩成岩作用的相对控制作用。该项目的结果将为裂孔内沉积和成岩作用提供一个工作模型，并允许评估Creede组沉积物在Creed热液系统演化中可能发挥的作用。总的来说，这些结果将有助于我们对破火山口演化和与破火山口相关的热液系统的理解，并为评价其他破火山口内沉积序列提供有价值的基线数据。

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.