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

CDP：加利福尼亚州比尤特谷上新世湖 ICDP 钻探现场调查

• 批准号: 2308334
• 负责人: Maria Beatrice Magnani
• 金额: $ 9.98万
• 依托单位: Southern Methodist University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2308334&HistoricalAwards=false
• 关键词: CDP; Site; survey; investigation; ICDP

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.

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，即以二氧化碳浓度和类似于现代的大陆构造为特征的持续的全球变暖时期。出于这些原因，上新世被认为是测试用于预测下个世纪气候和生态变化的模型能力的合适类比。例如，现代长期水文气候模拟预测，随着二氧化碳水平的上升，亚热带地区将变得更加干燥。然而，随着上新世全球变暖，这些地区表现出更潮湿和更温暖的条件，这表明存在不包括在当前模型预测中的降雨源。为了解释这些来源并了解导致它们的大气环流变化，我们需要重建上新世期间湿条件在广泛纬度范围内的分布和季节性以及水文气候变化。这种重建在北美西部大陆边缘是可能的，那里有一组深而永久的湖盆，保存着锁在沉积充填物中的上新世古气候条件的记录。要解开这一记录，需要钻探这些古湖相湖盆，提取和分析沉积岩心。PLIOWEST项目(向国际大陆科学钻探计划提出)计划钻探这些湖盆，并捕捉随着时间的推移不断变化的水气候梯度。为了规划钻探，该合同将资助一项必要的地球物理调查，以了解加利福尼亚州巴特谷的特征，该地区是被选为取回湖泊岩心的地点之一。该遗址是一个干燥的湖盆，就在喀斯喀特山脉以东，在上新世持续了105到106年，但后来在更新世变干了。该盆地由形成太平洋西北部的构造和火山过程雕刻而成，包含从上新世到更新世的最长和最完整的地球气候档案之一。地球物理测量将对沉积层序的特征和几何形状进行成像，并指导钻探地点的选择。湖泊沉积和山谷充填不仅与过去和现在的气候研究有关，而且也是关键的含水层和地下水资源，特别是在干旱时期，就像加州正在经历的那样。获得的数据和该项目的结果将与北美西部的流域管理者、农业规划者和利益攸关方有关，包括美洲原住民部落社区。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。利用一个100公斤的拖车安装的加速冲击震源，在5m的接收间隔上，以10m的间隔激发，将获得20公里的二维多道地震反射数据。这些参数具有实现确定钻探地点所需的高空间和高时间分辨率的优点。该项目的目标是成像盆地的结构和深至500米以下的湖泊沉积的几何形状，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查明可能干扰或阻止恢复完整地层序列的钻井和障碍物(例如玄武岩岩床)的潜在危险。此外，通过阐明湖盆填充物，调查将为解释钻井项目期间取回的岩芯中的岩性和地层信息提供背景。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。