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Virginia Geologic History and Regions Take a look at cities you might have visited • There are 5 regions…. These are on your notes sheet provided to you Coastal Plain • Youngest sedimentary rocks in VA • Low topographic relief: – Elevation on land: 0-300 ft – Lands slopes east under the Atlantic Ocean & forms continental shelf; extends 200 miles offshore Coastal Plain continued • Swamps: Great Dismal Swamp • Bays (Chesapeake) & estuaries • Extends westward to the “fall line” Piedmont Profile of the James River across the Fall Zone Elevation • Rolling landscape • Slopes eastward from 1000ft to 300ft in the east • Weathering over long time has produced soils 150ft deep • Metamorphic, igneous, & sedimentary rocks present Distance from source Blue Ridge • • • • Long & narrow region Elevations between 2300ft & 3200ft Highest peak: 5719ft Metamorphic & igneous Valley and Ridge • Large valley: Shenandoah & other narrow, parallel valleys • Valleys in SW are 1000ft or higher than in NE valleys • Folded Appalachians • Sedimentary:limestone Reported or known caves in Virginia Appalachian Plateau • • • • SW part of state Flat high elevations Sedimentary rocks (coal) Drained by Tennessee River (to the W) Observe the watersheds On the next slides… Read each slide Copy what is underlined Virginia’s Geologic History Virginia is unique because it has: Mountains Hills and valleys foothills Sandy beaches… All in 1 state!! 1 bya (billion years ago) • VA was a little chain of volcanoes where the Blue Ridge Mountains are today • Everything else was underwater 500 mya (million years ago) • Still underwater and a chain of volcanoes • Coastline located where valley and ridge are today • VA located S of the equator, had a tropical climate • Sediment was deposited over western VA, shells and coral were deposited, which explains the presence of sedimentary rock in the V & R (valley & ridge) and A.P. (appalachian plateau) regions 225 mya Africa collided with North America, collision hard enough to wrinkle up the crust under the inland sea west of the Blue Ridge “wrinkles” formed the Appalachian mountains continued The mountains were 15,000 to 20,000 ft, largest in the US (at that time) Force of collision produced heat and pressure which changed some sedimentary rocks of limestone into marble 190 mya African plate started to pull away and the Atlantic opened, the pulling caused the land west of Richmond to stretch and crack, erosion caused these rift valleys to fill with mud and clay 140 to 70 mya Sediment from the eroding Appalachian mountains gets carried across the Piedmont by streams and rivers which washes into the Atlantic Ocean Coastline is now located where Richmond is today Over millions of years, sediments continued to build up which formed the Coastal Plain … the sand on the beaches is actually rocks from the Appalachian Mountains Ice Age-1.8 mya o Due to cold temps ice piled up in Canada and northern US o Ice sheets covered areas of North America, including parts of VA o Much of the water evaporated and the sea level was 450ft lower than today, VA coastline was 60 miles farther to the East o As glaciers melted sea level rose rapidly