Bypassing sediment gravity flows play an important role in turbidite systems because they produce sole structures unconnected with the depositional processes of the casting bed. However, their role in facilitating seafloor colonization is underappreciated. The Aberystwyth Grits–Borth Mudstone turbidite system (Silurian, Welsh Basin) contains a famous ichnoassemblage with common graphoglyptids. This is interpreted to record colonization following erosion of surficial fluidal muds by flows that exposed firmer substrates. The burrows are developed at this level and formed beneath a thin, post-depositional mud blanket. They frequently cross-cut fluted surfaces indicating that basal turbidite bedding surfaces can record at least two, or more, bypassing flow events. Thus, even on a basin floor with thick mudstone deposition, the number of flow events will be under-represented. This Silurian turbidite system also illustrates that substrate conditions, not oxygenation, controlled trace fossil occurrence. Other than the burrows on turbidite soles, the remainder of the succession consists of thinly bedded and laminated strata typical of anoxic deposition but diverse geochemical proxies (e.g. iron speciation, trace metals) indicate full seabed oxygenation. The absence of macrofaunal bioturbation is attributed to a soft fluidal substrate in which only small-scale (meiofaunal) bioturbation is seen.

The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the early Jurassic Hettangian Stage. Testing this interpretation is complicated by spatially heterogeneous patterns of local marine redox conditions within the western Tethys European Epicontinental Shelf. In this study, we assess the redox state within this region by focusing on two carbonate successions in Italy, a peritidal platform at Mount Sparagio, Sicily, and an offshore ramp deposit at Val Adrara in the Southern Alps. Based on previously published I/Ca ratios, these locations record distinct local background redox conditions, with Val Adrara showing a notably lower pre-extinction oxygen saturation state than Mount Sparagio. Here, we measure S13C and S18O at Mount Sparagio and S44Ca and trace element ratios at both sites to identify the roles of mineralogical and diagenetic effects on the preservation of primary redox signals. A numerical framework of multiple elemental (Sr, Mg, Mn, I) and isotopic (S13C, S18O, S44Ca, S238U, and S34SCAS) ratios was constructed to recognize modes of carbonate diagenesis and source-mixing in the data. While diagenesis is impossible to completely rule out, our state-of-the-art approach provides robust evidence against common forms of diagenetic alteration as the main drivers of the overall paleoredox proxy trends. Where the redox signals are largely preserved, we interpret differences in pre-extinction I/Ca between the two sites to reflect distinct local oxygenation states. Drawing from published Community Earth System Model simulations, we propose that ocean circulation and hydrological regime could have been important drivers of spatial heterogeneity in paleo-redox conditions across the European Epicontinental Shelf.

The Permian-Triassic Mass Extinction (PTME), the most severe crisis of the Phanerozoic, has been attributed to intense global warming triggered by Siberian Traps volcanism. However, it remains unclear why super-greenhouse conditions persisted for around five million years after the volcanic episode, with one possibility being that the slow recovery of plants limited carbon sequestration. Here we use fossil occurrences and lithological indicators of climate to reconstruct spatio-temporal maps of plant productivity changes through the PTME and employ climate-biogeochemical modelling to investigate the Early Triassic super-greenhouse. Our reconstructions show that terrestrial vegetation loss during the PTME, especially in tropical regions, resulted in an Earth system with low levels of organic carbon sequestration and restricted chemical weathering, resulting in prolonged high CO2 levels. These results support the idea that thresholds exist in the climate-carbon system whereby warming can be amplified by vegetation collapse.

The ~ 66 Ma Cretaceous/Paleogene (K/Pg) boundary coincides with a severe mass extinction widely attributed to the Chicxulub impact and consequent abrupt climatic changes. However, it is unclear how long the subsequent climatic disruptions affected terrestrial and marine environments and what caused them. Here, we present magnesium isotope (δ²⁶Mg) and Chemical Index of Alteration data from an expanded section on Seymour Island, Antarctica, where a new cyclostratigraphic age model provides millennial-scale resolution. Pre-boundary weathering indices, including δ²⁶Mg values, record a stable, mild weathering regime. Post-boundary weathering saw a transition to a substantially variable regime with intervals of intense weathering revealed. This environmental instability persisted for at least 43.89 kyr after impact, and may reflect the climatic influence of Deccan volcanism. Thus, whilst the Chicxulub impact can be directly implicated in mass extinction, the recovery interval was substantially affected by Deccan volcanism.

ABSTRACT Factors that control the accumulation of organic‐rich shales are keenly debated and include basin redox variations, sediment provenance and diverse depositional processes. The relative importance of hemipelagic settling versus sediment gravity flows has been especially contentious in recent years. This study examines the Bowland Shale, a thick succession of organic‐rich mudrock with subsidiary facies, from the late Mississippian Bowland Basin of northern England that records a broad range of depositional processes. Interbedded amongst the mudrocks are several elongate, calciturbidite fans ca 10 km in length, sourced from a small carbonate platform to the south‐east of the basin, whilst a turbidite body of siliciclastic sand entered the basin from the east. An intrabasinal high in the north‐west of the basin deflected the progradation of the turbidite sandstones and was likely also responsible for the reflection of the carbonate‐carrying sediment gravity flows generating combined flow structures in the calciturbidite fans. Abundant, fine calcareous detritus was also sourced from the south‐east, forming an apron of calcareous mudstone delivered by low‐strength debris flows. Interbedded amongst these diverse facies types, the Bowland Shale primarily consists of hemipelagic, organic‐rich shale with a fabric consisting of compacted clay lenses (0.05–0.4 mm in width), hemipelagic components (including larval shells of bivalves, goniatites and syngenetic framboids) and organic filaments (marine snow). The lenses are interpreted to be faecal pellets formed above the redoxcline before settling to the seabed. An alternative idea, that has gained much traction in mudrock studies, is that the clay lenses are transported intraclasts and that black shales are substantially the product of deposition from traction currents sourced from adjacent basin margins. This idea is problematic because it fails to address why basinal shales have a euxinic geochemical signature rather than recording the well‐oxygenated conditions of the purported source area.

The Permian-Triassic (PTME, ~251.9 Ma) and Triassic-Jurassic (TJME, ~201.3 Ma) mass extinctions, both triggered by large igneous province (LIP) activity, represent two of the most significant extinction events in Earth’s history. Despite this similarity, there were contrasting impacts on land plants. Here, we compile global macrofossil records of Triassic-Jurassic flora and integrate them with lithological climate proxies, the HadCM3L climate model, and vegetation model FLORA to reconstruct vegetation dynamics across the TJME. Our findings suggest that, unlike the significant low latitude plant extinction during the PTME, the TJME coincides with floral compositional turnover and enhanced productivity, particularly in mid- to high- latitudes. High-resolution chemical weathering index, mercury, and plant biomarker records further suggest that global vegetation productivity and biotic weathering was enhanced after the TJME, stabilizing Earth’s temperature and facilitating rapid post-extinction cooling once LIP emissions ceased. This contrasts with the PTME when widespread deforestation trapped the Earth in a prolonged super-greenhouse climate. This study underscores the critical role of vegetation in modulating long-term climate and highlights plant thermal response and adaption as a key control on Earth's sensitivity to warming.

Flow-induced interfacial deformation structures (FIDS) are both diverse and common in turbidite successions where they form in soft, cohesive substrates beneath sediment gravity flows, but their significance has only recently been recognized. Their range of forms encompasses most of the morphological types attributed to microbially induced sedimentary structures (MISS) and the two have probably been widely conflated. Variants of FIDS include longitudinal ridges and furrows, polygonal networks and mamillated forms that are identical to structures assigned to MISS. A distinctive MISS form with flat-topped ridges and furrows called ‘Kinneyia’ is also found within the FIDS spectrum. Some FIDS may have also been assigned to Ediacaran taxa, notably the controversial Arumberia . Distinguishing FIDS from MISS in hand specimen is difficult, but their environmental context is important. Intertidal MISS occurrences are unlikely to be FIDS because the sediment gravity flows that produce deformation of the substrate are unlikely in such settings. However, MISS (mis)reported from turbidite settings are likely to be FIDS. One of the few distinctions between MISS and FIDS occurs when textured surfaces are developed on the upper surfaces of sandstone beds and they are overlain by fine-grained sediments; in this case a microbial origin is likely.

The Coqen area of the Lhasa Terrane, Xizang (Tibet, Southwest China) has provided key evidence for understanding Triassic history in the region. However, the stratigraphic subdivision of the Middle to Upper Triassic remains unclear. Here we present new results on the conodont biostratigraphy at Dibuco, a section in the Lhasa Terrane. Sixteen genera and forty-three species are identified, including one new species: Borinella dibucoensis sp. nov. of the Spathian (Olenekian) age. Eight conodont zones are established from the Late Olenekian to the Early Norian. These are, in ascending order, Triassospathodus homeri - Columbitella jubata Zone, Neogondolella constricta Zone, Paragondolella praeszaboi Zone, Budurovignathus mungoensis Zone, Quadralella polygnathiformis Zone, Quadralella praelindae Zone, Carnepigondolella oertlii - Carnepigondolella nodosa Zone and Ancyrogondolella aff. quadrata Zone. This is a relatively complete conodont succession for eastern part of Tethys region and it shows close relationship with western Tethys and eastern Tethys (South China). Based on the conodont biostratigraphy, the base of Zhulong Formation, previously lacking a precise age assignment, is shown to be of late Anisian age.

During the Permian-Triassic Mass Extinction (PTME) ~252Ma, diverse lowland forests were replaced by low diversity pioneer herbaceous lycopod communities that proceeded to dominate the Early and Middle Triassic landscape. The flourishing of Early-Middle Triassic herbaceous lycopods was coincident with data that suggests lethally warm surface temperatures (>40ºC) occurred across large regions of the planet. To explore how these plants were able to thrive during this interval of enhanced climatic stress, we collected data from over 400 fossil plant specimens from South China, supplemented by additional data from literature reviews from other regions and geological ages. Our studies on their morphology indicate that among all Phanerozoic lycopods the transitional Permian-Triassic genus Tomiostrobus (=Annalepis) has the closest morphological relationship with the recent lycopod Isoetes. Extant Isoetes are renowned for their flexibility with regard to the photosynthetic pathway they use and their capacity to absorb CO2 through their roots. To evaluate whether this photosynthetic flexibility was linked to their Early-Middle Triassic ecosystem dominance, we undertook carbon isotope and sedimentary facies analysis including plant taphonomy to test for the presence of the Crassulacean Acid Metabolism (CAM) photosynthetic pathway. Plants capable of CAM pathway growing in stressful environment typically have heavier isotopic signatures while show typical C3 plant signatures in hospitable environment. Our carbon isotope data shows that Permian Triassic Transition Tomiostrobus isotopic signature is on average ~2‰ less negative when compared to contemporary non lycophyte vegetation. Furthermore, the carbon isotope of the Middle Triassic lycopods ~1.07‰ heavier than the other plants, while Late Permian Lepidodendron exhibits a similar δ13C value with other contemporary plants. These findings suggest that CAM photosynthesis may have played a role in the dominance of the Triassic herbaceous lycopods. The dominance of CAM plants following the PTME has implications from an Earth Systems standpoint due to their diminished productivity and a lower capacity for biotic weathering, features that likely suppressed negative feedback loops important in driving climate stabilization during the ~5Ma PTME recovery phase.

The Smithian-Spathian transition during the Early Triassic was associated with significant environmental change, including global warming and oceanic anoxia. However, understanding ocean redox conditions in the pelagic Panthalassa during this period has been challenging due to a lack of well-dated sedimentary sections. Here, we provide new geochemical data for a Smithian-Spathian succession from an accretionary complex of central Japan (Inuyama, Aichi Prefecture), which was deposited in a low-latitude abyssal location. Conodont index fossils and carbon isotope stratigraphy reveal that the studied sections span the middle Smithian to lowermost Spathian (Momotaro-Jinja lower section), and the middle part of the Spathian (Momotaro-Jinja upper section). The Smithian-Spathian boundary is placed within a thick (similar to 40 cm), organic-rich, black claystone layer in the lower part of the section. We reconstruct water column redox conditions using pyrite framboid size ranges, Fe speciation and redox sensitive trace elements. During the middle to late Smithian, we find that the water column changed from oxic to ferruginous anoxic, with a transition to euxinic during the latest Smithian to earliest Spathian. During the middle Spathian, the water column fluctuated between oxic and euxinic conditions. We suggest that late Smithian seawater warming contributed to deoxygenation of Panthalassa whilst surface productivity and organic matter fluxes were low, leading to non-sulfidic ferruginous anoxia. Productivity then increased during the latest Smithian to earliest Spathian, thereby stimulating microbial sulphate reduction and inducing widespread ocean euxinia.

The end-Triassic mass extinction (ETME) marks a pivotal event in Earth's history, characterized by major environmental changes in both marine and terrestrial settings and significant perturbations in the carbon and nitrogen biogeochemical cycles alongside extinction events. Here we employ high-resolution organic carbon isotopes (delta C-13(org)), nitrogen isotopes from bulk samples (delta N-15(bulk)), total organic carbon (TOC) and nitrogen content (TN), complemented by carbon (delta C-13(kerogen)) and nitrogen isotopes (delta N-15(kerogen)) of kerogen extracts from the Kuhjoch section in Austria in order to investigate the interplay between marine redox state, nitrogen cycling, and the biotic crisis across the Triassic-Jurassic boundary. Our results reveal a significant positive shift (similar to 3 parts per thousand) in delta N-15(bulk) values, indicating a perturbed marine nitrogen cycle and expansion of the oxygen minimum zone prior to the ETME. The delta N-15 profiles suggest a transition from a nitrate-limited ocean dominated by nitrogen fixation to a post-extinction ocean with increased proportion of assimilation of NO3- undergoing non-quantitative denitrification. We also examine the spatial and temporal heterogeneity of the marine nitrogen cycle from different paleoenvironmental settings across the Triassic-Jurassic transition. Bioavailable nitrogen (NO3- and NH4+) limitation prevailed at some localities before and during the ETME. However, the development of N limitation was not synchronous across different locations: it emerged before the ETME in some European basins and intensified after the ETME on Panthalassan shelves. The early Hettangian saw an expansion of euxinic waters into the photic zone and shoaling of the chemocline. Enhanced continental weathering and deep-water upwelling increased nutrient supply, thereby alleviating N limitation. Our new observations point to an unstable and stratified marine environment during the Triassic-Jurassic transition, and suggest that nitrogen bioavailability and redox conditions may be key factors for the devastation of marine ecosystems.

The Raohe area of Heilongjiang Province, Northeast China belongs to the Nadanhada Terrane, which was in low latitudes of Panthalassa during the Triassic. The composition of the Late Triassic conodont fauna, derived from limestone lenses interpreted to formed on seamounts, provides important new information on the pelagic biota in this ocean. New conodont samples collected from sections at Minzhu, Minnan and Chigangbei sections belong to three Norian conodont zones. In ascending order, they are: Mockina postera Zone, Mockina bidentata Zone and Parvigondolella andrusovi Zone. The Norian conodont fauna in the Raohe area has distinct attributes: there are a lot of cosmopolitan species(e. g., Mockina postera, Mockina bidentata, Parvigondolella andrusovi) which enable good global correlation; endemic conodont species are also present(e. g., Mockina sakurae, Mockina shamiseni, Norigondolella nadanhadaensis) indicating that Panthalassa Ocean conodont populations also contained unique taxa; and some conodonts belong to taxa with much shorter ranges in surrounding epeiric seas(e.g., Carnepigondolella pseudoechinata, Neocavitella cavitata and Epigondolella vialovi). The presence of the latter “relicts ” indicates that the seamounts were persistently suitable habitats for many millions of years in the Late Triassic.

Numerous approaches have been developed for determining past redox conditions in marine settings (e.g., Fe speciation, redox sensitive trace metal (RSTM) systematics, pyrite morphologies, I/(Ca + Mg) ratios), enabling a broad range of redox conditions, from fully oxic to euxinic, to be potentially identified. However, many points along this spectrum remain difficult to constrain, including dysoxic and highly versus weakly euxinic conditions. This limits the broader scale inferences that can be drawn from paleoredox studies, including links between oxygen availability and biological evolution, and the potential for isotope systems (e.g., Mo) to record water column signals. Here, we develop a new approach using RSTM ratios (Re/Mo, Re/U, Re/V, Mo/U), in combination with modified RSTM enrichment factors (EF*) and Mo-EF*-U-EF* cross-plots, that potentially enables a robust, highly resolved reconstruction of ancient water column redox conditions to be achieved. We initially document the differential behaviour of RSTM EF* values and ratios in modern settings that range from fully oxygenated, through weakly (30-90 mu M O-2) and highly (<30 mu M O-2) dysoxic, to anoxic non-sulfidic and euxinic conditions. This redox behaviour is further resolved when the drawdown mechanisms for Mo are evaluated by Mo-EF*-U-EF* cross-plots. We subsequently ground-truth this approach by considering samples from the Carboniferous Bowland Basin, which have previously been studied for redox conditions via independent geochemical and mineralogical techniques, as well as the Jurassic Kimmeridge Clay Formation, where redox conditions have been defined based on paleoecological characteristics. A strong degree of consistency between RSTM behaviour in modern and ancient settings highlights that weakly to highly dysoxic conditions are characterized by increases in Re/Mo, Re/U and Re/V ratios, accompanied by RSTM EF* values that only become notably enriched under highly dysoxic conditions. Non-sulfidic water column anoxia is indicated by increased U-EF* values and low Re/ Mo ratios, while euxinia is readily identified by high Mo/U, low Re/U and very low Re/Mo ratios, alongside high Mo-EF* values. In addition, highly euxinic conditions may be distinguished from weak euxinia by particularly high Mo/U ratios and Mo-EF* values. This combined approach has the potential to provide a hitherto unprecedented level of insight into paleodepositional redox conditions, and consequently the chemical evolution of the biosphere.

The Hirnantian isotopic carbon excursion (HICE) records a dramatic perturbation to the global carbon cycle across the Late Ordovician Hirnantian glaciation. The HICE is characterized by variable duration and amplitude in global records, but its ultimate driver, and controls on the observed variability, are poorly understood. Here, we present a comprehensive compilation of geochemical data and paired carbon and calcium isotope records for two continuous Hirnantian sections at Wanhe and Shuanghe on the Yangtze Shelf (South China). Our results reveal a lateral gradient of up to 4 %o in organic carbon isotope (delta(13)Corg) values across the shelf, decreasing from nearshore to offshore. Carbonate carbon isotope (delta(13)Ccarb) data from the Wanhe and Shuanghe sections also show pronounced variability, which cannot be fully explained by primary mineralogical changes or early marine diagenesis. We therefore interpret the spatial delta(13)Corg patterns as reflecting, at least in part, shelf-scale heterogeneity in seawater dissolved inorganic carbon isotope (delta(CDIC)-C-13) values. Our compilation further suggests that substantial organic carbon burial likely triggered the HICE, while sea-level change subsequently drove the asynchronous, spatially heterogeneous changes in seawater delta(CDIC)-C-13 values. Additionally, enhanced carbonate weathering, linked to falling syn-glacial sea-level, amplified the spatial heterogeneity in regional marine delta(CDIC)-C-13 values. Moderate delta(13)Corg changes (<+2 %o) are observed in central shelf areas across the Hirnantian glaciation, suggesting that the global carbon cycle perturbations during this ice age were of more modest amplitude than often suggested.

The end-Triassic mass extinction (ETE), one of the “Big Five” in Earth history, was triggered by Central Atlantic Magmatic Province (CAMP) volcanism, releasing voluminous CO2, SO2 and halocarbons, which affected global marine and terrestrial ecosystems through atmospheric circulations. The terrestrial ecosystem collapse is commonly attributed to CO2-driven greenhouse effects changing climates that consequently impacted flora and fauna, but this fails to explain why atmospheric CO2 with long retention time just dominates a range of short-lived crises. Here, we investigate two terrestrial Triassic-Jurassic sections in each high- and low/middle- paleolatitude, finding anomalies of sulfur-associated molecular fossils, biomarker proxies of “high-temperature wildfires” and higher plants burial. These coincide with relatively short CAMP climax (lasting ~ 60,000 years). We propose a novel hypothesis that the high-intensity pulses of acid rains originated from CAMP climax dominated catastrophic defoliation, which oversupply dead moisture-free biomass as fuels in unusual rates, leaving coeval widespread abnormally high-temperature wildfires and spikes of sulfur compound-specific molecules in terrestrial sediments as fingerprints of acid rain deposition.

The Permian-Triassic mass extinction (PTME) interval is marked by major excursions in both inorganic and organic carbon (C) isotopes. Carbon cycle models predict that these trends were driven by large increases in productivity, yet organic C-rich rocks are not re-corded in most PTME shelf sedimentary successions. Anomalous C-rich facies have been reported from rare abyssal plains records now exposed in Japan and New Zealand, where black shales at the PTME are extraordinarily organic-rich units. We examined organic matter at the Waiheke, New Zealand, section, and results show that these deposits are dominated by lamalginites composed of unicellar solitary or colonial phytoplankton produced during algal blooms that falls as "marine snow." We modeled the impact of ash fall from eruptions in the Siberian Traps large igneous province and argue that they fertilized the Panthalassa Ocean with P and Fe, leading to a marine "snowstorm" and significant C drawdown marking this major biobloom during the PTME.

The establishment of the latest Permian geomagnetic polarity time scale has been inhibited by the inconsistent polarity patterns published by different teams for the section at Meishan, which hosts the Global Boundary Stratotype Section and Points (GSSPs) for the Permian-Triassic boundary (PTB) and base of the underlying Changhsingian Stage. We have analyzed the magnetostratigraphy of the Shangsi section, the former candidate for the PTB GSSP, and the alternate Chaotian section in South China to compile a reliable geomagnetic polarity timescale spanning the late Wuchiapingian and Changhsingian (Late Permian) to early Induan (Early Triassic). The late Wuchiapingian to early Changhsingian is dominated by normal polarity (chron “LP2n” of Hounslow and Balabanov, 2018) with three reversed-polarity subchrons (LP2n.0r to LP2n.2r) within the Clarkina wangi conodont Zone. The mid to late Changhsingian is dominated by reversed polarity, with the onset of this chron “LP2r” in the C. changxingensis Zone. The biostratigraphic placement of the brief normal-polarity chron “LP3n” of the late Changhsingian is within the C. yini Zone. The reversed-polarity chron “LP3r” of the latest Changhsingian (late C. yini to C. meishanensis Zones) is succeeded by the normal-polarity chron “LT1n” that spans from the very latest Changhsingian into the early Griesbachian substage of the basal Triassic. The onset of this chron LT1n coincided with the lowest occurrence of Hindeodus changxingensis, which is just after the onset of the latest Permian mass extinction in South China and slightly prior to the PTB. The integration of conodont biozones, carbon isotope excursions and the revised magnetostratigraphy composite from the Shangsi and Chaotian sections produces a high-resolution consistent sequence of the latest Permian mass extinction (LPME), the onset of chron LT1n and then the PTB; thereby enabling high-resolution global correlation of these latest Permian to basal Triassic events.