Geology of West Virginia

Prior to one billion years ago, the geologic history of West Virginia is obscure. 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. The oldest exposed rock, the Catoctin greenstone, began to form between about 1,100 and 800 million years ago. Lava was deposited in the extreme eastern part of the State. About 300 million years later, by the end of Cambrian time, a shallow sea covered essentially all of West Virginia. Marine deposition took place throughout most of this and the succeeding Ordovician Period. The Taconic orogeny near the end of Ordovician time formed a high mountainous area east of West Virginia. 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. Approximately 330 million years ago, resulting in the deposition of the Greenbrier Formation, predominantly limestone, the last marine deposit of significance in the State. Roughly 270 to 225 million years ago, the Appalachian Orogeny began. This orogeny played a major part in the formation of the Appalachian Mountains as we know them today. West Virginia was uplifted, important deposition of sediments ceased, and erosion began taking place. About 310 million years ago, West Virginia was essentially a land area, subject to erosion. Swamp conditions prevailed more than 50 million years, resulting in the deposition of thousands of feet of nonmarine sandstone and shale and the many important coal seams that we know today.

History

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.

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 66 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.

Article provided by the 'West Virginia Geological and Economic Survey.' (adapted from an educational booklet by Dudley Cardwell, 1975 with additions from Ron McDowell, 2007)^[1]

References