THE INCISION OF THE JAMES RIVER CAN WEATHERED RIVER DEPOSITS DETERMINE THE HISTORY OF EROSION

Our study examined the weathering of terraces of the James River to assess its evolutionary history. Two end-member models can explain the evolution of the river profile and the creation of river terraces from former floodplains: river terraces of similar elevation above the river were made at one time as the river cut vertically, or these terraces were caused by the propagation of a knickpoint due to a wave of incision working its way upstream (which makes the terraces increasingly younger age upstream). To correlate them we used a variety of analytical tools that included high powered spectrometry to global positioning system devices. We studied the weathering of soils on a suite of increasingly aged terraces in one location to apply it to a single terrace through space. We used ionically coupled plasma scanners (ICP), scanning electron microscope (SEM), and x-ray diffraction (XRD). To evaluate relative age we used a weathering scheme to give quartz grains from terrace soils a weighted weathered index. To account for clay and silt particle sizes we used a hydrometer analysis of soil samples.