Late Paleozoic icehouse

rdf:langString Late Paleozoic icehouse

rdf:langString The late Paleozoic icehouse, also known as the Late Paleozoic Ice Age (LPIA) and formerly known as the Karoo ice age, was an ice age that began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago (Mya), and large land-based ice-sheets were then present on Earth's surface. It was the second major icehouse period of the Phanerozoic. It is named after the tillite (Dwyka Group) found in the Karoo Basin of western South Africa, where evidence for the ice age was first clearly identified in the 19th century. The tectonic assembly of the continents of Euramerica and Gondwana into Pangaea, in the Hercynian-Alleghany Orogeny, made a major continental land mass within the Antarctic region, and the closure of the Rheic Ocean and Iapetus Ocean saw disruption of warm-water currents in the Panthalassa Ocean and Paleotethys Sea and an increase in carbon sequestration via silicate weathering, which led to progressive cooling of summers, and the snowfields accumulating in winters, which caused mountainous alpine glaciers to grow, and then spread out of highland areas. That made continental glaciers, which spread to cover much of Gondwana. Data from Serpukhovian and Moscovian marine strata of South China point to glacioeustasy being driven primarily by long-period eccentricity, with a cyclicity of about 0.405 million years, and the modulation of the amplitude of Earth's obliquity, with a cyclicity of approximately 1.2 million years. This is most similar to the early part of the Late Cenozoic Ice Age, from the Oligocene to the Pliocene, before the formation of the Arctic ice cap, suggesting the climate of this episode of time was relatively warm for an icehouse period. Evidence from the Middle Permian Lucaogou Formation of Xinjiang, China indicates that the climate of the time was particularly sensitive to the 1.2 million year long-period modulation cycle of obliquity. It also suggests that palaeolakes such as those found in the Junggar Basin likely played an important role as a carbon sink during the later stages of the LPIA, with their absorption and release of carbon dioxide acting as powerful feedback loops during Milankovitch cycle driven glacial and interglacial transitions. Interpretations of the LPIA vary, with some researchers arguing it represented one continuous glacial event and others concluding that as many as twenty-five separate ice sheets across Gondwana developed, waxed, and waned independently and diachronously over the course of the Carboniferous and Permian, with the distribution of ice centres shifting as Gondwana drifted and its position relative to the South Pole changed. At the beginning of the LPIA, ice centres were concentrated in western South America; they later shifted eastward across Africa and by the end of the ice age were concentrated in Australia. Evidence from sedimentary basins suggests individual ice centres lasted for approximately 10 million years, with their peaks alternating with periods of low or absent permanent ice coverage. The glacial episodes that occurred during the late Famennian and late middle to early late Tournaisian are sometimes considered discrete glaciations separate from and preceding the LPIA proper that began between 335 and 330 Mya during the Viséan or Serpukhovian. Likewise, the more geographically limited glaciations that persisted in some parts of Gondwana until the last alpine glaciers melted in what is now eastern Australia around 255 Mya are sometimes not considered part of the LPIA proper either, which is said to have peaked during the Asselian and early Sakmarian and ended in the late Sakmarian around 290 Mya or near the Artinskian-Kungurian boundary and the associated Kungurian Carbon Isotopic Excursion under this more restricted definition. At least two major periods of glaciation within the LPIA proper are known: * The first glacial period occurred from the Serpukhovian to the Moscovian: ice sheets expanded from a core in southern Africa and South America. A relatively warm interglacial interval spanning the Kasimovian and Gzhelian, coinciding with the Alykaevo Climatic Optimum, occurred between this first major glacial period and the later second major glacial period. * The second glacial period occurred from the late Gzhelian across the Carboniferous-Permian boundary to the early Sakmarian; ice sheets expanded from a core in Australia and India. From the late Sakmarian onward, and especially following the Artinskian Warming Event (AWE), these ice sheets declined, as indicated by a negative δ18O excursion. Other, minor or more geographically limited glacial intervals have also been identified: * The aforementioned interval of transient glaciations spanning from the Famennian to the late Visean or earliest Serpukhovian. * A glacial interval limited to Australia spanning the latest Sakmarian and the Artinskian, known regionally as P2 (P1 coinciding with the Gondwana-wide glaciations during the Asselian and early Sakmarian). This regional glaciation occurred amidst a global pulse of net warming and deglaciation, as evidenced by the retreat of ice sheets in Central Africa and in the Karoo Basin. * A second, longer regional interval also limited to Australia from the middle Kungurian to the early Capitanian, known as P3. Unlike the previous glaciations, this one and the following P4 glaciation were limited to alpine glaciation. * A final regional Australian interval lasting from the middle Capitanian to the late Wuchiapingian, known as P4. This glacial period was interrupted by a rapid warming interval corresponding to a surge in activity from the Emeishan Traps and corresponding Capitanian mass extinction event. The time intervals here referred to as glacial and interglacial periods represented intervals of several million years corresponding to colder and warmer icehouse intervals, respectively, were influenced by long term variations in palaeogeography, greenhouse gas levels, and geological processes such as rates of volcanism and of silicate weathering and should not be confused with shorter term cycles of glacials and interglacials that are driven by astronomical forcing caused by Milankovitch cycles.