Prior to one billion years ago, the geologic history of West Virginia is
obscure. Sometime between about 1,100 and 800 million years ago, lava was
deposited in the extreme eastern part of the State forming our oldest exposed
rock, the Catoctin Greenstone. Later, perhaps about 800 million years ago, a
narrow trough began to form in extreme eastern West Virginia. An arm of the
sea entered and sediments accumulated. As time went on, this shallow sea
transgressed westward. By the end of Cambrian time, about 300 million years
later, this shallow sea covered essentially all of West Virginia. Marine
deposition took place throughout most of this and the succeeding Ordovician
Period. During this total interval of about 370 million years, most of the
rocks exposed in Jefferson and eastern Berkeley counties and in scattered
areas southwestward along the Virginia boundary were deposited. Rocks of the
same age are found in abundance in the deep wells throughout the State.
The Taconic Orogeny near the end of Ordovician time formed a high
mountainous area east of West Virginia. These highlands formed the main source
of sediments for the succeeding Silurian Period and part of the Devonian Period.
Both clastics and carbonates were deposited in a mixed marine and nonmarine
environment, with clastics predominating in the eastern part of the State.
Evaporites were deposited in northern West Virginia in Late Silurian time.
During Middle and Late Devonian time the Acadian Orogeny, with the main
uplift to the northeast, resulted in a further source for the predominantly
clastic marine deposits of these epochs. However, near the end of Devonian
time, the sea was rapidly retreating westward and the continental red beds of
the Hampshire Formation were being deposited over most of the State.
The sea made one more important intrusion into West Virginia during
Middle Mississippian time, approximately 330 million years ago, resulting in
the deposition of the Greenbrier Formation, predominantly limestone, the last
marine deposit of significance in the State.
At the close of Mississippian time, about 310 million years ago, West
Virginia was essentially a land area, subject to erosion. Early in the
succeeding Pennsylvanian Period, the area dropped to near sea level and for
more than 50 million years continued to sink at about the same rate that
deposition was taking place. Only occasionally and for very short periods
of time did the area fall below sea level. Swamp conditions prevailed,
resulting in the deposition of thousands of feet of nonmarine sandstone and
shale and the many important coal seams that we know today.
Sometime during the Permian Period, roughly 270 to 225 million years
ago, the Appalachian Orogeny began. West Virginia was uplifted, important
deposition of sediments ceased, and erosion began taking place. Much folding
and thrust faulting occurred, especially in the eastern part of the State.
This orogeny played a major part in the formation of the Appalachian Mountains
as we know them today. Never again has the sea invaded West Virginia.
No sedimentary rocks from the Mesozoic Era, which extended from 225 to 66 million years ago, are present
in West Virginia. In other parts of world rocks of this age contain the remains of countless species of
dinosaurs and other reptiles; unfortunately, no such fossils are preserved in our State. During the early
part of the era, considerable igneous activity took place in neighboring states to the east. A few dikes of
gabbro and other mafic rock from the Jurassic Period, 210 to 145 million years ago, are present in Pendleton
and surrounding counties.
In the Cenozoic Era, which extended from 65 million years ago to present day, igneous activity was renewed
in the eastern part of the State. Approximately 45 million years ago, a complex of dikes and sills with
compositions ranging from basalt to rhyolite were intruded into the Paleozoic sedimentary rocks in the area
in and around Pendleton County. These unusual igneous rocks are some of the youngest in eastern North America.
Late in the Cenozoic Era, in fact extending to less than 100,000 years ago,
glaciers covered the northern part of the North American continent, extending
almost to the Northern Panhandle of West Virginia, but not into the State.
Prior to the advance of these ice sheets, drainage of the Monongahela River
was northward to the St. Lawrence River system. The ice sheet caused damming
and a lake extended as far south as Weston. Important lake deposits, predominantly
clay, were thus laid down in the Monongahela River basin. Drainage was diverted
westward into the Ohio River system. Divergence of the New River system that
formerly drained northwestward caused the deposition of similar deposits in the
old Teays River channel between Charleston and Huntington. Except for recent
alluvial deposits, there are no other known Cenozoic rocks.
The oldest evidences of life found in West Virginia occur in rocks about
600 million years old, in the Antietam Formation of Lower Cambrian age.
However, in this formation they are abundant and of forms that had already
developed through a substantial part of all evolution that has taken place
during the history of the earth. Evidences of life in other parts of the
earth are found in rocks at least 3 billion years old. Fossils are found in
increasing abundance and increasing stages of evolutional development in the
rocks of all ages since earliest Cambrian time.
(adapted from an educational booklet by Dudley Cardwell, 1975 with additions from Ron McDowell, 2007)
Page last revised: December 22, 2006
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