Multiple negative carbon-isotope excursions during the Carnian Pluvial Episode (Late Triassic)

The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean–atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years

Depositional systems of the Eastern Southern Alps (NE Italy, W Slovenia) during the late Carnian

Paleogeographic reconstruction and basin evolution during Late Carnia

Revision of the Conodont Mockina slovakensis and Its Paleogeographic Implications for the Upper Triassic Intraplatform Basins of the Alps

Mockina slovakensis, thought to have evolved from Epigondolella praeslovakensis, is an important species of the Norian (Upper Triassic), generally considered as the representative of the uppermost Alaunian to upper Sevatian in the Tethys. The previous description of M. slovakensis was incomplete, thus has led to some misidentifications. We thus update the description of M. slovakensis and discuss its comparisons and occurrence based on the new conodont investigations in Dolomia di Forni and the data from previous literatures. The conodont assemblage in the succession of Dolomia di Forni is dominated by M. slovakensis, along with rare M. postera and E. praeslovakensis. We described two morphotypes of M. slovakensis (morphotypes A and B), on the basis of shape of the lateral profile. These two morphotypes can also be observed in the E. praeslovakensis. Moreover, M. slovakensis is usually documented as almost monospecific conodont association in intraplatform basins, thus its paleogeographic implications are also discussed

Carnian-Norian paleogeography in the eastern Southern Alps

A detailed analysis of Upper Triassic basinal successions from Eastern Cadore, Carnia and Julian Alps allows us the reconstruction of the paleogeography of this important sector of the Southern Alps. The presence of Tuvalian basinal facies at the toe of slope of a prograding carbonate platforms in the Santo Stefano di Cadore area and the correlation with similar succession in the Julian Alps testifying the presence of a distinct branch of the Slovenian Basin here called Tarvisio Basin

Basinal inlets in a wide carbonate platform system: a case history from the Late Triassic of northeastern Dolomites (Southern Alps, NE Italy)

Upper Carnian to Norian successions cropping out in the Dolomites (eastern Southern Alps, ESA) are typically characterized by a thick (locally over to 1000 m) succession of peritidal cycles known as Dolomia Principale (DPR), mainly representing inner facies of one of the widest carbonate platform of the Mesozoic. Despite the Dolomites represent an area affected by minor tectonic deformation, faulting and displacements increase eastwards, resulting in the complex structural assessment of the S. Stefano di Cadore-Val Bordaglia area. Among several tectonic units, the Mt. Col Unit stands out for its peculiar Upper Triassic stratigraphic framework. Particularly attention has been paid to a Tuvalian carbonate-terrigenous basinal succession cropping out along the riverbed of the Rio di Mezzodì. Lithofacies are mainly represented by dark marl/pelite and limestone alternations, with irregular coarse to fine calcarenite intercalations. Carbonate grains of finer lithology are frequently represented by fragments of pelagic bivalves and benthic forams, whereas coarser beds commonly contain also gastropods, echinoderms and occasionally cortoids and Microproblematica-type fragments. Pyrite crystals and phosphatized shells are frequent, suggesting disoxic conditions on the sea bottom. The unit overlies a dolomitized interval consisting of bivalve and gastropod-rich packstones to grainstones, with common crustacean fecal pellets, attributable to a carbonate ramp environment (Heiligkreuz Fm.). No specific stratigraphic trend is identifiable in this basinal succession, but its top is always truncated and it is commonly flanked to massive facies of DPR. Recent and new ammonoid findings allocate the deep water series to the T. Dilleri/Subbullatus – A. Spinosus Zone, allowing good correlation with the Carnitza Fm. which crops out 90 km eastwards (Julian Alps, S. Karawanken). A georeferenced database containing all geological data available from literature about the Tuvalian substage of the ESA was created. Punctual and areal informations have been interpolated taking account of structural constraints, and a non-palinspastic paleoenvironmental map has been developed for the T. Subbullatus Zone. Results show a general SW to NE transition of environmental belts, respectively from subaerial/alluvial plain settings to shallow terrigenous- carbonate lagoons, with a narrow carbonate platform margin elongated in an approximate WNW-ESE direction, facing open pelagic environments northwards. Considering the polyphase Alpine tectonic displacement of the Mt. Col unit and its presumable northern provenance, the continuous occurrence of a W-E elongated basin could be hypothesized for the Carnic Alps, and likely for a restricted region north to the current Insubric-line position. In the wider paleogeographic scenario of the Tethyan region, a western pelagic inlet connected to the eastern Hallstatt marine domain can be depicted, separating thus the ESA from the Upper Australpine nappes, at least during late Carnian. Moving westwards, away from true open marine areas, water circulation became more and more restricted, justifying disoxic conditions inferred from sediments. Simultaneously, the terrigenous input increased in the same direction, because of the approach to inner sectors, where a direct connection of coastal carbonate-siliciclastic systems to the basin cannot be excluded. The occurrence of a sea-slice cutting the wide DPR carbonate platform environment cannot be ignored in future paleogeographic reconstruction, even if more work is needed to detect those causes that led to its onset