A rise in the Carbonate Compensation Depth of western Tethys in the Carnian (Late Triassic): Deep-water evidence for the Carnian Pluvial Event
The Upper Triassic of the Lagonegro Basin (southern Apennines, southern Italy) is represented by hemipelagic cherty limestones of the Calcari con Selce Formation, deposited in an oceanic setting. Two stratigraphic sections (Petina Chiana and Pignola 2), representative of the evolution of the Lagonegro Basin during the Carnian, have been studied in detail with a multidisciplinary approach. In the Pignola 2 section, within the Calcari con Selce Formation, a unique interval composed of green shales and radiolarites has been identified. The absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the Carbonate Compensation Depth. Conodont and palynomorph biostratigraphy constrain the age of this interval to the Julian/Tuvalian (lower Carnian/upper Carnian) boundary. The age and characteristics of this interval suggest correlation with a putative climatic event, known as the “Carnian Pluvial Event”, which has also been recognized in continental and shallow-marine successions from different European localities. This event is thus now documented also in a deep-marine setting. Like the continental and shallow-water settings, it is characterized by a sudden input of siliciclastics. Petina Chiana and Pignola 2 integrate current knowledge of the Carnian distribution of conodonts. Paragondolella praelindae Kozur, to date known only from the lower Tuvalian, has now been documented from the uppermost Julian. Moreover, a drastic turnover was recorded between Julian and Tuvalian conodont assemblages, which is clearly associated with the Carnian Pluvial Event. Thus, a biotic crisis, oceanographic changes associated with the rise of the Carbonate Compensation Depth, increased rainfall, and an anomalous siliciclastic input occur contemporaneously at the time of the Carnian Pluvial Event. A similar pattern is associated with perturbations of the carbon cycle that occur during the Jurassic and Cretaceous (e.g., in the early Aptian); thus, it is hypothesized that the Carnian Pluvial Event may have analogous causes.