Conference proceeding
Mapping the middle Wisconsin Sheldon Creek Formation boundary in north central Iowa
Minnesota Geological Survey Open-File Report, pp.90-91
Geologic mapping forum 2019
2019
Abstract
Geologic mapping in north central Iowa has redefined the Middle Wisconsin Sheldon Creek boundary. Work was initiated during a cooperative mapping project with the Natural Resources Conservation Service (NRCS) during a soil survey update of Worth County. This work indicated the Sheldon Creek extended beyond the margin mapped by Hallberg et al. (1991). Subsequent work by the Iowa Geological Survey (IGS) as part of the USGS STATEMAP program has substantially moved this boundary to the east (Quade et al. 2012; Tassier-Surine et al. 2015, 2016; Kerr et al. 2018).
Limited exposures of the Sheldon Creek Formation in Iowa make it difficult to evaluate, as much of its surface is covered by the Late Wisconsin Des Moines Lobe glacial advance. Further complicating identification of the eastern extent is the abundance of shallow bedrock and the pervasive erosion that occurred during the Last Glacial Maximum when the Iowan Surface landform region formed. Therefore, differentiating the Sheldon Creek glacial deposits from the much older Pre-Illinoian till can be difficult in this region. Due to this complexity, a varied set of characteristics was used to define the Sheldon Creek Formation boundary including physical properties, radiocarbon age dating, geomorphology, LiDAR, soil types, and drainage orientations.
The IGS and NRCS drilled over 200 borings in the study area over a 10 year period. Drill core descriptions, analytical data (grain-size, clast lithology, and pXRF data), and radiocarbon dates were used to constrain the stratigraphic framework. Samples for radiocarbon ages were collected in the mapping area from wood or soil organics in till. When combined with results from previous studies, these ages indicate that two Middle Wisconsin advances of the Sheldon Creek Formation are present in north central Iowa. The first advance occurred between 46,000 and 40,000 years ago with a younger advance between 34,000 and 29,000 years ago (Kerr, 2018).
Details
- Title: Subtitle
- Mapping the middle Wisconsin Sheldon Creek Formation boundary in north central Iowa
- Creators
- Stephanie Tassier-Surine - Iowa Geological Survey Iowa City, IA USA United StatesPhillip KerrKathleen WoidaE. Arthur BettisDeborah J. Quade
- Contributors
- Harvey Thorleifson (Editor) - Minnesota Geological Survey
- Resource Type
- Conference proceeding
- Publication Details
- Minnesota Geological Survey Open-File Report, pp.90-91
- Conference
- Geologic mapping forum 2019
- Publisher
- Minnesota Geological Survey
- Alternative title
- Geologic mapping forum 2019 abstracts
- Language
- English
- Date published
- 2019
- Academic Unit
- Earth and Environmental Sciences; Iowa Geological Survey; IIHR--Hydroscience and Engineering
- Record Identifier
- 9984702713802771
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