Ostracode Assemblages And Palaeoenvironmental Evolution Of The Latest Messinian Lago-Mare Event At Perticara (Montefeltro, Northern Apennines, Italy)

The latcst Messinian Iago-ma~ event, which affected the whole Mediterranean area, is wen constrained both litbostratigraphically and biosuatigraphically. The sediments lie between lhe evaporite deposition related to the Messinian salinity crisis and the clayey deposition related to the Early Pliocene transgression and it is marked by the appearance of ostracode assemblages with Paratethyan affinity. The Perticara Flion (Montefeltro, northern Apennines, Italy), characterised by a high sedi- \ mentation rate, has been sampled every 50 em. Ostracode assemblages have been analysed from the topmost portion of the sedimentary succession, with the aim of reconstructing the palaeoenvironmental evolution of the last 15-20.000 years of this event and investigate possible environmental changes on a millennian scale. Statistical analyses have been performed on the relative abundance in percentages of the species identified in 31 sediment samples. Populational structure has been studied through several.indexes such as Margalef, Shannon and equitability. Both species (R-mode) and samples (Q-mode) were grouped by cluster analyses and detrended correspondence analyses (DCA) using the software package PAST (ver. 1.06). The OCA analysis has shown that, during this short period. several environmental changes have been recorded. A short interval. 14 m below the Mio-Plioceoe boundary. testifies to a shallow mesohaline waterbody dominated by Leptocytherinae and Loxoconcbidae lLoxoconcha (LoxocorniculintJ) djafarovi and Loxoconcha (LoXOCOllCha) eichwaldi n. ssp.]. Within the upper intervals. salinity slowly shifts to oligo-freshwater conditions since LoxOCOllCbidae and Leptocytberinae progressively decrease and Candoninae increase (with dominant Co.spiocyprU pon/ka). A few meters below the MiolPliocene boundary, Candoninae are stiU dominant but Lepcocytherinae species increase again in frequency together with Loxoconchidae. These changes poinNo the restoration of oligo-mesohaline or mesohaline conditions. The uppermost 2 m of clays below the Mio-Pliocene boundary are barren of ostracodes preventing an investigation of the very late Miocene palaeoenvironment, but the first Lower Pliocene samples show clearly the abrupt restoration of fully marine conditions