The ‘Evaporiti di Monte Castello’ deposits of the Messinian Southern Apennines foreland basin (Irpinia–Daunia Mountains, Southern Italy): stratigraphic evolution and geological context

Abstract

Abstract An evaporitic limestone–gypsum succession, belonging to the Evaporiti di Monte Castello Formation, is recognized in the late Messinian (Upper Miocene) of the Irpinia–Daunia Mountains in the Southern Apennines arc (Southern Italy). This unit is formed by diatomaceous marls, massive and laminated evaporitic limestones, and by primary and clastic gypsum. Detailed stratigraphical, sedimentological and strontium geochemistry data has permitted reconstruction of stratigraphic and facies relations of gypsum deposits, depositional environment and basin evolution. Genetically related gypsum lithofacies can be grouped into two facies associations. The autochthonous gypsum facies association consists of shallow water selenitic, acicular and laminated gypsum and is characterized by the absence of high-energy sedimentary structures. The redeposited clastic gypsum facies association consists of shallow- to deeper-water fine-grained laminated gypsum, gypsarenites, pebbly gypsarenites and gypsrudites, showing common features of resedimented deposits. Nodular structures occurring in the laminated gypsum lithofacies seem to be mostly related to late diagenetic processes. The sedimentary evolution during the evaporative phase was characterized by a gradual increase in salinity until gypsum precipitated; then the sedimentary conditions in the basin were characterized by almost homogenous salinity conditions, and influenced by events of gypsum reworking and resedimentation probably related to flooding episodes and local tectonic activity. The gypsum was deposited from mainly marine brines, based on their Sr isotopic compositions. This sedimentary series is an equivalent of the Lower Evaporites of other parts of the Mediterranean. The Messinian Monte Castello Formation evaporites represent an uncommon type of evaporitic succession, probably developed in a extensional setting in a basin located along the Apulian foreland ramp, in contrast with the northern Apennines and Sicilian basins (e.g. Vena del Gesso, and Caltanisetta basins), which are considered to be thrust-top basins of the Apennine–Maghrebian foreland basin system.