3-D GEOLOGIC MAPPING OF QUATERNARY SEDIMENTS USING GIS AND PETREL IN WALWORTH COUNTY, WI

This study is focused in Walworth County, WI and expands on a previous mapping study in adjacent McHenry County, IL that used GIS and Petrel software packages to map Quaternary deposits in three dimensions. Data such as water well records, stratigraphic borings, geologic maps and digital elevation models were used in ArcGIS with customized tools to map and interpret the Quaternary geology in the 3-D environment. Those interpreted data were then integrated into Petrel and used to build a 3D geologic model of the Quaternary deposits. This mapping was done to better understand the aquifer distributions in Walworth County.

In the mapping area during the Wisconsin Episode, ice from the Lake Michigan Lobe and Delavan Sublobe advanced from the northeast to the southwest in several pulses leaving a complex assemblage of till and outwash sand and gravel units of varying thickness and extent. Tills range in thickness from 0’ to over 100’ thick and sand and gravel units range in thickness from 0’ to over 40’ thick throughout the study site. Depth to bedrock ranges from 50’ to over 500’ below ground surface. The southwestern most glacial advance is marked by the U-shaped Darien Moraine which trends northwest-southeast across the southern part of Walworth County. This moraine is composed of an upper sandy basal till and lower outwash sand and gravel. These units form the upper and lower members of the New Berlin Formation, which overlies the Tiskilwa Member of the Zenda Formation. The northwestern extent of the Delavan Sublobe in this area is marked by the Elkhorn Moraine, where the Tiskilwa Member is overlain by a thin layer of New Berlin till. Underlying the Tiskilwa Member is the Walworth Formation, which is composed of till and sand and gravel units deposited during the Illinoisan stage of glaciation.

For mapping purposes, glacial sediments in the assemblage were grouped into 6 units. Three of the mapped units were till deposits associated with the New Berlin, Zenda, and Walworth Formations, respectively. Two other mappable units included the outwash deposits of the Zenda and Walworth Formations. Lastly, the lowermost unit was mapped as the valley fill of a major local bedrock valley in the area.