Jurassic sequences of the Hebrides Basin, Isle of Skye, Scotland.

The hebridean area is well known for the spectacular Palaeocene igneous rocks (plutons, dykes, sills and flood basalts) that form part of the North Atlantic large igneous province. The exposures of Mesozoic sedimentary strata of the Hebrides have been less widely appreciated, partly because they are perceived as having been extensively altered by thermal metamorphism. Whilst this is undoubtedly true locally, the bulk of the succession remains only weakly affected, and much of significance has been learned from it of Jurassic palaeoenvironments, biostratigraphy and magnetostratigraphy. Additionally, because of recent hydrocarbon exploration in the Mesozoic basins offshore west of Scotland and Ireland (Trueblood & Morton, 1991; Fyfe et al., 1993; Stoker et al., 1993; Scotchman & Thomas, 1995) these succession have assumed a new importance as the nearest easily accessible outcrop analogue

Tectonic forcing of Early to Middle Jurassic seawater Sr/Ca

types: ArticleThis is the author formatted version of Ullman et al. (2013) Geology 41(12), 1211-1214. doi:10.1130/G34817.1 http://geology.gsapubs.org/content/41/12/1211.full Uploaded under the terms of Green Open Access in GSA's Open Access PolicyThe Jurassic Period (ca. 201–145 Ma) is marked by fundamental reorganizations of paleogeography, paleoceanography, ecosystems, and the progressive shift from aragonite to calcite as the favored marine biogenic carbonate polymorph. Sr/Ca ratios of well-preserved Jurassic oysters and belemnites from sections in the UK and Poland demonstrate that the Sr/Ca ratio of seawater varied systematically throughout the Early and Middle Jurassic in parallel with already documented seawater 87Sr/86Sr. The Sr flux from increased mid-ocean ridge activity in the Early Jurassic outbalanced the input of riverine Sr, leading to gradually lower seawater 87Sr/86Sr associated with the parallel and strong decrease in seawater Sr/Ca ratios. This downward trend was reversed by enhanced continental input in the Toarcian and Aalenian, but resumed in the Bajocian and continued to the Callovian. Parallel changes of seawater 87Sr/86Sr and Sr/Ca suggest a common cause for these long-term variations and are best explained by changes in the balance of continental weathering and hydrothermal fluxes. These findings underline the strong control of global tectonic processes on the evolution of biomineralization and downplay the role of biomineral evolution in influencing strontium chemistry of seawater in the mid-Mesozoi

Integrated stratigraphy of the Kimmeridge Clay Formation (Upper Jurassic) based on exposures and boreholes in south Dorset, UK

For the purposes of a high-resolution multi-disciplinary study of the Upper Jurassic Kimmeridge Clay Formation, two boreholes were drilled at Swanworth Quarry and one at Metherhills, south Dorset, UK. Together, the cores represent the first complete section through the entire formation close to the type section. We present graphic logs that record the stratigraphy of the cores, and outline the complementary geophysical and analytical data sets (gamma ray, magnetic susceptibility, total organic carbon, carbonate, [delta]13Corg). Of particular note are the new borehole data from the lowermost part of the formation which does not crop out in the type area. Detailed logs are available for download from the Kimmeridge Drilling Project web-site at http://kimmeridge.earth.ox.ac.uk/. Of further interest is a mid-eudoxus Zone positive shift in the [delta]13Corg record, a feature that is also registered in Tethyan carbonate successions, suggesting that it is a regional event and may therefore be useful for correlation. The lithostratigraphy of the cores has been precisely correlated with the nearby cliff section, which has also been examined and re-described. Magnetic-susceptibility and spectral gamma-ray measurements were made at a regular spacing through the succession, and facilitate core-to-exposure correlation. The strata of the exposure and core have been subdivided into four main mudrock lithological types: (a) medium-dark–dark-grey marl; (b) medium-dark–dark grey–greenish black shale; (c) dark-grey–olive-black laminated shale; (d) greyish-black–brownish-black mudstone. The sections also contain subordinate amounts of siltstone, limestone and dolostone. Comparison of the type section with the cores reveals slight lithological variation and notable thickness differences between the coeval strata. The proximity of the boreholes and different parts of the type section to the Purbeck–Isle of Wight Disturbance is proposed as a likely control on the thickness changes

Non-marine carbon-isotope stratigraphy of the Triassic-Jurassic transition in the Polish Basin and its relationships to organic carbon preservation, pCO2 and palaeotemperature

New carbon-isotope data obtained from homogenous organic material (separated microfossil wood; δ13Cwood) from the upper Rhaetian and entire Lower Jurassic permit chemostratigraphic correlation of these marginal/non-marine deposits with the biostratigraphically well-constrained Llanbedr (Mochras Farm) core in N Wales and other marine profiles, supported by sequence stratigraphic correlation and biostratigraphical markers. Statistically significant (Rs = 0.61) positive exponential correlation between δ13Cwood values and continental TOC (TOCcont) concentrations occurs and can be defined empirically by equation. Changes of δ13Cwood observed in C3 plants depends on δ13CO2 of atmosphere and can be modulated by other factors such as pCO2 causing fractionation (enrichment in 12C) of C isotopes in source C3 plants and, to lesser extent, by soil moisture content. Floral remains occurring in the relatively stable palaeolatitude and climatic zone of the Polish Basin in the time interval studied lend no support for significant precipitation impact on the δ13C fractionation, although enhanced precipitation could have had a limited impact during the Toarcian Oceanic Anoxic Event (T-OAE). We argue that the observed relation between δ13Cwood values and TOCcont reflects the global carbon cycle forcing. Such correlations may develop because fluxes of of 12C-enriched methane, mobilized from near-surface carbon sources, lead to global warming, decreased δ13Cwood and enhanced (usually fungally-mediated) decomposition of the terrestrial carbon pool, while subsequent massive burial of organic carbon results in higher δ13C values in all carbon cycle reservoirs, and the attendant drawdown of atmospheric CO2 leads to global cooling and promotes sequestration of soil organic matter. In turn, this relation can be used as an indirect indicator of atmospheric temperature trends, although organic carbon isotope records are potentially subject to many different influences. Based on the δ13Cwood /TOCcont relationship, an approximate qualitative estimation of general trends in air temperature is suggested for c. 40oN paleolatitude and the warm temperate climatic zone. The observed hypothetical trends in temperature are generally in concordance with pCO2 trends calculated from stomatal index. A weak δ13Cwood and TOCcont correlation in Rhaetian deposits is explained by local environmental factors (TOC concentration dependent on a more localized fluvial plain settings), while mostly deltaic – coastal deposits contain more representative, averaged material delivered from a large catchment area

Effect of a Jurassic Oceanic Anoxic Event on belemnite ecology and evolution.

notes: PMCID: PMC4104856types: Journal Article; Research Support, Non-U.S. Gov'tThis is the author formatted version of Ullman et al. (2014) PNAS 111(28), 10073-10076. The published version of this article is available at http://www.pnas.org/content/111/28/10073.fullThe Toarcian oceanic anoxic event (T-OAE; ∼ 183 million y ago) is possibly the most extreme episode of widespread ocean oxygen deficiency in the Phanerozoic, coinciding with rapid atmospheric pCO2 increase and significant loss of biodiversity in marine faunas. The event is a unique past tipping point in the Earth system, where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic C isotope records. Modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases. Potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the T-OAE. Here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early Toarcian belemnites. We combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early Toarcian global exogenic carbon cycle perturbation and belemnite paleoecology. The organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation, environmental change, and biotic response during the T-OAE. We infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

Palynological, geochemical, and mineralogical characteristics of the Early Jurassic Liasidium Event in the Cleveland Basin, Yorkshire, UK

A previously proposed hyperthermal episode in the Early Jurassic (mid-Sinemurian) is investigated from the shallow marine succession at Robin Hood’s Bay, Cleveland Basin, Yorkshire, UK. Palynological study confirms that the stratigraphical extent of the distinctive dinoflagellate cyst Liasidium variabile corresponds very closely to the oxynotum Zone. The range of Liasidium variabile also corresponds to an overall negative excursion in carbon-isotopes measured in bulk organic matter, which here exhibits a double spike in the middle oxynotum Zone. Additionally, Liasidium variabile abundances track overall transgressive-regressive facies trends with peak abundance of dinoflagellate cysts corresponding to deepest water facies and maximum flooding. Lithological cycles (parasequences), defined by visual description and hand-held X-ray fluorescence analysis of powdered samples, match previously suggested short eccentricity cycles, and allow a total duration for the event of at least one million years to be suggested. Changes in clay mineralogy throughout the section determined by whole rock X-ray diffraction and scanning electron microscopy are shown to be largely related to authigenic processes, and neither support nor refute the proposition of coeval palaeoclimate changes. The combined characteristics of the Liasidium Event described from Robin Hood’s Bay are similar to, but much less extreme than, the Early Jurassic Toarcian Oceanic Anoxic Event albeit, at this locality, there is no evidence for the development of significant bottom water deoxygenation

The toarcian oceanic anoxic event (Early Jurassic) in the Neuquén Basin, Argentina: A reassessment of age and carbon isotope stratigraphy

The Toarcian oceanic anoxic event (T-OAE) is recorded by the presence of globally distributed marine organic carbon– rich black shales and a negative carbon isotope shift, with δ13Corg values as low as -33‰, interrupting an overarching positive excursion. Here we present new biostratigraphic data and high-resolution δ13Corg data from two Southern Hemisphere localities: Arroyo Serrucho in the north and Arroyo Lapa in the south of the Neuquén Basin, Argentina. Previous studies at these localities aimed to provide an accurate numerical age for the T-OAE and characterization of its carbon isotope stratigraphy. The new carbon isotope data and ammonite biostratigraphy presented here from Arroyo Serrucho show the T-OAE to be recorded lower in the section than supposed by previous authors, thus calling into question the published age of the T-OAE in this section. A newly investigated exposure at Arroyo Lapa North shows a complex carbon isotope record with at least three high-amplitude fluctuations in the hoelderi zone (equivalent to the serpentinum zone in northwestern Europe), with δ13Corg values of <-28‰, and two intervening positive isotope excursions, with δ13Corg values around -24‰. At Arroyo Lapa South, the characteristic major stepped negative carbon isotope excursion is recorded, with δ13Corg values of <-30‰ and total organic-carbon contents increasing to 11%; above this level an erosional surface of a submarine channel truncates the section. These new data are globally correlative and unambiguously illustrate the global reach of the T-OAE.Fil: Al Suwaidi, Aisha H.. Petroleum Institute University; Emiratos Árabes UnidosFil: Hesselbo, Stephen P.. University of Exeter; Reino UnidoFil: Damborenea, Susana Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; ArgentinaFil: Manceñido, Miguel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; ArgentinaFil: Jenkyns, Hugh C.. University of Oxford; Reino UnidoFil: Riccardi, Alberto Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Angelozzi, Gladys Noemí. YPF - Tecnología; ArgentinaFil: Baudin, François. Université Pierre et Marie Curie; Franci

Orbital pacing and secular evolution of the Early Jurassic carbon cycle

Cyclic variations in Earth’s orbit drive periodic changes in the ocean–atmosphere system at a time scale of tens to hundreds of thousands of years. The Mochras δ13CTOC record illustrates the continued impact of long-eccentricity (405-ky) orbital forcing on the carbon cycle over at least ∼18 My of Early Jurassic time and emphasizes orbital forcing as a driving mechanism behind medium-amplitude δ13C fluctuations superimposed on larger-scale trends that are driven by other variables such as tectonically determined paleogeography and eruption of large igneous provinces. The dataset provides a framework for distinguishing between internal Earth processes and solar-system dynamics as the driving mechanism for Early Jurassic δ13C fluctuations and provides an astronomical time scale for the Sinemurian Stage

Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations

The Early Jurassic was marked by multiple periods of major global climatic and palaeoceanographic change, biotic turnover and perturbed global geochemical cycles, commonly linked to large igneous province volcanism. This epoch was also characterised by the initial break-up of the super-continent Pangaea and the opening and formation of shallow-marine basins and ocean gateways, the timing of which are poorly constrained. Here, we show that the Pliensbachian Stage and the Sinemurian–Pliensbachian global carbon-cycle perturbation (marked by a negative shift in δ13Cδ13C of 2–4‰2–4‰), have respective durations of ∼8.7 and ∼2 Myr. We astronomically tune the floating Pliensbachian time scale to the 405 Kyr eccentricity solution (La2010d), and propose a revised Early Jurassic time scale with a significantly shortened Sinemurian Stage duration of 6.9±0.4 Myr6.9±0.4 Myr. When calibrated against the new time scale, the existing Pliensbachian seawater 87Sr/86Sr record shows relatively stable values during the first ∼2 Myr of the Pliensbachian, superimposed on the long-term Early Jurassic decline in 87Sr/86Sr. This plateau in 87Sr/86Sr values coincides with the Sinemurian–Pliensbachian boundary carbon-cycle perturbation. It is possibly linked to a late phase of Central Atlantic Magmatic Province (CAMP) volcanism that induced enhanced global weathering of continental crustal materials, leading to an elevated radiogenic strontium flux to the global ocean