Geology of Georgia (U.S. state)
Encyclopedia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
consists of four distinct geologic regions, beginning in the northwest corner of the state and moving through the state to the southeast: the Ridge and Valley
Ridge-and-valley Appalachians
The Ridge-and-Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian division and are also a belt within the Appalachian Mountains extending from southeastern New York through northwestern New...
, the Blue Ridge
Blue Ridge Mountains
The Blue Ridge Mountains are a physiographic province of the larger Appalachian Mountains range. This province consists of northern and southern physiographic regions, which divide near the Roanoke River gap. The mountain range is located in the eastern United States, starting at its southern-most...
, the Piedmont
Piedmont (United States)
The Piedmont is a plateau region located in the eastern United States between the Atlantic Coastal Plain and the main Appalachian Mountains, stretching from New Jersey in the north to central Alabama in the south. The Piedmont province is a physiographic province of the larger Appalachian division...
and the Coastal Plain
Atlantic Coastal Plain
The Atlantic coastal plain has both low elevation and low relief, but it is also a relatively flat landform extending from the New York Bight southward to a Georgia/Florida section of the Eastern Continental Divide, which demarcates the plain from the ACF River Basin in the Gulf Coastal Plain to...
.
Ridge and Valley
The Ridge and Valley geologic region only passes through the extreme northwest corner of Georgia. During the middle Ordovician Period (about 440 - 480 million years ago), the tectonic plate carrying this area collided with another plate, leading to the creation of a new subduction zone and the beginning of the AppalachiansAppalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
As a result of this and later orogenies, alternating beds of hard and soft Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
sedimentary rocks were folded, looking much like the wrinkles one would find in a kicked floor rug. In Georgia, the Ridge and Valley includes limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
and other sedimentary rocks, which have yielded construction-grade limestone, barite
Barite
Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...
, ochre
Ochre
Ochre is the term for both a golden-yellow or light yellow brown color and for a form of earth pigment which produces the color. The pigment can also be used to create a reddish tint known as "red ochre". The more rarely used terms "purple ochre" and "brown ochre" also exist for variant hues...
and small amounts of coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
. The extent of the Ridge and Valley is bound by the Carters Dam Fault in the east and the Emerson Fault in the south.
Blue Ridge
The Blue Ridge geologic region forms the North Georgia mountainsNorth Georgia mountains
The Georgia Mountains Region or North Georgia mountains or Northeast Georgia is an area that starts in the northeast corner of Georgia, United States, and spreads in a westerly direction. The mountains in this region are in the Blue Ridge mountain chain that ends in Georgia...
. In this region, the highest points in Georgia are found, including Brasstown Bald
Brasstown Bald
Brasstown Bald is the highest natural point in the state of Georgia, USA, with a summit elevation of 4,784 feet above mean sea level....
. The Blue Ridge consists of metamorphic rocks, either metamorphosed equivalents of sedimentary rocks or igneous rocks, and the region includes the metavolcanic rocks of the Georgia Gold Belt
Georgia Gold Belt
The largest quantities of gold found in the eastern United States were found in the Georgia Gold Belt, which extends from eastern Alabama to Rabun County, Georgia. The biggest concentration of gold was found in White, Lumpkin, and northern Cherokee counties in Georgia. The gold in the Georgia Gold...
. The region also includes igneous intrusion
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
s of granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
and diabase
Diabase
Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. In North American usage, the term diabase refers to the fresh rock, whilst elsewhere the term dolerite is used for the fresh rock and diabase refers to altered material...
. From the discovery of gold in the Georgia Gold Belt in 1828, enough gold was mined in the area to cause a branch mint
Branch mint
-United States:The original and main Mint of the United States Mint, has been located in Philadelphia , since 1793. Its current facility, Philadelphia's fourth, opened in 1969.U.S...
of the United States Mint
United States Mint
The United States Mint primarily produces circulating coinage for the United States to conduct its trade and commerce. The Mint was created by Congress with the Coinage Act of 1792, and placed within the Department of State...
to be located in Dahlonega, Georgia
Dahlonega, Georgia
Dahlonega is a city in Lumpkin County, Georgia, United States, and is its county seat. As of the 2010 census, the city had a population of 5,242....
. Marble and talc are other resources produced in the Blue Ridge in Georgia.
Piedmont
The Piedmont geologic region is composed of igneous and metamorphicMetamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
rocks resulting from ancient (300 to 600 million year old) sediments that were subjected to high temperatures and pressures and re-exposed about 250 to 300 million years ago. Rocks typical of the region include schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
, amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
, gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
, migmatite
Migmatite
Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
, and granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
. This region is more hilly than mountainous and is marked by lower elevations than the Blue Ridge. Nevertheless, the Piedmont is home to prominent features like Stone Mountain
Stone Mountain
Stone Mountain is a quartz monzonite dome monadnock in Stone Mountain, Georgia, United States. At its summit, the elevation is 1,686 feet amsl and 825 feet above the surrounding area. Stone Mountain granite extends underground at its longest point into Gwinnett County...
and the Brevard Fault zone, an ancient fault zone that last moved about 185 million years ago.
Coastal Plain
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
to Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
periods. It is divided from the Piedmont by the Fall Line
Fall line
A fall line is a geomorphologic unconformity between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock. A fall line is typically prominent when crossed by a river, for there will often be rapids or waterfalls...
, which passes through Georgia from Augusta, Georgia
Augusta, Georgia
Augusta is a consolidated city in the U.S. state of Georgia, located along the Savannah River. As of the 2010 census, the Augusta–Richmond County population was 195,844 not counting the unconsolidated cities of Hephzibah and Blythe.Augusta is the principal city of the Augusta-Richmond County...
in the east, then southwestward to Macon, Georgia
Macon, Georgia
Macon is a city located in central Georgia, US. Founded at the fall line of the Ocmulgee River, it is part of the Macon metropolitan area, and the county seat of Bibb County. A small portion of the city extends into Jones County. Macon is the biggest city in central Georgia...
, then to Columbus, Georgia
Columbus, Georgia
Columbus is a city in and the county seat of Muscogee County, Georgia, United States, with which it is consolidated. As of the 2010 census, the city had a population of 189,885. It is the principal city of the Columbus, Georgia metropolitan area, which, in 2009, had an estimated population of 292,795...
and finally westward to Montgomery, Alabama
Montgomery, Alabama
Montgomery is the capital of the U.S. state of Alabama, and is the county seat of Montgomery County. It is located on the Alabama River southeast of the center of the state, in the Gulf Coastal Plain. As of the 2010 census, Montgomery had a population of 205,764 making it the second-largest city...
. The rocks in this region are from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
to Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
periods, with some marine and terrestrial fossils and rare fragments of dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. The main mineral resource of the Coastal Plain in Georgia is kaolin.
See also
- Basic geologic features of each state
- Geology of the AppalachiansGeology of the AppalachiansThe geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor - strong evidence that these rocks...