Midwest Paleozoic Carbonate Aquifers
The porosity of carbonate and dolomitic units in Midwest Paleozoic rocks has been enhanced by dissolution, and in many areas these rocks have undergone extensive karst development. The greatest karst development as occurred in Devonian-Silurian and Cambrian-Ordovician rocks. The vertical sequence of the aquifers and confining units varies across the region.
In Iowa and Michigan, solution-enhanced dissolution of Mississippian dolomitic rocks has resulted in karst flow systems.
Limestones in the Devonian-Silurian aquifer system in Ohio, Indiana, Illinois, Iowa, and Wisconsin have undergone extensive karst development. The limestones outcrop in some areas, and in others are overlain by up to several hundred meters of unconsolidated Quaternary deposit. Throughout this area, large well yields are possible from these units.
Some limestone and dolomites Cambrian-Ordovian rocks underlying the Silurian-Devonian aquifer also have undergone extensive karst development. These are water-producing units in parts of Illinois, Wisconsin, Minnesota and Iowa. In southeastern Minnesota and northern Iowa these are referred to as the upper carbonate aquifer, and is extremely productive.
Because of the prevalence of agriculture and livestock in this part of the United States, contamination of karst aquifers with nutrients, pesticides, and bacteria is of much concern. In Iowa, for example, regulations have been developed for some confined animal feeding operations in karst terrain.
Photos of Karst Features
Karst produces distinctive topographic features that can be prominent and distinctive. There are photographs available of the following karst features in Paleozoic karst aquifers of the Midwest:
- Disappearing Streams
There are 2 USGS scientists you can contact for more information about this aquifer.
The following websites are additional sources of information about this aquifer: