Indiana Geography and Geology Facts

Indianapolis Location: 39.826761 N, 86.138582 W
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Magnetic Declination of Indiana for 1999: 3º 7' W
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Total Indiana Population: 5,820,000
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Indiana Geology Today
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Indiana Geological Survey

Some Indiana Geology Facts (from Indiana Geology Today)

Bedrock Geology
The entire bedrock surface of Indiana consists of sedimentary rocks. The major kinds of sedimentary rock in Indiana include limestone, dolomite, shale, sandstone, and siltstone.

Indiana is a large anticline that plunges to the northwest.

Bedrock Ages
Rocks age from southeast to the west and north (geologic time scale, fun geologic time scale). The oldest (exposed in the southeast) are Upper Ordovician (~440-446 millions of years ago [mya]); this is the Maquoketa Group (shale and limestone). The youngest are exposed in the southwest; they are Pennsylvanian and comprise the McLeansboro Group (mostly sandstone and shale with discontinuous beds of coal and limestone).

Indiana Limestone
The most famous Indiana geology is a sequence of carbonate rocks that is 250 to nearly 500 feet thick and has significant amounts of gypsum, anhydrite, shale, chert, and calcareous sandstone. These rocks make up the Sanders and Blue River Groups. Within the Sanders Group is a formation known by geologists as the Salem Limestone and by architects as "Indiana Limestone." This thickly bedded limestone is quarried for a variety of architectural purposes and is known as one of the premier dimension stones in the world.

Another Indiana trademark is karst, the weathering of limestone by acid dissolution that produces sink holes, caves, and other features. The Mitchell Plain, an area of relatively low relief, is pockmarked by sinkholes and underlain by extensive cave systems developed in the Mississippian age limestone bedrock. Surface drainage on the Mitchell Plain is rare because most streams disappear at various points along their reach into caves and joints developed within the rock. Stream erosion and dissolution of limestone by weakly acidic precipitation are the principal means of erosion that produced the Mitchell Plain.

Finally, Central and Northern Indiana geology is the product of glaciation. The early 20th -century geographer C.R. Dryer referred to the terrain of central Indiana as so monotonous that a visitor to the region "may ride upon the railroad train for hours without seeing a greater elevation than a haystack or a pile of sawdust." Called the Tipton Till Plain, this flat to gently rolling surface is the product of continental glaciation during the Ice Age. Sediments borne by the ice sheets were deposited as till (an unsorted mixture of sand, silt, clay and boulders) when the glaciers advanced into Indiana and as outwash sand and gravel when the ice melted. Thick accumulations of till and outwash filled the bedrock valleys and covered the bedrock hills of northern Indiana to produce the flat to gently rolling landscape thought of by many as monotonous.

IGS Glossary (from whence most of the above definitions come)