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The Parts and Events
In
the Geologic History of Virginia
Many of Virginia's rocks include those that began their history in Virginia and ended up somewhere else, and rocks that began their history somewhere else and ended up in Virginia. The history also includes events that began and ended somewhere else before being transported to Virginia.
In addition, geological divisions do not remain constant. Continents form, and then rift apart. Oceans open, and then close again and cease to exist. Mountains build up, and then erode to the sea. And in the meantime Virginia, and North America, did not stay in one place but drifted across the globe from south of the equator 600 mya (million years ago) to its present northern temperate location.
In many places in Virginia are rocks now in contact that could not have been in contact when they formed. These include, for example, deep forming igneous rocks side by side with surface forming sedimentary rocks. These kinds of rocks form by mutually exclusive processes, and they had to have formed at different times and/or in different places and then later been brought together. To understand the geologic history of Virginia we must be able to reconstruct these past events, both separately and together. The tables below list most of the essential pieces and events that make up Virginia's geologic history.
SUPERCONTINENTS: In the geologic history of Virginia there were at least three supercontinents.
| SUPERCONTINENTS IN VIRGINIA'S HISTORY |
| CONTINENT |
AGE OF EXISTENCE |
| RODINIA: North America + "Africa" (plus other continents joined to "Africa") |
Latest Precambrian and earliest Cambrian |
| LARUSSIA (Old Red Sandstone Continent): North America + Baltica (parts of Europe, Scandinavia and Siberia) |
Devonian. This supercontinent created the Caledonian mountains. Its effects did not directly influence Virginia, but the Acadian mountains shortly joined with the Caledonian to form a long, continuous mountain chain. |
| PANGAEA: North America + Africa (plus South America, Antarctica, India, and Australia) |
Late Paleozoic and earliest Mesozoic |
OCEAN BASINS: These two supercontinents rifted at different times forming several ocean basins. It is likely that in the Proterozoic other rifting events occurred with remnants preserved in Virginia (Grenville) geology.
| OCEANS IN VIRGINIA'S HISTORY |
| OCEAN NAME |
AGE OF EXISTENCE |
| Protoatlantic (Iapetus) Ocean |
Earliest Cambrian to Late Paleozoic |
| Rheic Ocean |
Between the Acadian and Alleghenian orogenies (perhaps longer). Devonian to Pennsylvanian |
| Atlantic Ocean |
Early Mesozoic to the present |
TERRANES : There were at least four island arc terranes, although it is possible some of these are the same with different names in different places.
| ISLAND AC (+MICROCONTINENT?) TERRANES IN THE HISTORY |
| VOLCANIC ARC NAME |
AGE OF EXISTENCE |
| Virgilina |
Active in the Cambrian |
| Chopawamsic |
Active in the Cambrian, although it probably went through its entire history out in the Protoatlantic before docking with Virginia |
| Arvonia + Charlotte |
Active in the Ordovician |
| Carolina Slate Belt (+Eastern slate belt?) |
Active in the Ordovician |
MICROCONTINENTS : There were at least 3 microcontinent terranes, although it is possible some of these are the same with different names in different places.
| MICROCONTINENT TERRANES IN THE HISTORY |
| MICROCONTINENT NAME |
AGE OF EXISTENCE |
| Gander (=Raleigh/Goochland?) |
Attached to Virginia in the Ordovician and still present in the piedmont |
| Sauratown Mountain |
Attached mostly to North Carolina, but also to southern Virginia in the Ordovician and still present in the piedmont |
| Armorica/Avalon |
Attached to Virginia in the Devonian as Armorica. Partially rifted when the present Atlantic ocean opened; the part remaining with North America known as the Avalon terrane. |
DETACHED OROGENIES : There were orogenies that took place elsewhere on the earth, but their rocks have been moved to Virginia and preserved here.
| DETACHED OROGENIES IN THE HISTORY |
| OROGENY |
AGE OF EXISTENCE |
| Chopawamsic |
Middle Cambrian of the central and northern Piedmont. Attached to Virginia in the Ordovician. Arrived with the Arvonia volcanic arc and possibly the Raleigh/Goochland microcontinent. |
| Virgilina |
Cambrian of southwest Virginia and North Carolina. Probably came in in the Ordovician |
NON-AMERICAN OROGENIC EVENTS : There were orogenies that took place in other parts of the world at about the same time as those in Virginia but have different names. Often they are the same orogeny as in North America, caused by the same processes, just preserved in different places. For example, a collision orogeny is recorded on both colliding pieces, even though they are now separated.
| NON-NORTH AMERICAN OROGENIES IN THE HISTORY |
| OROGENY |
LOCATION |
AGE OF EXISTENCE |
| Caledonian |
Caused by collision between maritime provinces of Canada and Great Britain. |
Same Time as Acadian. |
| Ouachita |
Caused by collision between South America (as part of Gondwana) and the Gulf coast of North America. Remains exposed in Oklahoma and Texas. Other remains buried under the coastal plain. |
Same Time as Alleghenian. |
| Hercynian (Variscan) |
Southern Europe |
Same Time as Alleghenian. |
| Mauritanide |
Northwest Africa (Gondwana). This was the collsion effects opposite North America. |
Same Time as Alleghenian. |
VIRGINIA OROGENIES : There were four orogenies that took place in Virginia, and up and down the eastern seaboard.
| OROGENIES IN THE HISTORY |
| OROGENY |
AGE OF EXISTENCE |
| Grenville |
Late Proterozoic; between 9125-1130 mya, but may consist of more than one mountain building event. Several Wilson cycles may be preserved. |
| Taconic |
Mid to Late Ordovician, dated 435-350 mya |
| Acadian |
Mid to Late Devonian, dated 350-370 mya |
| Alleghenian |
Probably began in the Mississippian, peaked in the Pennsylvanian, and continued into the Permian. Some consider this orogeny continuous with the Acadian. |
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