Environment of West Virginia - Geology

Geology

Historical Geology Summary

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. 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. Permian Period, roughly 270 to 225 million years ago, the Appalachian Orogeny began which played a major part in the formation of the Appalachian Mountains as we know them today. Never again has the sea invaded West Virginia.

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.