The Geology of Kentucky

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The Geology of Kentucky

• Notes

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Kentucky Is Divided Into 6 Distinct Regions

• Bluegrass Region
• The Eastern Kentucky Coal Field
• The Knobs Region
• The Jackson Purchase or Mississippi Embayment
  Region
• The Mississippian Plateau or Pennyroyal Region
• The Western Kentucky Coal Field

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Bluegrass Region

• Characteristics 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.

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Eastern Kentucky Coal Field

• Is 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.

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The Eastern Kentucky Coal Field

• This 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.

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Knobs Region

• It 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.

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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.

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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.

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Mississippian Plateau /Pennyroyal Region

• Consists 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.

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• 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.

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Western Kentucky Coal Field

• Smaller 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.

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Geology of Kentucky
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• 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).

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• 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.

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• 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.

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• 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.

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• 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.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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• 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.

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Silurian Strata

• The 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.

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Silurian Strata

• At 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.

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Silurian Fossils

• Silurian 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.

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Ordovician Strata

• The 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).

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Ordovician Strata

• These 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.

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Ordovician Strata

• The 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.

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Ordovician Strata

• During 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.

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Strata of Cretaceous Age

• In 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.

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Strata of Cretaceous Age

• Cretaceous 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).

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Strata of Cretaceous Age

• Sediment 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.

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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

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Neogene and Paleogene (Tertiary) Age Strata

• THE END