EAR-PF: Channel network evolution in a tectonically active basin enlightened through innovative luminescence geochronology

Elizabeth L. Chamberlain博士获得了美国国家科学基金会EAR博士后奖学金，在哥伦比亚大学、范德比尔特大学和瓦赫宁根大学开展研究和教育计划。该项目将利用张伯伦博士关于光学激发发光（OSL）测年的最新创新。OSL根据石英颗粒在远离阳光的情况下积聚的电荷来估计沉积物沉积的时间。她将在孟加拉国的恒河-布拉马普特拉河三角洲应用OSL，以确定三角洲演化的机制和时间尺度。具体来说，这项工作将探索河流与大三角洲地震过程之间的联系。研究结果将描述沉积物向洪泛区和海岸的输送，这是在海平面加速上升的情况下维持三角洲的关键因素。此外，该研究将通过调查大地震发生的频率以及地震是否能够迫使河流自发改变路线，提供有关河流地震地质灾害的新信息。预期的发现与人口稠密的孟加拉国和世界其他沿海地区（如美国密西西比三角洲）的沿海管理有关。这项工作也将有助于OSL工具的方法发展。这项研究将促进美国、荷兰和孟加拉国工作组之间的知识转移，并将通过聘请孟加拉国理科硕士来支持学生教育。学生从事野外工作，美国本科生从事实验室工作。恒河-雅鲁藏布江三角洲为探索河流-构造耦合过程提供了难得的机会，因为它具有广泛的河道网络和几个活跃变形的板块边界。2018年，张伯伦博士及其同事在全新世晚期恒河漫滩发现了一组古震积岩结构，其中包括大型砂堤和软沉积物变形。这些特征位于一个巨大的（1.5公里宽）残余物和未填满的河道疤痕的边缘，表明大地震事件与主要的河道撕裂之间存在联系。张伯伦博士将使用她最近发表的OSL协议来确定震积岩、古河道河床和填塞物、点坝和邻近的洪泛平原沉积物的年代，从而测试可能调节大河崩裂时间尺度的两个过程：(1)通过大型、高震级地震事件的强迫增强崩裂频率；(2)通过小支流河道的三角洲平原的沉积抑制崩裂频率。这项研究的一个组成部分将探索新的发光地质年代学方法的发展，以确定沙堤就位的时间。张伯伦博士的研究将有助于delta动力学的理论和应用知识，并通过提供一种新的方法来确定以前不适合定年的结构，从而促进发光工具的进步。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。

Dr. Elizabeth L. Chamberlain has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education plans at Columbia University, Vanderbilt University, and Wageningen University. The project will make use of recent innovations by Dr. Chamberlain regarding optically stimulated luminescence (OSL) dating. OSL estimates the time of sediment deposition based on trapped charges that accumulate in quartz grains when they are removed from sunlight. She will apply OSL to the Ganges-Brahmaputra Delta, Bangladesh, to determine the mechanisms and timescales of delta evolution. Specifically, this work will explore the connection between river and seismic (earthquake) processes in a large delta. Findings will describe sediment delivery to floodplains and coasts, a key factor in sustaining deltas under accelerated rates of sea-level rise. In addition, the research will provide new information about river-seismic geohazards by investigating how often large earthquakes occur and whether earthquakes are capable of forcing rivers to spontaneously change course. The anticipated findings are relevant to coastal management within the densely populated nation of Bangladesh and in other coastal regions worldwide such as the Mississippi Delta, U.S. This work will also contribute to methodological development of the OSL tool. The research will facilitate knowledge transfer between work groups in the U.S., The Netherlands, and Bangladesh and will support student education by engaging Bangladeshi M. Sci. students in field work and a U.S. undergraduate in laboratory work. The Ganges-Brahmaputra Delta offers a rare opportunity to explore coupled fluvial-tectonic processes, given its extensive river channel network and position along several actively deforming plate boundaries. In 2018, Dr. Chamberlain and colleagues identified a cluster of paleo-seismite structures in the Late Holocene Ganges floodplain that include large sand dikes and soft sediment deformation. Located on the edge of an immense (1.5 km-wide) relict and underfilled channel scar, these features suggest a link between large seismic events and major channel avulsions. Dr. Chamberlain will use her recently published OSL protocol to date seismite, paleochannel bed and fill, point bar, and adjacent floodplain deposits, thereby testing two processes that may regulate the avulsion timescales of large rivers: (1) enhanced avulsion frequency through forcing by large, high-magnitude seismic events, and (2) suppressed avulsion frequency through aggradation of the delta plain fed by small distributary channels. A component of this investigation will explore the development of novel luminescence geochronology approaches to determine the timing of sand-dike emplacement. Dr. Chamberlain's research will contribute to both the theoretical and applied knowledge of delta dynamics, and to the advancement of luminescence tools by providing a new method to date structures previously not amenable to dating.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.