Mississippi embayment
Encyclopedia
The Mississippi Embayment is a physiographic feature in the south-central United States
, part of the Mississippi Alluvial Plain
. It is essentially a northward continuation of the fluvial sediments
of the Mississippi River Delta
to its confluence with the Ohio River
at Cairo, Illinois
. The embayment is a topographically
low-lying basin
that is filled with Cretaceous
to recent sediment
s. The northern end of the embayment appears as an anomalous break in regional geologic
structure with Paleozoic
sedimentary rocks both to the east in Kentucky
and Tennessee
and to the west in Missouri
and Arkansas
. The current sedimentary basin results from the filling of a Cretaceous tectonic basin and existed as a large bay in the Cretaceous through early Tertiary shoreline.
The New Madrid Seismic Zone
lies at the northern end of the embayment. It was the site of the large New Madrid Earthquake
s of 1811 - 1812. The area is underlain by some anomalous geology. The Reelfoot Rift is an ancient failed continental rift
that dates back to the Precambrian
break-up
of the supercontinent
Rodinia
. The more recent opening of the Atlantic Ocean
and Gulf of Mexico
during late Paleozoic
to early Mesozoic
break-up of Pangea no doubt affected and may have partially re-activated the old rift.
range, which runs roughly on a north-south axis along the Atlantic coast of the United States, and the Ouachita
range, which runs on a rough east-west axis west of the Mississippi River
. The ancestral Appalachian-Ouachita range was thrust up when the tectonic plate
carrying North America
came into contact with the plates carrying South America
and Africa
when all three became joined in the ancient supercontinent
Pangaea
about 300 million years ago. Explaining the formation of the embayment requires explaining how part of a mountain range became a basin.
Writing in the January 2007 issue of Scientific American
, Roy B. Van Arsdale and Randel Cox of the University of Memphis
offered the following explanation of the embayment's complex origin:
As Pangaea began to break up about 95 million years ago, North America passed over a volcanic "hotspot
" in the Earth's mantle
(specifically, the Bermuda hotspot
) that was undergoing a period of intense activity. The upwelling of magma
from the hotspot forced the further uplift to a height of perhaps 2–3 km of part of the Appalachian-Ouachita range, forming an arch
. The uplifted land quickly eroded and, as North America moved away from the hot spot and as the hotspot's activity declined, the crust beneath the embayment region cooled, contracted and subsided to a depth of 2.6 km, forming a trough
that was flooded by the Gulf of Mexico
. As sea levels dropped, the Mississippi and other rivers extended their courses into the embayment, which gradually became filled with sediment.
Evidence for the Van Arsdale-Cox explanation is found in the presence of the seismic zones centered on New Madrid, Missouri, and Charleston, South Carolina
, each the source of devastating earthquakes in the 19th century, and in diamond-bearing kimberlite
pipes in Arkansas
, which are products of volcanism.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, part of the Mississippi Alluvial Plain
Mississippi Alluvial Plain
The Mississippi River Alluvial Plain is an alluvial plain created by the Mississippi River on which lies parts of seven states, from southern Louisiana to southern Illinois....
. It is essentially a northward continuation of the fluvial sediments
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
of the Mississippi River Delta
Mississippi River Delta
The Mississippi River Delta is the modern area of land built up by alluvium deposited by the Mississippi River as it slows down and enters the Gulf of Mexico...
to its confluence with the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
at Cairo, Illinois
Cairo, Illinois
Cairo is the southernmost city in the U.S. state of Illinois. It is the county seat of Alexander County. Cairo is located at the confluence of the Mississippi and Ohio rivers. The rivers converge at Fort Defiance State Park, an American Civil War fort that was commanded by General Ulysses S. Grant...
. The embayment is a topographically
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
low-lying basin
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
that is filled with Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
to recent sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s. The northern end of the embayment appears as an anomalous break in regional geologic
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
structure with Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
sedimentary rocks both to the east in Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
and Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
and to the west in Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
and Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
. The current sedimentary basin results from the filling of a Cretaceous tectonic basin and existed as a large bay in the Cretaceous through early Tertiary shoreline.
The New Madrid Seismic Zone
New Madrid Seismic Zone
The New Madrid Seismic Zone , sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.The New Madrid fault system was responsible for the...
lies at the northern end of the embayment. It was the site of the large New Madrid Earthquake
New Madrid earthquake
The 1811-1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes remain the most powerful earthquakes ever to hit the eastern United States in recorded history...
s of 1811 - 1812. The area is underlain by some anomalous geology. The Reelfoot Rift is an ancient failed continental rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
that dates back to the Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
break-up
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
of the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Rodinia
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...
. The more recent opening of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
during late Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
to early Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
break-up of Pangea no doubt affected and may have partially re-activated the old rift.
Formation of the embayment: the Van Arsdale-Cox explanation
The Mississippi embayment represents a break in what was once a single, continuous mountain range comprising the modern AppalachianAppalachian 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...
range, which runs roughly on a north-south axis along the Atlantic coast of the United States, and the Ouachita
Ouachita Mountains
The Ouachita Mountains are a mountain range in west central Arkansas and southeastern Oklahoma. The range's subterranean roots may extend as far as central Texas, or beyond it to the current location of the Marathon Uplift. Along with the Ozark Mountains, the Ouachita Mountains form the U.S...
range, which runs on a rough east-west axis west of the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
. The ancestral Appalachian-Ouachita range was thrust up when the tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
carrying North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
came into contact with the plates carrying South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
when all three became joined in the ancient supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
about 300 million years ago. Explaining the formation of the embayment requires explaining how part of a mountain range became a basin.
Writing in the January 2007 issue of Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
, Roy B. Van Arsdale and Randel Cox of the University of Memphis
University of Memphis
The University of Memphis is an American public research university located in the Normal Station neighborhood of Memphis, Tennessee and is the flagship public research university of the Tennessee Board of Regents system....
offered the following explanation of the embayment's complex origin:
As Pangaea began to break up about 95 million years ago, North America passed over a volcanic "hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
" in the Earth's mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
(specifically, the Bermuda hotspot
Bermuda hotspot
The Bermuda hotspot is the supposed "hotspot" proposed to explain the Bermuda Rise , and also...
) that was undergoing a period of intense activity. The upwelling of magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
from the hotspot forced the further uplift to a height of perhaps 2–3 km of part of the Appalachian-Ouachita range, forming an arch
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
. The uplifted land quickly eroded and, as North America moved away from the hot spot and as the hotspot's activity declined, the crust beneath the embayment region cooled, contracted and subsided to a depth of 2.6 km, forming a trough
Trough (geology)
In geology, a trough generally refers to a linear structural depression that extends laterally over a distance, while being less steep than a trench.A trough can be a narrow basin or a geologic rift....
that was flooded by the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. As sea levels dropped, the Mississippi and other rivers extended their courses into the embayment, which gradually became filled with sediment.
Evidence for the Van Arsdale-Cox explanation is found in the presence of the seismic zones centered on New Madrid, Missouri, and Charleston, South Carolina
Charleston, South Carolina
Charleston is the second largest city in the U.S. state of South Carolina. It was made the county seat of Charleston County in 1901 when Charleston County was founded. The city's original name was Charles Towne in 1670, and it moved to its present location from a location on the west bank of the...
, each the source of devastating earthquakes in the 19th century, and in diamond-bearing kimberlite
Kimberlite
Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond in 1871 spawned a diamond rush, eventually creating the Big Hole....
pipes in Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, which are products of volcanism.
See also
- Crowley's RidgeCrowley's RidgeCrowley's Ridge is an unusual geological formation that rises 250 to above the alluvial plain of the Mississippi embayment in a line from southeastern Missouri to the Mississippi River near Helena, Arkansas. It is the most prominent feature in the Mississippi Alluvial Plain between Cape...
- Mississippi DeltaMississippi DeltaThe Mississippi Delta is the distinctive northwest section of the U.S. state of Mississippi that lies between the Mississippi and Yazoo Rivers. The region has been called "The Most Southern Place on Earth" because of its unique racial, cultural, and economic history...
— the subset of the embayment that lies in MississippiMississippiMississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...
state, noted for its distinct cultural history - Arkansas DeltaArkansas DeltaThe Arkansas Delta is one of the five natural regions of the state of Arkansas. It runs along the eastern border of the state next to the Mississippi River. It is part of the Mississippi River alluvial plain, itself part of the Mississippi embayment...
- BootheelBootheelThe Missouri Bootheel is the southeasternmost part of the state of Missouri, extending south of 36°30’ north latitude, so called because its shape in relation to the rest of the state resembles the heel of a boot. Strictly speaking, it is composed of the counties of Dunklin, New Madrid, and Pemiscot...