Mississippi embayment

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Coordinates: 33°45′04″N89°40′52″W / 33.751°N 89.681°W / 33.751; -89.681

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The Mississippi embayment stretches from central Louisiana into southern Missouri. Mississippi Embayment relief map 2.svg
The Mississippi embayment stretches from central Louisiana into southern Missouri.

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 current sedimentary area was formed in the Cretaceous and early Cenozoic by the filling with sediment of a pre-existing basin. An explanation for the embayment's formation was put forward by Van Arsdale and Cox in 2007: movement of the earth's crust brought this region over a volcanic "hotspot" in the Earth's mantle causing an upthrust of magma which formed the Appalachian-Ouachita range. Subsequent erosion caused a deep trough that was flooded by the Gulf of Mexico and eventually filled with sediment from the Mississippi River.

Geography

The embayment is a topographically low-lying basin that is filled with Cretaceous to recent sediments. 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 Cenozoic shoreline.

The New Madrid Seismic Zone lies at the northern end of the embayment. It was the site of the large New Madrid earthquakes of 1811-12. The area is underlain by some anomalous geology. The Reelfoot Rift is an ancient failed continental rift, an aulacogen, which 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.

Formation of the embayment

The Mississippi embayment represents a break in what was once a single, continuous mountain range comprising the modern Appalachian 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.

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. [1]

Evidence for this 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.

Maps

See also

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The geology of Kentucky formed beginning more than one billion years ago, in the Proterozoic eon of the Precambrian. The oldest igneous and metamorphic crystalline basement rock is part of the Grenville Province, a small continent that collided with the early North American continent. The beginning of the Paleozoic is poorly attested and the oldest rocks in Kentucky, outcropping at the surface, are from the Ordovician. Throughout the Paleozoic, shallow seas covered the area, depositing marine sedimentary rocks such as limestone, dolomite and shale, as well as large numbers of fossils. By the Mississippian and the Pennsylvanian, massive coal swamps formed and generated the two large coal fields and the oil and gas which have played an important role in the state's economy. With interludes of terrestrial conditions, shallow marine conditions persisted throughout the Mesozoic and well into the Cenozoic. Unlike neighboring states, Kentucky was not significantly impacted by the Pleistocene glaciations. The state has extensive natural resources, including coal, oil and gas, sand, clay, fluorspar, limestone, dolomite and gravel. Kentucky is unique as the first state to be fully geologically mapped.

The geology of Mississippi includes some deep igneous and metamorphic crystalline basement rocks from the Precambrian known only from boreholes in the north, as well as sedimentary sequences from the Paleozoic. The region long experienced shallow marine conditions during the tectonic evolutions of the Mesozoic and Cenozoic, as coastal plain sediments accumulated up to 45,000 feet thick, including limestone, dolomite, marl, anhydrite and sandstone layers, with some oil and gas occurrences and the remnants of Cretaceous volcanic activity in some locations.

The geology of Missouri includes deep Precambrian basement rocks formed within the last two billion years and overlain by thick sequences of marine sedimentary rocks, interspersed with igneous rocks by periods of volcanic activity. Missouri is a leading producer of lead from minerals formed in Paleozoic dolomite.

Geology of New York (state)

The geology of New York State is made up of ancient Precambrian crystalline basement rock, forming the Adirondack Mountains and the bedrock of much of the state. These rocks experienced numerous deformations during mountain building events and much of the region was flooded by shallow seas depositing thick sequences of sedimentary rock during the Paleozoic. Fewer rocks have deposited since the Mesozoic as several kilometers of rock have eroded into the continental shelf and Atlantic coastal plain, although volcanic and sedimentary rocks in the Newark Basin are a prominent fossil-bearing feature near New York City from the Mesozoic rifting of the supercontinent Pangea.

The geology of North Carolina includes ancient Proterozoic rocks belonging to the Grenville Province in the Blue Ridge. The region experienced igneous activity and the addition of new terranes and orogeny mountain building events throughout the Paleozoic, followed by the rifting of the Atlantic Ocean and the deposition of thick sediments in the Coastal Plain and offshore waters.

References

  1. Van Arsdale, Roy B.; Cox, Randel T. (January 2007). "The Mississippi's Curious Origins". Scientific American . Retrieved September 1, 2019.

General references