Browsing by Subject "bedrock topography"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    C-39, Geologic Atlas of Washington County, Minnesota
    (Minnesota Geologica Survey, 2016) Bauer, Emily J.
    A County Geologic Atlas project is a study of a county's geology, and its mineral and ground-water resources. The information collected during the project is used to develop maps, data-base files, and reports. This same information is also produced as digital files for use with computers. The map information is formatted as geographic information system (GIS) files with associated data bases. The maps and reports are also reproduced as portable document files (PDFs) that can be opened on virtually any computer using the free Acrobat Reader from Adobe.com.
  • Thumbnail Image
    Item
    The Influence of Bedrock Topography on the Origin of a Mid-Pleistocene Epoch Glacial Lake in Rock County, Southwest Minnesota
    (Minnesota Geological Survey, 2017) Southwick, David L
    A circular, closed depression 1.9 miles (3 kilometers) in diameter that was formerly occupied by a shallow lake is located in the glaciated landscape of northern Rock County, southwest Minnesota. The depression is partly framed by Sioux Quartzite and is situated above a bedrock swale on a broad, quartzite-supported upland that is thinly mantled by pre-Wisconsinan glacial deposits. The quartzite-supported upland has been a positive topographic feature since at least the Late Cretaceous Epoch; near the depression, its discontinuous cover of unconsolidated sediment consists of glacial till, outwash deposits, and loess that aggregate to a total preserved thickness between 1 and 82 feet (less than 1 to 25 meters). The depression originated from the melting out of a buried, tabular ice mass that was isolated near the stagnating margin of a mid-Pleistocene Epoch continental glacier. The ice mass was buried in outwash and then further buried by a thin till deposited when the glacier readvanced. The ice mass became isolated and was slow to melt because of its position in a bedrock swale on a topographic high that was near a dynamically fluctuating glacier margin; its relative thickness and protected location in the swale were key factors in its transient preservation. The closed depression that formed upon final melting of the ice mass has survived in the post-glacial landscape because of its location on a geomorphically persistent bedrock upland where the erosive energy of post-glacial and modern streams has been minimal. It has been speculated that this bedrock-framed, geographically unique circular depression may be a deeply eroded meteorite impact structure. No supporting evidence for this speculation has been discovered in the field or laboratory.
  • Thumbnail Image
    Item
    OFR16-4, Preliminary geologic maps of Lake and St. Louis Counties, northeastern Minnesota
    (Minnesota Geological Survey, 2016--2018) Jirsa, Mark A, Project Manager
    This Open-File Report (OFR) is a repository for on-going mapping in Lake and St. Louis counties that began in 2015 and will be largely completed by 2020. It contains preliminary bedrock and surficial geologic maps and associated products covering parts, and eventually all of the two counties. Because the counties are large, they have been divided for mapping purposes into subareas, each containing the name Arrowhead. Surficial, Bedrock Topography, and Depth to Bedrock maps are divided into 4 subareas referred to here as the Central (content prefixed “CA,” 2016, 2017); Southeastern (SeA, 2017, 2018); Southwestern (SwA, 2018), and Northern Arrowhead (NA) areas. Bedrock maps and associated files cover 3 subareas referred to as Central (CA, 2016); Southern (SA, 2017); and Northern Arrowhead (NA, 2018). Note that the boundaries of subareas differ somewhat between the surficial and bedrock maps. Products within this Open File Report include bedrock geologic maps, surficial geologic maps, bedrock topography and depth to bedrock maps, Quaternary stratigraphy, sand distribution models, corresponding GIS files, and other digital content. Ancillary files such as technical reports, geophysical imagery and models, and geochronologic data are included for bedrock mapping in the 3 bedrock subareas. Once these preliminary products are complete, the data and interpretations will be recombined into County Geologic Atlases that will supersede this OFR. Authors of individual maps and reports within the OFR include: Boerboom, T.J., Chandler, V.W., Dengler, E.L., Hamilton, J.D., Horton, J.M., Jirsa, M.A., Lively, R.S., Meyer, G.N., Peterson, D.M., Radakovich, A.L., Schmitz, M.D., Setterholm, D.R., Wagner, K.G., and Wall, C.