Rock and Soil Types in Blue Ridge Virginia
Geology of the Blue Ridge in Virginia
the Blue Ridge was cached vi-ten miles deep at once, before being exposed by erosion over the last 300 1000000 years
Source: Department of Justice
The cadre of the Blue Ridge is the basement rock of Virginia, the bedrock that is thought to lie beneath all other rocks of the state from the edge of the bounding main to the borders with West Virginia/Kentucky.
That basement igneous rock formed during the Grenville Outcome (or events, perhaps involving multiple continental collisions) between 1.1-1.0 billion years ago, as tectonic plates combined to grade the supercontinent of Rodinia.1
The rut and pressure of the Grenville collision(due south) melted whatsoever rocks previously existed in the area. Colliding chunks of continental chaff created mountains rising high on the surface, and pushing other rocks deep plenty to melt and alloy. The molten rock slowly solidified into crystalline granite and gneiss underneath the mountains. As the mountains on the surface eroded away, the granite roots were pushed upwards gradually, displaced past heavier rocks in the drapery.
The roots of the Grenville mountains were exposed by uplift/erosion at the surface, and rain/air current carved ridges and valleys into the surface. At in one case the i-billion-year quondam crystalline rocks at the core of the Blue Ridge were called the Pedlar formation. Today, geologists often lump the unlike components created by the Grenville orogeny and refer to the "basement" bedrock. That basement is exposed at the core of the Blue Ridge, but hidden underneath the Piedmont, Coastal Plain, and Continental Shelf to the east.
Ancient erosion created roughly ii,000 feet of topographic "relief" (the elevation difference betwixt tops of the mountain ridges and the valleys) by 600 one thousand thousand years agone. Sediments accumulated in the low spots on meridian of the igneous bedrock, and today those sediments are known equally the Swift Run formation.2
And so the crust of the Rodinia supercontinent croaky, the continental plates pulled apart, and the Iapetus Ocean formed on the edge of the N American tectonic plate. As the plates broke up, the crust thinned and molten basalt rose in places from 40-70 miles below the surface. The eroded surface that had adult with ridges and valleys was buried past 2,000 anxiety of basalt flows.
The landscape was leveled and black, with basalt reaching to the ocean. That basalt is known today as the Catoctin Germination. Places with "pillow basalt" testify where it erupted so cooled underneath the ocean.
During the several million years of eruptions, different lava flows had thicknesses between xx-100 feet. Those lava flows have been exposed today by modern erosion. Hikers in Shenandoah National Park can see ledges today, showing where i flow has eroded away faster than other.iii
the Chesapeake and Ohio Railroad identified the different geologic formations along its route, including the Blueish Ridge in 1872
Source: Library of Congress, Map showing the economic minerals along the route of the Chesapeake & Ohio Rail Manner (Thomas S. Ridgway, 1872)
At the time of the basalt flows, Virginia was twisted xc degrees from its present orientation and was located south of the Equator. In the last 600 million years, the crustal plate including Virginia has drifted north and rotated.4
Afterward the basalt flows, the Iapetus Ocean continued to widen. The continental plates drifted apart during the Cambrian Menses, and sediments washed from Virginia's surface down to the oceanfront shoreline. 500 million years ago, those sediments formed beaches similar to Virginia Beach today. Further offshore, rivers eroding the North American craton carried layer afterwards layer of sediment into deeper waters, creating a continental shelf of mud and quartz (silica) sand.
Initially, big sand particles eroded off the Catoctin basalts and basement rocks and settled in the Iapetus Body of water. Today, that sandstone is known every bit the Weverton Germination. As the mountains eroded to a lower elevation, or possibly as sea level rose and increased the distance from the eroding mountains, rivers lacked the energy to conduct anything larger than pocket-sized particles of silt and mud to coffin the Weverton Formation. Instead of more sand, silt-rich sediments known today every bit the Harpers Formation were deposited on acme of the Weverton sandstone.
the Blueish Ridge was thrust to the westward when Africa collided with North America 250 meg years agone
before being buried, then uplifted and exposed by erosion
Source: Usa Geological Survey Bulletin 1839-I, J, Middle Eocene Intrusive Igneous Rocks
of the Key Appalachian Valley and Ridge Province: Setting, Chemistry, and Implications for Crustal Structure
When ascent bounding main level enabled the Iapetus Ocean to drown the shoreline of Virginia, barrier islands developed that were comparable to those on the Eastern Shore or at Cape Hatteras today. The Antietam Formation, sand-sized particles on top of the Harpers Formation, is the residuum of those barrier islands.
Then, for whatever reason, the continental plates reversed direction. Africa and North America started to move together again, and the Iapetus Ocean began to close. The chunk of continental chaff known as Avalonia moved closer to the shoreline of Virginia, and a "foreland basin" developed to the westward of the continent's edge. In that bowl, zillions of tiny sea creatures - with tiny shells of limestone - lived and died in the table salt water.
As the Iapetus Ocean closed, "terranes" or island arcs and finally Africa crunched into Virginia and the rest of eastern North America, during the Taconic, Neo-Acadian, and Alleghenian orogenies. Those collisions with additional chunks of crust would bury those sediments and beaches deep plenty to lithify into rocks known today as the Chilhowee Grouping, with the Weverton Formation near the lesser, the Antietam Formation near the centre, and the Harpers Formation near the top.
The Catoctin basalt itself would be pushed down vi-ten miles, deep plenty to exist metamorphosed by heat/pressure that realigned atoms and created new minerals such as epidote. Epidote is a green mineral, and is then common in the metamorphosed basalt that the Catoctin formation in Shenandoah National Park is ofttimes referred to as "greenstone." The sediments on top of the basalt lava flows were also compressed and metamorphosed, converting sandstone into layers of quartzite. Thank you to cycles of deposition and erosion, the crystalline basement boulder has moved up and downwardly into the earth well-nigh like an elevator.5
Every bit function of the Alleghenian orogeny, when Africa collided with North America 300 million years ago and the supercontinent of Pangea formed, the border of Virginia was cracked and pushed due west. A slice of buried billion-year old granites, with metamorphosed sediments on top, was thrust 40-60 miles from its original position. As Africa pressed against North America, the younger carbonate bank and sandy beaches that had formed on the border of the Iapetus Ocean (exposed today in the Shenandoah Valley) ended upwardly beingness shoved underneath the older slice of "basement" that was lifted up and pushed inland.
It has been 300 million years since the collision with Africa cracked and transported the edge of Virginia. Since then, Pangea has cleaved up, like the predecessor supercontinent Rodinia. The ocean formed when Africa and North America parted is known equally the Atlantic Sea, and 300 million years of erosion has exhumed the slice of "basement."
That now-exposed basement bedrock forms the Blue Ridge. The core of the Blue Ridge mountains inside Shenandoah National Park (including Sometime Rag Mountain) was in one case located somewhere near I-95.
how Cambrian/Ordovician sediments (exposed in Shenandoah Valley) may lie underneath the Grenville-age rocks (exposed equally the Bluish Ridge)
Source: Virginia Department of Mines, Minerals and Energy, Virginia Minerals
Oil And Gas Exploration And Development In Virginia, 1979-1988 (Feb 1990)
The 1.1 billion yr former Grenville basement, exposed as the Blueish Ridge, was covered by new sediments. The Chilhowee Group consists of the Weverton Formation, Harpers/Hampton Formation and Antietam/Erwin Formation.
the Chilhowee Grouping creates more-acidic runoff on the western side of the Blue Ridge
Source: National Park Service, Geologic Diagram
Differential erosion has created the modern topography of Virginia. The Blueish Ridge was exposed in its new location as softer rocks effectually it accept eroded away faster than the basement gneiss and hard Catoctin greenstone.
the Blue Ridge is narrow northward of Roanoke (red X), just widens out to the south
Source: United states of america Geological Survey, National Map
To the west of the Bluish Ridge, softer Cambrian and Ordovician limestones in the Valley and Ridge physiographic province have eroded to course the Shenandoah Valley, New River Valley, and others which are sometimes lumped together as the "Valley of Virginia." Due east of the Blue Ridge, the geologic formations in the Piedmont take eroded faster than the harder and older igneous bedrock of the Blueish Ridge. The result: a ridge with i,000-3,000 feet of topographic relief, with a valley to the west and a gently sloping plain to the east.
Blue Ridge Tunnel
Exploring Westward to the Blue Ridge - and Beyond
onetime Bluish Ridge crystalline basement/volcanics thrust over Cambrian/Ordovician carbonates/shale (now exposed in Shenandoah Valley)
Source: Virginia Department of Mines, Minerals and Energy, Publication 066: Part 1:
Interpretive seismic profile forth Interstate I-64 in cardinal Virginia from the Valley and Ridge to the Coastal Plain
Links
- Appalachian Tectonic Studies Grouping
- Generalized Tectonic Map of the Appalachian Mts., Eastern U.s.A
- U.s.a. Geological Survey
- Open-File Report 00-263, A Hiker's Guide to the Geology of Erstwhile Rag Mountain, Shenandoah National Park, Virginia
- Harris, L.D., de Witt, Wallace and Bayer, Thou.C., 1982, Interpretive seismic profile along interstate I-64 from the valley and the ridge to the littoral obviously in central Virginia: U.S. Geological Survey, Oil and Gas Investigations Chart OC-123, scale 1:215000
the General Associates used the watershed divide at the crest of the Blue Ridge to define county boundaries
Source: Globe Resources Ascertainment and Science (EROS) Middle, The states Geological Survey (USGS),
Landsat State Mosaics
unravelling the story of Virginia'southward geology requires understanding the whole story of eastern North America
Source: Us Geological Survey (USGS) and Geologic Society of America (GSA), Geologic Map of North America - S
References
1. Richard T. Williams, William M. Dunne, and Lynn Glover Three, "Global Geoscience Transect xx- Central Appalachians: Cratonic Northward America to the Atlantic Abyssal Manifestly," International Geology Review, Volume 41, Issue 8, 1999, Pages 711 - 738 http://www.informaworld.com/smpp/content~db=all~content=a910212761 (concluding checked June 17, 2011)2. Gathright, T.M., II, 1976, Geology of the Shenandoah National Park, Virginia, Virginia Division of Mineral Resources Message 86, http://www.dmme.virginia.gov/commercedocs/BUL_86.pdf, p.47 (concluding checked June 23, 2011)
iii. Richard P. Tollo, James McLelland, Louise Corriveau, Mervin J. Bartholomew (ed.), Proterozoic tectonic development of the Grenville orogen in North America, The Geological Society of America Memoir 197, 2004, p.454 http://books.google.com/books?id=uT4HISRCon8C&pg=PA454; John C. Reed, Jr., "Ancient Lavas In Shenandoah National Park Near Luray, Virginia," US Geological Survey Bulletin 1265, 1969, https://pubs.er.usgs.gov/publication/b1265; "Greenstone lava flows," Shenandoah National Park, https://www.nps.gov/shen/learn/nature/greenstone.htm (last checked November 22, 2021)
4. Richard Diecchio and Richard Gottfried, "Regional Tectonic History of Northern Virginia" in Round 1264: Geology of the National Capital Region - Field Trip Guidebook, http://pubs.usgs.gov/circ/2004/1264/html/trip1/index.html (last checked June 23, 2011)
five. Christopher Grand. Bailey, "Heed the Gap! Where is Afton Mountain?," William and Mary, http://web.wm.edu/geology/virginia/field_loc/rfgweb.pdf (concluding checked Baronial 28, 2014)
erosion has carved a steeper slope on the eastern edge of the Blueish Ridge in southern Virginia
Source: USGS National Summit Dataset, NED Shaded Relief - Virginia
Rocks and Ridges - The Geology of Virginia
Virginia Places
Source: http://www.virginiaplaces.org/geology/blueridge.html
0 Response to "Rock and Soil Types in Blue Ridge Virginia"
Post a Comment