Intensifying aeolian activity following the end‐Permian mass extinction: Evidence from the Late Permian–Early Triassic terrestrial sedimentary record of the Ordos Basin, North China

Abstract

Sedimentary successions provide direct evidence of climate and tectonics, and these give clues about the causes of the mass extinction around the Permian–Triassic boundary. Terrestrial Permian–Triassic 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 cross‐bedded 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 cross‐bedding and aeolian structures (for example, inverse climbing‐ripple, translatent‐ripple lamination, grainfall and grainflow laminations) interchange vertically and laterally. The Heshanggou Formation is a rhythmic succession of mudstones interbedded with thin medium‐grained sandstones mainly deposited in a shallow lacustrine environment. Overall, the sharp meandering to braided to shallow lake sedimentary transition documents palaeoenvironmental changes from semi‐arid to arid and then to semi‐humid conditions across the Permian–Triassic boundary. The die‐off of tetrapods and plants, decreased bioturbation levels in the uppermost Sunjiagou Formation, and the bloom of microbially‐induced sedimentary structures in the Liujiagou Formation marks the mass extinction around the Permian–Triassic boundary. The disappearance of microbially‐induced 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 Permian–Triassic boundary extinction. This study is the first to identify the intensification of aeolian activity following the end‐Permian 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 Permian–Triassic boundary in Shanxi is largely linked to the development of an arid and subsequently semi‐humid climate condition, which probably directly affected the collapse and delayed recovery in palaeoecosystems.

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin, eastern Australia

“…The character of the Permo-Triassic system boundary in the Sydney Basin contrasts with that interpreted from some other palaeocontinental regions where abrupt changes in fluvial style have been inferred (e.g. Smith, 1995;Newell et al, 1999;Ward et al, 2000;Michaelsen, 2002;Arche & L opez-G omez, 2005;Zhu et al, 2019Zhu et al, , 2020. In the case of the Karoo Basin of southern Africa, researchers have recently provided more detailed logged sections that make a case for more gradual, progressive palaeo-environmental changes that are consistent with the findings of this study (e.g.…”

“…Fluvial channel facies across this interface in Fig. 12 exhibit a somewhat fining-upward trend (dominantly FA A below, passing up into dominantly FA B above), contrary to the notion of fluvial 'rejuvenation' across the EPE and PTB (sensu Smith, 1995;Newell et al, 1999;Ward et al, 2000;Michaelsen, 2002;Arche & L opez-G omez, 2005;Zhu et al, 2019Zhu et al, , 2020. Preservation of sandstone and mudrock-dominated partings, truncated by erosionally based conglomerate beds within FA A bodies of the uppermost Permian succession, suggest that many if not all of these bodies are multistorey (Figs 4 and 8A).…”

“…Resolution of the terrestrial EPE and the PTB in the Karoo Basin, for example, awaits wellconstrained ages close to those boundaries. In the recently published North China case (Zhu et al, 2019(Zhu et al, , 2020, the timing of events is constrained only by two maximum depositional ages from detrital zircon populations some (unspecified) distance apart (Zhu et al, 2019, fig. 2), and so the timing of reported palaeoenvironmental changes remains uncertain.…”

“…In the recently published North China case (Zhu et al. , 2019, 2020), the timing of events is constrained only by two maximum depositional ages from detrital zircon populations some (unspecified) distance apart (Zhu et al. , 2019, fig.…”

“…, 2000; Michaelsen, 2002; Arche & López‐Gómez, 2005; Zhu et al. , 2019, 2020). Preservation of sandstone and mudrock‐dominated partings, truncated by erosionally based conglomerate beds within FA A bodies of the uppermost Permian succession, suggest that many if not all of these bodies are multistorey (Figs 4 and 8A).…”