The Trave section (Monte dei Corvi, Ancona, Central Italy): An integrated paleontological study of the Messinian deposits

ABSTRACT: The paleontologic data (calcareous nannofossils, foraminifers, ostracods, molluscs and pollen) of the Trave section (south of Ancona, central Italy) are presented in order to describe the fossil content of the pre-evaporitic and post-evaporitc units and evaluate the paleoenvironmental evolution of the sedimentary deposits from the Tortonian/Messinian boundary to the top of the Messinian. Several calcareous plankton bio-horizons astronomically calibrated, temporally constrain the pre-evaporitic sequence between 7.44 Ma (FO of Amaurolithus primus) and 6.35 Ma (sinistral to dextral coiling change in Neogloboquadrina acostaensis). Resedimented evaporites mark the base of the post-evaporitic sub-unit p-ev1 (5.6 Ma) which is overlain by the cyclic stacking pattern of p-ev sub-unit. The MPl 3 zone of the Zanclean seals the section. The paleontological record of the post-evaporitic interval allows to verify that the p-ev1/p-ev boundary defined in terms of facies is well recognizable also in terms of bioevents; in fact, a Lago Mare low diversity assemblage first occurs a few meters below the boundary, while the first occurrence of Loxocorniculina djafarovi, continuously present all along the p-ev2, is observed above it. A second change in the overall assemblage is recorded a few meters above the physical boundary, where the ostracod assemblage diversifies and Parathetyan dinocysts appear. The open marine conditions during the late Tortonian gradually turned into the poor oxygenated water masses of the early Messinian (deposition of organic-rich layers) under a prevalent humid and warm climate. The presence, in the p-ev sub-unit, of small-sized foraminifers, reworked calcareous plankton, and the absence of ostracods and normal marine foraminifer assemblages suggest a diluted marine environment due to strong runoff responsible for the deposition of a great amount of clastic sediments. Towards the top of the p-ev 1 and within the p-ev the environment changes. The pollen record shows well evident wetter/drier fluctuations and the benthic foraminifers, ostracods, molluscs and dinocysts testify a decreasing water depth and alternating oligo-to mesohaline waters before the Pliocene deluge.