Triassic–Jurassic environmental instability on the subtropical eastern Tethyan margin linked to the dinosaur occurrence

Triassic–Jurassic environmental instability on the subtropical eastern Tethyan margin linked to the dinosaur occurrence | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Triassic–Jurassic environmental instability on the subtropical eastern Tethyan margin linked to the dinosaur occurrence Jianbo Chen, Yi-ning Niu, Rongyao Ma, Yan-ling Zhou, Wen-jie Liu, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6720557/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Jan, 2026 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Abstract 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. Earth and environmental sciences/Solid Earth sciences/Geology/Stratigraphy Earth and environmental sciences/Climate sciences/Palaeoclimate Earth and environmental sciences/Solid Earth sciences/Geochemistry Figures Figure 1 Figure 2 Figure 3 Main text The Triassic–Jurassic transition (TJT; ~201 Ma) represents one of the most critical intervals in Earth’s history, marked by profound environmental upheaval and a fundamental reshaping of the biosphere. It witnessed the catastrophic end-Triassic mass extinction (ETME), one of the Phanerozoic’s “Big Five” biotic crises, largely attributed to the emplacement of the Central Atlantic Magmatic Province (CAMP). This large-scale volcanic activity, linked to the stepwise disintegration of the Pangea supercontinent ( 1 ), released vast quantities of greenhouse gases (e.g., >5´10 12 tons CO 2 ), triggering climate warming, and oceanic acidification, and a severe collapse of the global carbon cycle, which altering both marine and terrestrial ecosystems ( 2 – 5 ). Yet, amidst this catastrophe, a remarkable evolutionary success unfolded: the rise of dinosaurs, which transitioned from regionally Carnian-age (early Late Triassic) origin assemblages to global dominance by the Early Jurassic, with the mechanisms remaining debated ( 6 – 9 ). This apparent paradox – mass extinction coinciding with the ascendancy of a major clade – raises critical questions: How did terrestrial ecosystems respond to CAMP-driven environmental stressors? And did these volcanic-induced changes actively facilitate the dinosaurs’ expansion into low-latitude western Tethys? While extensive marine records document the TJT environmental perturbations through characteristic carbon isotope excursions (CIEs) and mercury (Hg) anomalies indicative of CAMP volcanism ( 10 – 14 ), our understanding of the terrestrial realm lags significantly, which is exacerbated by a geographic bias, with most high-resolution TJT records clustered in North American and European basins (e.g., Newark Basin, St. Audries’s Bay), leaving a large portion of Pangean landmasses poorly documented. East Asian terrestrial sequences, particularly the dinosaur-rich Jurassic strata of Yunnan Province, Southwest China ( 15 – 17 ), offer an exceptional yet under-exploited window into this critical transition. A recent discovery of an early-diverging sauropodomorph in Wuding County, northern Yunnan, represents the stratigraphically lowest confirmed skeletal remains in the Triassic–Jurassic transitional interval that have been found so far in southern China, possibly East Asia. It provides a unique opportunity to examine biotic turnover dynamics on the eastern Tethyan subtropical continent during the TJT, given that sauropodomorphs have long been recognized as absent from the lower paleolatitudes before the end of the Triassic due to harsh environmental fluctuations ( 18 ). However, like a previously reported sauropodomorph footprint site in the neighboring Sichuan Basin ( 19 ), the precise age of this pivotal fossil remains unconstrained. This highlights a broader challenge: correlating terrestrial biotic events with the marine extinction timeline is severely hindered by the typical scarcity of datable volcanic ash layers within continental redbeds. To address these challenges in assessing volcanic forcing and establishing a robust chronostratigraphic framework, we conducted a multi-proxy investigation of a drill core (WK23-1) across the Triassic–Jurassic boundary (TJB) interval in the Wande section from Kunming Basin, Yunnan Province, Southwest China – the locality of the newly discovered sauropodomorph (Fig. 1A). By integrating the first high-resolution organic carbon isotope (δ 13 C org ) profile with mercury chemostratigraphy (Hg concentrations and isotopes), elemental geochemistry, and astronomically-tuned gamma-ray data (Fig. 2), this study aims to: (1) refine the TJB placement by correlating characteristic CIEs and Hg anomalies linked to CAMP activity; (2) provide the first age constraints for the earliest sauropodomorph skeletal remains found near the extinction-recovery interface in East Asia. By bridging a critical spatial and depositional gap in TJT records, our work underscores the utility of multi-proxy chemostratigraphy in terrestrial basins and advances our understanding of how volcanically driven environmental instability impacted terrestrial ecosystems during one of Earth’s major crises, and potentially shaped the diversification and biogeographic expansion of dinosaurs. Results In drill core WK23-1, the Triassic–Jurassic transitional Yubacun Formation is stratigraphically bounded by the overlying Lufeng Formation (Lower Jurassic) at 15.23 m depth and the underlying Shezi Formation (Upper Triassic) at 157.60 m depth, yielding a total thickness of 142.37 m (Figs. 1B–C). Astronomical tuning of the gamma-ray series identified more than eight full 405-kyr long-eccentricity cycles across the entire logged core, suggesting a total duration of ~3.2 Myr (Fig. 2A). Based on cycle counting, the depositional duration of the Yubacun Formation is estimated to be ~1.71 Myr. δ 13 C org values in the Upper Triassic Shezi Formation exhibit relatively limited variability, ranging from -27.9‰ to -23.5‰ (average of -24.8‰,1σ = 0.59 ‰, n = 65). A pronounced isotopic shift occurs in the Yubacun Formation, with values spanning from -28.4‰ to -21.3‰ (avg. of -24.3‰, 1σ = 1.27 ‰, n=167), and displaying three distinct CIEs: (1) a “precursor” CIE (P-CIE) localized between the depth of 143.10 to 146.68 m (duration: ~40 kyr), characterized by δ 13 C org minima (~ -26.6‰); (2) an “initial” CIE (I-CIE) between the depth of 106.01–121.49 m (duration: ~169 kyr), marked by a transient negative shift (avg. of -25.7‰); (3) a “main” CIE (M-CIE) initiated at 94.73–95.23 m depth, remaining low through the upper Yubacun Formation and into the basal Lufeng Formation (average of -24.5‰,1σ = 0.94 ‰, n = 14) (Fig. 2B). TOC contents show a marked overall decline upwards from the Shezi Formation (avg. of 34.2 wt%, 1σ = 27.5%, n = 58) to the Yubacun Formation (avg. of 5.1 wt%, 1σ = 4.4%, n = 166). A sharp drop occurs near the Shezi–Yubacun boundary. A minor increase in TOC (avg. of 8.6 wt%, 1σ = 8.5%, n = 14) is observed within the basal Lufeng Formation before declining again upwards (Fig. 2C). Three stratigraphically distinct intervals with elevated Hg concentrations normalized to TOC (Hg/TOC) are identified (Fig. 2D–E): the first Hg/TOC spike occurs between 151.61 m and 157.49 m coincides with the uppermost Shezi Formation and basal Yubacun Formation, reaching peak values of 24 ppb/wt%. This interval coincides with elevated concentrations of the element copper (Cu), which peaks at 58.2 ppm within this zone (Fig. 2F). The second Hg/TOC anomaly, between 95.32 m and 87.38 m, reaching 51 ppb/wt%, overlaps with the onset and initial phase of the M-CIE. The third Hg/TOC peak occurs between 55.68 m and 55.15 m in the upper Yubacun Formation, with values up to 51 to 24 ppb/wt%. Mercury isotope analysis was performed on ten samples from these anomalous zones. Mass-independent fractionation (MIF), indicated by Δ¹⁹⁹Hg values, is minimal. Most Δ¹⁹⁹Hg values cluster near zero, ranging from -0.10‰ to +0.04‰, with an average of -0.03‰. This near-zero MIF signature is commonly associated with volcanogenic Hg sources (Fig. 2D). Besides, the CIA values (56.55–86.2, avg. of 74.6, 1σ = 6.8, n = 88) exhibit moderate chemical weathering and minimal stratigraphic variations (Fig. 2G). Discussion Carbon–Mercury Dynamics: Linking CAMP Volcanism, Global Perturbations, and Regional Responses The Triassic–Jurassic transition (TJT) is characterized by profound disturbances in the global carbon cycle, often recorded as distinct negative carbon isotope excursions (CIEs) in both marine and terrestrial sedimentary archives ( 1 , 14 ). These CIEs serve as crucial chemostratigraphic tools for correlating sequences and understanding the environmental changes during the end-Triassic mass extinction (ETME) (e.g., 2 , 10 , 11 , 20 , 21 ). Our high-resolution δ 13 C org record from drill core WK23-1 in the terrestrial Kunming Basin reveals three distinct negative CIEs (termed P-CIE, I-CIE, M-CIE; Fig. 2 B), mirroring patterns observed globally, albeit with regional disparities. The most prominent “initial” CIE (I-CIE), manifested in our core as a significant negative shift lasting ~ 169 kyr (between 106.01 m and 121.49 m depth, Data S1), is widely recognized as marking the onset of the main ETME phase. Its remarkable synchronicity across geographically diverse marine (e.g., St. Audrie’s Bay; Fig. 3 A–C) and terrestrial settings [e.g., Junggar Basin ( 22 )], strongly implicates the CAMP volcanism through massive injections of CO 2 and/or thermogenic methane into the ocean-atmosphere system as the principal driver of this global carbon cycle instability (e.g., 11 , 23 , 24 ). Utilizing the established high-precision U-Pb age for the onset of the I-CIE (and thus the ETME) at 201.51 ± 0.15 Ma ( 25 , 26 ), we anchor our astrochronological timescale by assigning this age to the base of the I-CIE at 121.49 m depth in WK23-1 (Fig. 3 D, Data S1). Following established correlations where the Triassic–Jurassic boundary (TJB) often slightly post-dates the I-CIE onset ( 21 , 26 ), our cyclostratigraphic model places the TJB at a depth of 111.29 m within the transitional Yubacun Formation (Fig. 3 D & Fig. S1 B). This placement provides a critical temporal framework for evaluating biotic events relative to the extinction horizon. Further strengthening the link to volcanic activity, sedimentary mercury (Hg) anomalies concurrent with CIEs provide compelling evidence for pulsed, large-scale volcanic Hg emissions during the TJT ( 13 , 14 , 27 ). While many Hg records were documented from marine sections in Europe and North America ( 12 , 13 ), our study provides crucial terrestrial data for the Central Yunnan area from the eastern Tethyan realm. The WK23-1 core reveals three distinct Hg/TOC enrichment intervals stratigraphically associated with the CIEs (Figs. 2 D–E). Critically, the minimal mass-independent fractionation (MIF) observed, with Δ¹⁹⁹Hg values clustering near zero (-0.10‰ to + 0.04‰) in samples from the second and third Hg peaks, strongly supports a predominantly volcanic source for the mercury anomalies. This signature arises because volcanic emissions inject primarily Hg(0) into the atmosphere, lacking the significant MIF generated by photochemical reactions involving Hg in the upper atmosphere ( 28 , 29 ). Our findings align with the global pattern of volcanogenic Hg deposition during the TJT ( 13 , 27 , 30 , 31 ). However, beyond these global volcanogenic fingerprints, TJT environmental records often display significant regional variability, reflecting the interplay of global drivers with local factors like organic carbon sources, depositional settings, diagenesis, and regional climate ( 32 – 34 ). This is evident in the details of both the carbon and mercury records in WK23-1. For instance, the "precursor" CIE (P-CIE; 146.68–143.10 m) identified in our drill core, while potentially correlative with events seen in some other sections, lacks clear global synchronicity and thus its status as a truly global signal remains debated ( 26 , 35 ). In the Kunming Basin, the P-CIE coincides strikingly with a rapid decline in TOC content (Figs. 2 B–C), suggesting a localized collapse in terrestrial primary productivity or carbon burial. This short-lived negative CIE event (~ 40 kyr) preceding the main ETME, coupled with the TOC decline at the transition from the Shezi to Yubacun Formation, likely implies the demise of humid peat-forming ecosystems. This interpretation is consistent with palynological evidence for significant floral turnover in contemporaneous strata across southern China ( 36 ). The drivers could include early CAMP-induced environmental stress, such as aridification or toxic metal loading (Hg, Cu – note the elevated Cu coinciding with the first Hg peak; Fig. 2 F), synergistically impacting sensitive floras ( 13 , 37 ). The apparent absence of a distinct P-CIE in many distal marine sections could further support a predominantly regional hydroclimate or ecosystem control rather than a global atmospheric CO₂ perturbation ( 26 ). Furthermore, the first Hg peak (157.49–151.61 m), unlike the later peaks, exhibits slightly negative Δ¹⁹⁹Hg values (-0.11‰ to -0.05‰) deviating somewhat from a predominantly volcanic signature (Fig. 2 D). This subtle MIF signature might indicate transient contributions from reworked terrestrial Hg, potentially mobilized by enhanced erosion or the combustion of organic-rich soils/sediments during initial environmental upheaval ( 37 – 39 ). The regional disturbance is also apparent in the character of the "main" CIE (M-CIE) and the weathering proxy record. The M-CIE in WK23-1 appears somewhat muted and prolonged compared to sharp, pronounced excursions seen in some marine records ( 1 ), potentially reflecting differences in organic matter sources, degradation pathways, or depositional redox conditions influencing δ¹³C org preservation in this terrestrial setting ( 32 , 33 ). In addition, the CIA values remain relatively stable (56.5–86.2, avg. of 74.6, 1σ = 6.8) throughout the studied interval, indicating persistently moderate chemical weathering intensity in the source area (Fig. 2 G). This relative stability contrasts with evidence for extreme climatic fluctuations and potentially intense weathering shifts inferred from proxies in the basins to the north of Kunming Basin, such as Junggar Basin ( 40 , 41 ) or Sichuan Basin ( 42 ). While seemingly indicative of climatic stability, the CIA primarily reflects the intensity of chemical weathering of silicate minerals in the source area over longer timescales. It does not preclude significant changes in other climatic parameters like precipitation seasonality, frequency of extreme events (e.g., droughts, wildfires), or temperature fluctuations, especially in a subtropical setting potentially buffered from the most extreme weathering regime shifts seen at higher latitudes ( 43 ). Therefore, the stable CIA suggests a relatively consistent baseline weathering regime but does not rule out other forms of climate change impacting the ecosystem. Post-Extinction Emergence of Sauropodomorph Dinosaurs in Southwest China: Timing and Environmental Context Against the background of global volcanic catastrophe and regionally variable environmental responses, the TJT interval witnessed a pivotal moment in vertebrate history: the rise of dinosaurs to ecological dominance ( 6 , 7 ). Sauropodomorph dinosaurs, originating potentially in Gondwana soon after the Permian–Triassic crisis ( 44 ), had dispersed into mid-to-high latitudes of the Northern Hemisphere, including Northwest China (Junggar Basin) by the Late Triassic ( 9 ). However, their apparent absence from low-latitude regions during the Late Triassic has been attributed to harsh, fluctuating environmental conditions possibly related to extreme CO₂ levels ( 18 ). Consistent with this, extensive fieldwork has yielded no confirmed Late Triassic sauropodomorph skeletal remains from the lower paleolatitudes of southwestern China, potentially due to these environmental filters or geographic barriers ( 45 ), alongside geological preservation conditions and paleogeographic configuration of landmasses. Our astrochronologically-calibrated age model for WK23-1 places the sauropodomorph fossil horizon (occurring > 15.23 m depth in the topmost Yubacun Formation) at approximately ~ 200.17 Ma (Fig. 3 D & Fig. S1 ). This timing is unequivocally Early Jurassic, falling about 1.23 million years after the TJB (placed at 111.29 m, 201.4 Ma based on tuning relative to I-CIE onset at 201.51 Ma). This provides the first evidence that sauropodomorphs colonized Southwest China shortly in the aftermath of the end-Triassic mass extinction. The timing of this faunal expansion coincides with the recovery interval following the I-CIE and encompasses the M-CIE. While the precise environmental drivers facilitating dinosaur ascendancy remain to be investigated ( 46 , 47 ), the environmental stressors associated with CAMP volcanism likely played a complex role. The recurrent Hg/TOC spikes aligned with δ¹³C org shifts in our record (Fig. 2 ) serve as proxies for pulsed volcanic activity and associated environmental perturbations impacting the Kunming Basin during the TJT. These perturbations, potentially including toxic metal loading (Hg, Cu), climatic instability (though perhaps buffered in terms of weathering intensity), increased aridity or seasonality, and potentially more frequent wildfires fueled by stressed vegetation ( 48 , 49 ), could have selectively disadvantaged contemporaneous faunas and disrupted established ecosystems on land. This disruption may have created ecological opportunities ("vacant niches") for resilient and adaptable groups like dinosaurs ( 7 ). The prolonged environmental instability, potentially reflected in the extended duration of the M-CIE, might have favored taxa capable of coping with fluctuating resources or conditions, although the specific adaptations benefiting early sauropodomorphs require further investigation. The modest recovery of TOC during the M-CIE interval (Fig. 2 C) might signal the beginnings of ecosystem reorganization where these large herbivores arrived and flourished. This post-extinction dispersal into southwestern China likely occurred within a broader context of global climate change. Tectonic activity related to Pangea's fragmentation altered oceanic and atmospheric circulation, while elevated atmospheric CO₂ levels drove overall warming and potentially enhanced climate variability and seasonality ( 50 , 51 ). Evidence for increased seasonality, even under high CO₂, comes from findings like lake ice-rafted debris in the high-latitude Junggar Basin ( 9 ). The increased occurrence of carbonate nodules or concretions upwards the drill core suggests at least transient arid (and therefore seasonality) were becoming more prevalent across the TJT into the earliest Jurassic (Fig. 1 C & Fig. S2). Such shifts towards more seasonal climates could have profoundly impacted vegetation structure across various latitudes ( 36 , 52 ), potentially transforming previously less favorable habitats (perhaps persistently warm and humid) into landscapes (e.g., more open woodlands or savanna-like ecosystems) accessible or exploitable by large herbivores like sauropodomorphs. While the stable CIA values in the Kunming Basin suggest the source area weathering intensity did not undergo the dramatic swings seen elsewhere, increased seasonality in local precipitation patterns or temperature ranges could still have driven significant ecological shifts relevant to faunal turnover and migration, without necessarily altering the bulk silicate weathering signal captured by CIA. Thus, the arrival of sauropodomorphs in southwestern China around 200.17 Ma likely reflects a combination of post-extinction ecological opportunity and adaptation to evolving Early Jurassic climates, particularly the emergence of potentially more seasonal environments across former environmental barriers ( 47 ). This study investigated the terrestrial TJT in Southwest China's Kunming Basin using integrated multi-proxy chemostratigraphy (δ 13 C org , Hg concentrations, and isotopes) and astrochronology on drill core WK23-1. These high-resolution records documented the environmental impact of pulsed CAMP volcanism through correlative carbon isotope excursions (CIEs) and Hg anomalies exhibiting volcanogenic near-zero Δ¹⁹⁹Hg signatures. These global signals were also influenced by regional factors, reflected in localized ecosystem shifts linked to the P-CIE and TOC decline, potential terrestrial Hg reworking, and a relatively stable weathering intensity baseline (indicated by CIA) despite inferred climate shifts elsewhere. An astrochronological framework established the Yubacun Formation's duration (~ 1.71 Myr) and placed the Triassic–Jurassic boundary (TJB, 201.4 Ma) at 111.29 m depth. More importantly, the precise dating of the earliest sauropodomorph skeletal fossils in this region to ~ 200.17 Ma (Early Jurassic, ~ 1.23 Myr post-TJB) demonstrates the post-ETME colonization of the (sub)tropical eastern Tethys by these large herbivores. This research fills a critical geographic and depositional gap in TJT terrestrial records, validates the efficacy of applying multi-proxy chemo- and cyclostratigraphy for high-resolution dating in continental sequences lacking volcanic ashes, and provides crucial context for understanding the interplay between catastrophic volcanism, environmental upheaval, ecosystem recovery, and the early diversification dynamics of dinosaurs in a key, previously underexplored region. Material and Methods Geological Background The Kunming Basin in Yunnan Province, Southwest China (Fig. 1 A), situated within the Tethyan tectonic domain, preserves a critical terrestrial stratigraphic succession across the Triassic–Jurassic transition (TJT). The studied interval encompasses three formations (Figs. 1 B&C): the Upper Triassic Shezi Formation, the transitional Yubacun Formation, and the Lower Jurassic Lufeng Formation, in ascending order, which collectively record a continuum of depositional responses to evolving basin dynamics and climatic regimes. The Shezi Formation is assigned to the Norian–Rhaetian (Late Triassic) based on the presence of the Yunnanophorus – Indosinion bivalve zone and the Dictyophyllum–Clathropteris plant assemblage ( 53 ). The overlying ‌Yubacun Formation, considered the primary Triassic–Jurassic transitional unit, consists of ‌variegated clastic rocks‌ dominated by gray, grayish-green, and grayish-yellow sandstone intercalated with purplish-red siltstone or mudstone‌. Palynological assemblages constrain its deposition in the TJT interval ( 54 ), and the sauropodomorph fossils occur near its top. This formation records the demise of Late Triassic peat-forming environments and the shift towards Early Jurassic aridification environments, marked by an increased occurrence of calcareous components upwards (Fig. 1 C & Fig. S2). It archives the Kunming Basin’s transition from humid Late Triassic to semi-arid Early Jurassic oxidative regimes, likely linked to Tethyan tectonism and global TJT paleoclimatic as well as carbon cycle perturbations ( 55 ). The succeeding Lower Jurassic Lufeng Formation comprises maroon mudstones interbedded with quartzose sandstones and common calcareous nodules, indicative of seasonal aridity, oxidizing lacustrine-fluvial settings that host abundant vertebrate fossils like Lufengosaurus ( 15 , 16 ). Drill core WK23-1 (102°10'56" E, 26°03'30" N; Wande section, Fig. 1 B), recovered from the dinosaur fossil locality, spans the critical TJT interval and provides a continuous archive for investigating terrestrial responses to TJT events in the eastern Tethyan realm. The drill core andd outcrop correlation was accomplished through lithology of the Yubacun Formation’s variegated clastic characteristics and its thickness, confirming the dinosaur-bearing horizon occurs no higher than 12.53 m within the core (Fig. 1 C). Natural Gamma-Ray (GR) Logging and Astronomical Tuning To establish a high-resolution chronostratigraphic framework, natural gamma-ray (GR) logging was performed on core WK23-1 via wireline logging. Continuous GR measurements were acquired at 0.1 m vertical resolution. Assuming GR variations in this clastic succession primarily reflect changes in clay mineral content potentially driven by orbitally modulated climate cycles affecting weathering and sediment influx, we performed cyclostratigraphic analysis using the Acycle v2.8 software ( 56 ). Temporal calibration was achieved through iterative orbital tuning, whereby the 405-kyr eccentricity cycle component of the La2010d astronomical solution ( 57 ) was phase-locked to the GR-derived sedimentary cycles. Detailed methodological protocols are provided in the Supplementary Materials. Geochemical Analysis A total of 441 samples were collected from fine-grained lithologies (mudstone, siltstone) of drill core WK23-1, avoiding visible veins or significant alteration. The average sampling resolution was approximately 0.6 m. Samples were dried, crushed, and pulverized to ~ 200 mesh (< 75 µm) using a tungsten carbide mill for subsequent geochemical analyses. Major and trace element concentrations were determined for 88 samples at the Wuhan Sample Solution Analytical Technology Co., Ltd. Major elements were measured by X-ray fluorescence spectrometer (XRF), and the analytical precision is better than ± 2–5% with certified reference material (GBW07103, GBW07105, GBW07108, GBW07111, and GBW07112) for analytical quality monitor. Trace elements were measured by Agilent 7700e inductively coupled plasma mass spectrometry (ICP-MS). Accuracy and precision were monitored using certified reference materials BHVO-2 (basalt), RGM-2 (rhyolite), GSR-3, and JA-2 and replicate analyses. Bulk-rock major and trace element data are given in Data S1. TOC and δ 13 C org values were measured on 246 samples. Prior to analysis, powdered samples were treated with dilute hydrochloric acid overnight to remove carbonate minerals, followed by rinsing with deionized water and drying. About 1–10 mg of decarbonated powder was weighed into tin capsules and combusted at 960 ◦ C. The evolved CO 2 was measured using a Thermo Scientific Elemental Analyzer IsoLink coupled to Thermo Scientific Delta V Advantage at the Institute of Palaeontology, Yunnan University, China. Measurements were calibrated by the organic analytical standard (OAS, CatNo. IVA33802151, with a certified δ 13 C org value of -28.85 ± 0.10‰) and reported relative to Vienna Pee Dee Belemnite (V-PDB). Analytical precision was better than 0.1‰ (1σ) for δ 13 C based on replicate analyses of the standard. Total Hg concentrations were determined for 434 samples using a Direct Mercury Analyzer (DMA-80 evo) at the Institute of Palaeontology, Yunnan University. Analytical accuracy was monitored using the certified reference material GBW07405a (GSS-5a, yellow-red soil, certified Hg = 700 ± 100 ng/g). Replicate analyses of GSS-5a yielded a relative standard deviation (RSD) better than 5% (2σ), confirming analytical precision. Ten samples exhibiting elevated Hg concentrations were selected for Hg isotope analysis. Mercury was liberated via pyrolysis and subsequently analyzed using a Nu-Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China. Instrumental drift was monitored by interspersing NIST SRM 3133 standard measurements after every three unknown samples. Mercury mass-dependent fractionation (MDF) is reported in delta notation (δ) ( 58 , 59 ): $$\:{\delta\:}^{202}\text{H}\text{g}=\left[{\left(\frac{{}_{\:}{}^{202}\text{H}\text{g}}{{}_{\:}{}^{198}\text{H}\text{g}}\right)}_{\text{s}\text{a}\text{m}\text{p}\text{l}\text{e}}/{\left(\frac{{}_{\:}{}^{202}\text{H}\text{g}}{{}_{\:}{}^{198}\text{H}\text{g}}\right)}_{\text{N}\text{I}\text{S}\text{T}\:3133}-1\right]\times\:{10}^{3}$$ 1 Mass-independent fractionation (MIF) is quantified using capital delta notation (Δ) as the deviation from the theoretically predicted values by MDF laws: $$\:{\varDelta\:}^{\text{x}\text{x}\text{x}}\text{H}\text{g}={\delta\:}^{\text{x}\text{x}\text{x}}\text{H}\text{g}-{\beta\:}\times\:{\delta\:}^{202}\text{H}\text{g}$$ 2 , where xxx = 199, 200, or 201, and β-values are 0.252, 0.502, and 0.752 for isotopes 199 Hg, 200 Hg, and 201 Hg, respectively, following kinetic MDF law ( 28 ). Chemical Index of Alteration Paleoweathering intensity was assessed using the Chemical Index of Alteration (CIA), calculated from major element oxide weight percentages: CIA = [Al₂O₃ / (Al₂O₃ + CaO* + Na₂O + K₂O)] × 100 ( 60 ). CaO* represents the CaO incorporated in the silicate fraction only, corrected following the methodology of ref ( 61 ). Higher CIA values generally indicate more intense chemical weathering, since this proxy effectively tracks the decomposition of labile minerals (e.g., plagioclase) relative to weathering-resistant phases (e.g., clays) ( 62 – 64 ). Declarations Competing interests: The authors declare no competing interests. Data and materials availability All data are available in the main text or the supplementary materials. Author contributions: J.C., H.L.Y., X.X., S.Z.S., and Z.F. conceptualized and designed the research. J.C. and R.M. were responsible for core logging and completed the astronomical tuning. Sample preparation and subsequent analyses were performed by J.C., Y.N.N., Y.L.Z., and W.J.L. All coauthors contributed to the data analysis and the writing of the manuscript. Acknowledgments This study was supported jointly by the National Natural Science Foundation of China (42325201; 42372030), the Yunnan Province Science and Technology Department (202302AO370014), Yunnan Science & Technology Champion Project (202305AB350006), the Scientific Research Fund Project of Yunnan Education Department (2025Y0021) References S. D. Schoepfer, T. J. Algeo, B. van de Schootbrugge, J. H. Whiteside, The Triassic–Jurassic transition – A review of environmental change at the dawn of modern life. Earth-Science Reviews 232, 104099 (2022). J. C. McElwain, D. J. Beerling, F. I. Woodward, Fossil plants and global warming at the Triassic–Jurassic boundary. Science 285, 1386–1390 (1999). J. G. 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Chiaradia, N. Youbi, H. Bertrand, L. Reisberg, R. Merle, F. Jourdan, “The Central Atlantic Magmatic Province (CAMP): A Review” in The Late Triassic World (Springer International Publishing AG., 2018) Topics in Geobiology , pp. 91–125. Additional Declarations There is NO Competing Interest. Supplementary Files DataS1.xlsx Dataset 1 Supplementaryinformation.docx Supplementary information Cite Share Download PDF Status: Published Journal Publication published 13 Jan, 2026 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6720557","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":460274441,"identity":"5dd42ed7-c7f5-444e-bc67-db8aa6b0ab2c","order_by":0,"name":"Jianbo Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYBACxhkMbEDKBsLjIUFLGglaGCTAWg6ToIV5dvOzBx93nE/cLpHA+OBtG4O8OUGHzTlmbjjzzO3EnTMSmA3ntjEY7mwgpGVGDps0b9vtxA03EkAMhgSDA8Ro+dt2DqSF/TfxWhjbDoBtYSZOy5xjZpK9bcnGG848bJacc07CcAMhLYbAEJP42WYnu+F48sEPb8ps5AnaYtgAoR0bGBhBTAkC6oFAHkrbE1Y6CkbBKBgFIxYAAKZNQcSC6fy2AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-6291-202X","institution":"Yunnan University","correspondingAuthor":true,"prefix":"","firstName":"Jianbo","middleName":"","lastName":"Chen","suffix":""},{"id":460274442,"identity":"11f484f9-6f01-4907-91d6-b65b24ce3c01","order_by":1,"name":"Yi-ning Niu","email":"","orcid":"","institution":"Yunnan University","correspondingAuthor":false,"prefix":"","firstName":"Yi-ning","middleName":"","lastName":"Niu","suffix":""},{"id":460274443,"identity":"3f1d1fbf-ee42-4d6e-9e31-4b0679d4ff46","order_by":2,"name":"Rongyao Ma","email":"","orcid":"","institution":"Yunnan University","correspondingAuthor":false,"prefix":"","firstName":"Rongyao","middleName":"","lastName":"Ma","suffix":""},{"id":460274444,"identity":"31421080-4664-4006-9b98-7601c14796e4","order_by":3,"name":"Yan-ling Zhou","email":"","orcid":"","institution":"Yunnan University","correspondingAuthor":false,"prefix":"","firstName":"Yan-ling","middleName":"","lastName":"Zhou","suffix":""},{"id":460274445,"identity":"bca286ea-91b2-4fce-97a4-65d914677148","order_by":4,"name":"Wen-jie Liu","email":"","orcid":"","institution":"Yunnan University","correspondingAuthor":false,"prefix":"","firstName":"Wen-jie","middleName":"","lastName":"Liu","suffix":""},{"id":460274446,"identity":"bf406c1c-9b38-482e-b58b-8cbd73262e4b","order_by":5,"name":"Ya-Ming Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Ya-Ming","middleName":"","lastName":"Wang","suffix":""},{"id":460274447,"identity":"5e8f9f9a-3a18-4d4b-81fe-a19f95728f68","order_by":6,"name":"Hai-Lu You","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hai-Lu","middleName":"","lastName":"You","suffix":""},{"id":460274448,"identity":"b308d946-80b0-4770-ae53-c5ecee5f7413","order_by":7,"name":"Xing Xu","email":"","orcid":"https://orcid.org/0000-0002-4786-9948","institution":"Institute of Vertebrate Paleontology \u0026 Paleoanthropology, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xing","middleName":"","lastName":"Xu","suffix":""},{"id":460274449,"identity":"7ee6d724-8091-4996-81ba-90c7969e01cb","order_by":8,"name":"Shu-zhong Shen","email":"","orcid":"https://orcid.org/0000-0001-8380-0692","institution":"Nanjing University","correspondingAuthor":false,"prefix":"","firstName":"Shu-zhong","middleName":"","lastName":"Shen","suffix":""},{"id":460274450,"identity":"3a429aad-760b-493b-ae24-72a1c2b53c4b","order_by":9,"name":"Zhuo Feng","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Zhuo","middleName":"","lastName":"Feng","suffix":""}],"badges":[],"createdAt":"2025-05-22 03:05:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6720557/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6720557/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-03083-6","type":"published","date":"2026-01-13T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83351558,"identity":"f4fc8a4b-2fd9-4a42-866b-b2a15c58cc63","added_by":"auto","created_at":"2025-05-23 14:08:56","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":300313,"visible":true,"origin":"","legend":"\u003cp\u003eMaps and sedimentary sequences of the study area in Southwest China. (A) Geographic location of the study area. (B) Geological map of the study area, revised from the Regional Geological Survey Report by the Yunnan Institute of Geological Survey. (C) Correlation of outcrop and drill core in the Wande section, based on variegated clastic lithology and thickness of the transitional Yubacun Formation. Note: The dinosaur fossil occurrence is limited to below 12.53 m within the core (top of the grayish-green siltstone unit), and the Yubacun Formation exhibits an increasing calcareous component upwards.\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/fb6e443ed88cdc57b89ee8d7.jpeg"},{"id":83351557,"identity":"e90400ff-7423-4122-920e-ec2307dc67ef","added_by":"auto","created_at":"2025-05-23 14:08:56","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":296884,"visible":true,"origin":"","legend":"\u003cp\u003eComposite framework for reconstructing Triassic–Jurassic transition environmental dynamics. (A) Gamma-ray (GR) data with 405 kyr filtered output and Evolutionary Fast Fourier Transform (FFT) spectrogram of tuned GR data. (B-G) Geochemical data including (B) δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e, (C) Total Organic Carbon (TOC), (D) Hg concentration (with isotope insert), (E) Hg/TOC ratios, (F) Cu concentration, and (G) Chemical Index of Alteration (CIA). Gray, orange, and green bands highlight three Hg-anomaly intervals defined by Hg/TOC ratios. LOWESS curves with 95% confidence intervals are shown for δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e, TOC, Hg, and Hg/TOC. The grey rectangle indicates a potential direct volcanic input characterized by Δ\u003csup\u003e199\u003c/sup\u003eHg values of ~0‰.\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/41532c1cfe92054130ac8603.jpeg"},{"id":83351560,"identity":"1497820f-094d-4192-9282-e2e492b293ca","added_by":"auto","created_at":"2025-05-23 14:08:57","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":306972,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic correlation across the Triassic–Jurassic boundary (TJB) between the studied WK23-1 drill core from the Wande section and globally recognized reference sections. The Triassic–Jurassic boundary is marked by the first appearance of the ammonite Psiloceras spelae in marine successions. Data compilation for each section includes: (A) St. Audrie's Bay (UK): Organic carbon isotopes (\u003cem\u003e10\u003c/em\u003e), mercury concentrations (\u003cem\u003e31\u003c/em\u003e), and the proposed TJB level (\u003cem\u003e14\u003c/em\u003e). (B) Kuhjoch (Austria): δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e data (\u003cem\u003e11\u003c/em\u003e) and Hg data (\u003cem\u003e27\u003c/em\u003e). (C) Levanto (Peru): Composite δδ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e record and high-precision U-Pb age constraints (\u003cem\u003e26\u003c/em\u003e). (D) Wande section (this study): δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e and pulsed Hg anomaly data (this work), timing of peak Central Atlantic Magmatic Province (CAMP) volcanism (\u003cem\u003e65\u003c/em\u003e), evidence for paleoclimate changes [warming and drier;(\u003cem\u003e36\u003c/em\u003e)], indications of wildfire events (\u003cem\u003e48\u003c/em\u003e), and increased occurrence of calcareous components (this work).\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/18d3cb383c66e2c3f0bebd7c.jpeg"},{"id":101391375,"identity":"14453965-7b0b-4013-b63c-9cdeb943d684","added_by":"auto","created_at":"2026-01-29 08:29:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1686627,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/12f096b7-5f08-4157-bdcf-cd5576628b5c.pdf"},{"id":83351562,"identity":"b117f804-63f8-4a5a-acc0-51306d5a5cfb","added_by":"auto","created_at":"2025-05-23 14:08:57","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":64489,"visible":true,"origin":"","legend":"Dataset 1","description":"","filename":"DataS1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/0334046df9e9d82e10298ab7.xlsx"},{"id":83352043,"identity":"51c1daf7-8d57-4f79-9095-15ee291c507f","added_by":"auto","created_at":"2025-05-23 14:16:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":716151,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"Supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6720557/v1/fcf2c361a046d34afadc7c94.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Triassic–Jurassic environmental instability on the subtropical eastern Tethyan margin linked to the dinosaur occurrence","fulltext":[{"header":"Main text","content":"\u003cp\u003eThe Triassic\u0026ndash;Jurassic transition (TJT; ~201 Ma) represents one of the most critical intervals in Earth\u0026rsquo;s history, marked by profound environmental upheaval and a fundamental reshaping of the biosphere. It witnessed the catastrophic end-Triassic mass extinction (ETME), one of the Phanerozoic\u0026rsquo;s \u0026ldquo;Big Five\u0026rdquo; biotic crises, largely attributed to the emplacement of the Central Atlantic Magmatic Province (CAMP). This large-scale volcanic activity, linked to the stepwise disintegration of the Pangea supercontinent (\u003cem\u003e1\u003c/em\u003e), released vast quantities of greenhouse gases (e.g., \u0026gt;5\u0026acute;10\u003csup\u003e12\u003c/sup\u003e tons CO\u003csub\u003e2\u003c/sub\u003e), triggering climate warming, and oceanic acidification, and a severe collapse of the global carbon cycle, which altering both marine and terrestrial ecosystems\u0026nbsp;(\u003cem\u003e2\u003c/em\u003e\u0026ndash;\u003cem\u003e5\u003c/em\u003e). Yet, amidst this catastrophe, a remarkable evolutionary success unfolded: the rise of dinosaurs, which transitioned from regionally Carnian-age (early Late Triassic) origin assemblages to global dominance by the Early Jurassic, with the mechanisms remaining debated\u0026nbsp;(\u003cem\u003e6\u003c/em\u003e\u0026ndash;\u003cem\u003e9\u003c/em\u003e). This apparent paradox \u0026ndash; mass extinction coinciding with the ascendancy of a major clade \u0026ndash; raises critical questions: How did terrestrial ecosystems respond to CAMP-driven environmental stressors? And did these volcanic-induced changes actively facilitate the dinosaurs\u0026rsquo; expansion into low-latitude western Tethys?\u003c/p\u003e\n\u003cp\u003eWhile extensive marine records document the TJT environmental perturbations through characteristic carbon isotope excursions (CIEs) and mercury (Hg) anomalies indicative of CAMP volcanism (\u003cem\u003e10\u003c/em\u003e\u0026ndash;\u003cem\u003e14\u003c/em\u003e), our understanding of the terrestrial realm lags significantly, which is exacerbated by a geographic bias, with most high-resolution TJT records clustered in North American and European basins (e.g., Newark Basin, St. Audries\u0026rsquo;s Bay), leaving a large portion of Pangean landmasses poorly documented. East Asian terrestrial sequences, particularly the dinosaur-rich Jurassic strata of Yunnan Province, Southwest China (\u003cem\u003e15\u003c/em\u003e\u0026ndash;\u003cem\u003e17\u003c/em\u003e), offer an exceptional yet under-exploited window into this critical transition. A recent discovery of an early-diverging sauropodomorph in Wuding County, northern Yunnan, represents the stratigraphically lowest confirmed skeletal remains in the Triassic\u0026ndash;Jurassic transitional interval that have been found so far in southern China, possibly East Asia. It provides a unique opportunity to examine biotic turnover dynamics on the eastern Tethyan subtropical continent during the TJT, given that sauropodomorphs have long been recognized as absent from the lower paleolatitudes before the end of the Triassic due to harsh environmental fluctuations (\u003cem\u003e18\u003c/em\u003e). However, like a previously reported sauropodomorph footprint site in the neighboring Sichuan Basin (\u003cem\u003e19\u003c/em\u003e), the precise age of this pivotal fossil remains unconstrained. This highlights a broader challenge: correlating terrestrial biotic events with the marine extinction timeline is severely hindered by the typical scarcity of datable volcanic ash layers within continental redbeds.\u003c/p\u003e\n\u003cp\u003eTo address these challenges in assessing volcanic forcing and establishing a robust chronostratigraphic framework, we conducted a multi-proxy investigation of a drill core (WK23-1) across the Triassic\u0026ndash;Jurassic boundary (TJB) interval in the Wande section from Kunming Basin, Yunnan Province, Southwest China \u0026ndash; the locality of the newly discovered sauropodomorph (Fig. 1A). By integrating the first high-resolution organic carbon isotope (\u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e) profile with mercury chemostratigraphy (Hg concentrations and isotopes), elemental geochemistry, and astronomically-tuned gamma-ray data (Fig. 2), this study aims to: (1) refine the TJB placement by correlating characteristic CIEs and Hg anomalies linked to CAMP activity; (2) provide the first age constraints for the earliest sauropodomorph skeletal remains found near the extinction-recovery interface in East Asia. By bridging a critical spatial and depositional gap in TJT records, our work underscores the utility of multi-proxy chemostratigraphy in terrestrial basins and advances our understanding of how volcanically driven environmental instability impacted terrestrial ecosystems during one of Earth\u0026rsquo;s major crises, and potentially shaped the diversification and biogeographic expansion of dinosaurs.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eIn drill core WK23-1, the Triassic\u0026ndash;Jurassic transitional Yubacun Formation is stratigraphically bounded by the overlying Lufeng Formation (Lower Jurassic) at 15.23 m depth and the underlying Shezi Formation (Upper Triassic) at 157.60 m depth, yielding a total thickness of 142.37 m (Figs. 1B\u0026ndash;C). Astronomical tuning of the gamma-ray series identified more than eight full 405-kyr long-eccentricity cycles across the entire logged core, suggesting a total duration of ~3.2 Myr (Fig. 2A). Based on cycle counting, the depositional duration of the Yubacun Formation is estimated to be ~1.71 Myr.\u003c/p\u003e\n\u003cp\u003e\u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e values in the Upper Triassic Shezi Formation exhibit relatively limited variability, ranging from -27.9\u0026permil; to -23.5\u0026permil; (average of -24.8\u0026permil;,1\u0026sigma; = 0.59 \u0026permil;, n = 65). A pronounced isotopic shift occurs in the Yubacun Formation, with values spanning from -28.4\u0026permil; to -21.3\u0026permil; (avg. of -24.3\u0026permil;, 1\u0026sigma; = 1.27 \u0026permil;, n=167), and displaying three distinct CIEs: (1) a \u0026ldquo;precursor\u0026rdquo; CIE (P-CIE) localized between the depth of 143.10 to 146.68 m (duration: ~40 kyr), characterized by \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e minima (~ -26.6\u0026permil;); (2) an \u0026ldquo;initial\u0026rdquo; CIE (I-CIE) between the depth of 106.01\u0026ndash;121.49 m (duration: ~169 kyr), marked by a transient negative shift (avg. of -25.7\u0026permil;); (3) a \u0026ldquo;main\u0026rdquo; CIE (M-CIE) initiated at 94.73\u0026ndash;95.23 m depth, remaining low through the upper Yubacun Formation and into the basal Lufeng Formation (average of -24.5\u0026permil;,1\u0026sigma; = 0.94 \u0026permil;, n = 14) (Fig. 2B).\u003c/p\u003e\n\u003cp\u003eTOC contents show a marked overall decline upwards from the Shezi Formation (avg. of 34.2 wt%, 1\u0026sigma; = 27.5%, n = 58) to the Yubacun Formation (avg. of 5.1 wt%, 1\u0026sigma; = 4.4%, n = 166). A sharp drop occurs near the Shezi\u0026ndash;Yubacun boundary. A minor increase in TOC (avg. of 8.6 wt%, 1\u0026sigma; = 8.5%, n = 14) is observed within the basal Lufeng Formation before declining again upwards (Fig. 2C).\u003c/p\u003e\n\u003cp\u003eThree stratigraphically distinct intervals with elevated Hg concentrations normalized to TOC (Hg/TOC) are identified (Fig. 2D\u0026ndash;E): the first Hg/TOC spike occurs between 151.61 m and 157.49 m coincides with the uppermost Shezi Formation and basal Yubacun Formation, reaching peak values of 24 ppb/wt%. This interval coincides with elevated concentrations of the element copper (Cu), which peaks at 58.2 ppm within this zone (Fig. 2F). The second Hg/TOC anomaly, between 95.32 m and 87.38 m, reaching 51 ppb/wt%, overlaps with the onset and initial phase of the M-CIE. The third Hg/TOC peak occurs between 55.68 m and 55.15 m in the upper Yubacun Formation, with values up to 51 to 24 ppb/wt%.\u003c/p\u003e\n\u003cp\u003eMercury isotope analysis was performed on ten samples from these anomalous zones. Mass-independent fractionation (MIF), indicated by \u0026Delta;\u0026sup1;⁹⁹Hg values, is minimal. Most \u0026Delta;\u0026sup1;⁹⁹Hg values cluster near zero, ranging from -0.10\u0026permil; to +0.04\u0026permil;, with an average of -0.03\u0026permil;. This near-zero MIF signature is commonly associated with volcanogenic Hg sources (Fig. 2D). Besides, the CIA values (56.55\u0026ndash;86.2, avg. of 74.6, 1\u0026sigma; = 6.8, n = 88) exhibit moderate chemical weathering and minimal stratigraphic variations (Fig. 2G).\u003c/p\u003e"},{"header":"Discussion","content":"\u003ch2\u003eCarbon–Mercury Dynamics: Linking CAMP Volcanism, Global Perturbations, and Regional Responses\u003c/h2\u003e\u003cp\u003eThe Triassic\u0026ndash;Jurassic transition (TJT) is characterized by profound disturbances in the global carbon cycle, often recorded as distinct negative carbon isotope excursions (CIEs) in both marine and terrestrial sedimentary archives (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). These CIEs serve as crucial chemostratigraphic tools for correlating sequences and understanding the environmental changes during the end-Triassic mass extinction (ETME) (e.g., \u003cem\u003e2\u003c/em\u003e, \u003cem\u003e10\u003c/em\u003e, \u003cem\u003e11\u003c/em\u003e, \u003cem\u003e20\u003c/em\u003e, \u003cem\u003e21\u003c/em\u003e). Our high-resolution δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e record from drill core WK23-1 in the terrestrial Kunming Basin reveals three distinct negative CIEs (termed P-CIE, I-CIE, M-CIE; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eB), mirroring patterns observed globally, albeit with regional disparities. The most prominent \u0026ldquo;initial\u0026rdquo; CIE (I-CIE), manifested in our core as a significant negative shift lasting\u0026thinsp;~\u0026thinsp;169 kyr (between 106.01 m and 121.49 m depth, Data S1), is widely recognized as marking the onset of the main ETME phase. Its remarkable synchronicity across geographically diverse marine (e.g., St. Audrie\u0026rsquo;s Bay; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eA\u0026ndash;C) and terrestrial settings [e.g., Junggar Basin (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e)], strongly implicates the CAMP volcanism through massive injections of CO\u003csub\u003e2\u003c/sub\u003e and/or thermogenic methane into the ocean-atmosphere system as the principal driver of this global carbon cycle instability (e.g., \u003cem\u003e11\u003c/em\u003e, \u003cem\u003e23\u003c/em\u003e, \u003cem\u003e24\u003c/em\u003e).\u003c/p\u003e \u003cp\u003eUtilizing the established high-precision U-Pb age for the onset of the I-CIE (and thus the ETME) at 201.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 Ma (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e), we anchor our astrochronological timescale by assigning this age to the base of the I-CIE at 121.49 m depth in WK23-1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, Data S1). Following established correlations where the Triassic\u0026ndash;Jurassic boundary (TJB) often slightly post-dates the I-CIE onset (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e), our cyclostratigraphic model places the TJB at a depth of 111.29 m within the transitional Yubacun Formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eD \u0026amp; Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eB). This placement provides a critical temporal framework for evaluating biotic events relative to the extinction horizon.\u003c/p\u003e \u003cp\u003eFurther strengthening the link to volcanic activity, sedimentary mercury (Hg) anomalies concurrent with CIEs provide compelling evidence for pulsed, large-scale volcanic Hg emissions during the TJT (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). While many Hg records were documented from marine sections in Europe and North America (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e), our study provides crucial terrestrial data for the Central Yunnan area from the eastern Tethyan realm. The WK23-1 core reveals three distinct Hg/TOC enrichment intervals stratigraphically associated with the CIEs (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eD\u0026ndash;E). Critically, the minimal mass-independent fractionation (MIF) observed, with Δ\u0026sup1;⁹⁹Hg values clustering near zero (-0.10\u0026permil; to +\u0026thinsp;0.04\u0026permil;) in samples from the second and third Hg peaks, strongly supports a predominantly volcanic source for the mercury anomalies. This signature arises because volcanic emissions inject primarily Hg(0) into the atmosphere, lacking the significant MIF generated by photochemical reactions involving Hg in the upper atmosphere (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). Our findings align with the global pattern of volcanogenic Hg deposition during the TJT (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, beyond these global volcanogenic fingerprints, TJT environmental records often display significant regional variability, reflecting the interplay of global drivers with local factors like organic carbon sources, depositional settings, diagenesis, and regional climate (\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e). This is evident in the details of both the carbon and mercury records in WK23-1. For instance, the \"precursor\" CIE (P-CIE; 146.68\u0026ndash;143.10 m) identified in our drill core, while potentially correlative with events seen in some other sections, lacks clear global synchronicity and thus its status as a truly global signal remains debated (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). In the Kunming Basin, the P-CIE coincides strikingly with a rapid decline in TOC content (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eB\u0026ndash;C), suggesting a localized collapse in terrestrial primary productivity or carbon burial. This short-lived negative CIE event (~\u0026thinsp;40 kyr) preceding the main ETME, coupled with the TOC decline at the transition from the Shezi to Yubacun Formation, likely implies the demise of humid peat-forming ecosystems. This interpretation is consistent with palynological evidence for significant floral turnover in contemporaneous strata across southern China (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). The drivers could include early CAMP-induced environmental stress, such as aridification or toxic metal loading (Hg, Cu \u0026ndash; note the elevated Cu coinciding with the first Hg peak; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eF), synergistically impacting sensitive floras (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e). The apparent absence of a distinct P-CIE in many distal marine sections could further support a predominantly regional hydroclimate or ecosystem control rather than a global atmospheric CO₂ perturbation (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). Furthermore, the first Hg peak (157.49\u0026ndash;151.61 m), unlike the later peaks, exhibits slightly negative Δ\u0026sup1;⁹⁹Hg values (-0.11\u0026permil; to -0.05\u0026permil;) deviating somewhat from a predominantly volcanic signature (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eD). This subtle MIF signature might indicate transient contributions from reworked terrestrial Hg, potentially mobilized by enhanced erosion or the combustion of organic-rich soils/sediments during initial environmental upheaval (\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe regional disturbance is also apparent in the character of the \"main\" CIE (M-CIE) and the weathering proxy record. The M-CIE in WK23-1 appears somewhat muted and prolonged compared to sharp, pronounced excursions seen in some marine records (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e), potentially reflecting differences in organic matter sources, degradation pathways, or depositional redox conditions influencing δ\u0026sup1;\u0026sup3;C\u003csub\u003eorg\u003c/sub\u003e preservation in this terrestrial setting (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e). In addition, the CIA values remain relatively stable (56.5\u0026ndash;86.2, avg. of 74.6, 1σ\u0026thinsp;=\u0026thinsp;6.8) throughout the studied interval, indicating persistently moderate chemical weathering intensity in the source area (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eG). This relative stability contrasts with evidence for extreme climatic fluctuations and potentially intense weathering shifts inferred from proxies in the basins to the north of Kunming Basin, such as Junggar Basin (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e) or Sichuan Basin (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). While seemingly indicative of climatic stability, the CIA primarily reflects the intensity of chemical weathering of silicate minerals in the source area over longer timescales. It does not preclude significant changes in other climatic parameters like precipitation seasonality, frequency of extreme events (e.g., droughts, wildfires), or temperature fluctuations, especially in a subtropical setting potentially buffered from the most extreme weathering regime shifts seen at higher latitudes (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e). Therefore, the stable CIA suggests a relatively consistent baseline weathering regime but does not rule out other forms of climate change impacting the ecosystem.\u003c/p\u003e\n\u003ch3\u003ePost-Extinction Emergence of Sauropodomorph Dinosaurs in Southwest China: Timing and Environmental Context\u003c/h3\u003e\n\u003cp\u003eAgainst the background of global volcanic catastrophe and regionally variable environmental responses, the TJT interval witnessed a pivotal moment in vertebrate history: the rise of dinosaurs to ecological dominance (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Sauropodomorph dinosaurs, originating potentially in Gondwana soon after the Permian\u0026ndash;Triassic crisis (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e), had dispersed into mid-to-high latitudes of the Northern Hemisphere, including Northwest China (Junggar Basin) by the Late Triassic (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). However, their apparent absence from low-latitude regions during the Late Triassic has been attributed to harsh, fluctuating environmental conditions possibly related to extreme CO₂ levels (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Consistent with this, extensive fieldwork has yielded no confirmed Late Triassic sauropodomorph skeletal remains from the lower paleolatitudes of southwestern China, potentially due to these environmental filters or geographic barriers (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e), alongside geological preservation conditions and paleogeographic configuration of landmasses. Our astrochronologically-calibrated age model for WK23-1 places the sauropodomorph fossil horizon (occurring\u0026thinsp;\u0026gt;\u0026thinsp;15.23 m depth in the topmost Yubacun Formation) at approximately\u0026thinsp;~\u0026thinsp;200.17 Ma (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eD \u0026amp; Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). This timing is unequivocally Early Jurassic, falling about 1.23\u0026nbsp;million years after the TJB (placed at 111.29 m, 201.4 Ma based on tuning relative to I-CIE onset at 201.51 Ma). This provides the first evidence that sauropodomorphs colonized Southwest China shortly in the aftermath of the end-Triassic mass extinction.\u003c/p\u003e \u003cp\u003eThe timing of this faunal expansion coincides with the recovery interval following the I-CIE and encompasses the M-CIE. While the precise environmental drivers facilitating dinosaur ascendancy remain to be investigated (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e), the environmental stressors associated with CAMP volcanism likely played a complex role. The recurrent Hg/TOC spikes aligned with δ\u0026sup1;\u0026sup3;C\u003csub\u003eorg\u003c/sub\u003e shifts in our record (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e) serve as proxies for pulsed volcanic activity and associated environmental perturbations impacting the Kunming Basin during the TJT. These perturbations, potentially including toxic metal loading (Hg, Cu), climatic instability (though perhaps buffered in terms of weathering intensity), increased aridity or seasonality, and potentially more frequent wildfires fueled by stressed vegetation (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e), could have selectively disadvantaged contemporaneous faunas and disrupted established ecosystems on land. This disruption may have created ecological opportunities (\"vacant niches\") for resilient and adaptable groups like dinosaurs (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). The prolonged environmental instability, potentially reflected in the extended duration of the M-CIE, might have favored taxa capable of coping with fluctuating resources or conditions, although the specific adaptations benefiting early sauropodomorphs require further investigation. The modest recovery of TOC during the M-CIE interval (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eC) might signal the beginnings of ecosystem reorganization where these large herbivores arrived and flourished.\u003c/p\u003e \u003cp\u003eThis post-extinction dispersal into southwestern China likely occurred within a broader context of global climate change. Tectonic activity related to Pangea's fragmentation altered oceanic and atmospheric circulation, while elevated atmospheric CO₂ levels drove overall warming and potentially enhanced climate variability and seasonality (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e). Evidence for increased seasonality, even under high CO₂, comes from findings like lake ice-rafted debris in the high-latitude Junggar Basin (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). The increased occurrence of carbonate nodules or concretions upwards the drill core suggests at least transient arid (and therefore seasonality) were becoming more prevalent across the TJT into the earliest Jurassic (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eC \u0026amp; Fig. S2). Such shifts towards more seasonal climates could have profoundly impacted vegetation structure across various latitudes (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e), potentially transforming previously less favorable habitats (perhaps persistently warm and humid) into landscapes (e.g., more open woodlands or savanna-like ecosystems) accessible or exploitable by large herbivores like sauropodomorphs. While the stable CIA values in the Kunming Basin suggest the source area weathering intensity did not undergo the dramatic swings seen elsewhere, increased seasonality in local precipitation patterns or temperature ranges could still have driven significant ecological shifts relevant to faunal turnover and migration, without necessarily altering the bulk silicate weathering signal captured by CIA. Thus, the arrival of sauropodomorphs in southwestern China around 200.17 Ma likely reflects a combination of post-extinction ecological opportunity and adaptation to evolving Early Jurassic climates, particularly the emergence of potentially more seasonal environments across former environmental barriers (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study investigated the terrestrial TJT in Southwest China's Kunming Basin using integrated multi-proxy chemostratigraphy (δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e, Hg concentrations, and isotopes) and astrochronology on drill core WK23-1. These high-resolution records documented the environmental impact of pulsed CAMP volcanism through correlative carbon isotope excursions (CIEs) and Hg anomalies exhibiting volcanogenic near-zero Δ\u0026sup1;⁹⁹Hg signatures. These global signals were also influenced by regional factors, reflected in localized ecosystem shifts linked to the P-CIE and TOC decline, potential terrestrial Hg reworking, and a relatively stable weathering intensity baseline (indicated by CIA) despite inferred climate shifts elsewhere. An astrochronological framework established the Yubacun Formation's duration (~\u0026thinsp;1.71 Myr) and placed the Triassic\u0026ndash;Jurassic boundary (TJB, 201.4 Ma) at 111.29 m depth. More importantly, the precise dating of the earliest sauropodomorph skeletal fossils in this region to ~\u0026thinsp;200.17 Ma (Early Jurassic, ~\u0026thinsp;1.23 Myr post-TJB) demonstrates the post-ETME colonization of the (sub)tropical eastern Tethys by these large herbivores. This research fills a critical geographic and depositional gap in TJT terrestrial records, validates the efficacy of applying multi-proxy chemo- and cyclostratigraphy for high-resolution dating in continental sequences lacking volcanic ashes, and provides crucial context for understanding the interplay between catastrophic volcanism, environmental upheaval, ecosystem recovery, and the early diversification dynamics of dinosaurs in a key, previously underexplored region.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eGeological Background\u003c/h2\u003e \u003cp\u003eThe Kunming Basin in Yunnan Province, Southwest China (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), situated within the Tethyan tectonic domain, preserves a critical terrestrial stratigraphic succession across the Triassic\u0026ndash;Jurassic transition (TJT). The studied interval encompasses three formations (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eB\u0026amp;C): the Upper Triassic Shezi Formation, the transitional Yubacun Formation, and the Lower Jurassic Lufeng Formation, in ascending order, which collectively record a continuum of depositional responses to evolving basin dynamics and climatic regimes.\u003c/p\u003e \u003cp\u003eThe Shezi Formation is assigned to the Norian\u0026ndash;Rhaetian (Late Triassic) based on the presence of the \u003cem\u003eYunnanophorus\u003c/em\u003e\u0026ndash;\u003cem\u003eIndosinion\u003c/em\u003e bivalve zone and the \u003cem\u003eDictyophyllum\u0026ndash;Clathropteris\u003c/em\u003e plant assemblage (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e). The overlying \u0026zwnj;Yubacun Formation, considered the primary Triassic\u0026ndash;Jurassic transitional unit, consists of \u0026zwnj;variegated clastic rocks\u0026zwnj; dominated by gray, grayish-green, and grayish-yellow sandstone intercalated with purplish-red siltstone or mudstone\u0026zwnj;. Palynological assemblages constrain its deposition in the TJT interval (\u003cem\u003e54\u003c/em\u003e), and the sauropodomorph fossils occur near its top. This formation records the demise of Late Triassic peat-forming environments and the shift towards Early Jurassic aridification environments, marked by an increased occurrence of calcareous components upwards (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eC \u0026amp; Fig. S2). It archives the Kunming Basin\u0026rsquo;s transition from humid Late Triassic to semi-arid Early Jurassic oxidative regimes, likely linked to Tethyan tectonism and global TJT paleoclimatic as well as carbon cycle perturbations (\u003cem\u003e55\u003c/em\u003e). The succeeding Lower Jurassic Lufeng Formation comprises maroon mudstones interbedded with quartzose sandstones and common calcareous nodules, indicative of seasonal aridity, oxidizing lacustrine-fluvial settings that host abundant vertebrate fossils like \u003cem\u003eLufengosaurus\u003c/em\u003e (\u003cem\u003e15\u003c/em\u003e, \u003cem\u003e16\u003c/em\u003e).\u003c/p\u003e \u003cp\u003eDrill core WK23-1 (102\u0026deg;10'56\" E, 26\u0026deg;03'30\" N; Wande section, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eB), recovered from the dinosaur fossil locality, spans the critical TJT interval and provides a continuous archive for investigating terrestrial responses to TJT events in the eastern Tethyan realm. The drill core andd outcrop correlation was accomplished through lithology of the Yubacun Formation\u0026rsquo;s variegated clastic characteristics and its thickness, confirming the dinosaur-bearing horizon occurs no higher than 12.53 m within the core (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eNatural Gamma-Ray (GR) Logging and Astronomical Tuning\u003c/h3\u003e\n\u003cp\u003eTo establish a high-resolution chronostratigraphic framework, natural gamma-ray (GR) logging was performed on core WK23-1 via wireline logging. Continuous GR measurements were acquired at 0.1 m vertical resolution. Assuming GR variations in this clastic succession primarily reflect changes in clay mineral content potentially driven by orbitally modulated climate cycles affecting weathering and sediment influx, we performed cyclostratigraphic analysis using the Acycle v2.8 software (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e). Temporal calibration was achieved through iterative orbital tuning, whereby the 405-kyr eccentricity cycle component of the La2010d astronomical solution (\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e) was phase-locked to the GR-derived sedimentary cycles. Detailed methodological protocols are provided in the Supplementary Materials.\u003c/p\u003e\n\u003ch3\u003eGeochemical Analysis\u003c/h3\u003e\n\u003cp\u003eA total of 441 samples were collected from fine-grained lithologies (mudstone, siltstone) of drill core WK23-1, avoiding visible veins or significant alteration. The average sampling resolution was approximately 0.6 m. Samples were dried, crushed, and pulverized to ~\u0026thinsp;200 mesh (\u0026lt;\u0026thinsp;75 \u0026micro;m) using a tungsten carbide mill for subsequent geochemical analyses.\u003c/p\u003e \u003cp\u003eMajor and trace element concentrations were determined for 88 samples at the Wuhan Sample Solution Analytical Technology Co., Ltd. Major elements were measured by X-ray fluorescence spectrometer (XRF), and the analytical precision is better than \u0026plusmn;\u0026thinsp;2\u0026ndash;5% with certified reference material (GBW07103, GBW07105, GBW07108, GBW07111, and GBW07112) for analytical quality monitor. Trace elements were measured by Agilent 7700e inductively coupled plasma mass spectrometry (ICP-MS). Accuracy and precision were monitored using certified reference materials BHVO-2 (basalt), RGM-2 (rhyolite), GSR-3, and JA-2 and replicate analyses. Bulk-rock major and trace element data are given in Data S1.\u003c/p\u003e \u003cp\u003eTOC and δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e values were measured on 246 samples. Prior to analysis, powdered samples were treated with dilute hydrochloric acid overnight to remove carbonate minerals, followed by rinsing with deionized water and drying. About 1\u0026ndash;10 mg of decarbonated powder was weighed into tin capsules and combusted at 960 \u003csup\u003e◦\u003c/sup\u003eC. The evolved CO\u003csub\u003e2\u003c/sub\u003e was measured using a Thermo Scientific Elemental Analyzer IsoLink coupled to Thermo Scientific Delta V Advantage at the Institute of Palaeontology, Yunnan University, China. Measurements were calibrated by the organic analytical standard (OAS, CatNo. IVA33802151, with a certified δ\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eorg\u003c/sub\u003e value of -28.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u0026permil;) and reported relative to Vienna Pee Dee Belemnite (V-PDB). Analytical precision was better than 0.1\u0026permil; (1σ) for δ\u003csup\u003e13\u003c/sup\u003eC based on replicate analyses of the standard.\u003c/p\u003e \u003cp\u003eTotal Hg concentrations were determined for 434 samples using a Direct Mercury Analyzer (DMA-80 evo) at the Institute of Palaeontology, Yunnan University. Analytical accuracy was monitored using the certified reference material GBW07405a (GSS-5a, yellow-red soil, certified Hg\u0026thinsp;=\u0026thinsp;700\u0026thinsp;\u0026plusmn;\u0026thinsp;100 ng/g). Replicate analyses of GSS-5a yielded a relative standard deviation (RSD) better than 5% (2σ), confirming analytical precision.\u003c/p\u003e \u003cp\u003eTen samples exhibiting elevated Hg concentrations were selected for Hg isotope analysis. Mercury was liberated via pyrolysis and subsequently analyzed using a Nu-Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China. Instrumental drift was monitored by interspersing NIST SRM 3133 standard measurements after every three unknown samples. Mercury mass-dependent fractionation (MDF) is reported in delta notation (δ) (\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{\\delta\\:}^{202}\\text{H}\\text{g}=\\left[{\\left(\\frac{{}_{\\:}{}^{202}\\text{H}\\text{g}}{{}_{\\:}{}^{198}\\text{H}\\text{g}}\\right)}_{\\text{s}\\text{a}\\text{m}\\text{p}\\text{l}\\text{e}}/{\\left(\\frac{{}_{\\:}{}^{202}\\text{H}\\text{g}}{{}_{\\:}{}^{198}\\text{H}\\text{g}}\\right)}_{\\text{N}\\text{I}\\text{S}\\text{T}\\:3133}-1\\right]\\times\\:{10}^{3}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eMass-independent fractionation (MIF) is quantified using capital delta notation (Δ) as the deviation from the theoretically predicted values by MDF laws:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{\\varDelta\\:}^{\\text{x}\\text{x}\\text{x}}\\text{H}\\text{g}={\\delta\\:}^{\\text{x}\\text{x}\\text{x}}\\text{H}\\text{g}-{\\beta\\:}\\times\\:{\\delta\\:}^{202}\\text{H}\\text{g}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e,\u003c/p\u003e \u003cp\u003ewhere xxx\u0026thinsp;=\u0026thinsp;199, 200, or 201, and β-values are 0.252, 0.502, and 0.752 for isotopes \u003csup\u003e199\u003c/sup\u003eHg, \u003csup\u003e200\u003c/sup\u003eHg, and \u003csup\u003e201\u003c/sup\u003eHg, respectively, following kinetic MDF law (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eChemical Index of Alteration\u003c/h3\u003e\n\u003cp\u003ePaleoweathering intensity was assessed using the Chemical Index of Alteration (CIA), calculated from major element oxide weight percentages: CIA = [Al₂O₃ / (Al₂O₃ + CaO* + Na₂O\u0026thinsp;+\u0026thinsp;K₂O)] \u0026times; 100 (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e). CaO* represents the CaO incorporated in the silicate fraction only, corrected following the methodology of ref (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e). Higher CIA values generally indicate more intense chemical weathering, since this proxy effectively tracks the decomposition of labile minerals (e.g., plagioclase) relative to weathering-resistant phases (e.g., clays) (\u003cspan additionalcitationids=\"CR63\" citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e).\u003c/p\u003e"},{"header":"Declarations","content":" \u003ch2\u003eCompeting interests:\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003ch2\u003eData and materials availability\u003c/strong\u003e \u003cp\u003eAll data are available in the main text or the supplementary materials.\u003c/p\u003e \u003ch2\u003eAuthor contributions:\u003c/h2\u003e \u003cp\u003eJ.C., H.L.Y., X.X., S.Z.S., and Z.F. conceptualized and designed the research. J.C. and R.M. were responsible for core logging and completed the astronomical tuning. Sample preparation and subsequent analyses were performed by J.C., Y.N.N., Y.L.Z., and W.J.L. All coauthors contributed to the data analysis and the writing of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis study was supported jointly by the National Natural Science Foundation of China (42325201; 42372030), the Yunnan Province Science and Technology Department (202302AO370014), Yunnan Science \u0026amp; Technology Champion Project (202305AB350006), the Scientific Research Fund Project of Yunnan Education Department (2025Y0021)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eS. D. Schoepfer, T. J. Algeo, B. van de Schootbrugge, J. H. Whiteside, The Triassic\u0026ndash;Jurassic transition \u0026ndash; A review of environmental change at the dawn of modern life. \u003cem\u003eEarth-Science Reviews\u003c/em\u003e 232, 104099 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJ. C. 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Jourdan, \u0026ldquo;The Central Atlantic Magmatic Province (CAMP): A Review\u0026rdquo; in \u003cem\u003eThe Late Triassic World\u003c/em\u003e (Springer International Publishing AG., 2018)\u003cem\u003eTopics in Geobiology\u003c/em\u003e, pp. 91\u0026ndash;125.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6720557/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6720557/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Triassic\u0026ndash;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\u0026ndash;Jurassic boundary (TJB). Critically, the earliest regional sauropodomorph fossils occurred at ~\u0026thinsp;200.17 Ma (~\u0026thinsp;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.\u003c/p\u003e","manuscriptTitle":"Triassic–Jurassic environmental instability on the subtropical eastern Tethyan margin linked to the dinosaur occurrence","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-23 14:08:42","doi":"10.21203/rs.3.rs-6720557/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"13fce0f9-0d0a-45c0-8560-f324f04bc6c6","owner":[],"postedDate":"May 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":48890975,"name":"Earth and environmental sciences/Solid Earth sciences/Geology/Stratigraphy"},{"id":48890976,"name":"Earth and environmental sciences/Climate sciences/Palaeoclimate"},{"id":48890977,"name":"Earth and environmental sciences/Solid Earth sciences/Geochemistry"}],"tags":[],"updatedAt":"2026-01-29T08:29:32+00:00","versionOfRecord":{"articleIdentity":"rs-6720557","link":"https://doi.org/10.1038/s43247-025-03083-6","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2026-01-13 05:00:00","publishedOnDateReadable":"January 13th, 2026"},"versionCreatedAt":"2025-05-23 14:08:42","video":"","vorDoi":"10.1038/s43247-025-03083-6","vorDoiUrl":"https://doi.org/10.1038/s43247-025-03083-6","workflowStages":[]},"version":"v1","identity":"rs-6720557","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6720557","identity":"rs-6720557","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}