Palaeontological and geochemical evidence demonstrate that the PTB in the Shanxi red beds is at a horizon about 15 m below the top of Sunjiagou Formation (Figs 3 and 4), and the detrital zicon ages from the Sunjiagou and Liujiagou formations support this scenario (Supplementary Table S6). The synchronous dramatic negative excursion in δ13C and δ18O in the uppermost Sunjiagou Formation provide reliable evidence for reduced weathering, coolness, aridification, and anoxia69 (Fig. 6). Increasingly high negative values of δ13C and δ18O in the latest Permian in North China (Fig. 6) reveal the intensified coolness and aridity at that time. In particular, their remarkable shift indicates multiple rapid fluctuations of palaeoclimate, and the sharp negative excursion of δ13C in bed 51 of the Baode Section was coeval with the last occurrence of bioturbation before the end of the Permian. The sharp negative isotopic excursions were probably a result of dramatic climate perturbations on land and a decrease in vegetation density, which was a response to the ongoing cooling and aridification70,71. A similar shift and negative excursion of δ13C and δ18O around the terrestrial PTB were also confirmed in the Karoo Basin in South Africa18 and elsewhere (Supplementary Fig. S4). Moreover, the strong positive excursion of Sc/Zr and Lu/Hf also supports an abrupt arid palaeoclimate change67.

The negative excursion of weathering intensity proxies such as Ba/Sr, CIA, ∆W, Mg/Ca, Sr/Ca and Ba/Ca support the reduced weathering in the latest Permian, especially at the fossil horizons and the PTB interval, but increasingly intense weathering in the Early Triassic. The apparent increase of Rb/K at the fossil horizons and the PTB interval indicate a brief episode of drier and more arid conditions72. Mg/Ca, Sr/Ca and Ba/Ca (Fig. 6) are important proxies67,68 to distinguish the palaeoclimate of weathering intensity and palaeotemperature and they have been successfully applied to the monsoon of East Asian68.

The relatively cool palaeotemperature in the PTB interval and fossil horizons were proved by δ18O, (K + Na)/Al, Al/Si, Mg/Ca, Sr/Ca and Ba/Ca (Fig. 6 and Supplementary Table S5), which show synchronous negative shifts at these important times. Although palaeotemperatures calculated from the main elements might be affected by local conditions and changes of sediment provenance, they may play an important role in identifying palaeoclimate fluctuations when sampling is appropriate and combined with other indicators73. Our study indicates a relatively cool temperature across the PTB, which was supported by some previous studies74,75,76,77 though it is different from most views that indicate a rapid increase in palaeotemperature across the PTB. However, in models for the outcomes of a massive volcanic eruption, such as that of the Siberian Traps, release of massive volumes sulphur dioxide when mixed with atmospheric water may produce a transient cooling phase before the warming, driven by CO 2 , methane and water vapour. Such cooling can be localised around the volcanic source, or can spread worldwide and last for 1–2 years78. Whether the conflicting findings of either global warming or cooling following the PTB eruptions can be explained by these differing consequences of the eruption, perhaps acting in sequence, or whether these differing temperature changes reflect latitudinal or regional regional effects cannot at this stage be determined.

The atmospheric pCO 2 estimated from δ13C values66,70 and whole-rock CO 2 values79 consistently show an abrupt and remarkable increase at the fossil horizons and the PTB interval, which was an important part of deteriorating palaeoclimate and could be a crucial factor in biotic extinction36,80. The negative δ13C shift and sharp increase of whole-rock CO 2 are direct reflections of changes of atmospheric pCO 2 , which is supported by previous studies focusing on the abnormal occurrence of contemporaneous significant negative δ13C both in the ocean and on land81. They might have been caused by a significant input of methane into the atmosphere82 at the end of the Permian. The Siberian traps basaltic eruptions6 and the closure of the eastern segment of the Palaeo-Asian Ocean83 could have contributed to the input of methane at the PTB. Moreover, values of V/Cr > 2 are considered to represent anoxic depositional conditions79, which occasionally occurred in the PTB interval.

Above all, the fluvial environmental transition from meandering to braided river-aeolian, δ13C and δ18O, as well as geochemical proxies, reveal a consistent pattern of deteriorating environments (reduced weathering, cool, arid, and anoxic conditions) and climate fluctuations before and through the PTB. Nevertheless, the persisting uplifting tectonics in northern North China, as a response to the final closure of the Palaeo-Asian Ocean and collision between the Mongolian arc and North China Craton along the Solonker Suture Zone83, may contribute to the influx of masses of sediment through the Permian-Triassic transition. Moreover, matching the increasingly deteriorating environmental change across the PTB in North China, studies of the marine Permian-Triassic throughout the world show intensified chemical and physical weathering66,84,85,86 and anoxic conditions7,66,87,88 across the PTB.

It is reasonable to assume that the switch in fluvial style is largely linked to global climatic change when we combine the simultaneous environmental changes (e.g. arid, cool, and anoxic conditions) and mass extinction across the PTB. The abrupt environmental shocks (e.g. hypoxia, aridity, acid rain and wasting, etc.) were probably the main causes of the PTME on land7,8,9,10,11. The increasingly dry and deteriorating ecological environment resulting from warming and acid rain caused nearly worldwide mass wasting. The remarkable change in fluvial pattern at the PTB in Shanxi confirms results found earlier in Russia13 and South Africa16, and coincides with the increasingly arid palaeoenvironment throughout the terrestrial PTB in North China. In particular, the well-preserved aeolian deposits in the Liujiagou Formation are a critical sedimentological marker of aridity, highly-erodible land surfaces possibly related to reduced vegetation cover and sufficient wind energy to entrain and transport sediment. Elevated aeolian activity has been noted also in the Lower Triassic of the western German Basin36. Similar radical turnovers in fluvial style across the terrestrial PTB were also recognized in the Permian-Triassic red beds of eastern Europe13, the Karoo Basin16, and Australia80.

The distribution of climate zones near the PTB (Fig. 1) shows polar zones of cold, cool, and temperate humid climates, and a broad equatorial belt of tropical to subtropical semi-humid to humid climates, extending from Canada, Russia, and North China to central Africa, and the southern margin of Tethys10,37,89. Two mid-continental areas of subtropical arid climates occur over the eastern United States and western and central Europe, in the north, and central South America-Africa in the south. As noted before10, the most extreme changes occur in high-latitude, cool temperate settings (Australia, Antarctica, Siberia) and in the ever-wet coastal tropics (e.g. India, South China), where peat-forming swamps disappeared suddenly at the end of the Permian, initiating the coal gap15 of the Early and Middle Triassic. In tropical, semi-humid basins such as east European Russia13 and South Africa16, brown overbank mudstones with plant remains in the late Permian are replaced by highly oxidised red mudstones in the Early Triassic, often reworked into coarse braided river deposits. Our new evidence from North China is located at a similar latitude to the Russian red beds with PTB conglomerates, differing considerably from the successions 1200 km south, in South China.

Why do some terrestrial sections show the dramatic shift from meandering streams and lakes to arid alluvial fans-braided streams at the PTB10,13,16,80,90, and others do not21,22,23,24,25? It is not purely a question of palaeogeographic or palaeoclimatic locale, as noted. The PTB sections in which massive conglomerates are absent, for example in South China, India and Antarctica lie in equatorial, subtropical arid, hot, and humid climate belts (Fig. 1). One hypothesis is that the fan conglomerates were there but were lost through incomplete preservation. This might apply in some sections, but it is unlikely that such massive, coarse-grained units could be entirely removed from hundreds of sections in these regions. If the mass wasting model is correct, then the enhanced erosion following stripping of vegetation and increased aridity would be expressed in different ways in different sedimentary basins. Alluvial fan progradation can occur without tectonic uplift in the source area, and in such cases the progradation is largely controlled by a decrease in subsidence rates in the basin91,92. However, for substantial alluvial fans to develop as a result of plant and soil stripping requires a developing imbalance between source and receiving basinal areas, with tectonic uplift of upland areas round the basin, or subsidence of the basin. Perhaps at the PTB, in the face of worldwide mass wasting, as suggested by offshore records of terrestrial sediment flux19, those locations without conglomerates were simply in basins without surrounding mountainous source areas, or where the relative uplift-subsidence activity was inappropriate. In South China, for example, an abrupt shift in sedimentation is seen immediately following the disappearance of coal beds (beginning of the coal gap), with colour and grain-size changes in the sediments, together with indicators of a dramatic collapse of soil systems10. Besides, most dramatic shifts of fluvial deposits are distributed in areas of similar latitude. Comparison with the distribution of modern deserts along the equatorward margins of sub-tropical basins which are climatically sensitive93 may give some clues to the distribution of different terrestrial Permian-Triassic sections.

In this study, the terrestrial Permian-Triassic transition in North China is well constrained by multiple lines of evidence, namely sedimentology, carbon and oxygen isotopic results, geochemical proxies, and detrital zircon ages. In the near future, more integrated work on PTB sections in North China needs to be done in order to make a high-resolution regional stratigraphic comparison at regional and global scale.