The Geology of Kentucky

Notes

Kentucky Is Divided Into 6 Distinct Regions

Bluegrass RegionThe Eastern Kentucky Coal FieldThe Knobs RegionThe Jackson Purchase or Mississippi Embayment RegionThe Mississippian Plateau or Pennyroyal RegionThe Western Kentucky Coal Field

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Bluegrass RegionCharacteristics of this region are gently rolling hills and rich, fertile soils, which are perfect for raising horses.Layers of Ordovician aged limestone has been pushed up along the crest of a region called Cincinnati Arch.The rolling hills are caused by the weathering of these thick beds of limestone which is characteristic of Kentucky.

Eastern Kentucky Coal FieldIs dominated by forested hills and deeply cut V-shaped valleys.In southeastern Kentucky the highest elevation in the State, (before mining), was Black Mountain in Harlan County 4,145 feet.Pine Mountain another important feature is best described as a 125-mile long ridge that extends from Jellico, Tennessee to Elkhorn City, Kentucky. It is 3,200 feet high in Letcher County and is a direct result of the Pine Mountain Thrust Fault.Appalachian Mountains built for the last time during end of Paleozoic era, block of Earth's crust was pushed up and over Southeastern Kentucky.

The Eastern Kentucky Coal FieldThis region is formed from resistant Pennsylvanian-age sandstone and conglomerates in the form of an escarpment. An escarpment is a ridge of gently tipped rock strata with long, gradual slope on one side and a steep scarp or cliff on the other.The sandstones weather and are eroded along the escarpment.Results in cliffs, steep-walled gorges, rock shelters, waterfalls, natural bridges and arches, the most scenic areas in Kentucky.

Knobs RegionIt is the region bordering the Bluegrass. It consists of hundreds of isolated, steep sloping, cone-shaped hills.The hills are monadnocks or erosional remnants that were originally continuous with the Mississippian Plateau, but were separated by stream erosion.Hills composed Mississippian-age “Borden Formation” shales, which are less resistant to erosion than the overlying limestones and sandstones.

Jackson Purchase or Mississippi Embayment

Cretaceous and Tertiary & Quaternary sediments occur at the surface. These deposits are unconsolidated (not cemented) sediment instead of rock. Are easily eroded, so, this part of Kentucky is flat with numerous lakes, ponds swamps. Local relief is less than 100 feet, and the lowest spot in the State, at only 260 feet above sea level, is found here.

Jackson Purchase or Mississippi Embayment

Is underlain by faults of the New Madrid Fault Zone, the most active earthquake zone in the central United States.The strongest earthquakes in the history of the United States occurred during the winter of 1811-1812 were caused by movements along the New Madrid faults in Missouri and extreme western Kentucky.

Mississippian Plateau /Pennyroyal RegionConsists of limestone bedrock.

Characterized by tens of thousands of sink holes, sinking streams, streamless valleys, springs, and caverns. Karst is used to define this type of terrain.Region dominated by thick deposits of Mississippian-age limestones. Terrain occurs because limestone bedrock in the eastern and southern parts are soluble (i.e. will dissolve) by waters moving through the ground.

This type of region contains some of the largest caves in the world.The Mammoth Cave-Flint Ridge cave system is the longest cave in the world.Carter Caves State Park, in Carter County, is very well known.All of theses systems are formed in Mississippian-age limestones in the Mississippian Plateau Region.

Western Kentucky Coal FieldSmaller than eastern coal field. It is the southern edge of a larger geologic feature called the Illinois Basin, includes Indiana & Illinois coal fields.An outcrop of Pennsylvanian age strata, defines the limits of the Western Kentucky Coal Fields.

Geology of Kentucky

Pennsylvanian aged strata occur in Kentucky in 2 areas. Both shown as dark blue on the geologic maps we will use.The Pennsylvanian age in Kentucky is composed of inter-bedded shale, sandstone, conglomerates, and coals. Thin limestone beds may also occur.Coal is Kentucky's leading mineral commodity.Because of the coal-bearing Pennsylvanian strata, we are among the top three states in the Nation in annual coal production (160 to 180 million tons annually).

All of Kentucky was covered by sediments of Pennsylvanian age at one time but, erosion has completely removed them from all areas but the coal fields now. Pennsylvanian Period, often called the Coal Age, was a time of alternating land and sea. When the sea was out, the low coastal plains were covered with luxuriant forests of seed ferns, ferns, scale trees, and dense vegetation.During heavy rain, this dense vegetation fell to the forest floor to form (peat). This peat later became (millions of years) the coal.

When sea level rose, and it did periodically, it covered the peat & created large inland muddy seas. During these times, (many thousands of years), many types of marine (sea-dwelling) invertebrates and vertebrates lived in the shallow seas that would become Kentucky.Now Pennsylvanian marine fossils are found in Kentucky like Corals (Cnidarians), brachiopods, trilobites, snails (gastropods), clams (pelecypods), squid-like animals (cephalopods), crinoids (Echinoderms), fish teeth (Pisces), and microscopic animals.

Mississippian-age strata shown in light blue on the geologic map, are dominated by limestones, shales, and sandstones. A thick sequence of limestone can contain numerous oil reservoirs beneath the surface.Then the same limestone is quarried where it occurs at the surface. Reed quarry in western Kentucky, produces more limestone than any other quarry in the United States.

The limestone also contains large cave systems, including the Mammoth Cave-Flint Ridge cave system, and Carter Caves.Mississippian rocks are exposed at the surface in the Mississippian Plateau (Pennyroyal) and occur below the surface in both of the coal fields.Mississippian rocks are absent in the Blue Grass Region and in most of the Knobs.

During most of the Mississippian, Kentucky was covered by shallow tropical seas, but some very low lands may have been visible at times in central Kentucky.Periodically, during the later part of the Mississippian, tidal deltas and low coastal plains covered large parts of Kentucky.

During alternating times the sea would come in and cover the region.At this time thick limestones were created in these shallow seas. Through the following millennia many caves were developed in these limestones.So this area is now known as one of the world's most famous karst topographical areas.

Mississippian Fossils Mississippian fossils in Kentucky are very similar to Pennsylvanian age fossils. Also, some new life forms appeared like Crinoids & blastoids forms of echinoderms. When there was visible land in the form of low coastal plains, land plants & animals thrived. So their fossils are present.Since this area was a shallow sea we can also find amphibians. These were non-existent in the state until one was found in western Kentucky.

Devonian aged strata shown in red.Devonian strata consists of limestones and dolostones and a thick deposit of dark gray to black shale. The limestones are mined in the Louisville area and sometimes contain abundant fossils.The thick, dark gray to black shales are the dominant Devonian strata in many areas of Kentucky. The color of the shales comes from trapped organic material.

Late in the Devonian, organic muds were deposited in a shallow sea that covered most of the eastern United States.When these organic-rich sediments were buried deeper beneath the surface, pressure and temperature converted some of the organic material in the rock to liquid and gaseous forms.

The liquid form is called oil.The gaseous form is natural gas.

Eastern Kentucky has the largest gas field in the state and is estimated to contain billions of cubic feet of gas. (Big Sandy Gas Field).The oil found in Kentucky started out in Devonian shales, but due to gravity migrated to other rock layers.

Silurian StrataThe Ordovician rocks are surrounded by a ring of Silurian strata, shown in red. These rocks out crop in the Knobs Region and consist mainly of limestones and dolostones.In the Big Sinking-Irvine area, these rocks dip beneath the surface, and because they are very porous they form natural reservoirs for oil.The Silurian rock strata pinches out to the south in Boyle, Casey, Lincoln, & Montgomery Counties.

Silurian StrataAt this point, where Silurian strata are missing, Devonian tend to take their place and lie over Ordovician rocks. This is called an unconformity because a large segment of geologic time is missing from the rock record.

Silurian FossilsSilurian strata almost completely surrounds the Blue Grass Region in the form of the Knobs. In the Blue Grass Silurian rock strata does not exist but, occur below the surface in other parts of Kentucky.A shallow tropical sea covered Kentucky during most of the Silurian which allowed for the formation of thin beds of limestone.All Silurian rocks found in Kentucky are marine (sea-dwelling) so all the fossils are the invertebrates.

Ordovician StrataThe Bluegrass Region of the State is composed of limestones and shales from the Ordovician Period, and are colored pink on the geologic map.The Ordovician strata lies buried beneath the surface. The oldest rocks at the surface in Kentucky are limestones from the Late Ordovician Period (approximately 450 million years ago).

Ordovician StrataThese rock strata are exposed along the Palisades of the Kentucky River (for example, near Camp Nelson, in Jessamine County.Ordovician limestones are quarried from Covington to Danville for use in construction.Some of the limestones also produce natural spring water that is bottled and sold for drinking water.

Ordovician StrataThe city of Lexington was founded at McConnell Springs (pictured previously), which flows from Ordovician limestones.The oldest rocks exposed at the surface in Kentucky are Ordovician and are exposed in the Blue Grass Region.Rocks deposited during the first half of the Ordovician Period occur entirely below the surface throughout Kentucky.Some of these deep rocks contain oil, so some oil wells have been drilled down to them.

Ordovician StrataDuring most of the Ordovician, Kentucky was covered by shallow tropical seas. Accordingly, the fossils found in Kentucky's Ordovician rocks are marine (sea-dwelling) invertebrates. All common Ordovician fossils found in Kentucky are virtually the same as Pennsylvanian except sponges (Porifera) now makes an appearance.

Strata of Cretaceous AgeIn western Kentucky, in Jackson Purchase Land Between the Lakes, older rocks are not overlain by Pennsylvanian rocks.However, are overlain by Cretaceous (140 to 65 million years ago) strata shown in green on the geologic map.This relationship is another unconformity.

Strata of Cretaceous AgeCretaceous strata on the map are the only areas in Kentucky where dinosaur bones might be found, although none yet.The Cretaceous Period was the last period in the Age of Dinosaurs.Much of the Cretaceous strata in Kentucky are unconsolidated sediments (i.e., they are not rocks yet).

Strata of Cretaceous AgeSediment grains (e.g., sand, silt) have not been cemented together to form rock in many cases. Some areas contain a low-grade form of coal called lignite (some peat still present), but it is not currently economic to mine.The most common fossils are coalified tree limbs, but no dinosaurs yet.

Neogene and Paleogene (Tertiary) Age Strata

Paleogene and Neogene (65 to 1.6 million years ago) rocks & sediments were deposited after the dinosaur extinction, during the Cenozoic Era. Shown in green.Tertiary sediments in Kentucky include many deposits of ball clay, which can be used for ceramics and enameling.KY is the 2nd largest producer of ball clay.Common fossils are coalified limbs, logs, and stumps of lignite rank, few others

Neogene and Paleogene (Tertiary) Age Strata

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