Many communities in the upper Midwest, USA, draw municipal water from basal Cambrian formations that overlie the Precambrian unconformity. In Wisconsin, USA, the basal Cambrian section includes the Mount Simon, Eau Claire, and Wonewoc formations, which are collectively part of the Elk Mound Group. Single well analysis and county-specific studies have shown the Eau Claire Formation is an important regional aquitard. However, in Wisconsin, basal Cambrian units have variations in lithology depending on depositional environments. Depositional facies in the Eau Claire Formation become shallower in proximity to Precambrian paleogeographic highs, resulting in the thinning and local absence of the Eau Claire Aquitard. This spatial transition is poorly characterized regionally and has not been mapped. This study correlates hundreds of lower Cambrian wells and includes both outcrop and core data to characterize the depositional environments of the aquitard-aquifer system. These depositional environments are predictable within a sequence stratigraphic framework. Hydrogeologic data (flow logs and head measurements) show hydrologic head differences and variable flow gradients in aquifers separated by a high gamma ray, share-rich, Eau Claire Aquitard, which was deposited in basinal to shoreface environments. Hydrogeologic measurements show no perturbation to flow in time-equivalent, shallower-water, depositional environments that lack the high gamma ray, shale-rich strata. Within the study area, the Eau Claire Aquitard presence, thickness, and potential hydrogeologic impact is mapped within a range of uncertainty. This study shows that depositional and sequence stratigraphic concepts can be used to predict regional hydrogeologic behavior for Cambrian groundwater systems.
Stephens et al. (Fri,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: