Marine regression
Encyclopedia
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–Tertiary extinction event (65 Ma). At the time of the Permian or P/T extinction, the largest extinction event in the Earth's history, global sea level fell 250 meters, or more than 800 ft.
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 meters (400 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 major regression could, in and of itself, cause marine organisms in shallow seas to go extinct; yet 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." Yet this cause could not have applied in all, or even many, other cases.
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 this 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
.
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...
process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression
Transgression (geology)
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...
, 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
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
, among them the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...
(250 million years ago) and Cretaceous–Tertiary extinction event (65 Ma). At the time of the Permian or P/T extinction, the largest extinction event in the Earth's history, global sea level fell 250 meters, or more than 800 ft.
During the ice ages
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
of the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, a clear correlation existed between marine regressions and episodes of glaciation; as the balance shifts between the global cryosphere
Cryosphere
The cryosphere is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground . Thus there is a wide overlap with the hydrosphere...
and hydrosphere
Hydrosphere
A hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet....
, 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 meters (400 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
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...
in the Mediterranean
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
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
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...
being one example.
A major regression could, in and of itself, cause marine organisms in shallow seas to go extinct; yet 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
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....
: 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." Yet this cause could not have applied in all, or even many, other cases.
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 this view, major marine regressions are one aspect of a normal variation in rates of plate tectonic
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
activity, which lead to major episodes of global volcanism
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
like the Siberian Traps
Siberian Traps
The Siberian Traps form a large region of volcanic rock, known as a large igneous province, in the Russian region of Siberia. The massive eruptive event which formed the traps, one of the largest known volcanic events of the last 500 million years of Earth's geological history, continued for...
and the Deccan Traps
Deccan Traps
The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than thick and cover an area of and a volume of...
, which in turn cause large extinction events
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
.