Paper No. 33-3
Presentation Time: 2:10 PM
PROVENANCE VARIATION IN A LAURENTIDE ICE SHEET LAKE MICHIGAN LOBE DEPOSIT, PETRIFYING SPRINGS, KENOSHA, WISCONSIN
The Laurentide Ice Sheet (LIS) extended from Canada south to cover vast expanses of North America, consisting of irregular glacial lobe advances and retreats that began approximately 31,000 BP until about 11,000 BP when ice vanished from the Northern United States. The Lake Michigan (LM) Lobe began as part of the larger LIS in Canada near James Bay and advanced southwest; as it retreated, it deposited various moraines and glaciolacustrine materials throughout southeastern Wisconsin. There has been much research completed on the glacial history of Wisconsin, primarily focused on landform formation, glacial till composition, and lithostratigraphic unit identification. In addition, general flow lines from Canada have been established that outline the movement of the LIS into Wisconsin. This study aims to enhance the research regarding lithic material that was deposited by the glacial activity of the Lake Michigan Lobe in southeastern Wisconsin. Our objective is to classify the lithic material contained within a recessional moraine in order to qualitatively establish the point of origin of the material. Shallow samples were taken from four locations along the Petrifying Springs recessional moraine, located in Kenosha, Wisconsin. Within these samples, lithic fragments greater than two millimeters in size were gathered and classified according to their general rock type: igneous, metamorphic, or sedimentary. Based on previously determined glacial flowlines, a generalized location of the origin of the material within the Petrifying Springs recessional moraine could be determined. The majority of lithic material collected was sedimentary, including limestone, dolomite, sandstone, shale, and chert: 12 out of 14 samples contained 70% or more sedimentary materials. Igneous rocks composed about 20%, the second highest percentage, of the material collected, which included granitic, gabbroic, and basaltic clasts. Most igneous material was determined to be transported from Ontario and Quebec south of James Bay. Lastly, metamorphic rocks, mostly quartzite, comprised only 2% of the rocks analyzed. The coarse material incorporated in a recessional moraine of the Lake Michigan Lobe has been derived unequally from proximal and distant erosional sources, with more material from local sedimentary sources.