EAR-PF: Using distributions of channel geometry and channel belt properties to distinguish meandering and braided fluvial deposits in the rock record

美国国家科学基金会EAR博士后奖学金授予田东博士，在蒂莫西·高奇博士的指导下，他将在德克萨斯大学奥斯汀分校开展研究和教育计划。这个项目将研究地球上观察到的两种主要河流形态之间的区别：单线形态和辫状形态。在现代环境中，区分这些河流类型很简单，因为它们可以直接使用水文数据进行观测或预测。然而，事实证明，在沉积岩记录中区分河道模式更加困难，因为只有残存的河道被保存下来，而且它们只占整个记录的一小部分。识别地质记录中的河道模式对于预测地下水和油气藏的质量和非均质性具有重要意义。通过这一项目，将制定一套新的衡量标准，以便利用利用遥感数据从地球上的现代河流测量的河道和河道带的尺寸分布(即同一河流在不同时间的河道淤积)来区分河流类型。然后，这些指标将在区分古代岩石记录中的河流类型的背景下进行解释，预期的发现与美国和相关行业的能源和水资源安全相关。该项目还旨在通过GeoFORCE和德克萨斯大学奥斯汀分校的研究机会等推广计划，促进未被充分代表的群体参与各级STEM领域(K-12和本科)。在现代环境中，使用河道坡度、宽度、深度和水量等水力变量，可以相对较好地预测两种主要河流地貌、单线和辫状图案的形成。然而，识别岩石记录中的河道模式是困难的，因为只保留了原始河道的残留物。由于水力变量，如坡度和流量不能在岩层中直接测量，这项工作将依赖于地质代理。除了区分河流类型以评估地下储集层质量的重要性外，这种区分对于检验单线河流在陆生植物到达志留纪(~415至445 Ma)之前是否稀有的假设是重要的。以前的研究已经重建了上述四个水力变量，以区分岩石记录中的河道模式，但由于复合计算误差，这些结果具有高达数量级的不确定性。这项研究建议利用世界各地现代河流系统通过遥感技术测量的水力变量分布和渠道带特性(例如宽度和曲率半径)来开发新的诊断指标，最终目的是区分岩石记录中的渠道类型。具体地说，我们的目标是检验这一假设，即辫状河流和单线河流具有不同的河道几何分布和河道带特性，这一假设得到了河流分流理论的支持。我们预计，这项研究的结果将广泛适用，因为宽度和深度以及航道带宽度等几何变量很容易测量，或者可以通过最小的计算步骤在观测长度尺度上重建，从露头到地震图像，时间尺度，从现代系统到古代沉积沉积，以及跨越地点，从地球到其他行星。这个项目得到了地球科学部地貌学和土地利用动力学项目的共同资助。这个奖项反映了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。

An NSF EAR Postdoctoral Fellowship has been granted to Dr. Tian Dong to carry out research and education plans at the University of Texas at Austin under the mentorship of Dr. Timothy Goudge. This project will study the distinctions between the two dominant river morphologies observed on Earth: single-thread and braided patterns. Distinguishing between these river types is straightforward in the modern environment as they can be directly observed or predicted using hydrological data. However, distinguishing channel patterns in the sedimentary rock record has proven more difficult, as only remnants of the river channels are preserved and they only account for a small fraction of the overall record. Identifying channel patterns in geologic records is important for predicting the quality and heterogeneity of groundwater and hydrocarbon reservoirs. Through this project, a new set of metrics will be developed for distinguishing river types using distributions of the dimensions of river channels and channel belts (i.e., collections of channel deposits from the same river at different times), measured from modern rivers on Earth using remote sensing data. These metrics will then be interpreted in the context of distinguishing between river types in the ancient rock record, with the anticipated findings relevant for the security of energy and water resources in the United States and related industries. This project also aims to promote participation of underrepresented groups in STEM fields at all levels (K-12 and undergraduate) through outreach programs such as GeoFORCE and research opportunities at the University of Texas at Austin.Formation of the two main river morphologies, single-thread and braided patterns can be relatively well predicted in modern environments using hydraulic variables of channel slope, width, depth, and water discharge. However, recognition of channel patterns in the rock record is difficult because only remnants of the original river channels are preserved. Since hydraulic variables such as slope and discharge cannot be measured directly in rock formations, this work will rely on geologic proxies. In addition to the significance of distinguishing river types to assess subsurface reservoir quality, this distinction is important for testing the hypothesis that whether single-thread rivers were rare prior to the arrival of land plants in the Silurian (~415 to 445 Ma). Previous studies have reconstructed the above four hydraulic variables to distinguish channel patterns in the rock record, but such results have uncertainties that range up to an order of magnitude due to compounded calculation errors. This study proposes to develop new diagnostic metrics using distributions of hydraulic variables and channel belt properties (e.g., width and radius of curvature), measured from modern fluvial systems worldwide via remote sensing techniques, with the ultimate aim for distinguishing channel types in the rock record. Specifically, we aim to test the hypothesis that braided and single-thread rivers have distinct distributions of channel geometry and channel belt properties as supported by theories on river branching. We anticipate that the results of this study will be widely applicable, as geometry variables, such as width and depth, and channel belt width are easily measurable or can be reconstructed with minimum calculation steps across observational length scales, from outcrops to seismic images, timescales, from modern systems to ancient sedimentary deposits, and across localities, from Earth to other planets. This project received co-funding from the Geomorphology and Land-use Dynamics program in the Earth Science division.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.