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

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

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.