A marine regression is a geological process occurring when areas of submerged
seafloor are exposed during a drop in sea level. The opposite event,
marine transgression, occurs when flooding from the sea covers previously-exposed land.
Description
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)...." That view considers major marine regressions to be one aspect of a normal variation in rates of
plate tectonic
Plate may refer to:
Cooking
* Plate (dishware), broad, mainly flat vessel commonly used to serve food
* Plates, tableware, dishes or dishware used for setting a table, serving food and dining
* Plate, the content of such a plate (for example: r ...
activity, which leads to major episodes of global
volcanism like the
Siberian Traps and the
Deccan Traps, which in turn cause large
extinction events.
Evidence of marine regressions and transgressions occurs throughout the fossil record, and the fluctuations are thought to have caused or contributed to several
mass extinctions, such as the
Permian–Triassic extinction event
The Permian–Triassic extinction event (also known as the P–T extinction event, the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying,) was an extinction ...
(250 million years ago, Ma) and
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
(66
Ma). During the Permian-Triassic extinction, the largest extinction event in the Earth's history, the global sea level fell 250 m (820 ft).
A major regression could 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
Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
. The accumulation of all major landmasses into one body could have facilitated a regression by providing "a slight enlargement of the ocean basins as the great continents coalesced."
[Ward, Peter D. ''Rivers in Time: The Search for Clues to Earth's Mass Extinctions.'' New York, Columbia University Press, 2000; p. 77.] However, that cause could not have applied in all or even many of the other cases.
Ice ages
During the
ice ages
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and Gre ...
of the
Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
, a clear correlation existed between marine regressions and episodes of
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
. As the balance shifts between the global
cryosphere and
hydrosphere
The hydrosphere () is the combined mass of water found on, under, and above the Planetary surface, surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to ch ...
, more of the planet's water in ice sheets means less in the oceans. At the height of the
last ice age, around 18,000 years ago, 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
The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
basin. Some major regressions of the past, however, seem unrelated to glaciation episodes, with the regression that accompanied the mass extinction at the end of the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
being one example.
See also
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References
External links
Marine Transgression and Marine Regression: World of Earth Science
{{Geologic Principles
Sedimentology
Plate tectonics
Extinction events
Coastal geography
Oceanographical terminology