Late Miocene palaeoenvironmental evolution of the Baccinello Cinigiano Basin (Tuscany, central Italy) and new autoecological data on rare fossil fresh- to brackish-water ostracods

This paper reports the results of palaeoecological analyses on fossil ostracod communities of the Tortonian and Messinian deposits cropping out in the Baccinello-Cinigiano Basin, a Tuscan (central Italy) post-collisional continental basin. Through multivariate analyses, such as Cluster Analysis (UPGMA) and Detrended Correspondence Analysis (DCA), several physico-chemical variations in the water body have been recognised. The more ancient (Middle-Late Tortonian) lacustrine environmentwas characterised by a shallowproximal and a deep distal facies with oligo-mesohaline waters. During this stage, the salinity of the lake water was controlled by the dissolution of Triassic evaporites buried at shallow depth in the basin. Instead, the subsequent lower Messinian fluvio-lacustrine environment was characterised by shallow freshwater habitats with variable water flow conditions. During the uppermost lower Messinian, the lake was deep and contained brackish water again. These reconstructions add newinformation on the variability of several ecological parameters such as depth, salinity and water flowconditions and help to clarify the autoecology of poorly known fossil ostracods.Within the fossil genus Tavanicythere, the species Tavanicythere irregularis, Tavanicythere parva and Tavanicythere sp. Q are adapted to deep and saline waters, Tavanicythere lepida is a shallow and less saline water inhabiting species, while Tavanicythere nodosa occupies an intermediate position with respect to palaeodepths and palaeosalinities. Within the genus Loxoconchissa, Loxoconchissa (Loxoconchissa) kinoi and Loxoconchissa (Loxocaspia) tuberosa are characteristic of an oligohaline and deep environment, while Loxoconchissa (Loxocaspia) nuda and Loxoconchissa (Loxocaspia) sp.1 are more halophile species. Potamocypris gracilis is a polyrheophilic and rather profundal species that can tolerate shallower depths. Paralimnocythere bicornis is a freshwater to slightly halophylic and reophobic species. Vestalenula sp. is one of the few known Vestalenula species that can withstand slightly saline waters.