Jianbo Chen

The Permian–Triassic (P-Tr) transition (~252 Ma) witnessed Earth’s most severe biocrisis, which has long been linked to Siberian Traps volcanism and associated environmental upheaval. Major perturbation of the global carbon (C) and sulfur (S) cycles is mainly inferred from marine δ ¹³ C and δ ³⁴ S records, whereas few existing terrestrial records link δ ³⁴ S fluctuations to widespread dispersal and fallout of volcanogenic sulfate aerosols. Mounting evidence, however, reveals that the collapse of P-Tr terrestrial ecosystems was diachronous, questioning a hypothesized globally synchronous common forcing. Here, we present records of pyritic multiple-S isotopes (δ ³⁴ S _py and Δ ³³ S) and bulk organic δ ¹³ C for a paleotropical peatland drill core (HK-1) from Southwest China. The δ ³⁴ S _py variations define three distinct phases with a notable decline in δ ³⁴ S _py across the P-Tr transition, suggesting substantially elevated terrestrial sulfate influx coincident with major carbon cycle perturbation. Notably, overall small positive Δ ³³ S values (+0.01 to +0.12‰) rule out a dominant role for stratospheric sulfates. Collectively, the observed changes in δ ¹³ C _org , δ ³⁴ S _py , and Δ ³³ S support catastrophic collapse of the Cathaysian Flora leading to intensified weathering and sulfate release. This inferred event, slightly after the P-Tr marine extinction, postdates by several 100-ky terrestrial floral collapse and perturbation of the C–S cycles documented in the high-latitude Sydney Basin. Cross-latitudinal diachroneity of terrestrial ecosystem collapse and consequent C–S perturbation challenges the hypothesis of a single, global volcanic driver. Rather, regional deforestation and its cascading effects overprinted on the global perturbations of biogeochemical cycles emerge here as critical factors shaping Earth’s largest recorded crisis.

The Triassic–Jurassic transition marks a critical interval, witnessing major biotic turnovers, including the rise of dinosaurs and the end-Triassic mass extinction (ETME), triggered by the Central Atlantic Magmatic Province (CAMP). However, the volcanism linked to terrestrial ecosystem disturbance and dinosaur distribution remains poorly constrained. Here, we present an integrated dataset of chemostratigraphic and astrochronological records for a continental drill core from the Kunming Basin in Yunnan Province of Southwest China, where rich dinosaur assemblages have been previously identified. Three negative carbon isotope excursions coupled with volcanogenic mercury anomalies confirm pulsed CAMP environmental impacts on this subtropical terrestrial setting and placement of the Triassic–Jurassic boundary (TJB). Critically, the earliest regional sauropodomorph fossils occurred at ~ 200.17 Ma (~ 1.23 Myr post-TJB), indicating post-ETME colonization in low paleolatitudes by medium- to large-bodied dinosaurs. CAMP-induced stressors, potentially coupled with increased climate seasonality, likely created ecological opportunities facilitating dinosaur expansion in the Earliest Jurassic.

Continental records of the Permian–Triassic boundary are characterized by intense chemical weathering due to global warming and acid rainfall associated with volcanism. However, chemical weathering throughout the late Permian has not been interrogated in time-equivalent continental successions due to the lack of stratigraphically ‘continuous’ deposits. Here, we conducted geochemistry, petrology, and clay mineralogy investigations on several widely used chemical weathering proxies (i.e., CIA, CIW, PIA, CIX, and CPA) for the upper Permian to Lower Triassic rock samples both from outcrops and drilled cores. Their sediment sources are dominated by mafic weathering products of the Emeishan basalt with little influence by sediment sorting/recycling. However, diagenesis dominates their decreased values through the illitization of clay minerals in samples from the outcrop. For drilled core samples, decreased CIA, CIW, and PIA values partly result from the insufficient subtracting of CaO in secondary carbonates. After eliminating these effects using two modified proxies, the declining trend of CIX and CPA from the lower Xuanwei Fm. through the entire Kayitou Fm. is probably be caused by the cooling climate during the late Permian, which has also been suggested by previous work. However, lower values of CIX and CPA in the base of Dongchuan/Feixianguan Fm. likely indicated weak chemical weathering intensity due to physical denudation and subsequently rapid deposition in the earliest Triassic. This weakly developed chemical weathering is concerned with being accelerated by drier and more developed seasonal conditions in the sediment source area, as well as tectonics related to the closure of the eastern Tethys oceans. Our work is the first comparative study on chemical weathering proxies for drilled core and outcrop samples during the late Permian to the earliest Triassic, which straddled the severest bio-crisis and global environmental change of the Phanerozoic. It highlights the essential evaluation of non-weathering factor alteration on commonly used chemical weathering proxies by the use of multiple techniques. Compared to drilled core, sample collection from subsurface by excavation could not avoid weathering effects or sub-recent rock-water interaction influences.