Browsing by Subject "glacial geology"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Bulletin No. 12. Surface Formations and Agricultural Conditions of Northwestern Minnesota
    (Minnesota Geological Survey, 1915) Leverett, Frank; Purssell, U.G.
    This bulletin is a preliminary paper which treats the soils of only the northwest quarter of Minnesota. It will be followed by a report on the entire State, the field work for which will soon be completed. The work has been done in accordance with the agreement for cooperation between the United States Geological Survey and the Minnesota Geological Survey, entered into March, 1912. By this agreement the services of Professor Frank Leverett were secured for surveying the surface formations and soils. Mr. Leverett has been engaged for some twenty years in studying the surface geology of the Great Lakes region and because of his large experience in the greater area he is particularly well prepared to undertake the studies in Minnesota. He has spent, moreover, considerable time in the State studying its physiography in connection with the preparation of a monograph for the United States Geological Survey. Since the reorganization of the State Survey, the salary of Mr. Leverett has been met by the United States Geological Survey, while the greater part of his expenses have been paid by the State Survey. The State Survey has provided also for this work the services and expenses of Professor F. W. Sardeson, who has assisted in this work for the past three seasons. For brief periods, also, the State has supplied the services of Arthur H. Elftman, P. R. McMiller, and G. R. Mc- Dole. We wish to acknowledge the generous assistance of the Division of Soils of the Department of Agriculture of the University of Minnesota and of the United States Bureau of Soils, both of which have contributed unpublished data. The valuable contributions to the knowledge of the surface formations of Minnesota by the Minnesota Geological and Natural History Survey, under the direction of Professor N. H. Winchell, particularly those of Mr. Warren Upham of that Survey, have aided greatly in the preparation of this report. The section on climatic conditions in Minnesota has been generously contributed without any cost to the Survey by Mr. U. G. Purssell, Director of the Minnesota Section of the United States Weather Bureau. In the preparation of the maps and other data showing dates of killing frosts, lengths of growing season, rainfall, etc., Professor C. J. Posey has rendered efficient service.
  • Thumbnail Image
    Item
    Generation of a heavy-mineral glacial indicator dispersal train from a diabase sill, Nipigon region, northwestern Ontario
    (NRC Research Press, 2005) Larson, Phillip C; Mooers, Howard D
    The heavy clinopyroxene mineral pigeonite forms a glacial indicator dispersal train originating from diabase intrusions in the Nipigon region of northwestern Ontario. Analysis and interpretation of the pigeonite dispersal pattern adjacent to the up-ice portion of the diabase provides a number of insights into the nature of glacial erosion of bedrock and the generation of heavy-mineral dispersal trains. Bedrock erosion and entrainment rates at the time of pigeonite dispersal train formation were high (3–14 mm·a–1), suggesting that bedrock erosion was rapid yet spatially and temporally restricted. Contrasting erosion rates between the diabase and surrounding greenstone lithologies suggests that modern shield topography is not an assemblage of equilibrium bedforms with respect to the ice sheet. This agrees with hypothesized low total erosion of shield bedrock during the Pleistocene. Pigeonite grain size coarsens over the diabase source, indicating that most of the pigeonite was quarried from outcrops as coarse diabase fragments. Down-ice of the diabase source the mean particle size of pigeonite recovered from till decreases, suggesting most of the pigeonite was liberated from bedrock by the comminution of coarse diabase clasts during glacial transport. While the conclusions drawn from this study may not necessarily apply to all heavy-mineral dispersal trains, the interpretive framework provides a foundation for comparative studies.
  • Thumbnail Image
    Item
    Glacial indicator dispersal processes: a conceptual model
    (Taylor & Francis, 2004) Larson, Phillip C; Mooers, Howard D
    Interpretation of indicator dispersal trains preserved in till sheets is widely used to investigate past glacial processes and to explore for buried bedrock mineralization. We present a conceptual model of erosion and entrainment and transport of indicator material in a glacial system. Indicator concentration in an individual size fraction of till is controlled by dilution and comminution. Dilution is the result of incorporation of additional material to the glacier’s debris load down-ice of the indicator source, and is described in terms of erosivity and erosion length scale. Erosivity describes the amount of bed material eroded along a flowline, and is a function of both bed properties and the erosive power of the glacier. Erosion length scale describes the persistence of an indicator dispersal signal during transport, and controls both the maximum total indicator concentration and the eventual length of apparent dispersal. We adapt a modified batch grinding particle comminution model to describe breakdown of indicator material during transport and modification of the indicator particle size distribution. Indicator dispersal concentrations are the product of dilution and comminution processes.
  • Thumbnail Image
    Item
    Guidebook 7. Field Trip Guide Book for Geomorphology and Quaternary Stratigraphy of Western Minnesota and Eastern South Dakota
    (Minnesota Geological Survey, 1972) Matsch, C.L.; Tipton, Merlin; Steece, F.; Rutford, R.H.; Parham, W.E.
    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.
  • Thumbnail Image
    Item
    Minnesota at a Glance Quaternary Glacial Geology
    (Minnesota Geological Survey, 2017, 1997) Lusardi, B.A.; Dengler, E.L.
    The Quaternary Period, which began about 2.5 million years ago, is divided into the Pleistocene Epoch (2.5 million to 11,700 years ago) and the Holocene Epoch (11,700 years ago to the present). Although 2.5 million years is a relatively short period of time geologically, sediments deposited during this time mask nearly all of Minnesota's previous geologic history (over 3.6 billion years!). The Pleistocene Epoch, also called the Ice Age, is marked by a series of glacial (cold) and interglacial (warm) periods. Though the Laurentide Ice Sheet (Fig. 1) covered much of northern North America throughout the Pleistocene Epoch, during interglacial periods margins of the ice sheet likely retreated significantly. Because Minnesota was at the edge of the ice sheet, it was not always completely covered with ice during glacial periods. Instead, Minnesota experienced numerous episodes of glaciation followed by ice-free periods.
  • Thumbnail Image
    Item
    OFR10-07, Glacial Geology of Seven Mile Creek Watershed
    (Minnesota Geological Survey, 2010) Jennings, Carrie E.
    The Minnesota Geological Survey was responsible for helping to quantify the relative contributions of bluff versus upland erosion in the watershed in order to better constrain a computer model of the watershed (HSPF model) by mapping the glacial geology of the Seven Mile Creek watershed, identifying the glacial stratigraphic units exposed along Seven Mile Creek, preparing a report of findings, and presenting the results to local interested parties