The Carnian pluvial episode (CPE), often called the Carnian pluvial event, was a period of major change in global climate that coincided with significant changes in Earth's biota both in the sea and on land. It occurred during the latter part of the Carnian Stage, the first subdivision of the Late Triassic Epoch, and lasted for perhaps 1–2 million years (around 234–232 million years ago). Volcanic activity off the coast of North America led to global warming and increased rainfall on land, alongside a reduction of carbonate platforms in the oceans. Pluvial means "of or relating to rain; characterized by much rain, rainy."Oxford University Press. (n.d.). Pluvial, adj. & n.². In Oxford English dictionary. Retrieved October 31, 2025, from https://doi.org/10.1093/OED/8065084472
The CPE corresponds to a significant episode in the evolution and diversification of many taxa that are important today. The earliest dinosaurs (which include the ancestors of birds), lepidosaurs (the ancestors of modern-day lizards, snakes, and the tuatara) and potentially mammaliaforms (ancestors of mammals) all diversified during the event. In the marine realm it saw the first appearance among the microplankton of coccoliths and dinoflagellates, with the latter linked to the rapid diversification of scleractinian corals through the establishment of symbiotic zooxanthellae within them. The CPE also saw the extinction of many aquatic invertebrate species, especially among ammonoids, bryozoans, and crinoids.
Evidence for the CPE is observed in Carnian strata worldwide and in sediments of both terrestrial and marine environments. On land, the prevailing arid climate across much of the supercontinent Pangea shifted briefly to a hotter and more humid climate, with a significant increase in rainfall and runoff. In the oceans, carbonate minerals such as limestone saw reduced deposition, leaving mud-rich layers as prominent geological markers. Carbonate disruption may reflect the extinction of many carbonate-forming organisms, but may also be due to a rise in the carbonate compensation depth, below which most carbonate shells dissolve and leave few carbonate particles on the ocean floor to form sediments.
Climate change during the Carnian pluvial event is reflected in chemical changes in Carnian strata across the CPE. Major disruption to the carbon cycle and other natural systems show that global warming was prevalent at the time. This climate change was most likely linked to the eruption of extensive flood basalts and volcanic CO2 offgassing as the Wrangellia Terrane was accreted onto the northwestern end of the North American Plate.
History and nomenclature Environmental disturbance and high extinction rates were observed for sediments of the Carnian stage long before a global climate perturbation was proposed. Schlager & Schöllnberger (1974) drew attention to a dark siliciclastic layer which abruptly interrupted a long period of carbonate deposition in the Northern Limestone Alps. They termed this stratigraphic "wende" (turning point) the Reingrabener Wende, and it has also been called the Reingraben event or Raibl event. Several Carnian terrestrial formations (namely the Schilfsandstein of Germany and various members of the United Kingdom's Mercia Mudstone Group) are intervals of river sediments enriched with kaolinitic clay and plant debris, despite having been deposited between more arid strata. Humidity-adapted palynomorphs in New Brunswick, karst topography in the U.K., and a carbon isotope excursion in Israel were all reported for the middle of the Carnian prior to 1989. The Julian-Tuvalian boundary experienced high extinction rates among many marine invertebrates, while an extinction among land vertebrates was suggested to occur in the late Carnian.
In 1989, Michael J. Simms and Alastair H. Ruffell combined these disparate observations into a new hypothesis, pointing to an episode of increased rainfall synchronous with significant ecological turnover in the mid-Carnian. The paper was inspired by a conversation between Simms and Ruffell, on 10 November 1987 at Birmingham University, that connected Ruffell's research on lithological changes in the Mercia Mudstone Group to Simms's research on crinoid extinction. A key aspect of their hypothesis was that the evidence used to demonstrate the climate change was entirely independent of the evidence for biotic change; fossils were not used in any way to infer climate change. Their hypothesized climatic disturbance, which they named the Carnian pluvial episode, was tentatively considered to be a result of oceanic and/or volcanic instability related to the early rifting of Pangea, but at that time direct evidence of this possibility was lacking.
Simms and Ruffell published several more papers in subsequent years,Simms, M.J., Ruffell, A.H. and Johnson, A.L.A. 1994. Biotic and climatic changes in the late Triassic of Europe and adjacent areas. Pp. 352-365 in N.C.Fraser and Hans Dieter-Suess (eds), In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods, Cambridge University Press. but their hypothesis was not widely accepted. A strong critique by Visscher et al. (1994) argued that aridity-adapted pollen stayed abundant through the entire Carnian of Germany, suggesting that the Schilfsandstein was simply indicative of an invading river system rather than widespread climate change. Their critique also coined the term "Carnian pluvial event", which would eventually become among the most widespread names for the climatic disturbance.
The obscurity of Simms and Ruffell's hypothesis began to dissipate in the late 2000s, as further support accumulated from studies on Carnian sites in Italy. Interest in the hypothesis was greatly enhanced by a 2008 meeting and workshop on Triassic climate at the Museum of Nature South Tyrol in Bolzano, Italy. However, even as the global nature of the CPE became increasingly accepted, its ultimate cause was still hotly debated going into the 2010s. Even its nomenclature was not agreed upon, with various authors applying names such as the middle Carnian wet intermezzo, Carnian humid episode, Carnian pluvial phase, and Carnian crisis. Carbon and osmium isotope records published over the coming years supported a strong link between the Carnian climate disturbances and the Wrangellia large igneous province, but many questions remain unanswered. A geological workshop focusing on the CPE met in 2018 at the Hanse-Wissenschaftskolleg (HWK) Institute for Advanced Study in Delmenhorst, Germany. The workshop was intended to spur further research on the mechanisms, impact and stratigraphy of the CPE, as well as its relevance for understanding modern climate change. It also attempted to standardize the nomenclature of the CPE; rejecting descriptors such as "event" (typically applied to geological processes under a million years in duration) or "middle Carnian" (a nebulous term with no equivalent geological substage).
Environmental disruption
Climate during the Carnian pluvial episode The Carnian pluvial episode introduced markedly more humid conditions across the globe, interrupting the otherwise arid climate of the Late Triassic period. This humidity was related to increased rainfall during the CPE, evidenced by: Siliciclastic (high silica-content) sediment in sedimentary basins, reflecting a high level of continental weathering and runoff; Significant karst conduits (caves) in Palaeozoic limestone inliers beneath the Late Triassic terrestrial unconformity. The topographic context of these caves is consistent with a Carnian age, supported by radiometric dates from speleothems (stalagmites) in two of these caves . However, some researchers instead favour a Rhaetian age for formation and filling of the caves based on the localised occurrence of microfossils. The development of histic and spodic palaeosols, fossil soils which are typical of a tropical humid climate with more water entering through precipitation than leaving through evapotranspiration; Hygrophytic palynological (fossil pollen) assemblages that reflect vegetation more adapted to a humid climate; The widespread presence of amber.
This usually wet climate of the CPE was periodically interrupted by drier climates typical of the rest of the Late Triassic period. One climate simulation argues that the interior of Pangaea actually became drier during the CPE, even as its eastern margin and high-latitude regions became rainier. The onset of the episode may have been very rapid (~15,800 years), amplified by carbon cycle feedback effects.
Global warming Global warming was also prevalent during the Carnian pluvial event. This is evidenced by oxygen isotope analyses performed on conodont apatite from the CPE, which show an approximately 1.5‰ negative shift in the stable isotope δ18O. This result suggests global warming of at least 3–4 °C during the CPE and/or a change in seawater salinity. Wider sampling supports warming on the order of 4–8°C. This warming was almost certainly related to extensive volcanic activity at the time, evidenced by carbon isotope trends across the CPE. This volcanic activity was in turn probably related to the formation of the Wrangellia Large igneous province around the same time, which created vast quantities of igneous (volcanic) rocks that were accreted onto the northwest end of the North American Plate (now the Wrangell Mountains, Alaska, and an estimated 6km thick layer underlying most of Vancouver Island).
Increased weathering Chemical weathering intensified during the CPE, according to Lithium isotopes in volcanic lake ash in North China. Prior to the event, lithium is found in low concentrations, mostly sourced from airborne ash in a cool and dry climate. During the CPE, river input becomes a greater influence on the system, with the hot, wet climate increasing the amount of lithium weathering out of ash beds on land. Weathering was also seen in prehistoric coastal Europe, enhancing runoff of terrestrial sediments responsible for local mud-rich marine layers. High rates of weathering continued even after the earth returned to a drier climate, suggesting that the CPE eroded enough sediment in the region to expose basement rock.
Effects on carbonate platforms
The onset of the CPE marks a sharp change in the shape and composition of carbonate platforms across the entire Tethys Ocean, which extended from Central Europe to East Asia. The early Carnian was characterized by high-relief, mainly isolated, small carbonate platforms surrounded by steep slopes. During the CPE, these were replaced by low-relief carbonate platforms with low-angle slopes (i.e., ramps). This turnover is related to a major change in the biological community responsible for calcium carbonate precipitation (in other words, the "carbonate factory"). High-relief platforms relied on a highly-productive biological community of carbonate-secreting microbes. When microbial carbonate declined during the CPE, a less productive animal-dominated carbonate community was left to pick of the slack, leaving skeletal grains (shell fragments) and ooids as the primary component of limestone.
In many regions, rain and river activity on land led to an increased flow of sand, silt, mud, and clay into the ocean. These terrestrial siliciclastic sediments form distinct, easily-eroded layers in areas otherwise dominated by carbonate. Carbonate deposition is eliminated altogether in rare deep marine sediments found in Southern Italy. The carbonate compensation depth (the minimum depth where calcium carbonate dissolves completely) was probably shallower during the CPE than before or after. In Turkey, which was near the equator during the Carnian, the demise of carbonate platforms was delayed compared to more northerly seas.