Gli isotopi stabili del Carbonio organico nella serie di Dogna (Carnico, Triassico superiore)

Often, major environmental climatic and biotic changes occur together with large anomalies of the isotopic composition of carbon in the ocean-atmosphere system. Moreover, these events show a relationship with the onset of large igneous provinces, (LIPs). Although the Triassic climate was relatively stable and characterized by arid conditions, it was interrupted in the Carnian by an episode of increased rainfall, named Carnian Pluvial Event (CPE). The CPE occurs at the end of the early Carnian, at the same time of the eruption of a LIP called Wrangellia. This LIP erupted a large quantity of flood basalt and probably emitted a large amount of greenhouse gases, such as CO2. Unfortunately, there are still not enough data to establish a precise causal relationship between the eruption of Wrangellia and the onset of the CPE, except for the coincidence in timing and a carbon isotope escursion. The aims of this study are to investigate the evidence and the effects of the CPE in the Carnian succession of Rio Pontuz (Dogna area), using isotopic analysis of the organic carbon and diffrattometric analysis of clay minerals. The organic matter records a sharp negative excursion of it's δ13C (around 3‰) that roughly coincides with the deposition of coarse siliciclastics, supposed to mark the CPE. We suggest that the carbon isotope excursion is related to the eruption of a LIP, and a relationship between the CPE and the Wrangellia LIP is thus confirmed. Moreover the occurrence of arenites corresponds with the negative carbon isotope shift, therefore we suggest that the arenites formed because of the increase of run-off on the continent, related to the CPE