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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.

The two major oceanic anoxic events of the Cretaceous, those of the Early Aptian (OAE 1a) and the Cenomanian–Turonian boundary (OAE 2), registered some of the highest temperatures reconstructed for the Cretaceous Period, and are thought to be related to the input of volcanically derived carbon dioxide from one or more Large Igneous Provinces. Widely distributed deposition of marine organic matter, the hallmark of OAEs, and intensified silicate weathering in response to a globally accelerated hydrological cycle and/or reaction of seawater with freshly extruded basalt, are both potential mechanisms whereby the content of atmospheric carbon dioxide could have been drawn down to promote cooling, on the assumption that this potential effect was not offset by increased addition of this volcanically derived greenhouse gas. Reduction in the supply of such carbon dioxide, with deposition of organic matter and silicate weathering continuing at the same rate, could also have produced cooling. A transient fall in temperature and increase in marine dissolved oxygen levels is well documented for OAE 2, in the form of the so-called Plenus Cold Event or Benthic Oxic Event, associated with southward invasion of certain boreal faunas and an increase in many redox-sensitive and/or chalcophilic elements in seawater caused by temporary loss of anoxic–euxinic sinks as basalt–seawater interaction continued apace. High-resolution studies of OAE 1a show at least three cooling episodes of probable global distribution, one of which (recorded in the stratigraphy of the so-called C4 Segment) is documented at high enough resolution to show correlation with an increase in carbon-isotope values that was probably due to a rise in the quantities of organic matter being buried globally, with consequent potential drawdown of atmospheric CO2and/or reduction in volcanic input of this greenhouse gas. Both calcium- and lithium-isotope records suggest an increase in silicate weathering over the OAE 1a interval but current relatively low-resolution records cannot at present be tied to any one cooling episode, although the lowest Li-isotope values do derive from the C4 Segment. Evidence for reoxygenation of the ocean during the transient cooling episodes of OAE 1a is meagre, due to the lack of suitable sedimentary archives, although a negative sulfur-isotope excursion in a Pacific shallow-water carbonate section, which can be interpreted as due to oxidation of pyrite and/or sulfur-rich organic matter in the global ocean, suggests that this phenomenon may also have been a feature of the C4 Segment. Further work is required to elucidate the similarities and differences between OAE 2 and OAE 1a, but both phenomena are demonstrably global in reach and represent major disturbances to the carbon cycle with attendant effects on marine temperatures.This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.

The Lower Jurassic Toarcian Stage (c. 183–174 Ma) is marked by one of the largest global exogenic carbon-cycle perturbations of the Phanerozoic, which is associated with the early Toarcian Oceanic Anoxic Event (T-OAE; c. 183 Ma). Climatic and environmental change at the T-OAE is reasonably well constrained in the marine realm, with marine anoxic or euxinic conditions developing locally across both hemispheres, at the same time as the T-OAE negative carbon-isotope excursion. However, high-resolution stratigraphic comparison between different palaeo-ocean basins and with the continental realm can be complicated. Palaeomagnetic reversals can provide a precise and accurate stratigraphic correlation tool between marine and continental sedimentary archives, and even between sedimentary and igneous successions. Here, we present a high-resolution magnetostratigraphic record for the Toarcian Stage in the biostratigraphically complete and expanded Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales. This study provides the first geomagnetic polarity reversal scale that is integrated with high-resolution biostratigraphy and carbon-isotope stratigraphy for the entire Toarcian Stage. This stratigraphic framework also provides a new, precise correlation with the basalt lava sequence of the Karoo–Ferrar Large Igneous Province, linking the Pliensbachian–Toarcian boundary and T-OAE climatic and environmental perturbations directly to this episode of major volcanic activity. Supplementary material: Details of the palaeomagnetic data and dip direction are available at https://doi.org/10.6084/m9.figshare.c.4052720

Despite its assumed global nature, there are very few detailed stratigraphic records of the late Cenomanian to the early Turonian Oceanic Anoxic Event (OAE) 2 from the Southern Hemisphere. A highly resolved record of environmental changes across the Cenomanian–Turonian boundary interval is presented from Ocean Drilling Program Site 1138 on the central Kerguelen Plateau (southern Indian Ocean). The new data lead to three key observations. Firstly, detailed bio- and chemostratigraphy indicate that the record of OAE-2 is not complete, with a hiatus spanning the onset of the event. A decrease in glauconite and highly weathered clays after the onset of OAE-2 marks the end of the hiatus interval, which can be explained by a relative sea-level rise that increased sediment accommodation space on the Kerguelen Plateau margin. This change in depositional environment controlled the timing of the delayed peak in organic-matter burial during OAE-2 at Site 1138 compared with other OAE-2 locations worldwide. A second key observation is the presence of cyclic fluctuations in the quantity and composition of organic matter being buried on the central Kerguelen Plateau throughout the latter stages of OAE-2 and the early Turonian. A close correspondence between organic matter, sedimentary elemental compositions and sediments recording sea-floor oxygenation suggests that the cycles were mainly productivity-driven phenomena. Available age-control points constrain the periodicity of the coupled changes in sedimentary parameters to ~15–50 ka, suggesting a link between carbon burial and astronomically forced climatic variations (precession or obliquity) in the Southern Hemisphere mid-latitudes both during, and after, OAE-2: fluctuations that were superimposed on the impact of global-scale processes. Finally, trace-metal data from the non-sulphidic black shale unit at Site 1138 provide the first evidence from outside of the proto-North Atlantic region for a global drawdown of seawater trace-metal (Mo) inventories during OAE-2.

Large Igneous Provinces (LIPs) are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric CO2 levels, which were subsequently alleviated by drawdown of CO2 via enhanced continental weathering and burial of organic matter. Here, the sedimentary records of two such episodes of environmental change, the Toarcian Oceanic Anoxic Event (T-OAE) and preceding Pliensbachian–Toarcian (Pl–To) event (both potentially linked to the Karoo–Ferrar LIP), are investigated using a new suite of geochemical proxies that have not been previously compared. Stratigraphic variations in osmium-isotope ( 187Os/188Os) records are compared with those of mercury (Hg) and carbon isotopes (δ13C) in samples from the Mochras Core, Llanbedr Farm, Cardigan Bay Basin, Wales. These sedimentary rocks are confirmed as recording an open-marine setting by analysis of molybdenum/uranium enrichment trends, indicating that the Os-isotope record in these samples reflects the isotopic composition of the global ocean. The Os-isotope data include the first results across the Pl–To boundary, when seawater 187Os/188Os increased from ∼ 0.40 to ∼ 0.53, in addition to new data that show elevated 187Os/188Os (from ∼ 0.42 to ∼ 0.68) during the T-OAE. Both increases in 187Os/188Os correlate with negative carbon-isotope excursions and increased mercury concentrations, supporting an interplay between terrestrial volcanism, weathering, and climate that was instrumental in driving these distinct episodes of global environmental change. These observations also indicate that the environmental impact of the Karoo–Ferrar LIP was not limited solely to the T-OAE

Although a division of the Phanerozoic climatic modes of the Earth into "greenhouse" and "icehouse" phases is widely accepted, whether or not polar ice developed during the relatively warm Jurassic and Cretaceous Periods is still under debate. In particular, there is a range of isotopic and biotic evidence that favours the concept of discrete "cold snaps", marked particularly by migration of certain biota towards lower latitudes. Extension of the use of the palaeotemperature proxy TEX86 back to the middle Jurassic indicates that relatively warm sea-surface conditions (26-30°C) existed from this interval (~160 Ma) to the Early Cretaceous (~115 Ma) in the Southern Ocean. The Jurassic and Cretaceous "cold snaps" represent falls of only a few degrees. Belemnite δ18O data gives palaeotemperatures that are consistently lower by ~14°C than does TEX86 and these molluscs likely record conditions below the thermocline. Such long-term warm climatic conditions would only be compatible with the existence of continental ice and if appreciable areas of high altitude existed on Antarctica, and/or in other polar regions, during the Mesozoic Era.

A detailed carbon- and oxygen-isotope stratigraphy has been generated from Upper Cretaceous coastal Chalk sections in southern England and the British Geological Survey (BGS) Trunch borehole, Norfolk. Data are also presented from a section through the Scaglia facies exposed near Gubbio, Italian Apennines. Both the Chalk and Scaglia carbon-isotopic curves show minor positive excursions in the mid-Cenomanian, mid- and high Turonian, basal Coniacian and highest Santonian-lowest Campanian; there is a negative excursion high in the Campanian in Chalk sections that span that interval. The remarkable similarity in the carbon-isotope curves from England and Italy enables cross-referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the Turonian, Coniacian and Santonian stages. The oxygen-isotope values of the various Chalk sections, although showing different absolute values that are presumably diagenesis-dependent, show nonetheless a consistent trend. Regional organic-carbon burial, documented for this period, is credited with causing drawdown of CO2 and initiating climatic deterioration. Data from other parts of the world are consistent with the hypothesis that the Cenomanian-Turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth. -from Authors

An introductory section describes the morphology, structure and geological history of the Balearic Islands. Following this, 6 excursions are described which highlight areas of geological interest. A reference list and index are included. -A.W.Hall

The Early Jurassic was characterized by extreme carbon-cycle perturbations that are associated with abrupt environmental and climatic change. However, the evidence mainly derives from sections in the western Tethys and northern Europe: localities situated in the northern hemisphere. This paper presents new records of biostratigraphical (large benthic foraminiferal), sedimentological and carbonate carbon-isotope (δ13Ccarb) data from the Tibetan Kioto Platform formed in the southeastern Tethys (southern hemisphere) during the Sinemurian–earliest Toarcian interval. Six foraminiferal zones have been recognized: late Sinemurian Textulariopsis sinemuriensis, Pliensbachian Planisepta compressa, Bosniella oenensis, Cyclor-bitopsella tibetica and Streptocyclammina liasica, and earliest Toarcian Siphovalvulina sp. A. Based on biostratigraphy, δ13Ccarb data allow correlation with coeval records from the western Tethys and northern Europe by the identification of both negative and positive δ13C excursions. The negative excursions characterize the Sinemurian–Pliensbachian boundary event (SPBE) and the margaritatus–spinatum zone boundary event (MSBE); the positive δ13C excursion characterizes the margaritatus zone event (ME). Facies evolution in the Early Jurassic indicates that the establishment of carbonate sedimentation on the Kioto Platform occurred in the context of a global sea-level rise partly coincident with the SPBE and that, in common with other coeval platforms, carbonate production following the negative shift was predominantly made up of skeletal carbonates. Furthermore, the spread of the Lithiotis Fauna on the Kioto Platform followed the rebound of isotopic values after the SPBE. This phenomenon has been observed in the western Tethys and suggests that the global biocalcification event represented by the flourishing of the Lithiotis Fauna may have occurred synchronously across the Tethys, possibly reflecting the creation of more favourable marine conditions after the SPBE. Biostratigraphical data indicate that certain index larger benthic foraminifera became extinct around the onset level of the MSBE, likely due to the deleterious impact of this event. However, as in more northerly localities, the Lithiotis Fauna persisted during the late Pliensbachian in the shallow-water platforms of the Tethys until its disappearance in the early Toarcian.

Mesozoic Oceanic Anoxic Events (OAEs) are characterised by the widespread burial of organic-rich sediments and the spread of low-oxygen marine environments. These intervals represent some of most extreme perturbations to global climate, environment, and ocean chemistry in Earth’s history. Understanding the complex interplay of processes that caused and sustained these unusual environmental conditions requires proxies that allow quantification of global changes in ocean chemistry. This study explores the use of Zn- and Cd-isotopes as new palaeo-ocean chemistry proxies by using the Late Cretaceous Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE 2, ˜ 94 Ma) as a case study. Previous studies on the cycling of these elements in the modern ocean have suggested Cd and Zn may preserve valuable information on past redox and/or nutrient conditions if such signals are preserved in the sedimentary record. The data presented in this thesis suggest a strong control of local redox conditions on the Cd- and Zn-isotope composition of ancient organic-rich marine sediments. When these local effects are accounted for, δ66Zn and δ114Cd stratigraphic profiles offer insight into past change in redox environments at a global scale. Specifically, heavy δ66Zn and δ114Cd values observed during the main phase of the OAE 2 interval can be associated with an increase in organic-rich sediment burial globally, whereas lower values during the Plenus Cold Event interval can be linked to global oxygenation. The data presented in this study highlight the potential of δ114Cd and δ66Zn as new proxies for global changes in ocean redox chemistry. With improved understanding of the cycling of these elements in the modern ocean, these proxies may ultimately be used to quantify the global extent of ocean anoxia for past oceans.

The lack of a continuous high-resolution carbon-isotope (δ13C) record based on a single material, and thus a single carbon reservoir, has so far inhibited investigation on the secular evolution of the Early Jurassic (~201–175 Myr) carbon cycle. The existing δ13C records for the Lower Jurassic Series tend to cover short stratigraphic intervals, originate from a variety of different sedimentary basins and different carbon reservoirs, or are of relatively low stratigraphic resolution. New δ13CTOC data from the continuous strata of the stratigraphically expanded Llanbedr (Mochras Farm) drill-core provides the most expanded Lower Jurassic δ13CTOC record to date. The record aggregates several δ13CTOC excursions of different stratigraphical extent and magnitude. Based on stratigraphic correlations, several of these excursions appear approximately coeval in several NW European sedimentary basins, in multiple carbon reservoirs. Geochemical characterization reveals an organic-lean character of the Lower Jurassic sediments, dominated by terrestrial organic matter. Changes in the relative admixture of marine vs terrestrial organic matter appear as a likely subordinate mechanism driving changes in δ13C. Consecutively appearing small-amplitude fluctuations (~0.5–2 ‰) of comparable magnitude and stratigraphic thickness, including those recorded elsewhere, and hitherto unrevealed excursions, appear to be largely orbitally paced, corresponding to long (405-kyr) eccentricity cycles. Orbital tuning of the continuous Hettangian to Pliensbachian record allows an astronomical timescale to be established, which closely agrees with previous timescales for the Hettangian and Pliensbachian stages, and provides the basis for a Sinemurian chronology. Furthermore, a stratigraphical framework is developed on Lower Jurassic sections in the Neuquén Basin, Argentina, providing the grounds for future work on the radioisotopic dating of the onset of the Toarcian oceanic anoxic event (T-OAE). A chemostratigraphic dataset allows the correlation to same-age records. Coeval appearance of siderite in the lower Toarcian of the Mochras core and the Neuquén Basin suggests a disturbance of the global sulphur cycle (possible low sulphate ocean) during the T-OAE.

The Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) is recognized as possibly the most extreme oceanographic and global climatic change event of the Phanerozoic. The T-OAE was marked by massive carbon release into the ocean–atmosphere system, widespread oceanic de-oxygenation, global organic-matter burial, and a strongly perturbed global carbon cycle. Although effects of the T-OAE are extensively studied in the marine realm, the environmental and climatic response on the continents is effectively unknown. In this thesis, I identify the first lacustrine record of the T-OAE, in the Da'anzhai Member of the Sichuan Basin (China), and demonstrate that a major lake system developed contemporaneously with the T-OAE, likely due to enhanced hydrological cycling under elevated atmospheric pCO2. Increased lacustrine organic productivity from elevated fluvial nutrient supply resulted in ˜460 Gt of organic carbon burial in the palaeo-Sichuan lake alone, representing a major, but hitherto overlooked, carbon sink and negative feedback in the T-OAE global carbon cycle, and likely other similar events. Algal dominated biomass, deposited under a stratified water column during lake level rise, marks the Da’anzhai Member as potential hydrocarbon source rock. Given the challenges associated with Mesozoic stratigraphic correlation, I further present the first integrated (marine) stratigraphic reference framework for the complete Toarcian Stage from the Llanbedr (Mochras Farm) Borehole (Cardigan Bay Basin, UK), which allows precise correlation between the T-OAE and coeval Karoo-volcanism. I also show that accelerated global weathering rates during the T-OAE resulted in widespread mass transport deposits at different palaeolatitudes and changes in ocean chemistry leading to pronounced marine siderite deposition. Periodic smaller-magnitude carbon cycle perturbations in the Hettangian and Sinemurian were possibly in phase with short (∼100kyr) and long (~405kyr) eccentricity astronomical forcing, with the formation of organic-rich laminated black shales in the Bristol Channel Basin, similar to Mediterranean sapropels in the Pleistocene.

Major changes in watermass chemistry during the opening of the central segment of the South Atlantic, and oceanic anoxic events (OAEs 1a to 1d), represent dramatic events that affected the ocean–atmosphere system during the Early Cretaceous. This thesis addresses the chemostratigraphic correlation of Tethyan and South Atlantic sections based on carbon-, sulphur- and strontium-isotopes (δ13C, δ34S and 87Sr/86Sr) integrated with other methods to explore the causal links between these phenomena. Firstly, the sedimentation of massive evaporite deposits is discussed and its relationship with the Early Aptian OAE 1a explored. The proposed coincidence in timing between massive evaporite deposition and OAE 1a enhances the understanding of carbon and sulphur cycles in the Early Cretaceous. Secondly, the top of sub-evaporite carbonates in the southern Brazilian basins is identified as having been deposited in a continental environment, and further evidence for its deposition during part of the OAE 1a interval is presented. Thirdly, it is suggested that the formation of the Ontong Java Plateau, already linked to the genesis of OAE 1a, promoted a eustatic sealevel rise responsible for rapid seawater entrance into the southern Brazilian basins during the Early Aptian. Fourthly, the first record of OAE 1a from northeastern Brazil (Sergipe- Alagoas Basin) has been recognized, allowing stratigraphic correlation with southern Brazilian basins. Stratigraphic correlation between the southern Brazilian basins is extended to the Falkland Plateau, where the decrease in the content of organic matter upwards in the stratigraphy of DSDP Site 511 through the Barremian–OAE 1b interval can be related to the evolution of South Atlantic basinal geometry. Finally, in the context of a Tethyan reference section, the record of the Barremian-Aptian boundary and the OAE 1a interval has been characterized in the Tethyan Poggio le Guaine scientific core from Marche–Umbria, Italy.