High-resolution stratigraphy of the pre-evaporitic/evaporitic transition in the late Messinian Adriatic foreland domain

One of the most spectacular evaporative event in the Earth history occurred in the Mediterranean Basin, during the late Messinian (Messinian Salinity Crisis, MSC), as a consequence of the restriction in the Atlantic-Mediterranean connection. Enclosed marine environments could record evaporative deposition undergo restriction in circulation coupled with climate forcing. The aim of this paper is to investigate what happened in the sedimentary basin of the Adriatic foreland domain approaching the MSC by using an interdisciplinary study, which includes stratigraphy, paleontology, mineralogy, and magnetostratigraphy. The study area is the NW flank of the Maiella Mountains, where the MSC is well recorded by both the deposition of the Lower Evaporites and the post-evaporitic deposits of the Lago-Mare event. For getting a complete record of the pre-evaporitic/evaporitic transition in the study area, a 23m depth borehole was drilled starting from the 20cm-thick carbonate horizon (Calcare di Base) just at the base of the first gypsum cycle of the Lower Evaporites. Beneath the Calcare di Base, the sedimentary core recovered 3.8 m of dark clays rich in organic matter, punctuated by 5 carbonate-rich layers. The rest of the recovered sedimentary core is characterized by limestones and marly limestones rich in small lithotamnium, bryozoa, and benthic foraminifera, pertaining to the uppermost part of the Bolognano Formation. All the sedimentary core was analysed, collecting 5-10 cm thick samples. The occurrence of the carbonate-rich layers within the dark clays allows us to recognize 5 sedimentary cyles, possibly forced by precessional cyclicity. Calcareous nannofossils show two peaks of Sphenolithus abies within the 2nd and 4th cycle from the top. Small Reticulofenestra and Helicosphaera carteri show one peak within the 1st cycle, as well as in the 3rd and 4th cycles. Among the planktonic foraminifera, Turborotalita multiloba shows a peak within the 4th cycle whereas Orbulina universa has two peaks, within the 3rd and 4th cycles. The uppermost 50cm of the sedimentary core are completely barren. Although no major changes in lithology can be recognized in the fine-grained deposits, magnetic susceptibility decreases to extremely low values in the 1st and 2nd cycles, in the upper part of the sedimentary core. The depletion of magnetic minerals in this interval seems higher than can be attributed solely to dilution by magnetite-poor sediments, which implies that magnetite dissolution could have occurred. Our analyses on the paleontological record of the pre-evaporitic deposits in the Maiella foreland basin show results very similar to other pre-evaporitic Messinian successions from the Mediterranean Basin. Finally, the calibration of the sedimentary core with the insolation curve allow us to confirm the precessional forcing of the sedimentary record in the Messinian Adriatic foreland basin during the pre-evaporitic stage.