Browsing by Author "Austin, G.S."

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    Geologic map of Minnesota, New Ulm sheet, bedrock geology.
    (Minnesota Geological Survey, 1970) Austin, G.S.; Grant, J.A.; Ikola, R.J.; Sims, P.K.
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    Geologic map of Minnesota, St. Paul sheet, bedrock geology.
    (Minnesota Geological Survey, 1970) Sloan, R.E.; Austin, G.S.
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    Guidebook 4. Field Trip Guide Book for Paleozoic and Mesozoic Rocks of Southeastern Minnesota
    (Minnesota Geological Survey, 1972) Webers, G.F.; Austin, G.S.
    The Paleozoic rocks of southeastern Minnesota (fig. 1) were deposited from a marine sea which occupied the Hollandale Embayment (fig. 2), a shallow depression that extended northward from the Ancestral Forest City Basin (Iowa Basin) onto the cratonic shelf and into Minnesota and Wisconsin in Early and Middle Paleozoic time. The rocks that now remain within the embayment in Minnesota are bordered to the east by nearshore-facies Paleozoic rocks on the Wisconsin Arch, to the northeast by Precambrian rocks that constitute the Wisconsin Dome, and to the north and west by nearshore-facies Paleozoic rocks lying near the margins of the Hollandale Embayment and the Precambrian rocks of the Transcontinental Arch. The embayment overlies older basins and horsts that are bounded by largescale Precambrian faults (Sims and Zietz, 1967). Many smaller Paleozoic basins, depositional barriers, and faults within the embayment probably have resulted from relatively minor recurrent movements along Precambrian faults during Paleozoic time (Craddock and others, 1963).
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    Information Circular 6. Paleozoic Lithostratigraphic Nomenclature for Southeastern Minnesota
    (Minnesota Geological Survey, 1969) Austin, G.S.
    The Paleozoic lithostratigraphic nomenclature shown in the column was compiled from information obtained from several sources-outcrops, deep cores, and theses on the geology of southeastern Minnesota. It is a revision of the Paleozoic stratigraphic column published in 1956 (Schwartz, 1956). The purpose of this discussion is to describe the Paleozoic strata of southeastern Minnesota in terms of the revised nomenclature and to call attention to related post-1956 publications and other source materials.
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    RI-01 Geological Interpretation of Magnetic Map of McLeod County, Minnesota
    (Minnesota Geological Survey, 1963) Sims, P.K.; Austin, G.S.
    A ground magnetometer survey of McLeod County, Minnesota has delineated 3 structural blocks in the buried Precambrian basement rocks. The sources of the anomalies in each of the blocks have not been identified definitely because of a lack of subsurface data, but are interpreted qualitatively from an analysis of the anomalies and considerations of the regional geology. An anomaly in the northwestern part of the county, near Hutchinson, is interpreted to represent a folded, magnetic rock unit. Probably this unit is a magnetite-bearing schist, but the possibility of its being an iron-formation of the Cuyuna-type should be investigated further.
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    RI-02 Geology of Clay Deposits Red Wing Area, Goodhue and Wabasha Counties, Minnesota
    (Minnesota Geological Survey, 1963) Austin, G.S.
    Clay deposits that have been used in the ceramic industry occur sporadically over an area of about 50 square miles in eastern Goodhue County, southeastern Minnesota. The deposits are in the Ostrander Member of the Cretaceous Windrow Formation and to a lesser extent in Pleistocene lake deposits. Currently they are being used in the manufacture of vitreous drain pipe and related products. The Windrow Formation in the area overlies gently folded Cambrian and Ordovician strata. It consists of a lower Iron Hill Member, a ferruginous weathered residuum, and an upper Ostrander Member, a clastic unit. The Iron Hill Member was developed on a mature topographic surface; it formed through residual accumulation of limonite, clay, and chert, the relatively insoluble weathering products of the underlying carbonate rocks. The Ostrander Member formed as floodplain deposits, which were derived from a mixed Precambrian and Paleozoic source. The clay deposits in the Ostrander Member are lenses or tabular bodies as much as a few feet thick and several tens of acres in areal extent that are intercalated with ferruginous sands. The only l known deposit of Pleistocene age is laminated and is as much as 30 feet thick. It is interpreted to have been formed in a glacial lake.
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    RI-04 Interpretation of Lake Washington Magnetic Anomaly, Meeker County, Minnesota
    (Minnesota Geological Survey, 1964) Sims, P.K.; Austin, G.S.; Ikola, Rodney J.
    A magnetic anomaly centered at Lake Washington, in southeastern Meeker County, has been outlined by a ground magnetometer survey. The anomaly is arcuate in outline, about 8.5 miles long and a maximum of 5 miles wide, and has a maximum amplitude greater than 3,000 gammas. A gravity traverse was made across the anomaly to aid in interpretation. Combined magnetic and gravity data are interpreted to indicate that the source is a basin-shaped body having a substantially greater density than the adjacent rocks that lies at a shallow depth. The lithology of the source is not known because of a lack of subsurface data, but is inferred to be either Precambrian iron-formation or mafic igneous rock. The anomaly warrants further investigation.
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    RI-12 Deep Stratigraphic Test Well Near Hollandale, Minnesota
    (Minnesota Geological Survey, 1970) Austin, G.S.
    A deep stratigraphic test well, the Hollandale No.1, in Freeborn County, Minnesota was drilled in rocks that range in age from Devonian to Precambrian in search for reservoirs suitable for the underground storage of natural gas. The porous St. Peter Sandstone of Ordovician age and the Mt. Simon Sandstone of Cambrian age are potentially good reservoir rocks. The Ordovician Decorah Shale overlies the St. Peter Sandstone and probably is the most suitable cap rock in southeastern Minnesota. However, the Decorah is restricted geographically and generally lies relatively near the surface. The Eau Claire Formation, above the Mt. Simon Sandstone, also has been considered as a possible cap rock, but it is composed of shales that are interbedded with sandstones and is vertically permeable. As this was the first cored well in this part of southeastern Minnesota, a study was undertaken of the lithic units penetrated during drilling, and interpretations were inferred for the depositional environment of each unit. The rocks of Paleozoic age were deposited in a shallow-water environment in cyclic fashion. Four recurrent lithotopes that characterize the rocks are (1) quartzarenite, (2) poorly sorted lithotope with strata composed of clastic particles ranging in size from silt to granule or with arenaceous carbonate strata, (3) shale or argillaceous sandstone, and (4) carbonate rock. The recurrence of these lithotopes in the Paleozoic column in southeastern Minnesota has led to the identification of nine sedimentary rock cycles. Several of the cycles are bounded on their upper surfaces by unconformities; in others, rocks occur that appear to have been deposited by both transgressional and regressional seas. The general trend in the depositional cycles of Cambro-Ordovician rocks of southeastern Minnesota is from predominant sandstone and subordinate carbonate in the older cycles to subordinate sandstone and predominant carbonate in the younger cycles. This progression reflects the gradual degradation of the Precambrian surface and the covering of these basement rocks and older Paleozoic rocks by younger sediments.