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Chronology of Events in the Geologic History of Virginia
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Taconic mountains in Eastern Virginia eroded to peneplain; no direct evidence remaining
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.
(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
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  
Grenville mountains across Virginia eroded to peneplain. Nonconformity in Blue Ridge (Pedlar to Catoctin)
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

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