Abstract
The status of MIS 3 tills in Iowa, USA
Abstracts with programs - Geological Society of America, Vol.54(5)
Geological Society of America, 2022 annual meeting; GSA connects 2022
10/2022
DOI: 10.1130/abs/2022AM-383029
Abstract
Exposures of MIS 3 glacial sediment are thought to paltry within North America as MIS 2 ice buried/eroded older deposits. However, there are MIS 3 glacial diamictons in Iowa both beyond and below MIS 2 deposits. Numerous radiocarbon ages from wood collected from basal till and buried organic horizons returned ages between 45-30ka. These ages show two groupings, one at nearly equal 42ka and another at nearly equal 30ka which suggests two advances. Differentiating the MIS 3 boundary is problematic as glacial landforms from these advances, e.g., moraines, have been muted or removed by wide-scale periglacial erosion during MIS 2. Due to the mass wasting, remote sensing was utilized to identify a margin using broad glacial geomorphologic signals. Patterns such as river reorganization, drainage network integration, and landscape incision were used to differentiate distinct pre-MIS 2 glacial surfaces. These boundaries were tested using till lithology from boreholes. The MIS 2 till (Dows Fm.) and the MIS 3 tills (Sheldon Creek Fm.) have similar carbonate and shale rich lithologies which distinguishes them from older Pre-Illinoian tills (>MIS 6). These geomorphic and lithologic patterns were used to establish the MIS 3 boundary to the east and west of the Bemis Moraine (MIS 2 terminal moraine) in Iowa. The interpretation of two advances is supported stratigraphically. In a nearly equal 25m quarry section on the MIS 2 till plain, MIS 2 ice deposited Dows Fm. till was on Peoria Fm. loess which accumulated on a two till sequence which intern buried the Sangamon Geosol formed in Wolf Creek or Alburnett Fm. tills (>MIS 6). Other cores outside of the Bemis also have two carbonate and shale rich tills above older deposits. Together, these lines of evidence show a lobe of the Laurentide Ice Sheet was south of 42.5 degrees N during intervals in MIS 3.
Details
- Title: Subtitle
- The status of MIS 3 tills in Iowa, USA
- Creators
- Phil Kerr - University of Iowa, Department of Earth and Environmental Sciences Iowa City, IA USA United StatesStephanie Tassier-Surine
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.54(5)
- Conference
- Geological Society of America, 2022 annual meeting; GSA connects 2022
- Publisher
- Geological Society of America (GSA)
- DOI
- 10.1130/abs/2022AM-383029
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2022 annual meeting; GSA connects 2022
- Language
- English
- Date published
- 10/2022
- Academic Unit
- Iowa Geological Survey; IIHR--Hydroscience and Engineering
- Record Identifier
- 9984701804402771
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