The Carnian Pluvial Event is sometimes called the Carnian Pluvial Episode and is also known as "Reingrabener Wende", or "Raibl event".
Climate during the Carnian Pluvial Event
The arid climate of the Late Triassic was interrupted by the markedly more humid conditions of the Carnian Pluvial Event. Evidences of increased rainfall during the CPE are 1) the development of palaeosols hygrophytic palynological assemblages that reflect a vegetation more adapted to humid climate; 3) siliciclastic sediment input into the basins due to increased continental weathering and runoff; 4) the widespread presence of amber. However, wet climate was periodically interrupted by dry climate. Oxygen isotope analyses performed on conodont apatite show a ≈1.5‰ negative shift. This negative excursion suggests a global warming of 3 to 4 °C during the CPE and/or a change in seawatersalinity.
Biological turnover
Dinosaurs: the radiometric age of the most ancient-known dinosaurs found in the Ischigualasto Formation of Argentina dates back to 230.3 to 231.4 million years ago. This age is very similar to the minimum age calculated for the CPE. Calcareous nanofossils: the first planktonic calcifiers occurred just after the CPE and might have been calcareous dinocysts, i.e., calcareous cysts of dinoflagellates.
Effects on carbonate platforms
At the onset of the CPE a sharp change in carbonate platform geometries is recorded in western Tethys. High relief, mainly isolated, small carbonate platforms surrounded by steep slopes, typical of the early Carnian, were replaced by low-relief carbonate platforms featuring low-angle slopes. This turnover is related to a major change in the biological community responsible for calcium carbonate precipitation. The highly-productive, mainly bacterial-dominated biological community which action led to the carbonate production on high-relief platforms was substituted by a less productive mollusc-metazoan-dominated community. In the South China block the demise of carbonate platforms is coupled with the deposition of sediments typical of anoxic environments. These anoxic levels are often fossil Lagerstätten, very rich in crinoids and reptiles.
The recent discovery of a prominent negative shift in higher plants' n-alkanes suggests a massive CO2 injection in the atmosphere-ocean system at the base of the CPE. The minimum radiometric age of the CPE is similar in age to the basalts of the Wrangellia large igneous province. In the geological record, LIP volcanism is often correlated to episodes of major climate changes and extinctions, which may be caused by pollution of ecosystems with massive release of volcanic gases such as CO2 and SO2. Large release of CO2 in the atmosphere-ocean system by Wrangellia can explain the increased supply of siliciclastic material into basins, as observed during the CPE. The increase of CO2 in the atmosphere could have resulted in global warming and consequent acceleration of the hydrological cycle, thus strongly enhancing the continental weathering. Moreover, if rapid enough, a sudden rise of pCO2 levels could have resulted in acidification of seawater with the consequent rise of the carbonate compensation depth and a crisis of carbonate precipitation.
According to an alternative hypothesis, the Carnian Pluvial Event was a regional climatic perturbation mostly visible in the western Tethys and related to the uplift of a new mountain range, the Cimmerian Orogen, which resulted from the closing of a tethyan northern branch, east of the present European continent. The new mountain range was forming on the southern side of Laurasia, and acted then as the Himalayas and Asia do today for the Indian Ocean, maintaining a strong pressure gradient between the ocean and continent, and thus generating a monsoon. Summer monsoonal winds were thus intercepted by the Cimmerian mountain range and generated strong rain, thus explaining the switch to humid climate recognized in western Tethys sediments.
