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

The start-up of the Dolomia Principale/Hauptdolomit carbonate platform (Upper Triassic) in the eastern Southern Alps

Wide carbonate platform environments developed on the western passive margin of the Tethys during the Late Triassic, after a major climate change (Carnian Pluvial Episode) that produced a crisis of high-relief microbial carbonate platforms. The peritidal succession of this epicontinental platform (Dolomia Principale/Hauptdolomit, Dachstein Limestone) is widespread in the Mediterranean region. However, the start-up stage is not fully understood. The original platform to basin depositional geometries of the system have been studied in the north-eastern Southern Alps, close to the Italian/Slovenian boundary where they are exceptionally preserved. Sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile. The analysis of the facies architecture allowed reconstruction of the palaeoenvironments of the Dolomia Principale platform during its start-up and early growth stages in the late Carnian. The carbonate platform was characterized by an outer platform area, connected northward to steep slopes facing a relatively deep basin. Southward, the outer platform was connected to inner sheltered environments by a narrow, often emerged shelf crest. Behind this zone, carbonate sedimentation occurred in shallow lagoons and tidal flats, passing inward to a siliciclastic mudflat. The Dolomia Principale platform was initially aggrading and able to keep pace with a concomitant sea-level rise, and then prograding during the late Carnian. This stratigraphic interval was correlated with the Tuvalian succession of the Dolomites, allowing depiction of the depositional system on a wide scale of hundreds of kilometres. This large-scale depositional system presents features in common with some Palaeozoic and Mesozoic carbonate build-ups (for example, the Permian Capitan Reef complex, Anisian Latemar platform), both in terms of architecture and prevailing carbonate producers. A microbial-dominated carbonate factory is found in the outer platform and upper slope. The recovery of high-relief microbial carbonate platforms marks the end of the Carnian Pluvial Episode in the Tuvalian of Tethys

Surface aspects of the rabbit gallbladder mucosa and their functional implications

The morphology of the internal surface of the distended (filled) gallbladder and the sequence of its alterations during emptying were studied by scanning electron microscopy and light microscopy in the rabbit. Emptying was obtained by injecting a single dose intramuscularly or subcutaneously of caerulein varying from 0.01 μg/kg to 1 μg/kg. With scanning electron microscopy the mucosa in the distended state displays folds of differing heights, which frequently anastomose with each other, forming a network of bays varying in size. Many of the folds leave the network disappearing as a crescent-like ridge into the bays. Light microscopy shows a network of vessels particularly thick in the folds. During emptying, the mucosa shows both a progressive reduction in the size of the bays and a gradual elevation of the folds which become very twisted and are in close apposition to each other, producing a regularly waved surface. The vessels in the crescent-shaped folds connect the superficial with the deeper vasculature and act as fixed points determining the recurrence of a regular pattern of the mucosa each time the organ becomes empty. Therefore, emptying of the rabbit gallbladder results in a regular and repeatable modification of the mucosal pattern observed in the control animals

Response of carbonate systems to sea-level drop: a case study from Middle Triassic of the Dolomites (Italy)

Sequence stratigraphy models do not satisfactory explain the complex behavior of shallow water carbonate systems affected by sea-level changes, especially when difficulties are increased by a change in the carbonate factory, from M- to C-type as in the late Ladinian. The Carbonate Platforms (CPs) of the Dolomites are a natural laboratory to test these models and analyze the changes in stratal stacking through time