Environmental changes across the Triassic–Jurassic boundary and coeval volcanism inferred from elemental geochemistry and mineralogy in the Kendlbachgraben section (Northern Calcareous Alps, Austria)

The end-Triassic extinction (ETE), one of the five largest Phanerozoic mass extinctions, is associated with rapid and severe environmental change, but existing data permit alternative models of causation. Volcanism in the Central Atlantic Magmatic Province (CAMP) has been proposed as the main trigger, but direct evidence for this linkage is scarce. To help constrain scenarios for the ETE and other Triassic– Jurassic boundary (TJB) events, we obtained a temporally highly resolved, multidisciplinary dataset from the Kendlbachgraben section in the Northern Calcareous Alps in Austria. The section belongs to the same paleogeographic unit (Eiberg Basin) and share similar stratigraphy with the recently selected base Jurassic Global Stratotype Section and Point at Kuhjoch. Micromineralogic study of the topmost bed of the Rhaetian K¨ ossen Formation revealed pseudomorphs of altered, euhedral pyroxene and amphibole crystals. Their well-faceted morphology is consistent with their origin from distal mafic volcanic ash fallout. Spherical grains were also observed in the same bed, likely representing clay-altered volcanic glass. Clay minerals of this bed include lowto medium-charged smectite and Mg-vermiculite, both typical alteration products of mafic rocks. The same bed yielded a rare earth element pattern that differs from all other levels in an enrichment of heavy REEs, hinting at some minor contribution from mafic magmatic material. These features from a layer that was deposited very near to the TJB are interpreted as direct evidence of CAMP volcanism, coeval or immediately preceding the ETE and the initial negative carbon isotope anomaly. The kaolinite-dominated clay mineral spectrum of the overlying boundary mudstone records intensive weathering under hot and humid greenhouse conditions. Redox-sensitive minor and trace elements do not support the development of widespread anoxia in the studied section. Although pyrite is common in several layers, framboid size indicates formation within a reductive zone, below the sediment/water interface, rather than in an anoxic water column. Our data provide a direct link between uppermost Triassic marine strata and CAMP-derived material. They support scenarios where CAMP volcanism induced climate and other environmental change, which in turn triggered the ETE and that is also reflected in the carbon isotope anomalies

Viszlát triász, szia jura: Egy eseménydús időszakhatár rétegtana és földtörténete (Goodbye Triassic, hello Jurassic: Stratigraphy and Earth history across an eventful period boundary)

The boundary between the Triassic and Jurassic periods and systems has long been recognized to coincide with some of the most remarkable events in the Mesozoic. Here I briefly review the synchronous mass extinction in marine and terrestrial ecosystems, global greenhouse warming, and major perturbations in the carbon cycle recorded in carbon isotope excursions, as signals of linked changes in the Earth system. Extensive continental flood basalt volcanism ofthe Central Atlantic Magmatic Province is likely to have triggered all these events, starting a cascade of environmental and biotic crises. Recent studies by our research team in stratigraphic sections in Hungary and Austria have also contributed to the development of models ofTriassic-Jurassic boundary events. The Global Stratotype Section and Point for the Triassic-Jurassic boundary has recently been defined in the Kuhjoch section (Tyrol, Austria) at the first appearance of the ammonite Psiloceras spelae. This level slightly postdates the main changes in this and other correlative sections

Development of the Jurassic geochronologic scale

A reliable geochronologic scale is necessary for many aspects of Jurassic research. Time scales are built from chronostratigraphicallyconstrainedisotopic dates. An overview of Jurassic time scales published between 1964 and 1994 demonstrates significant differences in the estimated ages of stage boundaries. Apart from the evolution and growth of the isotopic age database, most of the discrepancies can be explained by differing approaches to data selection, the handling of uncertainties, and procedures for boundary estimation and interpolation. A fundamental shortcoming of all Jurassic scales proposed to date remains the inadequate number of isotopic dates used. Current and future research needs to generate new data which can resolve the ambiguities of currently competing scales. Significant improvements are expected through the preferential use of precise and accurate U-Pb or ^Ar-^’Ar dating of samples which are biochronologically constrained at the zonal level

MASS EXTINCTIONS AND CLADE EXTINCTIONS IN THE HISTORY OF BRACHIOPODS: BRIEF REVIEW AND A POST-PALEOZOIC CASE STUDY

Brachiopods are a key group in Phanerozoic marine diversity analyses for their excellent fossil record and distinctive evolutionary history. A genus-level survey of raw diversity trajectories allows the identification of the Brachiopod Big Five, episodes of major genus losses in the phylum which are compared with the established Big Five mass extinctions of Phanerozoic marine invertebrates. The two lists differ in that the end-Cretaceous extinction appears subdued for brachiopods, whereas the mid-Carboniferous is recognized as an event with significant loss of brachiopod genera. At a higher taxonomic level, a review of temporal ranges of rhynchonelliform orders reveals episodes of synchronous termination of multiple orders, here termed clade extinctions. The end-Ordovician, Late Devonian and end-Permian events are registered as both mass extinctions and clade extinctions. The Late Cambrian and the Early Jurassic are identified as the other two clade extinction events. Coincident with the Early Toarcian oceanic anoxic event, the last clade extinction of brachiopods is defined by the disappearance of the last two spire-bearing orders, Athyridida and Spiriferinida. Their diversity trajectory through the recovery after the end-Permian crisis parallels that of the extant terebratulides and rhynchonellides until a Late Triassic peak but diverge afterwards. The end-Triassic diversity decline and Toarcian vanishing of spire-bearers correspond with contraction in their spatial distribution. The observed patterns and extinction selectivity may be explained both ecologically and physiologically. The specialized adaptation of morphologically diverse spire-bearers, as well as their fixed lophophore and passive feeding put them at a disadvantage at times of environmental crises, manifest in their end-Triassic near-extinction and Toarcian demise. Similar analyses of other clade extinctions may further improve our understanding of drivers and processes of extinction

Mezozoós (triász, jura) faunadúsulások őskörnyezeti értelmezése hazai példákon = Environmental interpretation of Mesozoic (Triassic, Jurassic) faunal diversifications: Hungarian case studies

A Balaton-felvidék triász rétegsorában az ammonoidea, bivalvia és brachiopoda faunák diverzitása jelentős változásokat mutat. A rövid kora-triász felvirágzás összhangban van a globális bioszféra eseménnyel. A középső-triász diverzitásnövekedést tektonikus esemény okozta. A karni korszakban a medencék feltöltődésével a vízmélység csökkent. A diverzitásnövekedés másik oka a humiddá vált klíma, aminek hatására több tápanyag szállítódott a medencébe. A villányi jura rétegsor epizódikus üledékképződése elsősorban a helyi tektonikai mozgásokat tükrözi. Az egyes szintekben gazdag bentonikus fauna változásai részben a helyi őskörnyezeti változásokkal, részben a bioszféra globális változásaival hozhatók összefüggésbe. A jura bivalvia és brachiopoda dúsulások a Dunántúli-középhegységben az egykori tengeralatti magaslatokat határoló vetőzónákhoz kapcsolódnak. A jelentősen eltérő üledékes környezet ellenére, a Mecsek faunái a középhegységiekhez hasonló diverzitáscsökkenést mutatnak a jura során. Ennek egyik oka a tengeraljzat fokozatos mélyülése volt. A másik ok, a brachiopodák esetében, a törzs történetében végbement globális változásból következik. A rhynchonellid brachiopodák díszítettsége (a generikus diverzitással együtt) a mezozoikum során folyamatosan növekszik a jura közepéig, majd a jura végén és a kréta elején jelentősen csökken. Ez a tendencia határozott összefüggésben van a durofág (héjtörő) és fúró ragadozó szervezetek fokozatos térhódításával a mezozoikum során. | The diversity of ammonoids, bivalves and brachiopods changes considerably in the Triassic of the Balaton Highland. The short Early Triassic bloom corresponds to the global recovery of the biosphere. The Middle Triassic diversification was caused by tectonic events. In the Carnian, the basins were filled and the sea became shallower. Another cause of the diversification was the onset of humid climate and the increasing influx of organic matter to the basin. The episodic sedimentation of the Villány Jurassic reflects the local tectonic movements. The changes of the benthos/nekton/plankton in certain layers were partly influenced by the local environmental changes, partly by the global changes in the biosphere. In the Transdanubian Range the diversifications of the bivalves and brachiopods are connected to the fault scarps along submarine horsts. The gradual diversity decrease during the Jurassic was recorded also in the Mecsek, despite of the substantially different sedimentary environment. The main cause was the subsidence of the sea bottom. Another cause, in the case of brachiopods, arises from a global change in the history of the phylum. The generic diversity and the degree of ornamentation of Mesozoic rhynchonellid brachiopods gradually increases until the mid-Jurassic, then considerably decreases in the Late Jurassic and Cretaceous. This trend reflects the escalation of durophagous and boring predators in the course of the Mesozoic marine revolution

Palynology of a terrestrial coal-bearing series across the Triassic/Jurassic boundary (Mecsek Mts, Hungary)

Abstract Palynology and palynofacies patterns of terrestrial Triassic/Jurassic boundary series of the South Hungarian Mecsek Mountains were studied in search of paleoenvironmental and vegetation changes and climatic signatures related to one of the major mass extinction events in Earth's history. Two selected and studied boreholes comprise continuous boundary sections and yield a diverse Late Rhaetian to Hettangian palynomorph assemblage. The most striking feature within the boundary interval is the series of cyclic short-term paleoenvironmental changes from fluvial/deltaic to swamp settings, as inferred from changes in palynomorph associations. However, increasing humidity is documented by a striking increase in trilete spores. These signatures display the response of terrestrial vegetation to regional and global environmental changes, although we found no clear evidence for a mass extinction as documented in the microflora