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4.2.2 - Geologic Regions of South Carolina
http://sciway2.net/2001/sc-geology/
Background: South Carolina is an incredibly diverse
geographical state ranging from mountains to the barrier islands
that spot the coast. And it is constantly changing (in terms of
geological time). In order to try to discuss all of the different
geologic features, the state is divided into 5 distinct regions:
The Blue Ridge Region makes up only 2% of the land area of
South Carolina. The Blue Ridge Mountains extend from Georgia
to Virginia and are the eastern part of the Appalachian System
that runs from Alabama to Quebec. The Appalachian Mountains
are folded mountains, which means the formed when rock layers
are squeezed from opposite sides (specifically when Africa and
North America collided during the formation of Pangaea), causing
the rock layers buckle and fold. Large amounts of schist and
gneiss are found in the Blue Ridge Mountains, with the highly
metamorphosed gneiss rock being found further inland because
the center of the Appalachian Mountains experienced greater temperature and pressure than the outer regions.
These mountains are the source of many mountain streams and rivers, as well as much of the sediment that
composes much of the lower half of South Carolina. The southeast "border" of the Blue Ridge Region is the Brevard
fault. Sassafras Mountain is the highest peak at 3,560 feet above sea level, although it straddles the NC border. The
oldest rocks in South Carolina are found in this region, highly metamorphosed gneiss due to massive pressure and
temperature of continental collisions dating back to the Precambrian.
The Piedmont Region is a series of rolling hills and plateaus that make up 30% of South Carolina. Piedmont literally
means "foot of the mountain". In South Carolina the Piedmont region is typically hilly country containing
many monadnocks (isolated hills of bedrock rising conspicuously above the general level of the surrounding area
that are not yet eroded because of their denser composition). The Piedmont is underlain by metamorphic rocks of
various origins that were folded during the Paleozoic as the North American and African plates converged multiple
times. Surface soils of the Piedmont tend to be Sandy Loam, and display the process of weathering and erosion that
broke down the once massive Blue Ridge Mountains.
The Sandhills Region is made up of hilly, unconnected bands of sand left from the ocean dunes during the Miocene
Epoch. This region makes up no more than 4% of the state of
South Carolina, and is no more than a 10 miles wide at its widest
point. Above these sand deposits lies the Fall Zone (as seen in
the image to the right), where the rocky river beds meet the
sediment covered river bottoms of the Coastal Plain. The fall
zone runs along the entire East Coast, and many cities besides
Columbia (like Atlanta, Raleigh, Richmond, Washington D.C. and
Philadelphia) were built along the fall line as rapids at this point
provided many industries with needed hydropower. The fall zone
is also as far as boats could sail safely upriver from the ocean
because of these rapids, and at the fall line they would unload
their goods from the boat and transport them by land.
The Coastal Plains are large, relatively flat areas of land, which
span up to 150 miles wide and cover just shy of 60% of South Carolina. The Coastal Plain actually extends from
New Jersey to Florida to Texas. Coastal Plains of South Carolina extends from the sandy beaches of the Coastal
Zone to the Sandhills and the Fall line. This is the largest geographic region in SC and includes such features as
vast flood plains, marshland, swamps of moss-hung cypress trees, several man-made lakes, wild grass prairies
called savannahs, and Carolina Bays. The hills are remnants of ancient barrier islands, with the current plains that
stretch for miles being ancient continental shelves. The rocks on the surface are between 1.8 million years to 6,000
years old, while extensive limestone (most limestone is composed of skeletal fragments of marine organisms such
as coral, forams, and mollusks.) beds were formed along these ancient continental shelves. This limestone, being
very porous, is easily chemically eroded by water, so there are sinkholes, caves, and underground rivers throughout
much of the Coastal Plains. These different forms of erosion by water within the porous limestone are called Karst
Topography.
The Coastal Plain is divided into the lower and upper plain. The upper Coastal Plains are remains of land left by the
erosion and deposition of the constantly moving sea of the Pliocene, as well as deposition from rivers transporting
sediment from the Blue Ridge and Piedmont Zones. Much of the rock is sedimentary from Mesozoic or Cenozoic
times. This area has numerous marine fossils found within the sedimentary sandstone found within this region.
The lower Coastal Plains are made of six steep slopes at the edge of high ground and seven terraces (which are
basically step-like landforms). These terraces represent temporary oceans floors that go from the sea level rise and
fall over time, specifically the seven cycles over the last 5 million years (2 in the Pliocene, 4 in the Pleistocene, 1 in
Holocene), with the last coastal submergence merely 85,000 years ago.
The Coastal Zone is the last 10 miles before the ocean, making up about 6% of the state. In Mount Pleasant and
Charleston, Highway 17 is generally seen as the divider between the coastal zone and the coastal plains. The
coastal zone encompasses the 187 miles of coastline within South Carolina and the 35 barrier islands and seaislands. Only Florida has more barrier/sea islands than SC. It is comprised of salt marshes, barrier islands, and sea
islands, swampy forests and coastal rivers that rise & fall with the tides. Barrier Islands are deposited sand dunes
from the Holocene Epoch (Ex. Hilton Head, Isle of Palms, Sullivans, James, Johns, Folly, Morris, Kiawah, Fripp, and
Seabrook Islands https://en.wikipedia.org/wiki/Sea_Islands#South_Carolina). 76% of all barrier islands worldwide are on a
passive/trailing continental shelf and within a tidal range of 13 feet. South Carolina meets both of these conditions,
which explains it’s numerous barrier islands.
How do we know all this?
Remember, certain rocks form in certain environments. By determining the type of rock or sediment found in a given
area, and then using radiometric dating, we can determine which how long ago the rock formed and what the initial
topography and environment was. The table below gives us a very quick idea of the type of rock, or sediment that
we would expect to be found in a given environment. For instance, if we find limestone (which is composed of
calcite, a crystal form of calcium carbonate (CaCO3), a major component of marine skeletal structure), we know that
at one point that area was a continental shelf (an underwater landmass extending from a continent that is full of
marine life because of the shallow waters).
SC Sediment Type
Ancient Depositional Topography
Metamorphosed Rock
Mountain Building Episode (massive pressure)
Igneous Rock
Volcanic Activity
Conglomerates, Sand, Silt
Flood Plain
Sand, Clay
Barrier Island
Quartz Sand
Beach, Windblown Sand near Continental Shelf
Quartz Sand, Silt, Clay, Marble
Offshore Continental Shelf
Review Questions
Limestone
Offshore Continental Shelf
1. List the 5 geographical regions of South Carolina, tell what % of the state it encompasses, and give a 3-5
word description of each.
2. Which region(s) contains mostly metamorphic rock? Why?
3. Which metamorphic rocks specifically are found there, and is there any difference as to where they are found
in this region?
4. Knowing that much of the Lowcountry is sedimentary rock and soil, where did all of this sediment come from
and how did it get to the Lowcountry?
5. What is important about the Fall Zone/Fall Line?
6. Which region is the largest region?
7. What is Karst Topography.
8. Why are the lower Coastal Plains important to geologists?
9. Why are there so many barrier islands along South Carolina?
10. What do you think a passive/trailing continental shelf is?
11. Why is knowing the environment that certain rocks will be formed in (or the sediment that would settle in
certain areas) important?
12. Copy the above “SC Sediment Type and Ancient Depositional Topography” Table into your notebook.