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Browsing by Subject "southwestern Minnesota"

Now showing 1 - 4 of 4
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    Best management practices for Nitrogen use in southwestern and west-central Minnesota
    (University of Minnesota Extension, 2008) Rehm, George; Lamb, John; DeJong-Hughes, Jodi; Randall, Gyles
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    Guidebook 19. Field Trip Guidebook Kaolinitic Clays of the Minnesota River Valley and Southwestern Minnesota
    (Minnesota Geological Survey, 1992) Setterholm, Dale R.; Heine, John J.
    A thick mantle of chemical weathering products covers crystalline bedrock of Archean and Proterozoic age in much of central and western Minnesota. The mantle has a vertical profile typically composed of progressively more weathered material upward from fresh bedrock to an erosion surface now covered either by strata of Late Cretaceous age or by glacial and postglacial deposits of Quaternary age. In a pioneering study of regional relationships, Parham (1970) showed that most upland areas underlain by crystalline bedrock in western Minnesota have weathering profiles averaging 30 m in thickness, though profiles as great as 60 m thick may be present locally. Weathered materials are considerably thinner on steep side slopes and absent in many places along valleys cut into the bedrock surface. Nonetheless, their widespread occurrence has created considerable commercial interest. Much of our knowledge of the processes responsible for the origin of the weathering profile in southwestern Minnesota was established by S.S. Goldich in a 1936 University of Minnesota doctoral dissertation entitled "A study in rock weathering" (Goldich, 1938). Six samples of saprolite from the Redwood Falls-Morton vicinity in the Minnesota River Valley were compared chemically and mineralogically with fresh Archean gneiss, their probable parent material. Using these data, together with data from elsewhere, Goldich established an alteration sequence in which calcium-rich plagioclase was transformed to clay, followed by the dissolution of the potassium-rich feldspar and other mafic minerals. These observations are embodied in the so-called Goldich stability series, which in one form or another is taught to every beginning student in geology.
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    Information Circular 27. Minnesota Kaolin Clay Deposits: A Subsurface Study in Selected Areas of Southwestern and East-Central Minnesota
    (Minnesota Geological Survey, 1989) Setterholm, D.R.; Morey, G.B.; Boerboom, T.J.; Lamons, R.C.
    Large deposits of kaolin-the residual products of the weathering of igneous and metamorphic rocks-are common in southwestern and east-central Minnesota. Thin and discontinuous beds of sedimentary kaolin (resulting from the reworking of the residuum) are less common and volumetrically less significant. The weathering occurred prior to deposition of Late Cretaceous sedimentary strata. Because climatic conditions were uniform within the study area, the differences in the thickness and composition of the residuum are attributable to the mineralogic and hydrologic properties of the parent rock (protolith). Goldich (1938) and others have shown that weathering and the products of weathering are strongly controlled by the mineralogic composition of the protolith. Rocks rich in mafic minerals and plagioclase are generally more extensively weathered, and their residuum is richer in kaolinite. This susceptibility to weathering is evident in the mineralogic composition of the residuum and is reflected in the concentration of kaolin near the top, and in the addition of other minerals with increasing depth. The weathering process is also dependent on the movement of water and other fluids; therefore, permeability is a second important control on the production of kaolin. In igneous and metamorphic rocks, fractures in the form of joints or faults are the primary paths of fluid movement. Weathering follows these paths, and the resulting kaolin deposits mimic the shape and orientation of the structural features. Preservation is the final factor controlling the distribution of kaolin clays. The upper part of the residuum contains the largest amount of clay, but it also is the most vulnerable to erosion. Glacial erosion has had a profound effect on the distribution and thickness of kaolin clay deposits in the state. The thickest deposits are found where Late Cretaceous sediments overlie the kaolin and indicate total preservation of the weathered products.
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    Information Circular 39. Scientific Test Drilling, 1989-1992: Descriptions and Interpretations Pertinent to the Bedrock Geology and Quaternary Hydrogeology of Southwestern Minnesota
    (Minnesota Geological Survey, 1993) Southwick, D.L.; Setterholm, Dale R.; Runkel, Anthony J.; Patterson, Carrie J.; Chandler, V.W.
    In 1980 the Minnesota Geological Survey (MGS) started a program of scientific test drilling designed to acquire a better understanding of the complex Precambrian bedrock of Minnesota. A research approach that combined selective test drilling with geophysical surveying of the Precambrian terrane was dictated by the fact that the Precambrian rocks are covered by substantial thicknesses of quaternary glaciogenic sediment in most places and therefore are not amenable to standard outcrop mapping techniques. This circular is the seventh to report basic results from the drilling program. It contains data from 20 holes drilled for three separate studies undertaken in southwestern Minnesota in 1989-92. The drilling for two of the three projects reported here was closely coordinated with geophysical surveys, and the selection of drilling targets was guided by geophysics to the maximum extent practicable. The third study, consisting of the single hole PR-90-1, was somewhat abnormal in that drilling was targeted on a topographic rather than a geophysical feature (see discussion below for details). Apart from this one exception, our standard procedure was to formulate regional interpretations of the buried Precambrian geology from the geophysical data and then drill to verify, modify, or otherwise constrain the geophysical interpretation. Earlier applications of this approach have contributed to regional-scale geologic maps of the Penokean orogen (Early Proterozoic) in east-central Minnesota (Southwick and others, 1988) and an Archean greenstone belt in north-central Minnesota (Jirsa and Boerboom, 1990; Jirsa, 1990; Jirsa and others, 1991). The data tabulated in this circular will eventually contribute to a new geologic map for southwestern Minnesota.