Browsing by Subject "Surficial geology"

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    Geologic Map Series 2. Surficial Geology of the New Brighton Quadrangle, Minnesota
    (Minnesota Geological Survey, 1966) Stone, John E.
    The New Brighton quadrangle is underlain by as much as 500 feet of glacial drift, which lies directly on Paleozoic sedimentary rocks. The bedrock, which is part of the northern flank of the Twin Cities artesian basin, is traversed by a complex network of buried valleys as much as 400 feet deep that were cut during several cycles of erosion. Most of the surface morphology and the related deposits were formed about 12,500 years ago, during the advance and retreat of the Grantsburg Sublobe, which produced the following formations in the approximate order of their deposition: (1) the Hillside Sand, a proglacial outwash deposit; (2) the Twin Cities Formation, a complex mixture of gray and red till; (3) the Falcon Heights Sand, a retreatal outwash deposit; (4) the Turtle Lake Sand, a lake deposit; (5) the Arsenal Sand, a kame deposit; (6) the New Brighton Formation, a lake deposit; and (7) the Fridley Formation, another lake deposit. The units have been mapped at the surface and traced in the subsurface. After the active ice retreated from the immediate area, the West Campus Sand, a valley-train deposit, was deposited. Later, ice in the drift melted to produce many hundreds of kettle holes, some of which are now occupied by lake or swamp deposits; the valley train was dissected, leaving a terrace along the Mississippi River; and a poorly integrated drainage system was produced. In late-glacial and postglacial time, thin deposits of eolian sand, loess, and colluvium were laid down. The most significant changes in the landscape in postglacial time have been made by man, who settled the area in the 1830's and 1840's. Preliminary data are given on the engineering properties of the surficial deposits. These data in conjunction with the geology are useful for engineering and hydrologic studies, land-use planning, and resource evaluation.