Karst Aquifers: Midwest Paleozoic Carbonate Aquifers

Science Center Objects

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. This aquifer demonstrates karst features such as disappearing streams, springs, and caves.

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.

 

Disappearing Streams

USGS Hydrologist Chuck Taylor stands next to a stream that enters the subsurface through a cave entrance.

USGS Hydrologist Chuck Taylor stands next to a stream that enters the subsurface through a cave entrance.

 

Springs

A blue-hole spring, Orangeville Rise, Indiana (sixty feet in diameter).

A blue-hole spring, Orangeville Rise, Indiana. This spring is sixty feet in diameter. (Credit: Chuck Taylor, USGS.)

 

Caves

 

Additional Information

The following websites are additional sources of information about this aquifer: