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Geology of North Carolina in the Piedmont and Triassic Basin Regions

Triassic Basin Geology
The Triassic Basin gets its name from the triassic period, which was during the Mesozic Era between 245-208 millon years ago, which lasted 37 million years ago.  It is located all along the eastern coast of the U.S. The basin was formed due to many processes.  Erosion basically carved the newly raised mountains across the state of North Carolina and after 15-20 million years of erosion, and then the movement of material in the mantel began to produce forces which would alter, and then eventually tear up and separate the North American and Euro-African crustal plates. As this stressed increased, the crust began to fracture.  When it began to fracture, cracks developed throughout Europe, Africa and the east coast of North America.  These fractures formed in two separate sets.  One set runs Northeast to Southwest and the other runs North-South.  Many fractures remained exactly how they formed million of years ago.  The fractures can be seen across the Piedmont and Blue Ridge provinces as cracks in the older Paleozoic rocks.

Forces within the crust caused movement along some of the fractures, producing faults that reflected motion within the continential crustal plates.  Where the land shifted along such faults, enormous blocks of crust dropped slowly below the level of the surrounding land surface.  The subsiding blocks formed long, northeast-southwest trending basins that are inset into the Appalachians Piedmont from Nova Scotia to South Carolina. These are the triassic basins that have been found and can be seen on the picture below.

The deep river basin is where our mapping site was located. A picture of it can be seen below. It is divided into three sections known as the Durham, Sanford and Wadesboro basins.

The rocks nearest the edges of the basins are typically conglomerates, which mark the places where streams poured down the slope and across the basin floor.  The larger particles settled out near the edges of the basins and that is how the conglomerates developed.  Within the basin, streams formed fluvial fan-shaped deposits of sand and mud.  Stream channels moved back and forth, which deposited sequences of sand, silt and fine gravel.  There are three main sequences within the basin.  The lower sequence is made up of mainly reddish-brown arkosic sandstone and conglomerate materials.  The middle sequence is made up of gray to black fossiliferous siltstone, carbonaceous shale, and thin coal beds.  The upper sequence consists of mainly reddish-brown siltstone, arkosic sandstone, pebbly sandstone, mudstone and conglomerates.

Piedmont Geology

The Piedmont can be seperated into different sections to intepret the geology better. 

Inner Piedmont Belt - The Inner Piedmont Belt is the most intensely deformed and metamorphosed segment of the Piedmont. The metamorphic rocks range from 500 to 750 milllion years in age. They include gneiss and schist that have been intruded by younger granitic rocks. The northeast-trending Brevard fault zone forms much of the boundary between the Blue Ridge and the Inner Piedmont belts. Although this zone of strongly deformed rocks is one of the major structural features in the southern Appalachians, its origin is poorly understood. Crushed stone for road aggregate and building construction is the principal commodity produced.

Kings Mountain Belt - The belt consists of moderately deformed and metamorphosed volcanic and sedimentary rocks. The rocks are about 400-500 million years old. Lithium deposits here provide raw materials for chemical compounds, ceramics, glass, greases, batteries and television glass.

Milton Belt - This belt consists of gneisses, schist and metamorphosed intrusive rocks. The principal mineral resource is crushed stone forroad aggregate and buidlings.

Charlotte Belt - The belt consists mostly of igneous rocks such as granite, diorite and gabbro. These are 300-500 million years old. The igneous rocks are good sources for crushed and dimension stone for road aggregate and buildings.

Carolina Slate Belt - This belt consists of heated and deformed volcanic and sedimentary rocks. It was the site of a series of oceanic volcanic islands abou 550-650 million years ago. The belt is known for its numerous abandoned gold mines and prospects. North Carolina led the nation in gold production before the California Gold Rush of 1849. In recent decades, only monor gold mining has taken place, but mining companies continue to show interest in the area. Mineral production is crushed stone for road aggregate and pyrophyllite for refactories, ceramics, filler, paint and insecticide carriers.

Triassic basins - The basins are filled with sedimentary rocks that formed about 190-200 million years ago. Streams carried mud, silt, sand and gravel from adjacent highlands in rift valleys similar to those of Africa today. The mudstones are mined and processed to make brick, sewer pipe, structural tile and drain pipe.

Raleigh belt - The Raleigh belt contains granite, gneiss and schist. In the 19th century there were a number of small building stone quarries in this region, but today the main mineral product is crushed stone for construction and road aggregate.

Eastern Slate Belt - This belt contains slightly metamorphosed volcanic and sedimentary rocks similar to those of the Carolina slate belt. The rocks are poorly exposed and partially covered by the Coastal Plain sediments.The metamorphic rocks, 500-600 million years old, are intruded by younger, approximately 300 million-year-old, granitic bodies. Gold was once mined in the belt, and small occurrances of molybdenite, and ore of molybdenum, have been prospected here. Crushed stone, clay, sand and gravel are currently mined in this belt.

The geology of the area in the piedmont and triassic basins can affect the soils because of the parent materials that can be found in each location.  In the Piedmont, soils  were mainly formed from acid igneous rocks that are rich in alumnium and silicates, but not in calcium, magnesium and phosphorous.  Sediment was eroded from the mountains and deposited in the Triassic basin.  Organic material is then mixed with the parent material in order to form soils.  Climate also has an impact on soil formation.


Beyer, Fred.  North Carolina The Years Before Man. Carolina Academic: 1991.

Buol, S.W.  Formation of Soils in North Carolina.  http://agronomy.agr.state.nc.us/sssnc/3soilform.pdf.  November 28, 2003.

Horton, J. W. and Victora A. Zullo, eds.  The Geology of the Carolinas. University of Tennessee: Knoxville, 1991.

NC Geological Survey.  "Geology of North Carolina."  http://gw.ehnr.state.nc.us/faq.htm.  November 24, 2003.

NC Geological Survey. "Geology Map of North Carolina." http://www.geology.enr.state.nc.us/usgs/geomap.htm. November 24, 2003.

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