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The first record of the Early Toarcian Oceanic Anoxic Event (c. 183 Ma) from the Southern Hemisphere is described from the Neuquen Basin, Argentina, identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbon-isotope excursion ([[delta].sup.13][C.sub.org]) in bulk rock and fossil wood. The negative excursion of -6 [per thousand] in bulk organic carbon (falling to -31.3 [per thousand]) crosses the boundary of the tenuicostatum--hoelderi Andean ammonite Zones, equivalent to the tenuicostatum--falciferum/serpentinum zones of Europe. These data indicate that the Early Toarcian Oceanic Anoxic Event was a global phenomenon. Supplementary material: A detailed stratigraphic log, chemostratigraphic data and nannofossil data are available at http:// www.geolsoc.org.uk/SUP18411. doi: 10.1144/0016-76492010-025.

We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian--Turonian boundary, interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c. 4[per thousand] for TOC and phytane and c. 2.5[per thousand] for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak [[delta].sup.13]C values for all components are followed by intervals of high, near-constant [[delta].sup.13]C in the form of an isotopic plateau. Recognition of an unambiguous return to background [[delta].sup.13]C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcarcous nannofossil Quadrum gartneri at or near the Cenomanian--Turonian boundary as established by ammonite stratigraphy, in conjunction with the end of the [[delta].sup.13]C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage. Keywords: Oceanic Anoxic Event 2, Eastbourne, England, Gubbio, Italy, Tarfaya, Morocco, [sup.13]C.

Carbon- and oxygen-isotope stratigraphy of English Chalk and Italian Scaglia show similar trends in oxygen-isotope in various Chalk sections despite individual variation in values that are diagenesis-dependent. Warming till the Cenomanian-Turonian boundary interval and subsequent cooling are observed in the East Kent section. Climatic deterioration and CO2 drawdown result from regional organic-carbon burial.

A detailed isotopic profile is presented for a stratigraphically expanded Cenomanian-Turonian boundary section in Chalk facies exposed at Eastbourne, Sussex and compared with data from Pueblo, Colorado. In both sections macro- and micropalaeontological markers (first appearances and disappearances) are well-constrained, and their relative positions and relationship to the structure of the carbon-isotope curve are identical. This consistent relationship between two independent phenomena, one geochemical, the other biostratigraphical, is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon-isotope excursion in these two areas. This interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon-isotope excursion in Europe and North America.

Presents data from the Belemnite Marls, Dorset, southern England, using cyclostratigraphy and the early Jurassic timescale. Sedimentology and diagenesis; Paleographic setting; Analysis of time series; Nature of bundle cycles and paleoclimatic variations in early Jurassic time.

Oceanic Anoxic Event 2 (OAE 2), which took place around the Cenomanian–Turonian boundary (∼94 Ma), is associated with extreme perturbations to the global carbon cycle, affected ocean basins worldwide and was associated with significant biological turnover. Although this event has been well studied in the northern hemisphere, the evolution and character of OAE 2, particularly in terms of the vertical and lateral extent of anoxia, is poorly constrained in the palaeo-Pacific Ocean. Furthermore, the precise timing, duration and character of this event, and the exact mechanisms driving OAE 2 environmental changes, are still being debated. Here, we present the first high-resolution records of carbon isotopes, total organic carbon and magnetic susceptibility from the southern palaeo-Pacific Ocean during OAE 2, sampled at two sections in New Zealand. The carbon isotope records from both localities reveal a ∼2‰ positive excursion that represents the global change in the carbon cycle associated with OAE 2. When combined with a cyclostratigraphic age model, these new records constrain the duration of the OAE 2 carbon isotope excursion to at least 930 ± 25 ky and indicate a minimum duration of 200 ± 25 ky for the 'Plenus Cold Event' that took place during OAE 2. The lithologies and low organic-carbon contents of the New Zealand sections imply that oxic conditions prevailed along, at least parts of, the margins of the palaeo-Pacific Ocean at mid- to high southern latitudes during OAE 2 while, contemporaneously, conditions were locally anoxic in the mid-water column of the equatorial Pacific Ocean. Despite these apparently oxic conditions in the New Zealand region, there was a partial collapse of benthic ecosystems leading up to, and during, OAE 2, suggesting environmental deterioration caused by intermittent oxygen deprivation, or other chemical or biological disturbances in the South Pacific region that remain to be elucidated. • First high-resolution C-isotope stratigraphy for OAE 2 from a high southern latitude. • Duration of the OAE 2 CIE was ≥930 ± 25 ky. • Duration of the 'Plenus Cold Event' within the OAE 2 CIE was ≥200 ± 25 ky. • Oceanic conditions were mostly oxic in the Southwest (SW) Pacific during OAE 2. • Intermittent ocean anoxia likely degraded the SW Pacific environment during OAE 2. [ABSTRACT FROM AUTHOR]

The Sogno Core represents one of the deepest pelagic records of the Toarcian Oceanic Anoxic Event (T-OAE) in the Alpine-Mediterranean Tethys. New sedimentological, elemental, Rock-Eval, and biomarker data are presented here, with the aim of reconstructing the depositional conditions that characterized the sedimentation of this succession during the broad positive carbon-isotope excursion of the T-OAE, and its negative isotopic anomaly (Jenkyns Event). Higher Mn xs concentrations, inversely correlated with the δ18O curve, were observed starting slightly below the onset level of the Jenkyns Event up to the lowermost part of the negative carbon-isotope anomaly, reflecting a combination of a gradual warming and a progressive increase in fresh waters delivered by runoff. Increased weathering intensity was accompanied by enhanced detrital input with higher concentrations in lithogenic elements, and by a relative increase in palaeoproductivity, consistently with higher Si xs concentrations and changes in calcareous nannoplankton assemblages. The enhanced fresh-water input favored water-column stratification, less efficient deep-water circulation and oxygen depletion. Except for two discrete black shales characterized by anoxic pore waters, redox conditions at Sogno turned at maximum suboxic, as indicated by rare to absent bioturbation, limited enrichments in redox-sensitive elements, and molecular biomarkers. The Sogno Core record shows that dominant oxic–suboxic conditions were present also at bathyal depths in the Alpine-Mediterranean Tethys during the Jenkyns Event, thereby contrasting with the anoxic–euxinic environments present both in the shallower water basins and sub-basins of epicontinental northern Europe and, locally, in the relatively deep-water areas of the Alpine Tethys. • In the Lombardy Basin suboxic to oxic conditions prevailed during the Toarcian Oceanic Anoxic Event. • Water stratification caused by enhanced runoff and warmer conditions favoured the onset of bottom-water suboxia. • Reducing conditions became generally more severe around the lowest point in the δ13C trough that defines the Jenkyns Event. • The Alpine-Mediterranean Tethys was mainly characterized by suboxic conditions during the Toarcian Oceanic Anoxic Event. [ABSTRACT FROM AUTHOR]

The Mesozoic Era featured emplacement of a number of Large Igneous Provinces (LIPs), formed by the outpouring of millions of cubic kilometres of basaltic magma. The radiometric ages of several Mesozoic LIPs coincide with the dates of Oceanic Anoxic Events (OAEs). As a result of these coincidences, a causal link has been suggested, but never conclusively proven. This study explores the use of mercury as a possible direct link between the Karoo–Ferrar LIP and the coeval Toarcian OAE (T-OAE). Mercury is emitted to the atmosphere as a trace constituent of volcanic gas, and may be distributed globally before being deposited in sediments. Modern marine deposits show a strong linear correlation between mercury and organic-matter content. Results presented here indicate departures from such a simple linear relationship in sediments deposited during the T-OAE, and also during the Pliensbachian–Toarcian transition (an event that saw elevated benthic extinctions and carbon-cycle perturbations prior to the T-OAE). A number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events, suggesting a rise in the depositional flux of this element. Complications to this relationship may arise from very organic-rich sediments potentially overprinting any Hg/TOC signal, whereas environments preserving negligible organic matter may leave no record of mercury deposition. However, the global distribution of coevally elevated Hg-rich levels suggests enhanced atmospheric mercury availability during the Early Toarcian, potentially aided by the apparent affinity of Hg for terrestrial organic matter, although the relative importance of aquatic vs terrestrial fixation of Hg in governing these enrichments remains uncertain. A perturbation in atmospheric Hg is most easily explained by enhanced volcanic output. It is suggested that extrusive igneous activity caused increased mercury flux to the Early Toarcian sedimentary realm, supporting the potential of this element as a proxy for ancient volcanism. This interpretation is consistent with a relationship between LIP formation and a perturbed carbon cycle during the Pliensbachian–Toarcian transition and T-OAE. The recording of these two distinct Hg excursions may also indicate that the Karoo–Ferrar LIP released volatiles in temporally distinct episodes, due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile-rich lithologies. [ABSTRACT FROM AUTHOR]