In scattered places in the United States, carbonate rocks are interbedded with almost equal amounts of water-yielding sandstone. In most places where these two rock types are interbedded, the carbonate rocks yield much more water than the sandstone.
In scattered places in the United States, carbonate rocks are interbedded with almost equal amounts of water-yielding sandstone. In most places where these two rock types are interbedded, the carbonate rocks yield much more water than the sandstone.
Most carbonate rocks originate as sedimentary deposits in marine environments. Compaction, cementation, and dolomitization processes might act on the deposits as they lithify and greatly change their porosity and permeability. However, the principal postdepositional change in carbonate rocks is the dissolution of part of the rock by circulating, slightly acidic groundwater. Solution openings in carbonate rocks range from small tubes and widened joints to caverns that may be tens of meters wide and hundreds to thousands of meters long. Where they are saturated, carbonate rocks with well-connected networks of solution openings yield large amounts of water to wells that penetrate the openings, although the undissolved rock between the large openings may be almost impermeable.
This map of sandstone and carbonate-rock aquifers in the United States shows the shallowest principal aquifer. In some places, other, sometimes more productive, aquifers underlie those mapped. Only small areas of some aquifers may be shown on the map because they are covered in many places by other aquifers closer to the land surface. In other places, local aquifers, such as those along stream valleys, might overlie the aquifers mapped. Local aquifers are not shown because of the scale of the map. Some aquifers in sedimentary rocks are overlain by confining units, and the aquifers extend into the subsurface beyond the areas shown on the map.
Sandstone and carbonate-rock aquifers include:
Edwards-Trinity aquifer system (Texas and Oklahoma)
- Oklahoma and Texas (Chapter E)
- Arkansas, Louisiana, and Mississippi (Chapter F)
Valley and Ridge aquifers (eastern U.S.)
- Delaware, Maryland, New Jersy, North Carolina, Pennsylvania, Virginia (Chapter L)
- Alabama, Florida, Georgia, and South Carolina (Chapter G)
Mississippian aquifers (central and eastern U.S.)
- Iowa, Michigan, Minnesota, and Wisconsin (Chapter J)
- Illinois, Indiana, Kentucky, Ohio, and Tennessee (Chapter K)
- Delaware, Maryland, New Jersy, North Carolina, Pennsylvania, Virginia (Chapter L)
Paleozoic aquifers (northern Great Plains)
- Montana, North Dakota, South Dakota, and Wyoming (Chapter I)
Below are other web pages related to principal aquifers.
Principal Aquifers of the United States
Unconsolidated and semiconsolidated sand and gravel aquifers
Sandstone aquifers
Carbonate-rock aquifers
Igneous and metamorphic-rock aquifers
Minor aquifers, confining units, and areas identified as "not a principal aquifer"
- Overview
In scattered places in the United States, carbonate rocks are interbedded with almost equal amounts of water-yielding sandstone. In most places where these two rock types are interbedded, the carbonate rocks yield much more water than the sandstone.
Sources/Usage: Public Domain.The flat to gently rolling plains of the Edwards Plateau are locally interrupted by steep canyon walls. This view in western Crockett County, Texas, is toward the southwest and the Pecos River Valley. The road cut exposes the Fort Lancaster Formation. In scattered places in the United States, carbonate rocks are interbedded with almost equal amounts of water-yielding sandstone. In most places where these two rock types are interbedded, the carbonate rocks yield much more water than the sandstone.
Most carbonate rocks originate as sedimentary deposits in marine environments. Compaction, cementation, and dolomitization processes might act on the deposits as they lithify and greatly change their porosity and permeability. However, the principal postdepositional change in carbonate rocks is the dissolution of part of the rock by circulating, slightly acidic groundwater. Solution openings in carbonate rocks range from small tubes and widened joints to caverns that may be tens of meters wide and hundreds to thousands of meters long. Where they are saturated, carbonate rocks with well-connected networks of solution openings yield large amounts of water to wells that penetrate the openings, although the undissolved rock between the large openings may be almost impermeable.
This map of sandstone and carbonate-rock aquifers in the United States shows the shallowest principal aquifer. In some places, other, sometimes more productive, aquifers underlie those mapped. Only small areas of some aquifers may be shown on the map because they are covered in many places by other aquifers closer to the land surface. In other places, local aquifers, such as those along stream valleys, might overlie the aquifers mapped. Local aquifers are not shown because of the scale of the map. Some aquifers in sedimentary rocks are overlain by confining units, and the aquifers extend into the subsurface beyond the areas shown on the map.
Sources/Usage: Public Domain.Principal sandstone and carbonate-rock aquifers in the United States. Sandstone and carbonate-rock aquifers include:
Edwards-Trinity aquifer system (Texas and Oklahoma)
Sources/Usage: Public Domain.The three major aquifers that constitute the aquifer system are the Edwards-Trinity, the Edwards, and the Trinity. - Oklahoma and Texas (Chapter E)
- Arkansas, Louisiana, and Mississippi (Chapter F)
Valley and Ridge aquifers (eastern U.S.)
Sources/Usage: Public Domain.The most important aquifers in the Valley and Ridge province are northeast- to east-trending carbonate rocks. Undifferentiated sedimentary-rock aquifers that consist mostly of sandstone and yield moderate volumes of water separate the bodies of carbonate rocks. Coal-bearing beds are prominanat in parts of Pennsylvania and in a local area of southeast Virginia. - Delaware, Maryland, New Jersy, North Carolina, Pennsylvania, Virginia (Chapter L)
- Alabama, Florida, Georgia, and South Carolina (Chapter G)
Mississippian aquifers (central and eastern U.S.)
Sources/Usage: Public Domain.Generally, thick-bedded limestones and sandstones constitute the Mississippian aquifers. In Kentucky and Tennessee, water in the limestone bedrock moves through bedding planes and fractures enlarged by slightly acidic water. - Iowa, Michigan, Minnesota, and Wisconsin (Chapter J)
- Illinois, Indiana, Kentucky, Ohio, and Tennessee (Chapter K)
- Delaware, Maryland, New Jersy, North Carolina, Pennsylvania, Virginia (Chapter L)
Paleozoic aquifers (northern Great Plains)
Sources/Usage: Public Domain.Paleozoic aquifers extend over large areas in the subsurface of Montana, North Dakota, South Dakota, and Wyoming. The aquifers commonly contain highly mineralized water where they are deeply buried. - Montana, North Dakota, South Dakota, and Wyoming (Chapter I)
- Science
Below are other web pages related to principal aquifers.
Principal Aquifers of the United States
This website compiles USGS resources and data related to principal aquifers including Aquifer Basics, principal aquifers maps and GIS data, and the National Aquifer Code Reference List.Unconsolidated and semiconsolidated sand and gravel aquifers
Unconsolidated sand and gravel aquifers are characterized by intergranular porosity and all contain water primarily under unconfined, or water-table, conditions. They are grouped into four categories: basin-fill, blanket sand and gravel, glacial-deposit, and stream-valley aquifers. Semiconsolidated aquifers consist of semiconsolidated sand interbedded with silt, clay, and minor carbonate rocks...Sandstone aquifers
Sandstone aquifers are more widespread than those in all other kinds of consolidated rocks. Groundwater movement in sandstone aquifers primarily is along bedding planes, but joints and fractures provide avenues for the vertical movement of water. Sandstone aquifers can be highly productive and provide large volumes of water.Carbonate-rock aquifers
Aquifers in carbonate rocks are most extensive in the eastern U.S. Most of the carbonate-rock aquifers consist of limestone, but dolomite and marble locally yield water. The water-yielding properties of carbonate rocks vary widely; some yield almost no water and are considered to be confining units, whereas others are among the most productive aquifers known.Igneous and metamorphic-rock aquifers
Igneous and metamorphic-rock aquifers can be grouped into two categories: crystalline-rock and volcanic-rock. Spaces in crystalline rocks are microscopically small, few, and generally unconnected. However, because these aquifers extend over large areas, large volumes of water can be withdrawn. Volcanic-rock aquifers have a wide range of chemical, mineralogic, structural, and hydraulic properties...Minor aquifers, confining units, and areas identified as "not a principal aquifer"
Aquifer maps often include large-to-small areas that are designated "minor aquifer," "not a principal aquifer," or "confining unit.” These are usually areas are underlain by low-permeability deposits and rocks, unsaturated materials, or aquifers that supply little water because they are of local extent, poorly permeable, or both. - Publications