Depositional evolution of a lower Paleozoic portion of the Southalpine domain: the Mt. Pizzul area (Carnic Alps, Italy)

Abstract

The Carnic Alps represent the best exposed Paleozoic succession within the Alpine domain being fossiliferous, mostly non-metamorphic and largely complete. This study focuses on the area around Mt. Pizzul, because the bedrocks record well the basin dynamics and most of the units are conodont bearing. Our aims were to contribute to the procedure of formalization of the lithostratigraphic units and to understand the depositional and deformation history of the study area. The area has been mapped, tectonic overprint constrained and the successions described, measured and dated. As a second-order aim, we discuss these data to infer the relations with other parts of the Carnic basin and to recognize the global controls on sedimentation. The depositional evolution can be sketched as follows: pre-Hirnantian ramp-type margin; Hirnantian glacioeustatic-related deposits and unconformity; pelagic deposition in a ramp-type margin (Přidoli–Eifelian); slope formation and differentiation in buildup, foreslope and pelagic environments (Eifelian–Frasnian); transgression and reef drowning (Frasnian–Visean); probable subaerial exposures likely during in uppermost Famennian and Visean times; and turbidite deposition (Visean). Global controls or deposits suggesting a global control are documented, including the Boda Event, the Hirnantian glaciation, the Middle Devonian reef growth, the Kacak Event, and the high-frequency sea-level fluctuations around the Devonian–Carboniferous boundary. The drowning of the buildups here and elsewhere in the Carnic Alps started during the Frasnian, unlike observed globally. This suggests that local tectonics lead to progressive deepening up to the transition to turbidite deposition.