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The Geology of Kentucky
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
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.
Eastern Kentucky Coal Field
Is dominated by forested hills and deeply cut Vshaped 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 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.
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
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
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
Mississippian Plateau /Pennyroyal
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.
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
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 Field
Smaller than eastern coal field.
It is the southern edge of a larger
geologic feature called the Illinois
Basin, includes Indiana & Illinois coal
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
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
During heavy rain, this dense vegetation fell
to the forest floor to form (peat).
This peat later became (millions of years) the
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 (seadwelling) 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
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 CaveFlint Ridge cave system, and Carter
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
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
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 nonexistent 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
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
The oil found in Kentucky started
out in Devonian shales, but due to
gravity migrated to other rock
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
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 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.
Silurian Fossils
Silurian strata almost completely surrounds
the Blue Grass Region in the form of the
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 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).
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
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
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.
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
Strata of Cretaceous Age
Cretaceous strata on the map are the
only areas in Kentucky where dinosaur
bones might be found, although none
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 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.
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