Abstract The Jenkyns Event or Toarcian Oceanic Anoxic Event was an episode of severe environmental perturbations reflected in carbon isotope and other geochemical anomalies. Although well studied in the epicontinental basins in NW Europe, its effects are less understood in open marine environments. Here we present new geochemical (carbon isotope, CaCO 3 , [Mn]) and nannofossil biostratigraphic data from the Tölgyhát and Kisgerecse sections in the Gerecse Hills (Hungary). These sections record pelagic carbonate sedimentation near the margin of the Tethys Ocean. A negative carbon isotope excursion of c. 6‰ is observed in the Tölgyhát section, in a condensed clay and black shale layer where the CaCO 3 content drops in association with the Jenkyns Event. At Kisgerecse, bio- and chemostratigraphic data suggest a gap in the lower Toarcian. The presence of an uppermost Pliensbachian hardground, the absence of the lowermost Toarcian Tenuicostatum ammonite zone and the condensed record of the Jenkyns Event at Tölgyhát, together with a condensed Tenuicostatum Zone and the missing negative carbon isotope anomaly at Kisgerecse, imply arrested carbonate sedimentation. A calcification crisis and sea-level rise together led to a decrease in carbonate production and terrigenous input, suggesting that volcanogenic CO 2 -driven global warming may have been their common cause.

In the last decade, major advances have been made in our understanding of the end-Triassic mass extinction, related environmental changes, and volcanism of the Central Atlantic magmatic province. Studies of various fossil groups and synoptic analyses of global diversity document the extinction and subsequent recovery. The concomitant environmental changes are manifested in a series of carbon isotope excursions (CIE), suggesting perturbations in the global carbon cycle. Besides the earlier-recognized initial and main negative anomalies, a more complex picture is emerging with other CIEs, both negative and positive, prior to and following the Triassic-Jurassic boundary. The source of isotopically light carbon remains debated (methane from hydrate dissociation vs. thermogenic methane), but either process is capable of amplifying an initial warming, resulting in runaway greenhouse conditions. Excess CO 2 entering the ocean causes acidification, an effective killing mechanism for heavily calcified marine biota that appears implicated in the reef crisis. The spatial and temporal extent of Central Atlantic magmatic province volcanism is established through a growing data set of radiometric ages. Since the Central Atlantic magmatic province is one of the largest Phanerozoic large igneous provinces, volcanic CO 2 -driven warming is plausible as a key factor in the chain of Triassic-Jurassic boundary events. Greenhouse warming may have been punctuated by short-term cooling episodes due to H 2 S emission and production of sulfate aerosols, a process more difficult to trace in the stratigraphic record. Taken together, recently generated data significantly increase the support for Central Atlantic magmatic province volcanism as a viable trigger for the environmental and biotic changes around the Triassic-Jurassic boundary.

Abstract A review of geochronological data underlying the geological timescale for the Triassic yields a significantly different timescale calibration than that published in the most recent compilation (Geologic TimeScale 2004). This is partly due to the availability of new radio–isotopic data, but mostly because strict selection criteria are applied and complications arising from biases (both systematic and random) are accounted for in this contribution. The ages for the base and the top of the Triassic are constrained by U–Pb ages to 252.3 and 201.5 Ma, respectively. These dates also constrain the ages of major extinction events at the Permian–Triassic and Triassic–Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K–Ar ( 40 Ar/ 39 Ar) system, which requires accounting and correcting for a systematic bias of c . 1% between U–Pb and 40 Ar/ 39 Ar isotopic ages (the 40 Ar/ 39 Ar ages being younger). Robust age constraints also exist for the Induan–Olenekian boundary (251.2 Ma) and the Early–Middle Triassic (Olenekian–Anisian) boundary (247.2 Ma), resulting in a surprisingly short duration of the Early Triassic, which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian–Ladinian boundary is constrained to 242.0 Ma by new U–Pb and 40 Ar/ 39 Ar ages. Radio–isotopic ages for the Late Triassic are scarce, and the only reliable and biostratigraphically-controlled age is from an upper Carnian tuff dated to 230.9 Ma, yielding a duration of more than 35 Ma for the Late Triassic. All of these ages are from U–Pb analyses applied to zircons with uncertainties at the permil level or better. The resulting compilation can only serve as a guideline and must be considered a snapshot, resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publications. However, further advances will require revision of some of the data presented here.

Abstract The Jurassic System (199.6-145.5 Ma; Gradstein et al. 2004 ), the second of three systems constituting the Mesozoic era, was established in Central Europe about 200 years ago. It takes its name from the Jura Mountains of eastern France and northernmost Switzerland. The term ‘Jura Kalkstein’ was introduced by Alexander von Humboldt as early as 1799 to describe a series of carbonate shelf deposits exposed in the Jura mountains. Alexander Brongniart (1829) first used the term ‘Jurassique', while Leopold von Buch (1839) established a three-fold subdivision for the Jurassic (Lias, Dogger, Malm). This three-fold subdivision (which also uses the terms black Jura, brown Jura, white Jura) remained until recent times as three series (Lower, Middle, Upper Jurassic), although the respective boundaries have been grossly redefined. The immense wealth of fossils, particularly ammonites, in the Jurassic strata of Britain, France, Germany and Switzerland was an inspiration for the development of modern concepts of biostratigraphy, chronostratigraphy, correlation and palaeogeography. In a series of works, Alcide d'Orbigny (1842-51, 1852) distinguished stages of which seven are used today (although none of them has retained its original strati graphic range). Albert Oppel (1856-1858) developed a sequence of such divisions for the entire Jurassic System, crucially using the units in the sense of time divisions. During the nineteenth and twentieth centuries many additional stage names were proposed - more than 120 were listed by Arkell (1956) . It is due to Arkell's influence that most of these have been abandoned and the table of current stages for the Jurassic (comprising 11 internationally accepted stages, grouped into three series) shows only two changes from that used by Arkell: separation of the Aalenian from the lower Bajocian was accepted by international agreement during the second Luxembourg Jurassic Colloquium in 1967, and the Tithonian was accepted as the Global Standard for the uppermost stage in preference to Portlandian and Volgian by vote of the Jurassic Subcommission ( Morton 1974 , 2005 ). As a result, the international hierarchical subdivision of the Jurassic System into series and stages has been stable for many years.