Chert is widespread in the Carnian (Late Triassic) shallow-water carbonate platform sedimentary successions of the northwestern Sichuan Basin, an unusual setting compared with its more typical deep-marine occurrence. It is found in strata recording the sedimentary evidence of a Late Triassic hyperthermal Event, the Carnian Pluvial Episode (CPE). Besides in the Sichuan basin, chert at the CPE is also reported in shallow-water successions of the Western Tethys. The coincidence between the CPE and chert occurrence in shallow-water carbonate rocks suggest a potential link with the CPE environmental perturbation that has not been explored yet. We investigated cherts from the shallow-water carbonates of the Upper Triassic Ma'antang Formation in the northwestern Sichuan Basin using petrography and geochemistry. Cherts in the Ma'antang Formation are mainly composed of microcrystalline quartz, with remnants of calcite. Geochemical (e.g., REE + Y pattern and the Ge/Si ratio) and petrological characteristics indicate a primary biogenic origin. The elevated input of silica and nutrients triggered by the CPE, together with potential upwelling created favorable conditions for the proliferation of siliceous organisms. These organisms were not outcompeted by carbonate secreting organisms due to clastic influx and changes in the chemical properties of the seawater. During early burial process, siliceous sponges released silica into the sediments. When these became saturated, silica precipitated and evolved into chert. Our findings suggest that saturation with respect to silica was achieved in shallower settings. This was an unusual event as cherts are usually formed in deep water starved basins or under hydrothermal influence, where silica saturation is more easily reached.

The Carnian Pluvial Episode (CPE) is characterized by multiple negative carbon isotope excursions driven by massive CO2 emissions from the Wrangellia Large Igneous Province. Intense environmental perturbations during the CPE reorganized low-latitude carbonate factories. In paleo-tropic regions (e.g., Italy, Sichuan Basin), this triggered a shift to metazoan-dominated factories, followed by a post-CPE resurgence of microbial factories. However, the global relevance of this pattern remains uncertain. Here, we present a high-resolution microfacies and conodont biostratigraphy dataset from the subtropical Tibetan Himalaya to reconstruct Late Carnian–Early Norian carbonate platform evolution. Our results show the upper Qulonggongba Formation (Tuvalian 2) was deposited in a terrigenous-influenced mixed inner ramp, while the overlying Qimala Formation (Tuvalian 2–Lacian) developed in a middle-to-outer ramp environment. After the CPE, the western Tibetan Himalaya carbonate factory shifted from a metazoan-dominated skeletal factory to a productive peloidal factory. Crucially, petrographic evidence indicates these peloids predominantly originated from micritized bioclasts and reworked carbonate mud, demonstrating the system remained fundamentally driven by heterotrophic metazoans rather than transitioning to a microbial factory. This post-CPE heterogeneity among Tethyan domains is largely due to latitudinal controls on surface seawater temperature and carbonate saturation. Additionally, paleogeographic configurations further differentiated recovery patterns: semi-restricted, tropical low-latitudes favored microbial factories, whereas the subtropical, open-marine conditions of the Tibetan Himalaya sustained heterotrophic metazoan dominance.

The Carnian Pluvial Episode (CPE) was a major climatic and environmental perturbation during the Late Triassic, commonly linked to emplacement of the Wrangellia Large Igneous Province (LIP). Negative carbon isotope excursions (NCIEs) are key chemostratigraphic markers of the CPE, but their number, magnitude, and timing remain debated, particularly for the early phase of the event. Here we present an integrated stratigraphic study of the Carnian succession at the composite Chenjiabao (CJB) section in the Nanpanjiang Basin, based on ammonoid and conodont biostratigraphy and whole-rock organic- and carbonate‑carbon isotope records. The biostratigraphic framework indicates that the studied succession spans the Julian 1 to Julian 2 interval. A ~ 1.3‰ negative shift in δ13Corg (NCIE-0) occurs in the middle Zhuganpo Formation without a corresponding excursion in δ13Ccarb. A larger negative excursion (NCIE-1), marked by declines of ~2.3‰ in δ13Corg and ~ 4.7‰ in δ13Ccarb, is recorded from the uppermost Zhuganpo Formation to the basal Wayao Formation. Two alternative biostratigraphic constraints are available for the Julian 1/2 boundary in the CJB section. In the ammonoid-based framework, NCIE-0 predates the conventionally recognized CPE, whereas in the conodont-based framework it represents the first carbon-isotope excursion of the CPE. NCIE-1 can be more confidently correlated with the nearby Longchang section and western Tethyan records, and may be linked to 13C-depleted carbon input associated with emplacement of the Wrangellia LIP. These results support the view that carbon-cycle perturbations during the Carnian were not a single event, but rather evolved through a multi-stage, stepwise pattern, and also highlight the need for further refinement of Carnian biostratigraphic frameworks in the Nanpanjiang Basin to better constrain the timing and onset of the event.

Rare earth elements and yttrium (REY) serve as valuable tracers of the geochemical properties of paleo-seawater and diagenetic processes. Four different carbonate components, ooids, microbalites, cements and brachiopods, from upper Carnian (Upper Triassic) of the northwestern Sichuan Basin were analyzed for REY geochemistry. Petrographic and cathodoluminescence analyses were employed to identify diagenetic features. The bright luminescent microspar calcite cement, ooids and the microbialites from the lower part of Qingyangou (HWQ) section exhibit bell-shaped REYSN patterns. Microbialites from the upper part of HWQ section have relatively high REY concentrations with a flat REYSN pattern. The high content of Sigma REY and terrigenous elements (e.g., Al, Zr, Th) in ooids and microbialites reflect the input of terrigenous clastic in the northwestern Sichuan Basin during Late Carnian. Articulated terebratulid brachiopods in the study area display a generally modern seawater-like REYSN pattern. However, this pattern may be influenced by the presence of sparry cement that has infilled the cracks and punctae of the brachiopod shells. The ooids, microbalites, cements and brachiopods are unsuitable for reconstructing the REY characteristics of Carnian seawater in the northwestern Sichuan Basin due to diagenetic alteration and terrigenous input. This study also highlights the necessity of thoroughly evaluating carbonate components for diagenetic effects and terrigenous contamination when employing them for REY characteristic reconstruction.

The Norian Stage of the Late Triassic represents a significant interval in geological history marked by environmental and biological evolutions. One notable event during this time is the late Norian warming event (W3), occurring in the late Norian. Globally recorded, the warming event is associated with carbon cycle perturbations, temperature increases, changes in biodiversity, and enhanced weathering intensity. Previous studies have focused on carbon isotopes, sedimentology, and biostratigraphy in the Baoshan block. However, information on environmental changes in this area during the Norian Stage remains limited. In this study, we utilized redox conditions indexes (V/Cr, U/Th, MoEF/UEF, and Ce/Ce*) and paleo-productivity proxies (Porg, Baxs) to reconstruct the ocean paleoenvironment in the HYB section of the Baoshan block. Two stages of reducing conditions and paleo-productivity fluctuations were identified during the late Norian warming event interval. In addition, the size of 1606 well-preserved adult conodont pectiniform elements from the HYB section was measured. The mean length of conodonts increased before the Alaunian-Sevatian boundary and then decreased significantly after the boundary in the Sevatian. Conodont size variations are typically related to changes in living environments, but our study found no direct relation between changes in redox conditions, paleo-productivity, and variations in conodont size in the Baoshan block. It may be due to the predominant conodont fauna, Mockina, being surface water dwellers. These surface-dwelling conodonts were not influenced by changes in seafloor redox conditions in relatively deep water. The direct evidence is instead that the size variation of conodonts is more likely affected by temperature changes in Tethyan surface seawater during the late Norian warming event.

The Late Triassic was a time of complex and rapid carbon cycle perturbations, which can be better understood through global carbon-isotope correlations. This study presents an integrated biostratigraphic, geochronological, and carbon isotope chemostratigraphic analysis across the Norian-Rhaetian boundary (NRB) and End-Triassic Mass Extinction (ETME) intervals from the Tela section in Southern Tibet. Four conodont biozones are identified, Mockina bidentata Zone, Parvigondolella andrusovi-Misikella hernsteini Zone, Misikella posthernsteini Zone, and Misikella ultima Zone, indicating a continuous succession from the Sevatian (upper Norian) to the upper Rhaetian. Globolaxtorum tozeri, one of the most indicative upper Rhaetian radiolarian taxa, was found within the M. ultima Zone. Zircon U-Pb dating of three volcanic detritus-bearing limestone samples from the lower part of the section yields ages of 217.0 +/- 1.4 Ma, 214.5 +/- 1.9 Ma, and 214.4 +/- 1.4 Ma, aligning with the Mo. bidentata Zone further refining the biostratigraphy. Carbon and oxygen isotope data (S13Ccarb and S18Ocarb) are subdivided into a lower (0-54 m) and an upper (70-120 m) interval. Four carbon isotope excursions (CIEs) are here documented. Three negative excursions (CIE1, CIE2, CIE3) occur in the Sevatian, each visible in both S13Ccarb and S13Corg curves. The fourth carbon excursion of S13Corg, the Initial-CIE (-5.24 parts per thousand), coinciding with the appearance of radiolarians G. tozeri and spans the M. posthernsteini and M. ultima zones, linking it to the ETME. While the cause of the Initial-CIE is generally attributed to Central Atlantic Magmatic Province, the drivers behind the three Sevatian CIEs and around the NRB remain uncertain. Volcanogenic materials from the Tela section suggest that prolonged volcanic activity-likely associated with seafloor spreading in the Neo-Tethys Ocean and the rifting of the Lhasa Block from eastern Gondwana may have contributed to global carbon cycle disruptions from the Sevatian through the NRB interval.

Norian time interval is a crucial period in Earth’s evolutionary history, characterized by several organic carbon-isotope perturbations in the carbon cycle that are closely related to global environmental change and biotic turnover (Zaffani et al., 2017). Among them, the Norian “chaotic carbon episode” has been recently reported globally in North America, Italy, and Japan, from shallow to pelagic environments (Whiteside and Ward, 2011; Zaffani et al., 2017; Jin et al., 2022; Sato et al., 2023). However, the mechanisms and timing of these events are poorly understood, especially in the eastern Tethys. In this study, we have investigated the carbon isotope profiles and conodont assemblage changes from the middle to upper Norian bedded carbonate rock succession in the Sanhedong section, Southwest China, to provide new insights into the Norian carbon cycle perturbation and its impact on marine biodiversity. We thus collected several samples for conodont biostratigraphic investigations and organic and carbonate carbon isotope (δ13Corg, δ13Ccarb) and oxygen isotope data (δ18Ocarb) along the study section. We identified various conodont genera, including some typical Norian Arcyrogondolella, Norigondollela, Mockina, and Primatella, and established detailed conodont biostratigraphy that indicates a middle to upper Norian age for the Sanhedong section. Furthermore, we detected a significant negative carbon isotope excursion (NCIE) across the middle/upper Norian, which can be globally correlated with the NCIE events reported from North America, the central Panthalassa Ocean, and the Tethys Ocean. We have also observed changes in conodont diversity and abundance associated with the NCIE.Our study provides an accurate age and a high-resolution carbon isotope record for the Sanhedong section, revealing the global nature of the Norian carbon cycle perturbation and its impact on the biosphere in the eastern Tethys. Our preliminary results suggest that also the carbon isotope perturbation in Eastern Tethys may be associated to the middle-late Norian carbon-cycle perturbations, which were triggered by the emplacement of the Angayucham Large Igneous Province (Alaska). Further studies are needed to constrain the timing and magnitude of Norian volcanic activity.Keywords: Norian, conodont biostratigraphy, carbon isotope perturbation, Eastern Tethys Reference:Jin, X., Du, Y., Bertinelli, A., Shi, Z., Preto, N., Zou, H., Ogg, J.G., Han, L., Wu, Q. and Rigo, M., 2022. Carbon-isotope excursions in the Norian stage (Upper Triassic) of the Baoshan terrane, western Yunnan, China. Journal of Asian Earth Sciences, 230, p.105215.Sato, H., Nozaki, T., Onoue, T., Ishikawa, A., Soda, K., Yasukawa, K., Kimura, J.I., Chang, Q., Kato, Y. and Rigo, M., 2023. Rhenium-osmium isotope evidence for the onset of volcanism in the central Panthalassa Ocean during the Norian “chaotic carbon episode”. Global and Planetary Change, 229, p.104239.Whiteside, J.H. and Ward, P.D., 2011. Ammonoid diversity and disparity track episodes of chaotic carbon cycling during the early Mesozoic. Geology, 39(2), pp.99-102.Zaffani, M., Agnini, C., Concheri, G., Godfrey, L., Katz, M., Maron, M. and Rigo, M., 2017. The Norian “chaotic carbon interval”: new clues from the δ13Corg record of the Lagonegro Basin (southern Italy). Geosphere, 13(4), pp.1133-1148.

The Triassic was a critical period for a significant increase in the generic diversity of radiolarians after the disappearance of >80% of radiolarian genera during the Permian-Triassic mass extinction. In particular, the Upper Triassic radiolarian fauna is rich and has been documented in several world regions, such as North America, Western Europe, the Mediterranean area, Japan, the Philippines, Timor, and Far East Russia. In this study, a well-preserved and high-diversity fauna from a continuous pelagic-hemipelagic section deposited in western Tethys (Sicily, Italy) provides one of the most detailed radiolarian records of the Carnian-Norian boundary interval, which can be correlated worldwide, from high to low-latitude, from both sides of the Pangea and both Hemispheres. The 99 species belonging to 50 genera from this time interval have been collected from the Pizzo Mondello section (Sicanian Basin, Western Sicily), the selected GSSP for the base of the Norian stage, and then compared to the radiolarian associations documented in other coeval regions. Based on the occurrences of characteristic radiolarian species, we defined and proposed a new radiolarian biozonation across the Carnian-Norian boundary, which consists of five new assemblages (PM assemblage 1–5) that are correlated and calibrated to the already well-defined biozonation of bivalves, ammonoids, and conodonts.

The latest Triassic was characterised by protracted biotic extinctions concluding in the End-Triassic Extinction (~ 200 Ma) and a global carbon cycle perturbation. The onset of declining diversity is closely related to reducing conditions that spread globally from upper Sevatian (uppermost Norian) to across the Norian-Rhaetian boundary, likely triggered by unusually high volcanic activity. We correlate significant organic carbon cycle perturbations to an increase of CO2 in the ocean–atmosphere system, likely outgassed by the Angayucham igneous province, the onset of which is indicated by the initiation of a rapid decline in 87Sr/86Sr and 188Os/187Os seawater values. A possible causal mechanism involves elevated CO2 levels causing global warming and accelerating chemical weathering, which increased nutrient discharge to the oceans and greatly increased biological productivity. Higher export production and oxidation of organic matter led to a global O2 decrease in marine water across the Norian/Rhaetian boundary (NRB). Biotic consequences of dysoxia/anoxia include worldwide extinctions in some fossil groups, such as bivalves, ammonoids, conodonts, radiolarians.

The Norian “chaotic carbon episode” stands out as a compelling carbon cycle perturbation event within the Late Triassic period. This episode has been documented in marine stratigraphic sections across North America, Italy, Japan, and China. However, limited Norian chronostratigraphy available in the eastern Tethys inhibited the identification of this event in this broad area, and thus the possible global response to this carbon cycle perturbation. To address this issue, we analyzed the conodonts and carbon-isotope of the Norian Sanhedong (SHD) section in the Simao terrane, Southwest China. The identification of the Alaunian Epigondolella spiculata Zone has well documented the base of the Alaunian stage. Moreover, a conodont faunal turnover can be recognized at the base of the Alaunian, with the evolution of Mockina from Ancyrogondolella and Epigondolella, and it is characterized by a gradual decrease in specimen size. The E. spiculata conodont Zone from the SHD section correlates well with the homonymous conodont Zones documented in both the Tethys and the Panthalassa Oceans. Two carbon-isotope negative excursions (CIE1 and CIE2) have also been recorded in the Lacian to Alaunian of the SHD section that can be compared with coeval global sections.

The conodonts from the Carnian have been well studied in western Tethys, eastern Tethys, middle and eastern Panthalassa. However, in the Tethys Himalaya, namely the northern periphery of Gondwana, the Carnian conodont data is limited. Our conodont biostratigraphic investigation was conducted at Jiesheng (JS) section of the Tethys Himalaya area, south Tibet. The majority of the conodont species found in the JS section, such as Paragondolella(=Quadralella) polygnathiformis, P. praelindae, P. noah, P. oertlii, Carnepigondolella cf. zoae, C. tuvalica, C. pseudoechinata, Metapolygnathus cf. linguiformis, M. praecommunisti, Primatella triangulare, Pr. subquadrata, and Ancyrogondolella quadrata, represent the first record in this region. According to the conodont biostratigraphy, large part of the measured JS section can be assigned to middle Tuvalian to uppermost Tuvalian (upper Carnian); the topmost strata can be assigned to lower Lacian (lower Norian). In addition, the puzzle of Carnian conodont taxonomy should be brought to the forefront of Upper Triassic conodont research. The over-simplified Tethyan and the over-complicated North American taxonomic concepts hamper the classifications of Carnian conodonts and chances of global correlation. A taxonomic revision including previously overlooked morphological features is necessary, in which microreticulation may have the potential to serve as one of the distinguishing characteristics between taxa of the Carnian-Norian boundary interval.

准噶尔盆地是我国重要的含油气盆地,也是研究中亚造山带的天然实验室,盆地内物源体系一直是前人研究的热点.近年来随着勘探程度的加深,在准噶尔盆地永进地区西山窑组地层中单独划分出了齐古组地层,因此永进地区齐古组地层的物源研究还比较薄弱.为解决该问题,本次研究以永进地区齐古组钻井岩心为研究对象,同时选取研究观点相对统一的天山北缘中段露头剖面进行对比研究,以期使结论更加充分.通过岩石学(样品40件)、重矿物(样品22件)及主微量元素分析方法(样品7件)对其进行物源分析.经主微量元素与重矿物组成特征方法分析认为永进地区的源区母岩岩性为中—酸性岩,天山北缘中段为中—酸性岩浆岩+变质岩组合;岩石碎屑组分显示永进地区的源区构造背景为火山岛弧,而天山北缘中段为火山岛弧+再旋回造山带背景;古流向与ZTR指数指示永进地区物源方向来自北西向,天山北缘中段来自南东方向,微量元素均一化蛛网图、稀土元素标准化分配模式图和Q型聚类分析结果也显示物源区不同.综合以上分析认为永进地区物源区为扎伊尔山,且车—莫古隆起可能提供了 一定的物源;天山北缘中段物源区为北天山和中天山.

Microfossils are important components of sedimentary rocks used for palaeontological, biostratigraphic, palaeoenvironmental and palaeoclimatic investigations. They are usually extracted from rocks using an acid solution, which might vary depending on the embedding rock lithology. Here we propose a new method using common NaOH (sodium hydroxide; soda) to digest cherts (micro‐ and cryptocrystalline quartz) instead of the standard technique based on HF (hydrofluoric acid). This new method allows the collection of undamaged specimens of different kinds of microfossils, such as conodonts, radiolarians, teeth and dermal scales, the minerology of which is still preserved (e.g. biogenic apatite in conodonts). The use of soda is thus recommended, as it is less dangerous, less expensive, and it better preserves the extracted microfossils both in shape and mineralogy.

鄂尔多斯盆地位于华北克拉通的西部,处于中国西部活动带和东部稳定区域之间的结合部位,其物源体系研究是探讨该地区盆—山演化的关键,但是前人对于鄂尔多斯盆地下侏罗统的物源体系研究还较薄弱.以鄂尔多斯盆地东北部榆林安崖剖面富县组砂岩为研究对象,对富县组砂岩进行了岩石学及地球化学分析,利用地球化学和岩石学特征对富县组的物质来源、源区构造背景进行判别,并结合周缘潜在源区的稀土元素数据对物源体系进行了探讨.结果表明,研究区富县组物源来自同一物源体系,物源物质主要形成于再旋回造山带构造背景,母岩岩性为中酸性岩浆岩及变质岩;稀土元素分配整体表现为"缓右倾斜"的样式,呈平坦型分布,与阴山造山带源岩的稀土元素分配模式相似,指示鄂尔多斯盆地东北部富县组的主物源区为阴山造山带.二叠纪—三叠纪,古亚洲洋板块俯冲形成的洋壳根部发生断裂拆离导致大量的花岗岩侵入阴山造山带,至早—中侏罗世富县组时期被风化剥蚀,随后被搬运至鄂尔多斯盆地东北部沉积.

The Carnian Pluvial Episode (CPE, ∼233 Ma) was characterized by multiple negative carbon-isotope excursions, turnovers in marine and terrestrial biota, and a Tethys-wide humid climate accompanied by abundant terrigenous sediment and freshwater input into sedimentary basins. A general temporal coincidence between the CPE and the emplacement of the Wrangellia Large Igneous Province (Wrangellia LIP) has been well documented, however, it remains unclear whether fluctuations in the intensity of the LIP's activity could be linked to the biotic and climate changes at the CPE. We here present mercury (Hg) concentration and isotope ratio records from a pelagic deep-water succession (Section N-O, Inuyama, Japan) that encompasses the CPE interval. Data reveal concurrent peaks in the Hg concentrations and ratios of Hg to TOC and enrichment factors ThEF, AlEF, ZnEF, and NiEF implying that excess Hg loading in the sediments occurred, likely due to volcanic activity, prior to the CPE siliciclastic input. Furthermore, Δ199Hg values show a negative shift across the boundary between the Julian 1 and Julian 2, followed by a positive shift up to near-zero values at the Julian/Tuvalian transition. The near-zero Δ199Hg values at the Julian/Tuvalian boundary are associated with an increase in Hg and Cu loading, suggesting a peak of volcanogenic Hg and Cu input that may indicate a climax in the Wrangellia LIP activity. Most notably, the Julian/Tuvalian transition is where evidence of the most pronounced changes in carbonate platform evolution, biological turnover and climate change associated with the event has been highlighted. Our results therefore suggest that variations in the intensity of LIP volcanism may have played a major role in driving biotic and climate changes during the CPE. Our results provide a model for other mass extinction events associated with LIPs (e.g., the end-Permian) where low-intensity background volcanism was punctuated by high-intensity pulses, these latter being the real killers.

It is generally accepted that conodonts went extinct at the end of the Triassic, but younger conodont fossils have been reported, and it is becoming clear that conodont extinction occurred asynchronously across different regions. Although some reports of post-Triassic conodonts have been disproven, Lower Jurassic conodonts have been found in the Buda area of Hungary and the Inuyama area of Japan. Here, we report the discovery of more conodonts Misikella posthernsteini above the first occurrence of the typical Jurassic radiolarian Pantanellium tanuense, which is not know from the Triassic, in the Kastuyama section, Inuyama area, reaffirming the authenticity of the Lower Jurassic conodonts. The conodonts survived into the Jurassic in the Inuyama area might be due to their remote locations relative to the Central Atlantic Magmatic Province, which buffered them from hypoxia and ocean acidification. Although conodont survived into the Lower Jurassic, they failed to recover and quickly went extinct in post-extinction ecosystems. The “dead clades walking” (DCWs) of conodont may have been due to protracted ocean acidification in the earliest Jurassic. Food scarcity and competition with other organisms may have led to the eventual extinction of conodonts.

The biostratigraphy and carbon stable isotopes of the Norian Stage (Upper Triassic) are well studied in the western Tethys, but little information is available from the eastern Tethys. Therefore, we studied the Hongyan-B (HYB) section in the Baoshan terrane, western Yunnan Province, SW China, which was located in the eastern Tethys during the Late Triassic. The HYB section was investigated for conodonts, radiolarians, total organic carbon, carbonate carbon and oxygen stable isotopes (delta C-13(carb) and delta O-18(carb)), and carbon isotopes of organic matter (delta C-13(org)). The Mockina slovakensis and Mockina bidentata conodont biozones proposed in the HYB section are associated with two radiolarian zones of the Sevatian substage, the Praemesosaturnalis multidentatus and Praemesosaturnalis pseudokahleri zones (TR8A and TR8B Sugiyama zones). This biostratigraphy places the Alaunian-Sevatian substage boundary (middle-upper Norian) at meter 23 of the HYB section. Unfortunately, the delta C-13(carb) and delta O-18(carb) values suggest that they might have been influenced by diagenesis. However, the delta C-13(org) record preserves multiple carbon-isotope excursions across the Alaunian-Sevatian boundary that can be correlated with other coeval global sections. The carbon-isotope excursions registered at this middle-upper Norian boundary are perhaps related to the major outgassing of light carbon during the emplacement of Angayucham flood basalts.

In this paper, sea-level fluctuations during the Carnian Pluvial Episode (CPE) are investigated. A revision of published data from multiple successions worldwide indicates a sea-level drop that occurred in different geodynamic settings after the onset of the first of multiple carbon-isotope perturbations that characterize the CPE. New stable isotope data, zircon U-Pb geochronology, carbonate petrology, conodont and foraminifer biostratigraphy from the Carnian of the Sichuan Basin and comparison to the well-dated coeval successions of the Dolomites allow pinpointing with unprecedented precision this sea-level fall and determine that it occurred after the onset of the first, but prior to the third negative delta C-13 shift of the CPE. These lines of evidence indicate that such sea-level oscillation was eustatic. Facies analysis and sequence stratigraphy of units deposited during the ensuing sea-level rise in the Sichuan and Dolomites, further show that a Tethys-wide crisis of microbial carbonate production and drowning of carbonate platforms were followed by a recovery of marine calcification, widely testified by the deposition of oolitic bodies. Whereas a Tethys-wide recovery of microbial carbonate production is documented at the end of the Carnian, this increase in chemical calcification occurred earlier, at the beginning of the Tuvalian, and suggest that global transformations in carbonate systems coincident with the CPE were complex and share commonalities with other times in the geological record when a similar evolution was linked to ocean acidification. (C) 2022 Elsevier B.V. All rights reserved.

滇西兰坪–思茅地块晚三叠世诺利期（Norian）发育一套海相碳酸盐岩沉积（三合洞组）。对巍山三合洞剖面进行了实测与采样,分离了三合洞组碳酸盐岩中的牙形石,经鉴定其种属为Epigondolellavialovi,Epigondolella uniformis和Epigondolella aff. triangularis,时代为早诺利期（Lacian亚期）。通过野外剖面及室内显微薄片观察,采用微相分析的方法对剖面三合洞组碳酸盐岩的微相类型和沉积环境进行研究,将巍山三合洞剖面三合洞组沉积归纳为9种微相,并根据微相特征结合野外宏观特征,将三合洞剖面划分为3种沉积相类型,即局限台地相、开阔台地相和台地边缘礁相。在剖面不同层位的碳酸盐岩中发现的热液矿物石榴子石及发黑的牙形石化石（CAI指数约为5）,表明该区曾遭受热液作用的影响,可能与三合洞组沉积后大陆边缘裂谷下陷或板块拼合引起的热卤水上涌有关。