CDP: Site survey investigation for ICDP drilling in Pliocene lake at Butte Valley, CA

上新世（530万至260万年前）与我们现在的时代有许多地质上的相似之处，作为一个以二氧化碳浓度和与现代相似的大陆构造为特征的持续全球变暖时期。由于这些原因，上新世被认为是测试用于预测未来一个世纪气候和生态变化的模式的能力的适当类比。例如，现代长期水文气候模拟预测，由于二氧化碳水平的增加，亚热带地区将变得更加干燥。然而，这些地区在上新世期间随着全球变暖而表现出更湿润和更温暖的条件，这表明存在当前模式预估中未包括的降水来源。为了解释这些来源并理解引起它们的大气环流的变化，我们需要重建上新世期间大范围纬度和水文气候变化的潮湿条件的分布和季节性。这种重建在北美西部大陆边缘是可能的，那里有一组深的、永久的湖泊盆地，保存了沉积填充物中锁定的上新世古气候条件的记录。解开这一记录需要钻探这些古湖泊盆地，提取和分析沉积物岩心。PLIOWEST项目（向国际大陆科学钻探计划提出）计划钻探这些湖盆，并捕捉随时间变化的水文气候梯度。为了制定钻探计划，该奖项将资助一项必要的地球物理调查，以了解加州Butte Valley的特征，Butte Valley是选定的湖泊岩心检索地点之一。该遗址位于喀斯喀特山脉以东的一个干涸的湖泊盆地，在上新世期间持续了105至106年，但随后在更新世期间干涸。这个盆地是由构造和火山作用塑造的，这些构造和火山作用塑造了西北太平洋，它包含了上新世和更新世期间最长、最完整的地球气候档案之一。地球物理调查将成像沉积层序的特征和几何形状，并指导钻探地点的选择。湖泊沉积物和河谷填充物不仅与过去和现在的气候研究有关；它们也是重要的含水层和地下水资源，尤其是在干旱时期，就像加州正在经历的那样。该项目获得的数据和结果将与北美西部的流域管理者、农业规划者和利益相关者，包括美洲土著部落社区有关。该项目将通过收集和解释地震反射数据进行高分辨率地球物理现场调查。使用100公斤的拖车式加速冲击震源，以10米间隔在5米的接收器间隔上发射，将获得20公里的二维多通道地震反射数据。这些参数的优点是可以实现高空间和高时间分辨率，以确定钻井地点。该项目的目标是对深度超过500米的盆地结构和湖泊沉积物的几何形状进行成像，以解决不整合，并确定可能导致沉积中断和/或沉积记录截断的断层的存在。地球物理调查还将确保确定钻探的潜在危险和可能干扰或阻止完整地层演替的障碍（例如玄武岩岩）。此外，通过阐明湖盆充填，该调查将为钻井项目期间获取的岩心中的岩性和地层信息的解释提供背景。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Pliocene Epoch (5.3 to 2.6 million years ago) shares many geological similarities to our current time, as a period of sustained global warmth characterized by CO2 concentrations and a continental configuration similar to modern. For these reasons, the Pliocene is considered an appropriate analogue for testing the capabilities of models used to predict climate and ecological changes over the coming century. Modern long-term hydroclimatic simulations, for example, forecast subtropical regions to become drier in response to increasing CO2 levels. These regions, however, show wetter and warmer conditions with global warming during the Pliocene, suggesting the presence of sources of precipitation that are not included into current model projections. To account for these sources and to understand the changes in atmospheric circulation that cause them, we need to reconstruct the distribution and seasonality of wet conditions across a wide range of latitudes and hydroclimatic changes during the Pliocene. This reconstruction is possible across the western North American continental margin, where a set of deep, permanent lake basins preserves the record of Pliocene paleoclimate conditions locked in the sedimentary fill. Unlocking this record requires drilling into these paleolacustrine lake basins, retrieving and analyzing sediment cores. The PLIOWEST project (proposed to the International Continental Scientific Drilling Program) plans to drill these lake basins and to capture the changing hydroclimate gradients over time. To plan for drilling, this award will fund a geophysical investigation necessary to understand the characteristics of Butte Valley, California, one of the sites selected for retrieving of lacustrine cores. The site is a dry lake basin just east of the Cascade Range that persisted for 105 to 106 years during the Pliocene, but subsequently dried during the Pleistocene. The basin has been sculpted by the tectonic and volcanic processes that shaped the Pacific northwest, and contains one of the longest and most complete archives of Earth climate through the Pliocene and Pleistocene. The geophysical survey will image the characteristics and geometry of the sedimentary sequences and guide the selection of the drilling site. The lacustrine deposits and the valley infill are not only relevant for past and current climate studies; they are also critical aquifer and groundwater resources, particularly in a time of drought, as the one California has been experiencing. The data acquired and the results of this project will be relevant to watershed managers, agricultural planners and stakeholders in western North America, including Native American tribal communities.The project will carry out a high-resolution geophysical site investigation through collection and interpretation of seismic reflection data. Twenty kilometers of 2D multichannel seismic reflection data will be acquired using a 100 kg trailer-mounted accelerated impact seismic source firing at 10 m intervals on a 5 m receiver interval spread. These parameters have the advantage of achieving both the high spatial and high temporal resolutions required for defining the drilling site. The goals of the project are to image the architecture of the basin and the geometry of the lacustrine deposits down to depths greater than 500 m, to resolve unconformities, and to identify presence of faults that may result in hiatuses in sedimentation and/or truncations of sedimentary record. The geophysical investigation will also ensure the identification of potential hazards to drilling and obstacles (e.g., basaltic sills), that may interfere or prevent the retrieval of complete stratigraphic succession. In addition, by illuminating the lacustrine basin infill, the survey will provide the context for the interpretation of lithological and stratigraphic information in cores retrieved during the drilling project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.