C-Isotope Perturbation and Hg Deposition in the Reifling Basin at “Event1” of the Carnian Pluvial Episode (Late Triassic)

The Carnian was a pivotal time of environmental change and biological turnover. In this period new faunas radiated and rose to then dominate Mesozoic ecosystems. The long-term changes that ecosystems experienced are linked to discrete short-term events. These events perturbed terrestrial and marine environments, plunging older faunas into crisis and favoring the explosion of animals and plants presenting modern characters. The Carnian events are roughly coeval with the emplacement of Wrangellia Large Igneous Province (LIP), which could release large quantities of volcanic gases, including greenhouse gases such as CO2, and may have triggered the observed environmental changes. The initial abrupt event of this relatively long (max 2.5 Myr) interval of ecosystem reorganization—known collectively as the Carnian Pluvial Episode (CPE)—is chiefly recorded in the Reifling Basin of the Northern Calcareous Alps, Austria. Here, the Carnian crisis was noted for the first time in the 1970s and named “Reingraben Wende” (Reingraben Turnover) after the Reingraben Formation that represents this first Event of the CPE interval (CPE-Event1) in that area. The Reifling Basin is therefore a reference locality for the study of the Carnian, thanks in part to the spectacular fossil preservation of the Polzberg Konservat-Lagerstätte. Despite the increasing number of studies published on the CPE in recent years, the mechanisms of each Event that marked the interval and the timing of the environmental-biological response to it are still not fully understood. The succession of the Reifling Basin offers the opportunity to investigate the CPE-Event1—the original “Reingraben Wende”—in detail to disentangle the global and local processes that drove the environmental change. In this chapter we focus on the record of the negative C-isotope excursion that marks the CPE-Event1, which is evidence of CO2 injection in the system, and on coeval changes in mercury (Hg) concentrations in the sediments, which indicate changes in the loading of volcanic and/or terrestrial Hg to the Reifling Basin. A revision of published C-isotope records in conjunction with new Hg data contributes to the understanding of global and local phenomena modulating volcanic contribution and terrigenous supply to the Reifling Basin. Furthermore, this study clarifies the relative timing between the onset of the global perturbation and the local environmental response to it.