Guidebook 7. Field Trip Guide Book for Geomorphology and Quaternary Stratigraphy of Western Minnesota and Eastern South Dakota

Abstract

The land surface of eastern South Dakota and southwestern Minnesota is underlain mainly by sediments of Quaternary age, and most of the land forms themselves are the result of erosional and depositional events that were closely controlled by climatic fluctuations during the Pleistocene Epoch. As a result of climatic changes, glacier ice advanced and retreated across the region, leaving a complicated stratigraphy of glacier-derived sediments. So recently did the last glacier deteriorate that the present landscape still retains the forms impressed by that complicated process. Even though geologists have been studying the Quaternary sediments of the region for almost 100 years, their interpretations are still controversial. Fundamental questions still incompletely answered are (1) how many drift sheets are present?; (2) where do the drifts fit into the mid-continent Quaternary time scale?; and (3) what is the surface distribution of each of the major drift units? During the last two decades the availability of aerial photography and topographic maps has facilitated detailed surface mapping projects. Absolute age determinations have been helpful in establishing a chronology for events during the last 40,000 years. The recognition, definition and tracing of lithostratigraphic units, begun several years ago, have added new dimensions to Quaternary studies in the region.