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- Johnson, Mark D., 1954, et al.
(author)
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A FORMAL LITHOSTRATIGRAPHY FOR THE QUATERNARY OF MINNESOTA
- 2011
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In: Geological Society of America abstracts with programs Minneapolis 2011.
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Conference paper (peer-reviewed)abstract
- The Minnesota Geological Survey has created a formal lithostratigraphy for the Quaternary deposits of Minnesota that will be published on-line and in-print, fall 2011. We followed guidelines of the North American Commission on Stratigraphic Nomenclature (2005) to create a framework for establishing formal lithostratigraphic units in Minnesota, and we evaluated the approximately 120 lithostratigraphic names and units that have been identified and used in Minnesota since the time when geologic mapping of glacial deposits began. Of these, eighty-one (81) units are considered to be useful lithostratigraphic units of formation and member rank, and these are formally accepted in this open-file report or will be in future volumes. These 81 units include previously named formal lithostratigraphic units that are recognized and accepted as originally defined, but also formally defined units that we have revised or redefined to better fit into our stratigraphic framework. The remaining lithostratigraphic units have been used informally in earlier reports or are newly named. Twenty-three units are no longer considered valid as lithostratigraphic units are abandoned even though some of these are well-known among state geologists. These units include previously used units of both formal and informal status. Many units, especially in the subsurface, are undefined at the present time because their character and extent are poorly known.
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| 2. |
- Lusardi, Barbara A., et al.
(author)
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QUATERNARY STRATIGRAPHY OF MINNESOTA—CHARACTERIZATION AND CORRELATION OF UNITS
- 2011
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In: Geological Society of America abstracts with programs Minneapolis 2011.
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Conference paper (peer-reviewed)abstract
- Much of Minnesota is covered by Quaternary sediment largely deposited by multiple ice lobes that emanated from different source areas within the Laurentide ice sheet. Subdivision of this sediment sequence as stratigraphic units is ongoing and provides a basis for interpreting the history of glaciation, as well as sedimentation in associated rivers and lakes. In addition, quantitative characterization of the properties of these strata increasingly is needed for applications such as groundwater management. To support characterization and correlation of these sediments, primarily consisting of diamicton interpreted as till, Minnesota Geological Survey staff have built a database of analyses for over 26,000 glacial sediment samples. The database includes location and descriptive information, along with matrix texture as percent sand, silt, and clay. For most samples, the very coarse sand fraction (1-2 mm) is further subdivided on the basis of the percentage of crystalline, carbonate, and shale grains, along with identification of indicator rock types within these groups. Lithologic data are used to assign tills to one of four source areas: shale-rich Riding Mountain provenance to the northwest, carbonate-rich Winnipeg provenance, carbonate-free and Lake-Superior erratic-free Rainy provenance, and finally red sandstone and rhyolite-bearing Superior provenance to the northeast. Recent progress on Minnesota Quaternary stratigraphy suggests that the sediments can be correlated across the state and can be subdivided as follows: old tills and associated sediment including magnetically reversed deposits, the bulk of which are derived from the Winnipeg provenance, but also includes Rainy and Superior provenance units; pre-Sangamonian, Winnipeg-source Browerville Formation which may be older or younger than the Superior-source tills such as the Hawk Creek, Henderson, and River Falls formations; Wisconsinan Traverse des Sioux and associated sediment that is a mix of both Winnipeg and Rainy sources; Rainy provenance sediments including the Independence formation; Superior provenance sediments including the Cromwell and Barnum formations; Riding Mountain provenance sediments mostly consisting of the New Ulm Formation; and sorted sediments such as the deposits of Lake Agassiz.
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