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| Chronology of Events in the Geologic History of Virginia PAGE ONE - Oldest History. Read from bottom to top. Go to Page Two |
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| AGE (mya) |
EVENTS | VIRGINIA PROVINCES |
OBSERVATIONS/ INTERPRETATIONS |
CROSS SECTION |
| UNCONFORMITY Taconic mountains in Eastern Virginia eroded to peneplain; no direct evidence remaining |
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| 450 - 435 Mid to Late Ordovician |
TACONIC OROGENY GANDER TERRANE (Chopawamsic+ Arvonia +? microcontinent) collides with east coast. First stage of Protoatlantic closing. | BLUE RIDGE, and PIEDMONT east to about Richmond | Mountain building; Hayesville fault active in Blue Ridge; metamorphism and deformation | |
| VALLEY AND RIDGE Shenandoah valley and west | Shenandoah valley=flysch basin (lithic rich turbidintes). Cratonic basin to west dominated by storm shelf deposits (Reedsville fm.). Queenston clastic wedge. | H | ||
| 570 - 435 Cambrian to middle Ordovician (events out in Protoatlantic while Virginia is a tectonically stable continental margin. |
ARVONIA VOLCANIC ARC (active in lower to middle Ordovician) |
Volcanic terranes inPIEDMONT begin in Iapetus ocean; later collide with North America to cause Taconic orogeny | Graptolite bearing flysch unconformable overlying Chopawamsic arc volcanics and batholiths. | G |
| CHOPAWAMSIC VOLCANIC ARC (active in middle Cambrian) | PIEDMONT: Chopawamsic Belt - now in a narrow synclinal terrane just west of Fredricksburg | Mafic volcanics cut by granite plutons at 500 mya, plus flysch deposits. Probably created by a west dipping subduction. | E, F | |
| 570 - 450 Cambrian-mid Ordovician |
CONTINENTAL MARGIN DEPOSITION | VALLEY AND RIDGE, esp. Shenandoah Valley and subsurface under PIEDMONT | Deposition of eastward thickening wedge of tidal flat and shelf carbonates as rifted margin cools and subsides. "Africa" drifts away. | D |
| 640 - 570 Late Proterozoic |
RIFTING of "Africa" and North America and opening of the Protoatlantic (Iapetus) ocean | BLUE RIDGE, including far western PIEDMONT, in a belt running through the Charlottesville and Culpepper area | Rifts are filled. Earliest stable continental margin deposition; transgressive quartz sandstone (Antietam). | C B |
| Catoctin flood basalts indicate initiation of ocean crust formation | ||||
| Active rifting; rifts filled with meta. (sub)arkosic sandstones/conglom/ & basin shales | ||||
| 690 - 570 Late Protero. |
CROSSNORE PLUTONIC EVENT | BLUE RIDGE | Felsic (alkali) volcanics at Mt. Rogers and South Mountain hot spots, plus Robertson River pluton. Early Stage Rifting | |
| UNCONFORMITY Grenville mountains across Virginia eroded to peneplain. Nonconformity in Blue Ridge (Pedlar to Catoctin) |
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| 915-1800 Early-Mid-Late Protero. |
GRENVILLE EVENTS "Africa"/North America collide(915-940)=Rodinia | BLUE RIDGE and same age rocks in Piedmont (Sauratown Mtn and Goochland belts) | A very complex history 8-900 million years long involving perhaps serveral orogenies and rifting events (Wilson cycles) | A |
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| Last Update: 9/13/00 | |||