Marine transgression

A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water (or decreasing in capacity). Transgressions and regressions may be caused by tectonic events such as orogenies, severe climate change such as ice ages or isostatic adjustments following removal of ice or sediment load.

During the Cretaceous, seafloor spreading created a relatively shallow Atlantic basin at the expense of deeper Pacific basin. This reduced the world's ocean basin capacity and caused a rise in sea level worldwide. As a result of this sea level rise, the oceans transgressed completely across the central portion of North America and created the Western Interior Seaway from the Gulf of Mexico to the Arctic Ocean.

The opposite of transgression is regression, in which the sea level falls relative to the land and exposes former sea bottom. During the Pleistocene Ice Age, so much water was removed from the oceans and stored on land as year-round glaciers that the ocean regressed 120 m, exposing the Bering land bridge between Alaska and Asia.

Duinkerketransgressies
Maps illustrating 3 transgressions of the Belgian coast.

Characteristic facies

Sedimentary facies changes may indicate transgressions and regressions and are often easily identified, because of the unique conditions required to deposit each type of sediment. For instance, coarse-grained clastics like sand are usually deposited in nearshore, high-energy environments; fine-grained sediments however, such as silt and carbonate muds, are deposited farther offshore, in deep, low-energy waters.[1]

Thus, a transgression reveals itself in the sedimentary column when there is a change from nearshore facies (such as sandstone) to offshore ones (such as marl), from the oldest to the youngest rocks. A regression will feature the opposite pattern, with offshore facies changing to nearshore ones.[1] The strata represent regressions less clearly, as their upper layers are often marked by an erosional unconformity.

These are both idealized scenarios; in practice identifying transgression or regressions can be more complicated. For instance, a regression may be indicated by a change from carbonates to shale only, or a transgression from sandstone to shale, and so on. Lateral changes in facies are also important; a well-marked transgression sequence in an area where an epeiric sea was deep may be only partial farther away, where the water was shallow. One should consider such factors when interpreting a specific sedimentary column.

See also

  • Current sea level rise – The current long-term trend for sea levels to rise mainly in response to global warming
  • Dunkirk transgression – Events of rising sea levels around the shores of the Low Countries in the late Roman period.
  • Ingression coast – A generally low coastline that is shaped by the penetration of the sea as a result of crustal movements or a rise in the sea level
  • Raised beach, also known as Marine terrace – A beach or wave-cut platform raised above the shoreline by a relative fall in the sea level
  • Sequence stratigraphy – Study and analysis of groups of sedimentary deposits
  • Submerged forest

References

  1. ^ a b Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution, 2nd ed. Belmont: West Publishing Company, 1997, pp. 112 - 113 ISBN 0-314-09577-2
Ayacara Formation

The Ayacara Formation is a sedimentary formation made up of interbedded sand and siltstone cropping out around Hornopirén and Ayacara Peninsula in western Los Lagos Region, Chile. Less common rocks are tuff and conglomerate. The formation dates to the Early and Middle Miocene (no earlier than 21.8–17.6 million years ago) when it deposited during a marine transgression.

Chaicayán Group

Chaicayán Group is a group of poorly defined sedimentary rock strata found in Taitao Peninsula in the west coast of Patagonia. The commones rock types are siltstone and sandstone. Conglomerate occur but is less common.Study of fossils and uranium–lead dating of detrital zircons indicate a Miocene age, at least for the upper sequences. The Chaicayán Group deposited likely as a result of a marine transgression that drowned much of Patagonia and Central Chile in the Late Oligocene and Miocene.The group is intruded by porphyritic stocks and sills of Pliocene age.

Coihaique Group

The Coihaique Group is a group of geological formations in northwestern Patagonia. From top to bottom the formations that make the group are Apeleg, Katterfeld and Toqui. The contact between the formations of the group are diachronous with Katterfeld Formation interfingering with the formations on top and below it. The lower and upper boundaries of the group are unconformities formed by erosion. The older parts of Coihaique Group represent a marine transgression while the younger parts evidences a return to non-marine conditions.

Diachronism

In geology, a diachronism (Greek dia, "through" + chronos, "time" + -ism), or diachronous deposit, is a sedimentary rock formation in which the material, although of a similar nature, varies in age with the place where it was deposited.Typically this occurs as a result of a marine transgression or regression, or the progressive development of a delta. As the shoreline advances or retreats, a succession of continuous deposits representing different environments (for example beach, shallow water, deeper water) may be left behind. Although each type of deposit (facies) may be continuous over a wide area, its age varies according to the position of the shoreline through time.

An example is the sandy beds near the end of the lower Carboniferous of the west of England (the Drybrook sandstone of the Forest of Dean). Deposition of this began much later in the Bristol area than further north.The detection of diachronous beds can be quite problematic since fossil assemblages tend to migrate geographically with their environment of formation. They are generally revealed by the presence of marker species, fossils which can be dated reliably from other beds.

Geology of Denmark

The geology of Denmark includes 12 kilometers of unmetamorphosed sediments lie atop the Precambrian Fennoscandian Shield, the Norwegian-Scottish Caledonides and buried North German-Polish Caledonides. The stable Fennoscandian Shield formed from 1.45 billion years ago to 850 million years ago in the Proterozoic. The Fennoscandian Border Zone is a large fault, bounding the deep basement rock of the Danish Basin—a trough between the Border Zone and the Ringkobing-Fyn High. The Sorgenfrei-Tornquist Zone is a fault-bounded area displaying Cretaceous-Cenozoic inversion.

Geology of Egypt

The geology of Egypt includes rocks from Archaean - early Proterozoic times onwards. These oldest rocks are found as inliers in Egypt’s Western Desert. In contrast, the rocks of the Eastern Desert are largely late Proterozoic in age. Throughout the country this older basement is overlain by Palaeozoic sedimentary rocks. Cretaceous rocks occur commonly whilst sediments indicative of repeated marine transgression and regression are characteristic of the Cenozoic Era.

Geology of Georgia (country)

The geology of Georgia is the study of rocks, minerals, water, landforms and geologic history in Georgia. The country is dominated by the Caucasus Mountains at the junction of the Eurasian Plate and the Afro-Arabian Plate, and rock units from the Mesozoic and Cenozoic are particularly prevalent. For much of its geologic history, until the uplift of the Caucasus, Georgia was submerged by marine transgression events. Geologic research for 150 years by Georgian and Russian geologists has shed significant light on the region and since the 1970s has been augmented with the understanding of plate tectonics.

Geology of Libya

The geology of Libya formed on top of deep and poorly understood Precambrian igneous and metamorphic crystalline basement rock. Most of the country is intra-craton basins, filled with thick layers of sediment. The region experienced long-running subsidence and terrestrial sedimentation during the Paleozoic, followed by phases of volcanism and intense folding in some areas, and widespread flooding in the Mesozoic and Cenozoic due to a long marine transgression. Libya has the largest hydrocarbon reserves in Africa, as well as deposits of evaporites.

Geology of Mauritania

The geology of Mauritania is built on more than two billion year old Archean crystalline basement rock in the Reguibat Shield of the West African Craton, a section of ancient and stable continental crust. Mobile belts and the large Taoudeni Basin formed and filled with sediments in the connection with the Pan-African orogeny mountain building event 600 million years ago and a subsequent orogeny created the Mauritanide Belt. In the last 251 million years, Mauritania has accumulated additional sedimentary rocks during periods of marine transgression and sea level retreat. The arid country is 50% covered in sand dunes and has extensive mineral resources, although iron plays the most important role in the economy.

Geology of Morocco

The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.

Geology of Nigeria

The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.

Nigeria has tremendous oil and natural gas resources housed in its thick sedimentary basins, as well as reserves of gold, lead, zinc, tantalite, columbite, coal and tin.

Geology of the United Arab Emirates

The geology of the United Arab Emirates includes very thick Paleozoic, Mesozoic and Cenozoic marine and continental sedimentary rocks overlying deeply buried Precambrian. The region has extensive oil and gas resources and was deformed during the last several million years by more distant tectonic events.

Marine regression

Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land.Evidence of marine regressions and transgressions occurs throughout the fossil record, and these fluctuations are thought to have caused or contributed to several mass extinctions, among them the Permian-Triassic extinction event (250 million years ago) and Cretaceous–Paleogene extinction event (66 Ma). At the time of the Permian-Triassic extinction, the largest extinction event in the Earth's history, global sea level fell 250 m (820 ft).A major regression could itself cause marine organisms in shallow seas to go extinct, but mass extinctions tend to involve both terrestrial and aquatic species, and it is harder to see how a marine regression could cause widespread extinctions of land animals. Regressions are, therefore, seen as correlates or symptoms of major extinctions, rather than primary causes. The Permian regression might have been related to the formation of Pangaea: the accumulation of all the major landmasses into one body could have facilitated a regression, by providing "a slight enlargement of the ocean basins as the great continents coalesced." However, that cause could not have applied in all, or even many, other cases.

During the ice ages of the Pleistocene, a clear correlation existed between marine regressions and episodes of glaciation; as the balance shifts between the global cryosphere and hydrosphere, more of the planet's water in ice sheets means less in the oceans. At the height of the last ice age, at around 18,000 years before the present, the global sea level was 120 to 130 m (390-425 ft) lower than today. A cold spell around 6 million years ago was linked to an advance in glaciation, a marine regression, and the start of the Messinian salinity crisis in the Mediterranean basin. Some major regressions of the past, however, seem unrelated to glaciation episodes — the regression that accompanied the mass extinction at the end of the Cretaceous Period being one example.

A clear and certain understanding of major marine regressions has not yet been achieved; according to one hypothesis, regressions may be linked to a "slowdown in sea-floor spreading, leading to a generalized drop in sea level (as the mid-ocean ridges would take up less space)...." In that view, major marine regressions are one aspect of a normal variation in rates of plate tectonic activity, which lead to major episodes of global volcanism like the Siberian Traps and the Deccan Traps, which in turn cause large extinction events.

Mississippian (geology)

The Mississippian (also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earliest/lowermost of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley.

The Mississippian was a period of marine transgression in the Northern Hemisphere: the sea level was so high that only the Fennoscandian Shield and the Laurentian Shield were dry land. The cratons were surrounded by extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas.In North America, where the interval consists primarily of marine limestones, it is treated as a geologic period between the Devonian and the Pennsylvanian. During the Mississippian an important phase of orogeny occurred in the Appalachian Mountains. It is a major rock-building period named for the exposures in the Mississippi Valley region. The USGS geologic time scale shows its relation to other periods.In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous system, and sometimes called the Upper Carboniferous and Lower Carboniferous instead.

Retrogradation

Retrogradation is the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result, retrogradation is most common:

during periods of sea-level rise which results in marine transgression. This can occur during major periods of global warming and the melting of continental ice sheets.

with extremely low sediment input.

Sawatch Formation

The Sawatch Formation is a geologic formation in eastern Colorado. It is a sedimentary sequence formed approximately 530 million years ago during a marine transgression. It preserves fossils dating back to the Cambrian period.

Submerged forest

A submerged forest is the in situ remains of trees (especially tree stumps) that lie submerged beneath a bay, sea, ocean, lake, or other body of water. These remains have usually been buried in mud, peat or sand for several thousand years before being uncovered by sea level change and erosion and have been preserved in the compacted sediment by the exclusion of oxygen. A forest can become submerged as the result of a lake or sea level rise that results in a lacustrine or marine transgression and in place drowning of the forest. A submerged forest that lies beneath a lake can also be formed by the blockage of a river valley by either a landslide or manmade dam.

Tejas sequence

The Tejas sequence was the last major marine transgression across the North American craton. Following the late Cretaceous regression that ended the Zuñi sequence, the oceans advanced again early in the Cenozoic, peaking during the Paleocene and Eocene epochs. There were no dramatic epeiric seas in North America; indeed, the Atlantic coast advanced only as far as the Mississippi Embayment. The Tejas was deeper in Eurasia and Africa, which experienced widespread carbonate deposition during the Eocene. There was a final transgression before the end of the Oligocene, the end of which marked the end of the Tejas sequence.

Transvaal Basin

The Transvaal Basin is one of three basins of the Transvaal Supergroup on the Kaapvaal craton. The evolution of this 2.65–2.05 Ga Neoarchaean–Palaeoproterozoic basin is thought to have been derived largely from magmatism, palaeoclimate and eustasy, while plate tectonics played an intermittent role. The supergroup is made up of basal ‘protobasinal’ rocks, upon which followed the Black Reef Formation, Chuniespoort Group and the uppermost Pretoria Group.The Transvaal Supergroup displays three unconformity-bounded sequences that surface in two

geographically distinct areas – the Transvaal Basin, which circumscribes the Bushveld Igneous Complex, and the Griqualand West basin, lying between Kimberley and Sishen at the western Kaapvaal craton rim, extending into southern Botswana beneath the Kalahari Sands as the Kanye Basin. The two basins are

separated by the broad Vryburg Arch.Between approximately 2.640 and 2.516  Ga, two successive stromatolitic carbonate platforms developed in the basin of the Kaapvaal craton. Oldest was the Schmidtsdrif Subgroup, deposited in the southwestern part of the basin, showing stromatolitic carbonates, siliciclastic sediments and small lava flows. This was followed by the Nauga formation carbonates deposited on peritidal flats in the southwest, which were inundated during a marine transgression of the Transvaal Supergroup continental sea, at some 2.550  Ga. This resulted in a carbonate platform in the Transvaal and Griqualand West Basins, lasting

for 30–50  Ma. Shales were deposited during this period over the Nauga Formation carbonates. Following this a subsidence led to immersion of the stromatolitic platform and to sediments of iron-rich banded iron formations being laid down over the entire basin.

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