FACIES DISTRIBUTION OF A RIMMED CARBONATE PLATFORM AND OVERLYING REGRESSIVE CARBONATES: THE ESINO LIMESTONE AND CALCARE ROSSO FACIES IN THE CENTRAL SOUTHERN ALPS (LOMBARDY, ITALY)

Close to the Ladinian-Carnian boundary, a major sea level drop led to the exposure of the flat-topped, early cemented prograding Esino Limestone carbonate platform (Central Southern Alps). The subaerial exposure caused a reduction in size and efficiency of the carbonate factory, and the reduced accommodation lead to deposition of a thin (from a few to 60m) regressive unit: the Calcare Rosso. The thickness and distribution of the Calcare Rosso facies indicate a strict relation with the underlying facies of the Esino Lmst. and reflect the existence of higher-subsidence sectors. From the inner platform to the upper slope, thickness of Calcare Rosso increases and peritidal, tepee deformed limestones capped by Terra Rossa deposits are replaced by residual breccias. A different creation of accommodation space on the top of the Esino Lmst. can be main ascribed to differential subsidence. In the inner platform domain, the reduced accommodation and the inherited paleotopography control the great facies changes. Several discontinuity surfaces with associated karst structures characterize the Calcare Rosso deposits and the boundary with Esino Lmst. The development of karst structures into Esino Lmst. provide values of sea level fall, estimated about 20 m. The effects of the subaerial exposure on the Esino Lmst. and Calcare Rosso deposits have been investigated at both macro- and microscopic scale, and with catodoluminescence and geochemical analyses. Data collected both in inner and margin platform areas show the lack of evidences of vadose cementation and confirm the influx of meteoric diagenesis in the uppermost meters of the Esino Lmst. The hight variability of the δ13C and δ18O isotopic values suggests a tendency to climatic shift (‘pluvial Carnian event’) in according to the results of the paleosols analysis.