Doctoral Dissertation Research: Late Pleistocene and Early Holocene Evolution of the Lower Mississippi Valley

密西西比河是大陆尺度排水网络的主干流，在上一次冰河时代结束时，该网络曾是劳伦蒂冰盖南缘融化水和沉积物的主要管道。根据冰川动力学和海平面变化对河流(河流)动力学的解释意义，用三代年龄模型描述了密西西比河谷(LMV)下游的大型辫状河流阶地。这些模型是概念性的和/或仅基于相对年龄关系，在梯田表面上提供的数字年龄控制很少。因此，密西西比河对融水流量、冰川沉积物负荷、海平面上升和构造活动变化的动态响应在很大程度上仍然未知。为了探讨密西西比河谷下游河流对这些变化条件的响应问题，这一博士论文研究项目将提供一项实地研究和测年活动。将对梯田的地貌、沉积学和地层学进行研究。阶地的年龄将通过一种新的测年技术(光激发发光，OSL测年)来确定，该技术可以测量沉积物本身的年龄。有机材料将进行放射性碳测年。测年结果将与测绘和沉积物数据相结合，以产生密西西比河流域下游从全冰川条件向非冰川条件过渡期间的综合河流动力学模型。这项拟议的研究将首次提供从晚更新世全冰期向早全新世非冰期条件过渡期间密西西比河谷下游阶地形成的数字年龄年代学。在此期间，密西西比河河口经历了海平面的快速上升，加上原冰缘的流量和泥沙负荷的大规模变化，以及前冰川湖泊的华丽排水。这项研究将为了解密西西比河谷下游河流对这些冲击强迫机制的动态响应提供洞察；由于河流系统的大陆规模，这对河流动态群落做出了重要贡献。这项研究还将有助于理解河流对环境变化的反应，这是一个令人感兴趣的问题，因为全球变暖对河流系统的影响不确定，以及与河流相关的灾害带来的经济成本。作为博士论文研究改进奖，该奖项将提供支持，使有前途的学生建立一个强大的独立研究事业。

The Mississippi River is the trunk stream of a continental-scale drainage network that served as the principle conduit for meltwater and sediment discharged from the southern margin of the Laurentide ice sheet during the end of the last ice age. The large braided-stream terraces in the lower Mississippi valley (LMV) have been described in three generations of age models based on the interpreted significance of glacial dynamics and sea-level change on fluvial (riverine) dynamics. These models are conceptual and/or based only on relative age relationships, providing little numerical age control on the terrace surfaces. The dynamic responses of the Mississippi River to changes in meltwater discharge, glacial sediment load, sea-level rise, and tectonic activity therefore remain largely unknown. To approach the question of lower Mississippi valley fluvial response to these changing conditions, this doctoral dissertation research project will provide a field study and dating campaign. The geomorphology, sedimentology, and stratigraphy of the terraces will be examined. Terraces ages will be determined from a new dating technique (optically stimulated luminescence, OSL dating) that can measure the age of the sediments themselves. Organic material will be radiocarbon dated. The dating results will be combined with mapping and sediment data to produce a comprehensive model of lower Mississippi valley fluvial dynamics during the transition from full-glacial to non-glacial conditions. The proposed research will provide, for the first time, a numerical age chronology for lower Mississippi valley terrace formation during the transition from late Pleistocene full-glacial to early Holocene non-glacial conditions. During this time period the Mississippi River experienced rapid sea-level rise at its mouth coupled with large-scale changes in discharge and sediment load from the former ice margin and flashy drainage of pro-glacial lakes. This research will provide insight into the lower Mississippi valley fluvial dynamic response to these impacting forcing mechanisms; an important contribution to the fluvial dynamic community because of the continental-size scale of the river system. This study also will contribute to the understanding of river response to environmental change, an issue of interest due to the uncertain impact of global warming on river systems and the economic costs associated with river related disasters. As a Doctoral Dissertation Research Improvement award, this award will provide support to enable a promising student to establish a strong independent research career.