Browsing Earth and Environmental Systems by Author "De Rego, Kathryn G."
Holocene Landscape Evolution of the Ohio River Valley from Knob Creek to Rosewood BottomDe Rego, Kathryn G. (2012-10-19)Rivers and floodplain environments have provided human settlements with resources for thousands of years. By understanding how rivers shape the land around them, we can use landforms to reconstruct ancient fluvial processes and to examine how they have conditioned the way humans interact with their environment. This study investigates the Lower Ohio River during the Holocene. During this period, Midwestern landscapes were adjusting to a variety of processes, including millennial-scale climate change involving the transition from a glacial to an interglacial environment. At the same time, Archaic hunter-gatherers adopted a settlement strategy that favored large river valleys. The cause of this shift has not been resolved. This study examined floodplain sedimentation and change along the Lower Ohio from Knob Creek to Rosewood Bottom through two different scales of analysis: the regional (geologic) scale and within local bottoms. A model of floodplain structure from Madison to Tell City, Indiana was created using a GIS and used to examine differences between geologic regions and Early and Late Holocene sediment. Swales were identified using a DEM, and depth, area, and perimeter-area ratio were used as proxies of their characteristics, which are correlated with backwater environments. Subsurface soil and sediment data were collected from a transect across Rosewood Bottom and within a paleochannel common to the study reach and used to reconstruct floodplain production within an individual bottom. Radiocarbon dates from geologic and archaeological contexts were used to examine Early and Late Holocene sedimentation rates. The Ohio River was active during the Early Holocene. It migrated rapidly and constructed most of the modern floodplain. In some areas, it was anabranching because resistant Pleistocene braid bars formed obstructions to flow that became islands. During the Late Holocene, deposition has been mainly characterized by overbank backwater/slackwater deposition in swales. There is not enough evidence to assign an exogenic cause to this phenomenon. Significant differences in floodplain structure between individual bottoms and regions, the influence of underlying Pleistocene gravels on river migration, and different dates for paleochannel abandonment are indicators of autogenic controls on the Ohio’s behavior and show that bottoms have independent histories. This study complements current models of environmental change for river basins in the Midwest, but it suggests that the stability of the floodplain be given more consideration when analyzing Archaic settlement strategy.