EAGER: Early-mid Pliocene Climate Change in Northern Chile

这个探索性研究的早期概念提案的目的是确定奥帕奇组的气候意义，奥帕奇组是一种碳酸盐岩单元，沉积于智利北部的阿塔卡马沙漠，距今约780万至337万年前。阿塔卡马的降雨，无论是在其中部地区还是在其东部的安第斯山脉，都受到El Niño（太平洋年代际振荡）的强烈影响，而在更长的时间尺度上则受到南美季风的影响。奥帕奇由两个碳酸盐岩相组成，一个是由盆地溢溢形成的层状凝灰岩相，另一个是泥相单元。本研究的目的是根据沉积学特征（如层厚）重建气候（水文平衡）。研究人员认为，每年有两个层带沉积，季节周期大约每17年加强一次，但他们想证明每年有两个层带形成，并且与气候直接相关。在气候重组时期，利用卡拉马盆地沉积的泥相碳酸盐岩单元来推断该地区的长期气候。这个建议将集中在现代的类似物上，以帮助解释岩石记录。奥帕奇在安第斯山脉中部是独一无二的，就其大小而言，而不是形成机制。在30公里范围内，地下水泉和高海拔湖泊中的活跃碳酸盐沉积发生在里约热内卢Loa及其附近，这两者都可以为两种Opache相的形成提供重要的信息。除了对薄片沉积物结构的研究外，研究人员还将使用稳定同位素来限制对二氧化碳的动力学影响，如脱气。这些现代模拟研究的年代测定将利用Ra-226（半衰期1599年），结合罗格斯大学的U-Th年代测定。层序旋回度可以通过计算活跃生长表面的年代水平并与记录的气候资料进行比较来确定。这个EAGER提案包括添加U-Pb层压单元的日期，将该技术带到罗格斯大学。对可能有年代际气候记录这一假设的成功测试将导致提交一份完整的提案，该提案将在受ENSO影响的地区产生上新世早期至中期的罕见大陆年代际气候记录。该项目将包括本科生参与国际研究并与罗格斯大学合作，以拓宽他们的研究经验。研究人员对从现代模拟研究中提取最近的气候记录抱有很高的期望。

Godfrey/EAR-1117496/Rutgers UniversityThe aim of this early-concept proposal for exploratory research is to determine the climate significance of the Opache formation, a carbonate rock unit deposited in the Atacama Desert of northern Chile between ~7.8 and 3.37 million years ago. Rainfall in the Atacama, both in its central area and in the Andes to its east, is strongly influenced by El Niño, the Pacific Decadal Oscillation, and on longer timescales by the South American monsoon. The Opache is made up of two carbonate facies, a laminated tufa which formed from basin over-spill and a palustrine unit. The aim of this study is to reconstruct climate (hydrologic balance) from sedimentological features such as lamina thickness. The investigators believe that two bands were deposited annually with the seasonal cycle strengthening roughly every seventeen years, but they want to demonstrate that two laminae form annually and are directly related to climate. The palustrine carbonate unit deposited in the Calama Basin will be used to infer the long-term climate of the region during a time of climate re-organization.This proposal will focus on modern analogs to aid in interpreting the rock record. The Opache is unique in the central Andes in regard to its size rather than formation mechanism. Within 30 km, active carbonate deposition occurs in and close to the Rio Loa from groundwater springs as well as in high altitude lakes and both can provide important insight to the formation of both Opache facies. In addition to study of sediment fabrics from thin section, the investigators will use stable isotopes to constrain kinetic effects on CO2 such as degassing. Dating for these modern analog studies will utilize Ra-226 (half life 1599 years), combined with U-Th dating at Rutgers. Laminae cyclicity can be determined by counting between dated horizon from active growth surface and compared with recorded climate data. This EAGER proposal includes addition of dates of the laminated unit by U-Pb, bringing the technique to Rutgers.Successful testing of the hypothesis that a decadal climate record is possible will result in a submission of a full proposal which will yield a rare continental decadal climate record from the early-mid Pliocene in a region influenced by ENSO. This project will include undergraduate involvement in international research and collaboration with Rutgers University which broadens their research experience. The investigators have high expectations that a recent climate record will be extracted from the modern analog studies.