Stratigraphy, Sedimentology, and Deformational Significance of Cambrian and Early Ordovician Strata Along the Southeast Wisconsin Arch

Abstract

A detailed study of the stratigraphic units in and around the Wisconsin Arch of central and southeast Wisconsin are presented to refine the sedimentologic record and the geologic implications within the Cambrian and early Ordovician strata. The Cambrian and early Ordovician sediments in central and southeast Wisconsin unconformably overlie a topographic high composed of Precambrian basement rocks, called the Wisconsin Arch, and consist of various clastic deposits, dolostones, and several horizons of deformation. Bedrock cores, made available through the Wisconsin Geological and Natural History Survey (WGNHS), were analyzed, to understand sedimentation in the Cambrian and early Ordovician. My analyses focused on: (1) lateral distribution of strata and changes in depositional environments, (2) the nature of deformation (e.g., soft sediment, karst collapse, tectonic, or glacial overriding) observed along significant erosional contacts, (3) the effect of the Precambrian Wisconsin arch on sedimentation, and (4) the presence of unconformities including incised valleys. This research analyzed a high-resolution imagery dataset of 22 cores from Columbia, Dodge, Fond du Lac, and Jefferson counties. Published literature describes the central Wisconsin Arch region, near Dane County, as having three unconformities that are situated between many fining upward sequences, areas of deformation, and multiple incised valleys. This study uses descriptions of newly available cores to reevaluate literature and interpretations that address stratigraphy, facies description, depositional environment, deformation, and local unconformities in strata surrounding the Wisconsin Arch in southeast Wisconsin.