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Abstract

Ammonites underwent an evolutionary diversification after the mass extinction of the end Triassic induced by the formation of a Large Igneous province (LIP), and this group provides the most useful marine biostratigraphy. Only two levels within the Jurassic are relatively well determined using U–Pb dating from single zircons in ash beds, at the base Hettangian and the Pliensbachian–Toarcian boundary. Otherwise the Lower Jurassic is scaled using astrochronology and the Middle and Upper Jurassic scaled from Pacific seafloor spreading rates correlated to magnetic reversals. LIP activity during the Early Jurassic (Triassic–Jurassic boundary and Toarcian) perturbed global environments to extents not evidenced since the end Permian, and age relationships allow for a strong causal connection between these LIP eruptions and mass extinctions caused by major paleoenvironmental change, including ocean anoxia. Breakup of the supercontinent Pangea dominated paleogeography and paleoceanography and created shallow seaways that form sources and traps for hydrocarbons. Calcareous planktonic algae diversified and migrated from shallow seaways to open oceans to set the stage for the beginning of modern oceanic biogeochemical cycling; calcareous nannofossils provide additional widely used correlation tools.

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An accurate chronostratigraphy of the timing and magnitude of global sea-level trends and their short-term variations is an indispensable tool in high-resolution correlations, exploration, and paleoenvironmental and geodynamic models. This paper is a reappraisal of the Jurassic sealevel history in view of recent updates in time scales and a large body of new chronostratigraphic data accrued since 1998, when the last such synthesis was presented. A review of the Jurassic sea-level history has also been keenly awaited by explorationists given that the Jurassic continues to be a major exploration target for the industry. As in previous eustatic models of this period, the updated Jurassic sealevel curve remains largely Eurocentric due to the limitations imposed by biostratigraphic correlation criteria (provinciality of ammonite and microfossil zones), though it can now be extended to some parts of the Tethys toward the east. The updated long-term curve indicates that there was a general rise of sea level through the Jurassic that began close to a level similar to or below the present-day mean sea level (pdmsl) in the early Jurassic, culminating in the peak high in the late Kimmeridgian-early Tithonian interval, before stabilizing in the earliest Cretaceous at ∼110 m above pdmsl. Within this long-term trend are relative secondorder highs in the Toarcian and Aalenian, and at Bathonian-Callovian and Kimmeridgian-Oxfordian boundaries. Superimposed are 64 third- and fourthorder fluctuations of which 15 are considered major with base-level falls of more than 75 m, although precise amplitudes of drawdowns are often difficult to establish. Higher resolution fourth-order cyclicity (∼410 k.y.) is also observable in many Jurassic sections whenever sedimentation rates were high. Causes for the third-order cyclicity, in the absence of major ice sheets in the Jurassic, remains enigmatic.
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The stratigraphy, palaeoecology and palaeobiogeography are outlined for two genera and ten species of Jurassic planktonic foraminifera described in Gradstein et al. (Swiss J Palaeontol 2017. doi:10.1007/s13358-017-0131-z). The two genera are Globuligerina and Conoglobigerina. Globuligerina probably appeared in late Toarcian (late Early Jurassic) and Conoglobigerina first occurred in Middle Oxfordian (early Late Jurassic). Within the two genera ten species are defined, including from older to younger: Globuligerina dagestanica (Morozova), G. avariformis (Kasimova), G. balakhmatovae (Morozova), G. oxfordiana (Grigelis), G. bathoniana (Pazdrowa), G. jurassica (Hofman), G. oxfordiana (Grigelis) calloviensis Kuznetsova emended, G. tojeiraensis Gradstein, Conoglobigerina helvetojurassica (Haeusler), C. grigelisi Gradstein and C. gulekhensis (Gorbachik and Poroshina). Globuligerina balakhmatovae, G. oxfordiana and G. bathoniana are longer ranging, although there are subtle evolutionary trends in these taxa that may refine stratigraphic usage. Other taxa have shorter stratigraphic ranges. Using stratigraphic trends, test morphology and wall texture changes, the species are tentatively assembled in four evolutionary groups, termed A–D, and in six zones from Late Toarcian through Tithonian. The greater species diversity and possibly also specimen abundance took place in the Kimmeridgian, a time of high global sea level and greenhouse palaeoclimatic conditions. Jurassic planktonic foraminifera preferred marine continental margin conditions instead of the distal open ocean and spread from offshore Eastern Canada to offshore Western Australia along the margins of the Tethys Ocean. The group did not venture into austral or boreal realms, likely reasons why migration probably failed to the west coasts of South and North America.
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The Central Atlantic Magmatic Province (CAMP) has long been proposed as having a causal relationship with the end-Triassic extinction event (∼201.5 Ma). In North America and northern Africa, CAMP is preserved as multiple basaltic units interbedded with uppermost Triassic to lowermost Jurassic sediments. However, it has been unclear whether this apparent pulsing was a local feature, or if pulses in the intensity of CAMP volcanism characterized the emplacement of the province as a whole. Here, six geographically widespread Triassic-Jurassic records, representing varied paleoenvironments, are analyzed for mercury (Hg) concentrations and Hg/total organic carbon (Hg/TOC) ratios. Volcanism is a major source of mercury to the modern environment. Clear increases in Hg and Hg/TOC are observed at the end-Triassic extinction horizon, confirming that a volcanically induced global Hg cycle perturbation occurred at that time. The established correlation between the extinction horizon and lowest CAMP basalts allows this sedimentary Hg excursion to be stratigraphically tied to a specific flood basalt unit, strengthening the case for volcanic Hg as the driver of sedimentary Hg/TOC spikes. Additional Hg/TOC peaks are also documented between the extinction horizon and the Triassic-Jurassic boundary (separated by ∼200 ky), supporting pulsatory intensity of CAMP volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of CAMP emplacement. Pulsatory volcanism, and associated perturbations in the ocean-atmosphere system, likely had profound implications for the rate and magnitude of the end-Triassic mass extinction and subsequent biotic recovery.
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The global silica cycle is an important component of the long-term climate system, yet its controlling factors are largely uncertain due to poorly constrained proxy records. Here we present a ∼70 Myr-long record of early Mesozoic biogenic silica (BSi) flux from radiolarian chert in Japan. Average low-mid-latitude BSi burial flux in the superocean Panthalassa is ∼90% of that of the modern global ocean and relative amplitude varied by ∼20–50% over the 100 kyr to 30 Myr orbital cycles during the early Mesozoic. We hypothesize that BSi in chert was a major sink for oceanic dissolved silica (DSi), with fluctuations proportional to DSi input from chemical weathering on timescales longer than the residence time of DSi (<∼100 Kyr). Chemical weathering rates estimated by the GEOCARBSULFvolc model support these hypotheses, excluding the volcanism-driven oceanic anoxic events of the Early-Middle Triassic and Toarcian that exceed model limits. We propose that the Mega monsoon of the supercontinent Pangea nonlinearly amplified the orbitally paced chemical weathering that drove BSi burial during the early Mesozoic greenhouse world.
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The end-Triassic extinction is one of the Phanerozoic’s largest mass extinctions. This extinction is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP). However, recent work suggests that the earliest known CAMP basalts occur above the extinction horizon and that climatic and biotic changes began before the earliest known CAMP eruptions. Here we present new high-precision U-Pb ages from CAMP mafic intrusive units, showing that magmatic activity was occurring B100 Kyr ago before the earliest known eruptions. We correlate the early magmatic activity with the onset of changes to the climatic and biotic records. We also report ages from sills in an organic rich sedimentary basin in Brazil that intrude synchronously with the extinction suggesting that degassing of these organics contributed to the climate change which drove the extinction. Our results indicate that the intrusive record from large igneous provinces may be more important for linking to mass extinctions than the eruptive record.
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During the Phanerozoic, Earth has experienced a number of transient global warming events associated with major carbon cycle perturbations. Paradoxically, many of these extreme greenhouse episodes are preceded or followed by cold climate, perhaps even glacial conditions, as inferred from the occurrence of glendonites in high latitudes. Glendonites are pseudomorphs of ikaite (CaCO3·6H2O), a hydrated carbonate mineral increasingly stable at low temperatures. Here, we show that methane seepage and oxidation provide an overriding control on Mesozoic glendonite formation (i.e., ikaite fossilization). Geochemical and petrological analyses of 33 Early Jurassic to Early Cretaceous glendonites from five sections in Siberia (Russia) reveal that most of their infilling carbonate phases are reminiscent of methane-derived authigenic carbonates. Bulk glendonites and surrounding sediments exhibit exceptionally high and low carbon isotope values (+20‰ to –45‰ VPDB [Vienna Peedee belemnite]), typical for carbon sources linked to methane generation and oxidation. Gas inclusion data confirm the presence of methane and longer-chain hydrocarbon gases, suggesting a thermogenic source for the methane. Glendonite-bearing layers can be traced for hundreds of kilometers, suggesting widespread trapping of methane in the sub-seafloor during the Jurassic. As such, glendonites constitute an unexplored archive for detecting past episodes of methane release and oxidation in polar settings.
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One of the key requirements for a Global Stratotype Section and Point (GSSP) is the absence of tectonic disturbance. The GSSP for the Triassic–Jurassic system boundary was recently defined at Kuhjoch, Northern Calcareous Alps, Austria. New field observations in the area of the Triassic–Jurassic boundary GSSP site demonstrate that the overturned, tight, and almost upright Karwendel syncline was formed at semibrittle deformation conditions, confirmed by axial planar foliation. Tight to isoclinal folds at various scales were related to a tectonic transport to the north. Brittle faulting occurred before and after folding as confirmed by tilt tests (the rotation of structural data by the average bedding). Foliation is ubiquitous in the incompetent units, including the Kendlbach Formation at the GSSP. A reverse fault (inferred to be formed as a normal fault before folding) crosscuts the GSSP sections, results in the partial tectonic omission of the Schattwald Beds, and thus makes it impossible to measure a complete and continuous stratigraphic section across the whole Kendlbach Formation. Based on these observations, the Kuhjoch sections do not fulfil the specific requirement for a GSSP regarding the absence of tectonic disturbances near boundary level.
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Variations in the ¹⁸O/¹⁶O ratio of marine fossils and microfossils record changes in seawater ¹⁸O/¹⁶O and temperature and provide the basis for global correlation. Based on more than 64,000 measurements, this chapter presents oxygen isotope curves for Phanerozoic foraminifera, mollusks, brachiopods, and conodonts, as well as for Precambrian limestones, dolostones, and cherts. Periodic oxygen isotopic variations in deep-sea foraminifera define marine isotope stages that, when combined with biostratigraphy and astronomical tuning, provide a late Cenozoic chronostratigraphy with a resolution of several thousand years. Oxygen isotope events of late Cenozoic, Mesozoic, and Paleozoic age mark local and global climate change and serve as chemostratigraphic markers for regional and global correlation. Precambrian oxygen isotope stratigraphy is hampered by the lack of unaltered authigenic marine carbonate and phosphate.
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The ¹³C/¹²C value of dissolved inorganic carbon (DIC) in the ocean has varied through time and can be determined from the marine carbonate record as changes in δ¹³Ccarb. These variations provide insight into global carbon cycle dynamics, as well as relative age information (chronostratigraphy) that can be used to correlate sedimentary successions globally. The global carbon cycle includes both short- and long-term components, and their interactions dominate the isotopic record presented in this chapter. The partitioning and sequestration of carbon between organic and carbonate rock reservoirs, and their fluxes to and from the ocean–atmosphere–biosphere system, drive secular changes in the δ¹³C of DIC in the oceans that are ultimately recovered from the stratigraphic record. The pre-Cenozoic data presented here utilize bulk carbonate data for compilation, but a wide range of materials has been analyzed in the literature to produce previous composites. Care must be taken to consider what materials have been analyzed in comparing global carbon isotope records from the literature.
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Fossil shells of benthos and nektobenthos have been shown to be faithful recorders of seawater carbon- and oxygen-isotope geochemistry, and thus also useful to track the relationship between carbon cycle and palaeotemperature. In this study we present an extensive dataset from Lower Jurassic (Hettangian and lower Sinemurian) mollusc and brachiopod hard parts collected from biostratigraphically well-calibrated UK coastal outcrops (Bristol Channel and Hebrides basins). These basins lay palaeogeographically in the southern part of the Laurasian Seaway that connected the Tethys and Boreal oceans. All samples have been subject to screening for diagenesis on the basis of elemental composition, light microscopy, and SEM observations. In the case of some localities within the Hebrides Basin, alteration by hydrothermal systems around Paleogene intrusions has led to re-setting of carbonate oxygen isotopes, but the original carbon isotope values from the shells are largely preserved. Above the prominent and apparently short-lived, ~3 per mil δ¹³Ccarb amplitude positive carbon-isotope excursion (CIE) that occurs immediately above the Triassic-Jurasic (T-J) boundary (in the tilmanni ammonite biozone), a pronounced negative CIE (the so-called Main Negative CIE) spans the entire Hettangian Stage. At the Hettangian-Sinemurian boundary, and through the lower Sinemurian, the carbon-isotope values of the skeletal carbonate again trend towards progressively more positive values, but representing a time of several million years. The heaviest δ¹³Ccarb values of about ~ +4.3 per mil are evident towards the top of the lower Sinemurian, and are comparable with values observed from the tilmanni Zone, and from the lower Toarcian, higher in the Jurassic. This long-term positive hump, which confirms trends derived from bulk organic matter carbon-isotope records, is supporting evidence of prolonged enhanced organic carbon burial that is inferred to have occurred in the extensive system of lacustrine and marine rifts that traversed a fragmenting Pangaea after emplacement of the Central Atlantic Magmatic Province. In parallel, oxygen-isotope values of the skeletal carbonate show a continuous downward trend from the lower part of the Hettangian (~ −1 per mil δ¹⁸Ocarb in the planorbis Zone) to the top of the lower Sinemurian (~ −4 per mil δ¹⁸Ocarb in the higher turneri Zone). Oxygen-isotope values may be interpreted as due to gradually increasing palaeotemperature, and/or addition of a meteoric or cryospheric water component; in the case of the Laurasian Seaway, palaeoceanographic and palaeoecological considerations point towards a dominant palaeotemperature signal. Consequently, any atmospheric carbon-dioxide drawdown effect on global palaeotemperatures, as suggested by progressively increasing δ¹³Ccarb values, and assuming a constant silicate weathering sink, was more than counterbalanced in the seaway by regional processes that led to significantly warmer bottom water temperatures.
Chapter
Detailed cyclostratigraphical analyses have been made from five TithonianeBerriasian sections of the Vaca Muerta Formation, exposed in the Neuquén Basin, Argentina. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marlstones and limestones, showing a well-ordered hierarchy of cycles, where elementary cycles, bundles of cycles and superbundles have been recognized. According to biostratigraphic data, elementary cycles have a periodicity of 21 ky, which correlates with the precession cycle of Earth’s axis. Spectral analysis based on time series of elementary cycle thicknesses allows us to identify frequencies of w400 ky and w90e120 ky, which we interpret as the modulation of the precessional cycle by the Earth’s orbital eccentricity. Correlation between studied sections allowed us to estimate a minimum duration for each Andean ammonite zone. Moreover, cyclostratigraphic data allowed us to build the first continuous floating astronomical time scale for the Tithonian e Berriasian, which is anchored to the geological time scale through magnetostratigraphy. We estimated a minimum duration of 5.67 myr for the Tithonian and 5.27 myr for the Berriasian. The resulted durations of some polarity chrones are also different with respect to the GTS2016, however such differences could be due to condensation or discontinuities not detected in the studied sections.
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Black shale samples from sedimentary layers below and between the Unterer Stein, Oberer Stein, Inoceramus Bank, and Nagelkalk horizons from the Dormettingen quarry, SW Germany were analysed for their Re and Os isotope composition and content. The ~12-m-thick sedimentary sequence of the Posidonia Shale Formation, composed of multiple layers of black shale and intercalated limestone beds, was deposited during the Early Jurassic (Toarcian), a time during which black shale sedimentation was ubiquitous in Western Europe during a widespread oceanic anoxic event. Both the marl and shale layers beneath the black shales and adjacent to the Oberer Stein limestone layer show signs of bioturbation. The excellent biostratigraphic constraints and the high Re and Os contents (24–290 ppb and 290–1050 ppt, respectively) of the Dormettingen shales thus make these samples ideal for testing the influence of bioturbation on the Re-Os isotope system, as well as refining age constraints for the Toarcian OAE and potential triggers for this event. The calculated isochron age for the Dormettingen shales is 183.0 ± 2.0 Ma, with a low initial ¹⁸⁷Os/¹⁸⁸Osi of 0.377 ± 0.065, indicating a Pliensbachian to Toarcian age. This age is in agreement with published U-Pb and Re-Os ages for other Lower Jurassic sites, astronomical constraints, and biostratigraphic correlations, suggesting limited disturbance of the isotope system by minor degrees of biological activity. The low ¹⁸⁷Os/¹⁸⁸Osi is consistent with significant influx of mantle-derived material into the Toarcian ocean, likely from weathering of Karoo-Ferrar Large Igneous Province basalts.
Article
Abstract. At Peniche, Portugal, the GSSP for the base of the Toarcian and in a Submediterranean province, a value of 0.707 073 ± 0.000 002 (2s. e., n = 13) is determined for 87Sr/86Sr at the base of the Toarcian. In Yorkshire, UK, a Subboreal province, the base of the Toarcian has an 87Sr/86Sr value of0.707 072 ± 0.000 002 (2s. e., n = 23). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. At Peniche, the base of the Serpentinum (Falciferum/Levisoni) Chronozone has an 87Sr/86Sr value of 0.707 096 ± 0.000 003 (2.s.e, n = 4). The value for this boundary in Yorkshire is 0.707 094 ± 0.000 002 (2s. e., n = 27). The similarity of the values shows that, within analytical uncertainty, these levels are exactly equivalent in time. The same ammonite successions occur through the lowermost Toarcian successions at Peniche and in Yorkshire. Between Peniche and Yorkshire, there is therefore an exact coincidence, within measurement uncertainty, between the Lower Toarcian, Tethyan Realm, Tenuicostatum (Polymorphum) [ammonite] Chronozone of Peniche and the Lower Toarcian, Boreal Realm, Tenuicostatum [ammonite] Chronozone of Yorkshire. The 87Sr/86Sr profile through the Tenuicostatum Subchronozone at Peniche reveals large variations in sedimentation rate, with lowest rates in a condensed basal 3 m of the zone, highest rates in mid-zone, with rates decreasing upward through the upper half of the zone. Apportioning time in proportion to 87Sr/86Sr shows that around half of Tenuicostatum time is condensed into the basal 3 m of the section.
Article
The JK2018 meeting was held from the 5 th to the 7 th of December 2018 at the "Muséum d'Histoire Naturelle de Genève" (Switzerland). It was intended to bring together people with interests in the transition period of the latest Jurassic to the earliest Cretaceous times, i.e., a ca. 20 Ma interval of time spanning the Tithonian-Berriasian (Volgian-Ryazanian)-Valangin-ian interval (eventually overlapping slightly its lower and upper boundaries) in the Tethys area, as well as in the Panthalassa, Boreal and Austral regions. It was also intended to feature disciplines covering the many aspects of stratigraphy (litho-, bio-, magneto-, chemo-, cyclo-, sequence), as well as sedimentology, paleontology, paleogeography and global tectonics, at all scales, from the SEM-Scanning Electron Microscopy-to basin analyses.
Article
The Puchezh‐Katunki impact structure, 40–80 km in diameter, located ~400 km northeast of Moscow (Russia), has a poorly constrained age between ~164 and 203 Ma (most commonly quoted as 167 ± 3 Ma). Due to its relatively large size, the Puchezh‐Katunki structure has been a prime candidate for discussions on the link between hypervelocity impacts and extinction events. Here, we present new ⁴⁰Ar/³⁹Ar data from step‐heating analysis of five impact melt rock samples that allow us to significantly improve the age range for the formation of the Puchezh‐Katunki impact structure to 192–196 Ma. Our results also show that there is not necessarily a simple relationship between the observed petrographic features of an impact melt rock sample and the obtained ⁴⁰Ar/³⁹Ar age spectra and inverse isochrons. Furthermore, a new palynological investigation of the postimpact crater lake sediments supports an age significantly older than quoted in the literature, i.e., in the interval late Sinemurian to early Pliensbachian, in accordance with the new radioisotopic age estimate presented here. The new age range of the structure is currently the most reliable age estimate of the Puchezh‐Katunki impact event.
Article
The main objective of this study is to provide a review of the Tithonian succession of the Neuquén Basin and related Andean areas with an update from recent results on biostratigraphy and radio-isotopic geochronology. The studied successions include continental clastics and volcaniclastics of the Tordillo Formation and economically-important hydrocarbon source rocks such as the widespread black shales of the Vaca Muerta Formation, which has been ranked in recent studies as one of the most important recoverable shale oil and gas resources at global level. Significant recent data include the discovery of hyaline calpionellids associated with global nannofossil markers which are relevant to investigations of the definition of the Tithonian/Berriasian boundary. In addition, new high precision radio-isotopic data provide robust evidence to modify the absolute ages presently assigned to the base and top of the Tithonian Stage by the International Commission on Stratigraphy.
Article
The Jurassic system of the Western Canada Sedimentary Basin records the transition in its tectonic setting from a “passive” back-arc platformal basin to a foreland basin at the western margin of ancient North America. We report new U-Pb zircon ages from bentonite layers and from probable volcanic ash components of clastic detritus in other strata of the Fernie Formation, which encompasses most of the Jurassic in the western portions of the basin and which is now deformed in the Rocky Mountain fold-and-thrust belt. The bentonite ages come from the lower Nordegg Member (Pliensbachian) and an equivalent ash layer in the Lower Fernie phosphatic shale. Detrital zircon spectra from the Bathonian Gryphaea Bed silty limestone and the zircon ages from the mainly Oxfordian Green Beds glauconitic sandstone also are likely indicative of contemporaneous ash-falls. In addition, we review previously published U-Pb bentonite ages from the Fernie Formation and comment on the Jurassic time scale as represented on the International Chronostratigraphic Chart. We have compiled an updated local stratigraphic correlation chart against a time scale that incorporates ages for some of the Middle and Upper Jurassic stage boundaries, from the literature, that differ from those on the current standard charts. The presence of multiple volcanic ashes throughout the Jurassic system in the Western Canada Sedimentary Basin supports tectonostratigraphic models with relatively nearby western magmatic activity. The southeastern Omineca crystalline belt and Quesnellia terrane contain magmatic rocks with ages that could account for all of the Fernie ashes, and are closest to the depositional basin, but source terranes farther afield cannot be ruled out. © 2018, Canadian Society of Petroleum Geologists. All rights reserved.
Article
Shallow water carbonate rocks are especially prone to diagenetic alteration. As such they are sometimes problematic archives of past carbon cycle perturbations, casting doubt on the reliability of shallow-water carbonates carbon isotopes analyses for chemostratigraphic purposes. In this paper, bulk organic carbon isotopes (δ13Corg) is used as a robust replacement of the more sensitive carbonate carbon isotope systems for the establishment of a refined chronostatigraphic framework for the evolution of Sinemurian-Pliensbachian neritic carbonate systems in the Central High Atlas Basin of Morocco. These data show very similar patterns and characteristics in the organic carbon isotope curves of basinal and platform sections and thus illustrate the reliability of these archives. Simultaneously, we explore the expression of the global carbon isotope excursion at the Sinemurian-Pliensbachian boundary (S-P event) in the study area in Morocco. This event has been previously described as a negative carbon isotope excursion of ∼2‰ associated with a large transgression in numerous basins. In Morocco and other neritic carbonate records, the S-P event is better described as a return to previous values after a positive carbon isotope excursion coinciding with a major latest Sinemurian regression recognized on a global scale. Similar patterns are also found in other sections, although sometimes poorly expressed. However, it shows, that the S-P event has ambiguous characteristics and questions the conventional hypothesis of it being linked to the massive injection of 13C-depleted carbon into the atmosphere-ocean system.
Article
The Toarcian oceanic anoxic event (T-OAE, ~183 Ma) marks a geologically brief and severe global warming, associated with a profound perturbation in the global carbon cycle. The carbon cycle perturbation has been documented worldwide in marine and continental sedimentary records with a pronounced negative carbon isotope excursion (CIE) in the long-term δ ¹³ C profile. However, the cyclostratigraphically inferred duration of the CIE, which was mainly derived from the Paris (France) and Lusitanian (Portugal) basins, remains controversial, resulting in two notably different estimates of 300–500 and 900 kyr. Here, we present an early Toarcian cyclostratigraphic record from the High Atlas in Morocco (Talghemt section), based on high-resolution δ ¹³ C and %CaCO 3 data, which capture the Pliensbachian-Toarcian (Pl-To) transition event and the T-OAE, and strongly correlate to previous δ ¹³ C key records. Orbital tuning based on the short and long, stable 405 kyr (g2–g5) eccentricity cycles, provides a duration of ~400 to ~500 kyr for the T-OAE. This duration is very close to that previously inferred from the Sancerre Core in the Paris Basin (300 to 500 kyr), and similar to that recently revised from the Peniche section (Lusitanian Basin, Portugal) (~472 kyr). In addition, the 405 kyr%CaCO 3 timescale at Talghemt calibrates high-frequency δ ¹³ C variations at the Pl-To transition and the initiation part of the T-OAE to the obliquity cycle band, thus concuring with previous studies for obliquity forcing during these time intervals. The 405 kyr calibrated O1 obliquity period (~30 kyr) is shorter than the astronomically predicted one (~35 kyr), hence supporting the hypothesis of shortened obliquity periods during the Early Jurassic, and providing constraints on Earth's tidal dissipation factor during this geologic epoch. Finally, a remarkable phase change between %CaCO 3 and δ ¹³ C orbitally paced cycles is observed for the first time at the T-OAE, suggesting a change in the carbon reservoir in relation with volcanically released greenhouse gases and major carbonate crisis. However, this phase shift is not observed at the Pl-To event implying different causal mechanisms on the carbon cycle perturbation between the Pl-To and T-OAE events.
Article
The numerical age of the Jurassic-Cretaceous boundary has been controversial and difficult to determine. In this study, we present high-precision U-Pb geochronological data around the Jurassic-Cretaceous boundary in two distinct sections from different sedimentary basins: the Las Loicas, Neuquén Basin, Argentina, and the Mazatepec, Sierra Madre Oriental, Mexico. These two sections contain primary and secondary fossiliferous markers for the boundary as well as interbedded volcanic ash horizons, allowing researchers to obtain new radioisotopic dates in the late Tithonian and early Berriasian. We also present the first age determinations in the early Tithonian and tentatively propose a minimum duration for the stage as a cross-check for our ages in the early Berri-asian. Given our radioisotopic ages in the early Tithonian to early Berriasian, we discuss implications for the numerical age of the boundary.
Article
The Earth's cryosphere represents a huge climate-sensitive carbon reservoir capable of releasing carbon dioxide (CO2) and methane (CH4) from permafrost soils or gas reservoirs capped by permafrost and ice caps upon rising global temperatures. Carbon release from these reservoirs has the potential to further accelerate global warming. Present day cryosphere demise is a focus of scientific research. The potential role of cryosphere carbon reservoirs in Mesozoic climate perturbations is even lesser known and currently underinvestigated. In contrast to previous views of a constantly warm Early Jurassic period, virtually lacking a cryosphere, recent studies have identified icehouse conditions for this time interval. Following these icehouse conditions, global warming occurred during the early Toarcian (~183 Ma) and was accompanied by a major carbon cycle anomaly as manifested in recurring negative carbon isotope excursions (CIEs). We propose that an initially volcanic-driven gentle rise of atmospheric temperature in the Early Toarcian triggered a melt-down of Earth's cryosphere which during the preceding Pliensbachian had expanded to the mid-latitudes and thus was highly vulnerable to warming. The rapid release of greenhouse gases, mainly as 13C-depleted CH4, or its oxidation product CO2, is recorded in the carbon isotope ratios of sedimentary organic matter and carbonates. Toarcian sediments display a series of orbitally-forced negative CIEs characterized by a frequency shift from eccentricity to obliquity cycles comparable to Pleistocene climate rhythms. This pattern is explained by a self-sustaining destabilization of labile cryosphere carbon reservoirs which started at mid-latitudes where eccentricity is most effective and then rhythmically progressed poleward to latitudes where obliquity dominates. The hitherto underestimated presence of a temperature-sensitive Pliensbachian cryosphere constituted an essential precondition for the early Toarcian climate change and its associated sea-level rise. The Pliensbachian cooling had transferred water into the terrestrial cryosphere causing a severe sea-level fall. Transgressive pulses at the Pliensbachian-Toarcian boundary and in the early Toarcian occurred concomitant to rising global temperatures and resulted from the meltdown of continental ice caps. This ice-volume effect and the massive discharge of freshwater into the oceans is well preserved in the exceptionally low δ18O values of carbonates formed during the cryosphere demise and sea-level increase. Carbon and oxygen isotope ratios, climate and sea-level shifts thus underpin the presence of an Early Jurassic cryosphere and thereby highlight the role of glacio-eustatic mechanisms as main drivers of late Pliensbachian to early Toarcian geodynamics.
Article
Different lines of evidence suggest that the main trigger mechanism for the end-Triassic mass extinction was the release of volcanic and thermogenic gases during the emplacement of the Central Atlantic Magmatic Province (CAMP). However, the short duration of the biotic and environmental crisis and the magmatic activity hinders precise control on the relative timing between these events, especially when comparing the continental sedimentary record where there is no independent age control with the magmatic record. In order to disentangle the temporal relationships of the end-Triassic events, we have analyzed the palynology of the sedimentary strata interlayered with CAMP lava flows from eleven sites throughout Morocco (Western and Central High Atlas, Middle Atlas, Western Meseta). The recovered sporomorphs help to constrain the age of CAMP volcanism, allowing the stratigraphic correlation of the basaltic volcanism with the extinction and geochemical records such as carbon-isotope and mercury shifts, recorded in marine sedimentary successions worldwide. Our new data show that CAMP erupted almost entirely during the end-Triassic mass extinction interval, just before the Triassic–Jurassic boundary (Tr-J). Hence, a very rapid emplacement of the CAMP very likely triggered the carbon cycle and ecological disruption at the Tr-J boundary.
Article
Dinosaurs were large-bodied land animals of the Mesozoic that gave rise to birds. They played a fundamental role in structuring Jurassic-Cretaceous ecosystems and had physiology, growth, and reproductive biology unlike those of extant animals. These features have made them targets of theoretical macroecology. Dinosaurs achieved substantial structural diversity, and their fossil record documents the evolutionary assembly of the avian body plan. Phylogeny-based research has allowed new insights into dinosaur macroevolution, including the adaptive landscape of their body size evolution, patterns of species diversification, and the origins of birds and bird-like traits. Nevertheless, much remains unknown due to incompleteness of the fossil record at both local and global scales. This presents major challenges at the frontier of paleobiological research regarding tests of macroecological hypotheses and the effects of dinosaur biology, ecology, and life history on their macroevolution.
Article
A composite largely Middle Jurassic succession spanning the Toarcian–Aalenian transition to the lowermost Bathonian exposed at Cabo Mondego and São Gião in the northern Lusitanian Basin, western Portugal, was examined palynologically. The 129 samples are correlated to ammonite biozones spanning Pleydellia aalensis to Zigzagiceras zigzag. The Cabo Mondego succession comprises the type section of the Cabo Mondego Formation and spans virtually the entire interval studied. This is a significant interval because it includes the Global Stratotype Section and Point (GSSP) and the Auxiliary Stratigraphical Section and Point (ASSP) for the Bajocian and Bathonian stages respectively. The Cabo Mondego Formation largely yielded relatively abundant palynomorph associations in the 68 productive samples recovered. By contrast, the Pó'voa da Lomba Formation at São Gião only includes the Toarcian–Aalenian transition; the 21 productive horizons produced sparse assemblages. The uppermost Toarcian to lowermost Bajocian is characterised by a low diversity dinoflagellate cyst association, typified by Nannoceratopsis. Above this is a markedly more diverse assemblage. This influx, in the Witchellia laeviuscula ammonite biozone AB, represents a global evolutionary radiation which may be linked to sea level rise. The trend of increasing dinoflagellate cyst diversity continued at the Bajocian–Bathonian transition. The Middle Jurassic dinoflagellate cyst assemblages of the Lusitanian Basin are significantly less diverse than coeval palynobiotas from eastern and northern Europe, and the Arctic. The Toarcian Oceanic Anoxic Event (T-OAE) profoundly inhibited cyst-forming dinoflagellates in this depocentre, and the recovery was protracted. Hence the T-OAE may have suppressed dinoflagellate cyst diversity well into the Middle Jurassic. This phenomenon may have been exacerbated by the absence of typically Arctic taxa through latitudinal controls and/or global cooling during the early Aalenian. These low levels of dinoflagellate cyst species richness may also be related to the palaeogeography of the Lusitanian Basin. This relatively isolated deepwater depocentre close to the Proto Atlantic, may have precluded extensive biotal exchange with the widespread shelfal areas of the western Tethys. The absence of Dissiliodinium giganteum in the Lusitanian Basin is consistent with this scenario. The pollen and spores observed in this study are typical of Middle Jurassic assemblages worldwide. Araucarian pollen, largely Callialasporites, diversified and became prominent during the Aalenian.
Article
The Late Pliensbachian–Early Toarcian is a pivotal time in the Mesozoic era, marked by pronounced carbon-isotope excursions, biotic crises and major climatic and oceanographic changes. Here we present new high-resolution carbon-isotope and magnetic-susceptibility measurements from an expanded hemipelagic Late Pliensbachian–Early Toarcian section from the Middle Atlas Basin (Morocco). Our new astronomical calibration allows the construction of an orbital time scale based on the 100-kyr eccentricity cycle. The Early Toarcian Polymorphum Zone contains 10 to 10.5 repetitions of the 100-kyr eccentricity both in the carbon-isotope and the magnetic-susceptibility data, leading to an average duration of 1.00±0.08 myr. We also show that the Late Pliensbachian–Early Toarcian global carbon-cycle perturbation has an average duration of 0.24±0.02 myr. These durations are comparable to previous astrochronological time scales provided for this time interval in the most complete sections of the Tethyan area, and longer than what has been provided in condensed sections. Anchoring this framework on published radiometric ages and astrochronological time scales, we estimate that the carbon-cycle perturbation of the Late Pliensbachian–Early Toarcian corresponds with the early phase of the Karoo and Chonke Aike large igneous provinces. Likewise, our new age constraints confirm that the Toarcian oceanic anoxic event is synchronous to the main phase of the Ferrar volcanic activity. Thus, these successive and short phases of the volcanic activity may have been at the origin of the successive phases of the mass extinctions observed in marine biotas in the Pliensbachian and Toarcian times.
In the Upper Bathonian and Lower Callovian (Middle Jurassic), the ammonite genus Kepplerites is an important guide fossil. With its help, Jurassic rocks can be correlated from North America, Greenland, Russia to Central Europe. The basis of the Callovian Stage is defined by the keppleri horizon, which occurs in more than 20 localities in Southern Germany and Switzerland, as well as in England, the Caucasus and on the Russian Platform. Probably Kepplerites keppleri or at least closely related species also occur in Greenland and Arctic Canada. In parts of the Boreal Upper Bathonian (Canada, Alaska, Greenland and Russian Platform) Cadoceras and Kepplerites are the most common ammonites. Across the territory of the present Caucasus, some species migrated to Central Europe, namely K. (Kepplerites) aigii MITTA, K. (K.) traillensis DONOVAN and K. (K.) radiatus SAKHAROV & LOMINADZE. These species are described in detail, in addition to Kepplerites keppleri and K. herscheli nov. sp., which belongs to the new subgenus Tychoites. The widespread extinction of Kepplerites soon after the beginning of the Callovian was possibly caused by an eustatic sea level fall. © 2017 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Article
Chemical weathering consumes atmospheric carbon dioxide through the breakdown of silicate minerals and is thought to stabilize Earth’s long-term climate. However, the potential influence of silicate weathering on atmospheric pCO2 levels on geologically short timescales (10^3–10^5 years) remains poorly constrained. Here we focus on the record of a transient interval of severe climatic warming across the Toarcian Oceanic Anoxic Event or T-OAE from an open ocean sedimentary succession from western North America. Paired osmium isotope data and numerical modelling results suggest that weathering rates may have increased by 215% and potentially up to 530% compared to the pre-event baseline, which would have resulted in the sequestration of significant amounts of atmospheric CO2. This process would have also led to increased delivery of nutrients to the oceans and lakes stimulating bioproductivity and leading to the subsequent development of shallow-water anoxia, the hallmark of the T-OAE. This enhanced bioproductivity and anoxia would have resulted in elevated rates of organic matter burial that would have acted as an additional negative feedback on atmospheric pCO2 levels. Therefore, the enhanced weathering modulated by initially increased pCO2 levels would have operated as both a direct and indirect negative feedback to end the T-OAE.
Article
Changes in and from marine strata occur globally in association with the end-Triassic mass extinction and the emplacement of the Central Atlantic Magmatic Province (CAMP) during the break up of Pangea. As is typical in deep time, the timing and duration of these isotopic excursions has remained elusive, hampering attempts to link carbon cycle perturbations to specific processes. Here, we report and from Late Triassic and Early Jurassic strata near Levanto, Peru, where intercalated dated ash beds permit temporal calibration of the carbon isotope record. Both and exhibit a broad positive excursion through the latest Triassic into the earliest Jurassic. The first order positive excursion in is interrupted by a negative shift noted in many sections around the world coincident with the extinction horizon. Our data indicate that the negative excursion lasts kyrs, longer than inferred by previous studies based on cyclostratigraphy. A kyr positive shift follows, during which the first Jurassic ammonites appear. The overall excursion culminates in a return to pre-perturbation carbon isotopic values over the next kyrs. Via chronologic, isotopic, and biostratigraphic correlation to other successions, we find that and return to pre-perturbation values as CAMP volcanism ceases and in association with the recovery of pelagic and benthic biota. However, the initiation of the carbon isotope excursion at Levanto predates the well-dated CAMP sills from North America, indicating that CAMP may have started earlier than thought based on these exposures, or that the onset of carbon cycle perturbations was not related to CAMP.
Article
A study is conducted to supplement the uppermost Lower Jurassic–lowermost Cretaceous marine strontium isotope dataset and to present new statistical fits of the Middle–Late Jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme. The use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations. The presented correlation tables enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks. New strontium isotope data have been obtained from well-preserved Lower Bajocian, uppermost Callovian, Oxfordian, Kimmeridgian, and Upper Volgian belemnite rostra.
Article
By 1849, Alcide d'Orbigny had proposed a very modern looking global subdivision of a Jurassique ‘System’, into a sequence of 10 étages. D'Orbigny's stages were based on a basic biostratigraphical framework, but there were still a number of issues with its actual demonstrable applicability internationally. In 1856, Albert Oppel took d'Orbigny's framework and, as stated by W.J.Arkell in 1933, ‘breath[ed] new life into it…placing the whole science of stratigraphical geology on a new footing’. Oppel recognized eight ‘Etagen’, divided into a sequence of ‘zones’ which he considered to be time-related to correlation units of theoretically universal application – a very clear and unambiguous statement of what now would be considered to be chronostratigraphical practice. Subsequently, evolution of Jurassic stratigraphy had, by the end of the 18th century led to S.S Buckman's high-resolution ammonite correlation schemes using hemera – essentially the same as modern biohorizons. Although some of this detail was subsequently lost in his syntheses, from around 1933–1956, W.J. Arkell took many pre-existing ‘zonal’ schemes and began to develop global ‘standard’ ammonite correlation schemes – again explicitly chronostratigraphical. Nevertheless, the potential for very high-resolution ammonite-based correlation schemes – with a resolution of only around 100,000 or less – was soon rediscovered and promoted by J.H. Callomon and by a very active ‘French School’. Despite all this activity, however, we still have not quite realized the ordered stratigraphical dreams of Oppel and his successors. Of the 11 stages now formally recognized within the Jurassic, four still do not have a ratified GSSP, and within the entire system, there still appear to be no formal agreements on what really are the ‘standard’ zones for each stage. Crucially, however, confusion is still widespread as to the ‘meaning’ of these zones – Jurassic ‘Standard Zones’ are chronozones not biozones – they have been explicitly so since Oppel's day, and as the stratigraphical building blocks of all ‘modern’ Jurassic stages, they must still be.