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.[1]

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).[2]

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."[3] 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)...."[4] 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.

See also

References

  1. ^ Monroe, James Stewart, and Reed Wicander. Physical Geology: Exploring the Earth. Fifth edition; Thomson Brooks/Cole, 2005; p. 162.
  2. ^ Courtillot, Vincent. Evolutionary Catastrophes: The Science of Mass Extinction. Cambridge, Cambridge University Press, 1999; p. 89.
  3. ^ Ward, Peter D. Rivers in Time: The Search for Clues to Earth's Mass Extinctions. New York, Columbia University Press, 2000; p. 77.
  4. ^ Courtillot, p. 141.

External links

Ambolafotsy Formation

The Ambolafotsy Formation is a Turonian aged geological formation in the Diego Basin of Antsiranana Province in Madagascar. It is a mostly terrestrial unit deposited during a marine regression close to the shoreline. The dinosaur Dahalokely has been discovered in the formation.

Archaeodobenus

Archaeodobenus is an extinct genus of pinniped that lived during the Late Miocene of what is now Japan. It belonged to the Odobenidae family, which is today only represented by the walrus, but was much more diverse in the past, containing at least 16 genera. Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion.

The first known specimen was collected in 1977 from the Ichibangawa Formation in Tobetsu Town on the island of Hokkaido. The specimen consists of a partial skull, vertebrae, and limb bones, and was made the holotype specimen of the new genus and species A. akamatsui by the Japanese palaeontologists Yoshihiro Tanaka and Naoki Kohno in 2015. The generic name consists of archaio, the Greek word for ancient, and the generic name of the walrus, Odobenus; in full, "ancient walrus". The specific name honours Morio Akamatsu, a curator of the Hokkaido Museum.The diversity of odobenids increased during the Late Miocene and Pliocene (about 12.5 million to 10.5 million years ago), perhaps linked to marine regression and transgression, which could have geographically isolated their ancestors. Archaeodobenus was the contemporary of the odobenid Pseudotaria from the same formation, which it may have diverged from in the western North Pacific during the Late Miocene. Archaeodobenus appears to have been closer related to later odobenids such as Imagotaria, Pontolis, the subfamily Odobeninae, whereas Pseudotaria seems to have been more basal.The holotype specimen appears to have been a young adult male of about 3 metres (10 ft) in length, which would have weighed around 473 kg (1,042 lb). This is intermediate between the size of the Steller sea lion and the South American sea lion. Its canines were 86.3 mm (3.4 in) long, while those of a walrus are up to 1 m (3 ft 3 in) long in comparison. Archaeodobenus can be distinguished from Pseudotaria by features such as the shape and size of the occipital condyle (which connects with the first neck vertebra at the back of the skull), the foramen magnum (the opening through which the spinal chord passes into the cranium), the mastoid process (where various muscles attach to the back of the skull), as well as some features in the postcranial skeleton.

Cloppenburg Geest

The Cloppenburg Geest (German: Cloppenburger Geest) is a geest region near the town of Cloppenburg in North Germany and the centre of the Saalian glaciation Upper Pleistocene terrain of the Ems-Hunte Geest region. The meltwater sands (Schmelzwassersande) of the advancing ice sheet covered the old terrain with outwash sands (Vorschüttsande). Woldstedt (1955: 159) spoke about underlying sands that, in the "Cloppenburg-Bassum Geest", belonged to the Elster glaciation. A covering of boulder clay was deposited over the outwash sands during the Saale glaciation, or more precisely the Drenthe stage.

A series of meltwater valleys characterises the surface of the Cloppenburg Geest, something that was vital to the emergence of the river network. "Numerous parallel, flat channels cross the terrain and so create a landscape of parallel ridges" writes Woldstedt (1955: 158). There are two opposing theories for the formation of the rivers. Hausfeld (1983; 1984) put their emergence down to large cracks in the Drenthe ice sheet, through which meltwaters flowed as the glacier thawed, cutting through the ground moraines and down into the outwash sands. Woldstedt (1956) spoke of channels (Rinnen) in another connexion. The advancing ice followed the depth contours, conserving and deepening them. When the ice sheet retreated, dead-ice (Toteis) remained deep in these channels; it was their thawing that then enabled the rivers to flow down their old valleys.

During the marine regression of the Weichselian glaciation that ended about 12,000 years ago, in which the northwest German plain was not covered by ice, the rivers of the Cloppenburg Geest cut deeply into the valley sands. At that time the windborne and dune sands were formed especially as the area around the perimeter dried out.

The climate of the post-glacial period was moister and warmer. The rise in sea level, the base level for river erosion, probably led to a rise in the water table in the geest depression (Roeschmann, 1971: 189). In the valleys vast fen peats formed, whilst on the valley edges and the larger basins raised bogs were formed (Hausfeld, 1983: 245).

Cretaceous–Paleogene boundary

The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K-T) boundary, is a geological signature, usually a thin band of rock. K, the first letter of the German word Kreide (chalk), is the traditional abbreviation for the Cretaceous Period and Pg is the abbreviation for the Paleogene Period.

The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at around 66 Ma (million years ago), with radiometric dating yielding a more precise age of 66.043 ± 0.011 Ma.The K–Pg boundary is associated with the Cretaceous–Paleogene extinction event, a mass extinction which destroyed a majority of the world's Mesozoic species, including all dinosaurs except for birds.Strong evidence exists that the extinction coincided with a large meteorite impact at the Chicxulub crater and the generally accepted scientific theory is that this impact triggered the extinction event.

Geology of Jordan

The geology of Jordan includes thick sedimentary sequences of sandstone, marl and evaporites atop ancient Precambrian crystalline igneous and metamorphic basement rock.

Geology of Laos

The geology of Laos includes poorly defined oldest rocks. Marine conditions persisted for much of the Paleozoic and parts of the Mesozoic, followed by periods of uplift and erosion. The country has extensive salt, gypsum and potash, but very little hydrocarbons and limited base metals.

Geology of North Korea

The geology of North Korea has been studied by the Central Geological Survey of Mineral Resources, rare international research and by inference from South Korea's geology.

Grünbach Formation

The Grünbach Formation is a fossil rich Austrian geological formation that dates to the lower Campanian age of the Late Cretaceous. it forms part of the Gosau Group, and represents a marine regression event, representing a coastal/brackish environment, being underlain by the marine carbonate Maiersdorf Formation and overlain by the deep marine siliciclastic Piesting Formation. The main lithology is Clay, Marl, Siltstone and Sandstone, with a minor Conglomerate component. Coal seams have also been noted.

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. A grouping of geographically or geologically related islands is called an archipelago, such as the Philippines.

An island may be described as such, despite the presence of an artificial land bridge; examples are Singapore and its causeway, and the various Dutch delta islands, such as IJsselmonde. Some places may even retain "island" in their names for historical reasons after being connected to a larger landmass by a land bridge or landfill, such as Coney Island and Coronado Island, though these are, strictly speaking, tied islands. Conversely, when a piece of land is separated from the mainland by a man-made canal, for example the Peloponnese by the Corinth Canal or Marble Hill in northern Manhattan during the time between the building of the United States Ship Canal and the filling-in of the Harlem River which surrounded the area, it is generally not considered an island.

There are two main types of islands in the sea: continental and oceanic. There are also artificial islands.

Land bridge

A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands. A land bridge can be created by marine regression, in which sea levels fall, exposing shallow, previously submerged sections of continental shelf; or when new land is created by plate tectonics; or occasionally when the sea floor rises due to post-glacial rebound after an ice age.

Mudflat

Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A recent global analysis suggested they are as extensive globally as mangroves. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land. Several especially shallow mudflat areas, such as the Wadden Sea, are now popular among those practising the sport of mudflat hiking.

On the Baltic Sea coast of Germany in places, mudflats are exposed not by tidal action, but by wind-action driving water away from the shallows into the sea. These wind-affected mudflats are called windwatts in German.

Nacientes del Biobío Formation

Nacientes del Biobío Formation (Spanish: Formación Nacientes del Biobío) is a geological formation that crops out near the uppermost reaches of Bío Bío River, in south-central Chile, and nearby areas of Argentina. The formation is made up of basalt and pyroclastic rocks and marine sedimentary rocks, such as sandstone and mudstone. Some less abundant sedimentary lithologies are conglomerate, volcaniclastic sedimentary rock. The formation is intruded by Grupo Plutónico Galletué which is of Late Jurassic to Late Cretaceous age. Further north in Chile the formation is similar to Nacientes del Teno Formation while in Argentina it is similar to Los Molles Formation and Lotena Formation.

Progradation

In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion.

Progradation can be caused by:

Periods of sea-level fall which result in marine regression. This can occur during major continental glaciations within ice ages, be caused by changes in the rates of seafloor spreading that affects the volume of the ocean basins, or tectonic effects on the regional mantle density structure that can change the geoid elevation.

Extremely high sediment input, such as by the Huang He (Yellow River) in China, which drains the Loess plateau, or from high sediment loads in proglacial rivers.

Refugio County, Texas

Refugio County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 7,383. Its county seat is Refugio. The county was created as a municipality of Mexico in 1834 and organized as a county in 1837.

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.

Sauk sequence

The Sauk sequence was the earliest of the six cratonic sequences that have occurred during the Phanerozoic in North America. It was followed by the Tippecanoe, Kaskaskia, Absaroka, Zuñi, and Tejas sequences.

It dates from the late Proterozoic through the early Ordovician periods, though the marine transgression did not begin in earnest until the middle Cambrian.At its peak, most of North America was covered by the shallow Sauk Sea, save for parts of the Canadian Shield and the islands of the Transcontinental Arch. The stratigraphy of the Sauk sequence indicates shallow-water deposition, primarily consisting of well-sorted sandstones and clastic carbonates. A marine regression ended the Sauk sequence early in the Ordovician, to be followed by the Tippecanoe sequence later in the period.

Surf zone

As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves (now reduced in height) continue to move in, and they run up onto the sloping front of the beach, forming an uprush of water called swash. The water then runs back again as backswash. The nearshore zone where wave water comes onto the beach is the surf zone. The water in the surf zone, or breaker zone, is shallow, usually between 5 and 10 m (16 and 33 ft) deep; this causes the waves to be unstable.

Zechstein

The Zechstein (German either from mine stone or tough stone) is a unit of sedimentary rock layers of Middle to Late Permian (Guadalupian to Lopingian) age located in the European Permian Basin which stretches from the east coast of England to northern Poland. The name Zechstein was formerly also used as a unit of time in the geologic timescale, but nowadays it is only used for the corresponding sedimentary deposits in Europe.

The Zechstein lies on top of the Rotliegend; on top of the Zechstein is the Buntsandstein or Bunter.

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