Browsing by Subject "bedrock geology"

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    Geologic Map Series 3. Geology of the Cloquet Quadrangle Carlton County, Minnesota
    (Minnesota Geological Survey, 1970) Wright, H.E. Jr; Mattson, L.A.; Thomas, J.A.
    The Cloquet quadrangle is bisected by the St. Louis River, a major stream that flows into the western end of Lake Superior. Precambrian rocks are extensively exposed in the river valley where overlying Pleistocene glacial deposits have been eroded. The Precambrian rocks are dominated by the Thomson Formation, which consists of interbedded slates, slaty graywackes, and graywackes. Small-scale cross-bedding, graded bedding, flute casts, load casts, clastic dikes, and other primary and penecontemporaneous structures are common, as are calcareous and siliceous concretions. The formation probably was deposited in a relatively deep-water basin, in part by turbidity currents. It has only one conspicuous marker bed, the Otter Creek unit, so the stratigraphic thickness across the intricate folds of the region is difficult to determine, but it probably is about 20,000 feet. Normal and reverse faults with displacements of a few tens of feet are common, as are steeply dipping conjugate joints of northwest and northeast trends. Cleavage is well developed in slaty units. The Thomson Formation is correlated with the Animikie Group. Abundant microgabbro dikes were intruded during subsidence of the Lake Superior syncline. The Pleistocene glacial history was marked by three phases of advance and retreat of the Superior Lobe, preceded by a phase of the Rainy Lobe. Drumlins, moraines, outwash plains, eskers, lake plains, and diversion channels constitute distinctive landforms. During final withdrawal of the Superior Lobe from the area, the St. Louis River, which carried the outflow from Glacial Lake Upham, was diverted to form prominent erosional channels leading to the St. Croix River at progressively lower elevations, until it finally flowed into the proglacial Lake Nemadji, whose outlet formed a final channel in the sequence.
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    Information Circular 11. The Basis for a Continental Drilling Program in Minnesota
    (Minnesota Geological Survey, 1976) Morey, G.B.
    The use of drill holes for the direct sampling and measurement of materials and properties beneath the earth's surface is the only really effective method of solving many basic scientific and practical problems. Although two to three million holes have been drilled in North America, they are concentrated in oil producing regions or in sedimentary rock. Comparatively few holes have been drilled in igneous and metamorphic rock, and many areas of scientific interest but less obvious economic importance have not been drilled at all. A select committee at a workshop on continental drilling held June 10-13, 1974 at Ghost Range, Abiquiu, New Mexico (Shoemaker, 1975) has proposed a 10-year program, aimed at the systematic exploration of the North American plate in much the same way that the Deep Sea Drilling Project has attacked the problems of the ocean basin. This program calls for the drilling of many shallow holes 30-300 m) and a few intermediate to deep holes (300-9,000 m). The impact of the results of deep sea drilling on geologic thought already has profound implications for future development of the earth's resources and should justify similar research on the continents.
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    Information Circular 23. Scientific Core Drilling in Central Minnesota: Summary of Lithologic and Geochemical Results
    (Minnesota Geological Survey, 1986) Southwick, D.L.; Meyer, Gary N.; Mills, Sarah J.
    In 1980 the Minnesota Geological Survey (MGS) began a program of scientific test drilling for the purpose of acquiring a better understanding of the complex Precambrian bedrock of central Minnesota. The areas investigated in this project contain very few bedrock outcrops; the Precambrian rocks are thickly covered by unconsolidated surficial deposits of Quaternary age, and the only way they can be directly sampled and studied is by core drilling. This circular is an essentially uninterpreted summary of basic lithologic and chemical data derived from the scientific core drilling project.
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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.
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    Report on methods and results of geologic investigations in the Pearl Lake study area.
    (Minnesota Geological Survey, 1984) Jirsa, M.A.
    Preliminary report on the geology in the area of Pearl Lake as one candidate for hazardous waste disposal. Much of the data from this study are in somewhat haphazard condition,and interpretations are tentative largely because of the abrupt termination of this project by the Minnesota Waste Management Board (2/27/84). All maps, figures and interpretive material are therefore in draft form and should be considered preliminary.