STREAM PROFILE, TERRACE, AND DEPTH-TO-BEDROCK DATA FOR THE UPPER MISSISSIPPI RIVER REGION, ELK RIVER-BRAINERD: PRELIMINARY RESULTS

Stream profiles for the Upper Mississippi River and major tributaries between Elk River and Brainerd are being investigated. The stream profiles, together with terrace elevation data, depth-to-bedrock, and drainage patterns are being used to evaluate several key questions. First, whether the present-day (or earlier) stream profiles and terrace levels provide evidence for Quaternary reactivation of Precambrian faults as a result of isostatic readjustment. Second, whether there is evidence for Holocene and Pleistocene stream systems carrying a ‘memory' of the lithologic changes in buried bedrock type and/or buried bedrock faults, and/or the bedrock topography. Third, whether the thicknesses of Pleistocene glacio-fluvial and other sediment beneath present-day stream channels correlates in any way with changes in bedrock lithology. Feedback on the preliminary results from this investigation will be used to guide further work.