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| 2. |
- Dalton, April S., et al.
(author)
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Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1
- 2023
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In: QUATERNARY SCIENCE REVIEWS. - 0277-3791 .- 1873-457X. ; 321
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Journal article (peer-reviewed)abstract
- The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of Be-10, 459 measurements of Al-26 and 35 measurements of Cl-36 from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly 'unzipping' of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km(2). All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
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| 3. |
- Jennings, Carrie, et al.
(author)
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The Quaternary of Minnesota
- 2011
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In: In J. Ehlers, P.L. Gibbard and P.D. Hughes, editors: Developments in Quaternary Science, Vol. 15, Amsterdam, The Netherlands, 2011, © Copyright 2011 Elsevier B.V.. - Amsterdam : Elsevier. - 9780444534477 ; , s. 499-511
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Book chapter (other academic/artistic)abstract
- The rich and complex sedimentary record of glaciation in Minnesota includes deposits of glaciers, associated rivers and lakes, as well as windblown and other periglacial deposits that span the Quaternary Period and are at the surface in nearly every part of the state. The thickness of these deposits is commonly more than 100 m. One of the thickest, and perhaps most stratigraphically complete, records of the Quaternary in Minnesota lies beneath the Coteau des Prairies, an inter-ice stream sediment highland that spans the Minnesota–South Dakota border where over 300-m of fine-grained diamictons are preserved (Fig. 38.1). Though the glacial deposits of the state are dominated by a complex Late Wisconsinan history (marine isotope stage (MIS) 2), Minnesota has many lithostratigraphical units from the Middle and likely Early Pleistocene. For example, Minnesota has units older than the Sangamon Geosol (>125 ka), units older than volcanic ashes derived from Yellowstone (>610 ka) (Boellstorff, 1978), as well as magnetically reversed units from prior to the Brunhes– Matayuma boundary (>788 ka). Recent cosmogenic burial dating of glacigenic sediment (Balco et al., 2005) indicates that numerous glacial stratigraphical units were deposited prior to MIS 14. A rare bedrock exposure in the southern part of the Coteau des Prairie highland was striated as early as 640–740 ka (MIS 16 or 14) based on cosmogenic exposure dating of the quartzite using a paired-isotope system (Bierman et al., 1999). A stack of 12 tills surrounding this isolated bedrock high is therefore most likely a record of glaciation prior to and including MIS 14–16. Ice streams that were active primarily during MIS 2 focused erosion on either side of the Coteau des Prairie leaving it as a remnant between broad erosional unconformities (Fig. 38.1). The southeastern corner of Minnesota was also glaciated many times early in the Quaternary Period but remained ice-free duringMIS2–4, during which time it was affected by strong, northwesterly, periglacial winds and permafrost (Zanner, 1999). Thus, the earlier record of glaciation of this part of Minnesota is obscured and in places, confined to sinkholes and caves (e.g. Milske et al., 1983). The southern margin of the Late Wisconsinan (MIS 2) Laurentide ice sheet produced many dynamic ice protuberances or lobes that emanated from discrete ice-source areas (Fig. 38.2). Some of the tributary ice sheds had distinctive bedrock geology allowing the provenance of the ice as well as the evolution of ice sheds to be discerned. This condition has produced distinct lithologic compositions for the tills derived from different ice centres and has provided a basis for differentiating and formalising lithostratigraphical units (Johnson et al., in preparation). Four broad source regions have been identified and their characteristics are shown in Table 38.1 and Fig. 38.3. Minnesota’s pre-MIS 2 till units share the same broadly defined provenance regions indicating that older glaciations had similar sources areas. However, the shape of the former ice margins is much more difficult to determine from the scattered subsurface information and therefore ice dynamics more difficult to infer. Where the pre-MIS 2 ice limits are at the surface, their breadth and more southerly extent suggest that at the very least, the ice lobes were broader. It remains possible that the ice dynamics were substantially different at times in the past and did not lead to the creation of ice streams and lobes, for example, during the ice-sheet-build-up phase of each glaciation and prior to the Middle Pleistocene transition (when the frequency of glaciation and volume of changed from 41,000-year periodicity to
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| 4. |
- 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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| 5. |
- Johnson, Mark D., 1954, et al.
(author)
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Lithostratigraphy for Quaternary glacial deposits: “If it ain’t broke, don’t fix it!”
- 2009
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In: GSA Today. ; 19:9, s. 15-15
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Journal article (peer-reviewed)abstract
- (A response to an article by Räsänen) Räsänen and others (2009) claim that lithostratigraphic classification of Quaternary glacial deposits is so problematic that it is time to use allostratigraphy instead. Our immediate response from a Midwest perspective is—what problems? Formal lithostratigraphic classification of glacial deposits works. Since its initial use to define Pleistocene units in the Midwest (Willman and Frye, 1970), there has never been a serious reason to question this practice. Indeed, formal lithostratigraphies have been progressively established in most Midwestern states.
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| 6. |
- 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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| 7. |
- Rodriguez, Sébastien, et al.
(author)
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Science goals and new mission concepts for future exploration of Titan's atmosphere, geology and habitability : titan POlar scout/orbitEr and in situ lake lander and DrONe explorer (POSEIDON)
- 2022
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In: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 54:2-3, s. 911-973
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Journal article (peer-reviewed)abstract
- In response to ESA’s “Voyage 2050” announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn’s largest moon Titan. Titan, a “world with two oceans”, is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan’s remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a “heavy” drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan’s northern latitudes with an orbiter and in situ element(s) would be highly complementary in terms of timing (with possible mission timing overlap), locations, and science goals with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan’s equatorial regions, in the mid-2030s.
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