3 research outputs found
Altered fluvial patterns in North China indicate rapid climate change linked to the Permian-Triassic mass extinction
The causes of the severest crisis in the history of life around the Permian-Triassic boundary (PTB) remain controversial. Here we report that the latest Permian alluvial plains in Shanxi, North China, went through a rapid transition from meandering rivers to braided rivers and aeolian systems. Soil carbonate carbon isotope (ÎŽ13C), oxygen isotope (ÎŽ18O), and geochemical signatures of weathering intensity reveal a consistent pattern of deteriorating environments (cool, arid, and anoxic conditions) and climate fluctuations across the PTB. The synchronous ecological collapse is confirmed by a dramatic reduction or disappearance of dominant plants, tetrapods and invertebrates and a bloom of microbially-induced sedimentary structures. A similar rapid switch in fluvial style is seen worldwide (e.g. Karoo Basin, Russia, Australia) in terrestrial boundary sequences, all of which may be considered against a background of global marine regression. The synchronous global expansion of alluvial fans and high-energy braided streams is a response to abrupt climate change associated with aridity, hypoxia, acid rain, and mass wasting. Where neighbouring uplands were not uplifting or basins subsiding, alluvial fans are absent, but in these areas the climate change is evidenced by the disruption of pedogenesis
Intensifying aeolian activity following the end Permian mass extinction: evidence from the Late PermianâEarly Triassic terrestrial sedimentary record of the Ordos Basin, North China
Sedimentary successions provide direct evidence of climate and tectonics, and these give clues about the causes of the mass extinction around the PermianâTriassic boundary. Terrestrial PermianâTriassic boundary strata in the eastern Ordos Basin, North China, include the Late Permian Sunjiagou, Early Triassic Liujiagou and late Early Triassic Heshanggou formations in ascending order. The Sunjiagou Formation comprises crossâbedded sandstones overlaid by mudstones, indicating meandering rivers with channel, point bar and floodplain deposits. The Liujiagou Formation was formed in braided rivers of arid sand bars interacting with some aeolian dune deposits, distinguished by abundant sandstones where diverse trough and planar crossâbedding and aeolian structures (for example, inverse climbingâripple, translatentâripple lamination, grainfall and grainflow laminations) interchange vertically and laterally. The Heshanggou Formation is a rhythmic succession of mudstones interbedded with thin mediumâgrained sandstones mainly deposited in a shallow lacustrine environment. Overall, the sharp meandering to braided to shallow lake sedimentary transition documents palaeoenvironmental changes from semiâarid to arid and then to semiâhumid conditions across the PermianâTriassic boundary. The dieâoff of tetrapods and plants, decreased bioturbation levels in the uppermost Sunjiagou Formation, and the bloom of microbiallyâinduced sedimentary structures in the Liujiagou Formation marks the mass extinction around the PermianâTriassic boundary. The disappearance of microbiallyâinduced sedimentary structures, increasingly intense bioturbation from bottom to top and the reoccurrence of reptile footprints in the Heshanggou Formation reveal gradual recovery of the ecosystem after the PermianâTriassic boundary extinction. This study is the first to identify the intensification of aeolian activity following the endâPermian mass extinction in North China. Moreover, while northern North China continued to be uplifted tectonically from the Late Palaeozoic to Late Mesozoic, the switch of sedimentary patterns across the PermianâTriassic boundary in Shanxi is largely linked to the development of an arid and subsequently semiâhumid climate condition, which probably directly affected the collapse and delayed recovery in palaeoecosystems