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 around 360 to 255 million years ago, and large land-based ice sheets were then present on Earth's surface. It was the second major icehouse period of the Phanerozoic, after the Hirnantian glaciation.
Timeline Interpretations of the Late Paleozoic icehouse vary, with some researchers arguing it represented one continuous glacial event and others concluding that as many as 25 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 Late Paleozoic icehouse, 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 around 10 million years, with their peaks alternating with periods of low or absent permanent ice coverage. The first glacial episodes of the Late Paleozoic icehouse occurred during the late Famennian and the Tournaisian, with δ15N evidence showing that the transition from greenhouse to icehouse was a stepwise process and not an immediate change. These Early Mississippian glaciations were transient and minor, with them sometimes being considered discrete glaciations separate from and preceding the LPIA proper. Between 335 and 330 million years ago, or sometime between the middle Viséan and earliest Serpukhovian, the LPIA proper began. A start in glacioeustatic sea level changes is recorded from Idaho at around this time. The first major glacial period occurred from the Serpukhovian to the Moscovian: ice sheets expanded from a core in southern Africa and South America. During the Bashkirian, a global eustatic sea level drop occurred, signifying the first major glacial maximum of the Late Paleozoic icehouse. The Lhasa terrane became glaciated during this stage of the Carboniferous. 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 Paraná Basin nonetheless experienced its final glaciation during the early Gzhelian. 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. This was the most intense interval of glaciation of the LPIA; in Australia, it is known as P1. An exceptionally intense cooling event occurred around 300 million years ago. From the late Sakmarian onward, and especially following the Artinskian Warming Event (AWE), these ice sheets declined, as indicated by a negative δ18O excursion. Ice sheets retreated southward across Central Africa and in the Karoo Basin. A regional glaciation spanning the latest Sakmarian and the Artinskian, known as P2, occurred in Australia amidst this global pulse of net warming and deglaciation. This massive deglaciation during the late Sakmarian and Artinskian is sometimes considered to be the end of the LPIA proper, with the Artinskian-Kungurian boundary and the associated Kungurian Carbon Isotopic Excursion used as the boundary demarcating the ice age's end. Nonetheless, ice caps of a much lower volume and area remained in Australia. Another long regional interval also limited to Australia from the middle Kungurian to the early Capitanian, known as P3, though unlike the previous glaciations, this one and the following P4 glaciation was largely limited to alpine glaciation. A final regional Australian interval lasted from the middle Capitanian to the late Wuchiapingian, known as P4. As with P3, P4's ice sheets were primarily high altitude glaciers. 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 final alpine glaciers of the Late Paleozoic icehouse melted in what is now eastern Australia around 255 million years ago, during the late Wuchiapingian. 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.
Geologic effects
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