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Global climate change and carbon cycle perturbations during the Mesozoic have been shown to have a significant effect on the biosphere, including vegetation. During the early Toarcian Anoxic Event or Jenkyns Event (Early Jurassic), increased oceanic and continental carbon burial, global warming, increased storminess, enhanced hydrological cycle and runoff are all linked to the large-scale release of 12C-enriched carbon into the ocean- atmosphere system. Compared to the marine realm, the terrestrial record of the Jenkyns Event is relatively less known. We have investigated the vegetation response to this event conducting palynological analysis extended with Hg and Cu concentrations from the lacustrine Anya section in the Ordos Basin, North China. Palynostratigraphy constrained the studied Anya section with two negative carbon isotope excursions (CIE) to the late Pliensbachian-early Toarcian interval. The palynological assemblages show a significant turnover between the Pliensbachian, pre-CIE and the early Toarcian, characterized by the pronounced increase in Classopollis abundance. The rise of Cheirolepidiaceae pollen is paralleled by the decrease in fern spores and seed-fern-related pollen grains. The loss of these understory and low-mid canopy vegetation elements, exacerbated by increased wildfire activities from PAH and fossil charcoal data, contributed to enhanced runoff from the inundated land to the lacustrine basin. During the CIE interval, the increase of unbalanced and conjoined Classopollis tetrads and the increase of spore tetrads together with dwarfism in ferns spores indicate severe environmental stress. Mutagenesis in spores and pollen, such as the formation of unbalanced spore-pollen tetrads, have been related to heat stress, UV-B radiation, heavy metal toxicity or in the case of Classopollis grains, polyploidy. The latter, in many cases, represents evolutionary advantage for the parent plant which might explain the proliferation of Cheirolepidiaceae conifer pollen during the early Toarcian.

The Toarcian oceanic anoxic event (T-OAE, ~183 Ma) was marked by a rapid global warming, pronounced negative carbon-isotope excursion, ocean deoxygenation, volcanic activity and turnover of marine and terrestrial biota. This warming world affected global weather patterns leading to increased seasonality and storminess, with erratic precipitation patterns, climatic extremities, enhanced hydrological cycle and runoff. The biotic feedbacks during these Mesozoic hyperthermals are important archives of how the Earth’s ecosystems respond to severe environmental crisis. We have investigated the link between geochemical climate proxies Sr/Cu, Rb/Sr and the vegetation composition from the palynological dataset (fossil spore and pollen) in the lacustrine Anya section, from the Ordos Basin, North China. The Ordos Basin was situated at low-middle latitudes during the Mesozoic and spread across the warm-temperate to subtropical climate belts. The rise in the thermophilic drought-adapted Cheirolepidiaceae conifer and cycad pollen during the T-OAE negative carbon excursion is paralleled by the decrease in more water-dependent ferns and seed ferns simultaneously with a shift to a more seasonal semihumid–semiarid climate indicated by the Sr/Cu, Rb/Sr ratios. The vegetation experienced only temporal biodiversity losses but the decrease of mainly mid-canopy and understory elements indicates loss on functionality in the terrestrial ecosystem. This shift to a more open landscape reduced the slope stabilization function of the vegetation that increased the run-off rate from the hinterland during high rain periods. In addition, the proliferation of Cheirolepidiaceae conifers with low stomatal density and lower transpiration rate may have enhanced the weathering and transport of sediments and nutrients into the lake. The T-OAE scenario resonates well with climate model projections that suggests an increase in the number of extreme precipitation events, and longer and more frequent droughts for the future of forest ecosystems. The results even suggest that changes in vegetation composition may increase the severity and consequences of the ongoing climate change.

Records suggest that the Permo–Triassic mass extinction (PTME) involved one of the most severe terrestrial ecosystem collapses of the Phanerozoic. However, it has proved difficult to constrain the extent of the primary productivity loss on land, hindering our understanding of the effects on global biogeochemistry. We build a new biogeochemical model that couples the global Hg and C cycles to evaluate the distinct terrestrial contribution to atmosphere–ocean biogeochemistry separated from coeval volcanic fluxes. We show that the large short-lived Hg spike, and nadirs in δ202Hg and δ13C values at the marine PTME are best explained by a sudden, massive pulse of terrestrial biomass oxidation, while volcanism remains an adequate explanation for the longer-term geochemical changes. Our modelling shows that a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant biogeochemical changes, and cascaded organic matter, nutrients, Hg and other organically-bound species into the marine system.

Large Igneous Province eruptions coincide with many major Phanerozoic mass extinctions, suggesting a cause-effect relationship where volcanic degassing triggers global climatic changes. In order to fully understand this relationship, it is necessary to constrain the quantity and type of degassed magmatic volatiles, and to determine the depth of their source and the timing of eruption. Here we present direct evidence of abundant CO2 in basaltic rocks from the end-Triassic Central Atlantic Magmatic Province (CAMP), through investigation of gas exsolution bubbles preserved by melt inclusions. Our results indicate abundance of CO2 and a mantle and/or lower-middle crustal origin for at least part of the degassed carbon. The presence of deep carbon is a key control on the emplacement mode of CAMP magmas, favouring rapid eruption pulses (a few centuries each). Our estimates suggest that the amount of CO2 that each CAMP magmatic pulse injected into the end-Triassic atmosphere is comparable to the amount of anthropogenic emissions projected for the 21st century. Such large volumes of volcanic CO2 likely contributed to end-Triassic global warming and ocean acidification.

The Permo-Triassic marine mass extinction has been blamed on a range of culprits including anoxia, acidification, high temperature and increased sedimentation and nutrient influx, the last two being a direct consequence of terrestrial biomass die-off and climatic changes. In marine settings, the role of these kill mechanisms is likely to be depth-dependent with siltation and high temperatures potentially the most consequential in shallowest waters. These ideas have been investigated in a study of the Permo-Triassic boundary beds in western Guizhou and eastern Yunnan (WGEY) which record the transition from littoral coal swamps to an inner shelf/platform fringed by a coastal mudbelt. Anoxic conditions were not developed in such shallow waters but weak dysoxia is seen in the extinction interval, recorded by the presence of pyrite framboids and glauconite, and may have been a factor in the crisis even in coastal waters. High temperatures may also be an extinction factor as evidenced by the brief bloom of microgastropods in the immediate aftermath. The Late Permian peat-forming swamps were subject to considerable in situ erosion that reworked authigenic minerals (chamosite and kaolinite). This material, together with considerable amounts of charcoal, was concentrated in distinctive green sandstone beds. However, the notion that the marine extinction was caused by increased sediment supply, a death-by-siltation mechanism following the collapse of terrestrial biomass, is not supported by the field evidence because a surge in clastic influx onto the shelf is not observed during the extinction interval when a range of carbonates, including microbialites, developed. The sediment was likely trapped in alluvial plains during base-level rise and/or a short period of more arid conditions occurred, reducing the clastic supply in the coastal–shallow marine environments. Ocean acidification is another potent kill mechanism but the occurrence of the extinction within a transgressive, carbonate-dominated interval in the shallow-water locations of WGEY does not support this cause.

The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.

An integrated sporomorph and ammonoid biostratigraphy has been carried out in three upper Anisian (Middle Triassic) stratigraphic sections in the Southern Alps (Italy). Two main sporomorph assemblages have been defined and calibrated with ammonoids. The TrSM-A assemblage is marked by the co-occurrence of Stellapollenites thiergartii, Dyupetalum vicentinense, Cristianisporites triangulatus and Staropollenites antonescui. The TrSM-B assemblage is marked by the first occurrence of Cannanoropollis scheuringii. The boundary between the TrSM-A and TrSM-B assemblages falls in the upper part of the reitzi ammonoid subzone (Hungarites zone; Illyrian). The TrSM-A and TrSM-B assemblages have been compared and correlated with other existing sporomorph biozonations for the northwestern Tethys, the Germanic Basin and the Barents Sea. The first occurrence of the genus Ovalipollis is recorded within the assemblage TrSM-A, in the lower-middle reitzi ammonoid subzone. Quantitative palynological data coupled with previously published studies show a shift from hygrophytic to xerophytic elements in the trinodosus-lower reitzi ammonoid subzones. This change in precipitation range can be recognised in other sections in the northwestern Tethys but seems to have preceded a similar shift recorded in the Boreal realm.

Major climate changes and mass extinctions are associated with carbon isotope anomalies in the atmosphere-ocean system and have been shown to coincide with the onset of large igneous provinces (LIPs) and, by association, their emissions of greenhouse gases and aerosols. However, climatic and biological consequences of some known LIP eruptions have not yet been explored. During the Carnian (Late Triassic) large volumes of flood basalts were erupted to form the so-called Wrangellia LIP (western North America). This huge volcanic province is similar in age to a major climatic and biotic change, the Carnian Pluvial Event (CPE), but no evidence of a causal relationship exists other than timing. Here we report a sharp negative delta C-13 excursion at the onset of the CPE recorded in organic matter. An abrupt carbon isotope excursion of similar to-4% occurs in terrestrial and marine fossil molecules, whereas total organic carbon records an similar to-2% shift. We propose that this carbon isotope negative shift was caused by an injection of light carbon into the atmosphere-ocean system linked to the eruption of Wrangellia flood basalts. This carbon-cycle perturbation occurs slightly before two major evolutionary innovations: the origin of dinosaurs and calcareous nannoplankton.

The end-Triassic mass extinction (ETME) was associated with intensified deep-water anoxia in epicontinental seas and mid-depth waters, yet the absolute oxygenation state in the shallow ocean is uncharacterized. Here we report carbonate-associated iodine data from the peritidal Mount Sparagio section (Southern Italy) that documents the ETME (~ 200 Ma) in the western Tethys. We find a sharp drop in carbonate I/(Ca + Mg) ratios across the extinction horizon and persisting into the Early Jurassic. This records local dissolved oxygen and iodate decline in the near-surface ocean of low-latitude Tethys due to the development of depleted oxygen concentrations. Consequently, during the ETME even shallow-water animals, such as the megalodonts seen at Mount Sparagio, were likely the victims of oxygen-poor conditions. The shallow ocean deoxygenation coincides with the synchronous spread of deeper anoxic waters and widespread anoxic deposition on continental shelves and slopes. An upwards expansion of the mid-water oxygen minimum zone in the latest Triassic shoaled the oxycline and triggered a major marine crisis.

High-resolution carbonate carbon-isotope stratigraphy of Lower Jurassic marine shallow-water limestones are compared with the distribution of the Lithiotis Fauna on the Trento Platform (Southern Alps, Italy). The Lithiotis Fauna is the first example of globally distributed mound-building bivalves in the geological record and experienced global diffusion in the Early Jurassic. A set of carbonate carbon-isotope excursions of 2-3 parts per thousand, illustrating three distinct negative shifts followed by positive rebounds, are recorded in the isotope stratigraphy and can be correlated with the global negative delta C-13 shift of the Sinemurian-Pliensbachian boundary Event (S-P Event) and to the subsequent phase of C-isotope perturbation that characterized the lower Pliensbachian. In the studied stratigraphic sections, the S-P Event likely triggered eutrophic conditions illustrated by the presence of organic-rich facies and by fossil associations characteristic of poorly oxygenated waters. After the eutrophic phase, the amelioration of environmental conditions was marked by a positive similar to 3 parts per thousand rebound of the delta C-13(carb) values, and by the occurrence of marine stenotypic faunas. On the Trento Platform, the stabilization of the delta C-13(carb) values coincided with the appearance of the Lithiotis Fauna that subsequently became widely distributed in the entire range of platform environments and thrived in the late Pliensbachian when metric-scale bivalve mounds were generated. During the same time, the maximum proliferation of the Lithiotis Fauna is recorded both in the Tethyan and Panthalassa regions. Hence, the reported relationships between the delta C-13(carb) data and the distribution and ecological characteristics of the genera contained in the Lithiotis Fauna suggest that the S-P Event and its aftermath, possibly coupled with the undergoing coeval continent reorganization that led to the opening of the Hispanic Corridor, could have set the stage for the rapid diffusion of these unusual bivalves across many parts of the globe.