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The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Ma) was marked by a pronounced negative carbon- isotope excursion, rapid global warming, ocean deoxygenation, and turnover of marine and terrestrial biota. The T-OAE has been linked to carbon (C) release from volcanism, but the mechanisms controlling the cycling of C, metals, and nutrients during the event are still not fully understood. Here we show that lacustrine strata (Anya section) through the T-OAE in the Ordos Basin (China) record large increases in Hg/TOC (up to 453 ppb/wt.% relative to a background of 23 ppb/wt.%), which are coincident with the sudden demise of spore producing plants and seed ferns and the acme of Classopollis pollen of the thermophilic Cheirolepidiaceae conifers. These changes occurred during the peak of the negative carbon-isotope excursion that marks the T-OAE in the Anya section. Hg-isotopes are a useful proxy for recognizing changes in Hg sources and fluxes (notably from atmospheric deposition and terrestrial biomass) in sediments and sedimentary rocks. The negative Hg and Hg throughout the Anya section are consistent with a constant terrestrial Hg source in the studied interval. Hence, the recorded Hg enrichment suggests that terrestrial Hg loading increased during the T-OAE. Coupled with evidence for a large increase in hydrological cycling, weathering and runoff, our data indicate that the T-OAE floral crisis was associated with a massive release of terrestrial Hg to oceanic and terrestrial ecosystems. This work provides new insights into the links between toxic metal cycling and mass extinction during times of large- scale volcanism.

In the early Late Triassic, the Carnian Pluvial Episode (CPE) is a phase with increased siliciclastic influx into the marine-carbonate dominated depositional setting of the Western Tethys assumingly caused by a shift to more humid climatic conditions and increased continental runoff. Here, vegetation changes inferred from the palynological assemblages and weathering proxies (αAli) have been studied from the Transdanubian Range (TR), western Hungary to reveal climate variations and detect episodes with hygrophytic vegetation and enhanced continental hydrolysis. Palynostratigraphy has been applied to correlate the clastic pulses known from elsewhere in the Western Tethys. The quantitative palynological analysis indicates a shift towards hygrophytic elements in the Julian 2, and return to xerophytic associations in the Tuvalian. The increase in the hygrophytic vegetation elements is coincident with elevated kaolinite and partially with the increase of α-values indicating strong terrestrial runoff, enhanced continental hydrolysis and more humid climate in the lower part of the Veszprem Formation in the early Julian 2. The wetter conditions in the Julian 2 were periodically interrupted by shorter periods of drier climate manifested in the progradation of carbonate platforms and the deposition of carbonate series and breccias interbedded between the marl units. In the late Julian 2 the high amount of hygrophytes points to another humid episode, but the decrease of kaolinite in the clay mineral profile and the weathering indices might suggest stronger seasonality. Although, the multiple clastic pulses in the western Tethys were related primarily to more humid climate during the CPE, the comparison to clay mineralogy and weathering proxies suggest a more complicated scenario in the TR. The enhanced continental weathering related to a more humid climate is only suggested for the lower part of the Veszprem Formation in the early stages of the CPE in the Julian 2.

The biota of the brackish-water Lake Pannon in the Pannonian Basin is characterised by remarkable endemism due to the isolated evolution of the lake for 8 myr after the last Miocene marine connection ceased (∼11.6 Ma). A conspicuous feature of this endemism is the large, probably ecophenotypic variation in the morphology of brackish-water dinoflagellate cysts that challenges taxonomy and complicates biostratigraphical and ecological interpretations. We conclude that a widely debated Lake Pannon genus, Pontiadinium, includes several proximate dinoflagellate cyst species with prominent apical and antapical protuberances, and we show how the genus differs from the morphologically similar gonyaulacacean cyst genera Impagidinium, Leptodinium, Cribroperidinium and Komewuia. The generic description of Pontiadinium is emended together with the species descriptions of Pontiadinium inequicornutum, Pontiadinium obesum and Pontiadinium pecsvaradanesis. A new species is described as Pontiadinium szentaiae sp. nov. from Našice (northern Croatia) that is characterised by unique trabeculate sutural septa formed from a beaded tegillum supported by columellae or rod-like luxuriae. The dinoflagellate cyst assemblages of the long-lived brackish-water Lake Pannon clearly demonstrate that dinoflagellate cysts in low-salinity, isolated epicontinental seas display greater morphological plasticity than their normal-marine relatives. The development of an antapical horn appears to be a previously undocumented example of phenotypic morphological features that developed in response to subnormal salinities within at least two dinoflagellate cyst genera endemic to Lake Pannon and the Post-Paratethyan seas of the Ponto-Caspian realm. This ecophenotypic variation resulted in a higher level of morphological adaptation, leading to the evolutionary development of new dinoflagellate cyst species and genera.