ROCKS, LEAVES, AND SOIL: DISCOVERING THE CRETACEOUS OF WESTERN WISCONSIN

The stratigraphy of western Wisconsin is largely early Paleozoic (450-500 Ma) marine sedimentary bedrock overlain by Quaternary glacial materials deposited less than 700,000 years before present. Only a few studies have documented isolated, rare deposits in this vast interval of time. The objective of this research was to investigate two lithologically and stratigraphically unique localities in western Wisconsin. The Thompson locality is a recent foundation excavation that exposed a variably cemented iron-oxide coated quartz sandstone. In addition, nine partial to complete leaf imprints and numerous wood chip impressions were found at the site. One of the leaves has been tentatively assigned to the Lauraceae family. The Barsness locality is a road cut exposing an iron-rich conglomerate with iron oxide concretions and abundant chert clasts. The deposits at both localities are distinctly different than the Paleozoic bedrock and glacial sediments of the region and have been assigned to the Cretaceous-aged Windrow Formation based on past literature, laboratory analysis, and field correlation with more extensive deposits in Minnesota. As such, the leaves at the Thompson locality are the first in-place Cretaceous fossils from Wisconsin. Also at the Thompson locality, a soil with distinct characteristics was found developing in association with the Cretaceous deposit. Detailed soil maps (1:24,000) produced by the Natural Resources Conservation Service show that the unique soil is spatially extensive in the areas surrounding the two localities studied, along with other areas in western Wisconsin. The ability of soil maps to identify new Cretaceous localities is currently being investigated. This research highlights the value of an interdisciplinary approach to improving our overall understanding of the geology of the western Wisconsin.