Palynological evidence of Middle Pleistocene palaeoenvironmental changes from the 'Buca dell'Onice' flowstone (Alpi Apuane, Central Italy)

Buca dell'Onice di Monte Girello is a small cave located in the Alpi Apuane (central Italy). It preserves an exceptionally thick flowstone deposited intermittently during the Middle Pleistocene. Two main depositional cycles, separated by a physical discontinuity, have been recognised and described. This discontinuity and the top surface of the flowstone attest to two main phases of interrupted growth related to palaeoenvironmental and palaeoclimate changes. Pilot palynological investigations support the existence of such changes. Despite the high number of barren pollen samples and the overall very low concentration of pollen grains per gram of sediment, palynology furnishes some interesting insights especially regarding floral composition, vegetation cover and local to regional climate. The pollen record also contributes to the definition of the stratigraphic distribution of taxa no longer growing in this area (i.e. Carya and Picea). According to the pollen assemblage characteristic of arboreal vegetation cover, the flowstone was deposited predominantly during humid phases under both warm and cool climate conditions (interglacials/interstadials and at the end of interglacials). The warm and cool phases correspond, respectively, to increases of mixed thermophilous forest taxa and montane arboreal taxa. On the other hand, the pollen record does not show the major expansion of open vegetation associated with the coldest and driest conditions, which apparently fall at the main middle discontinuity and at the top interruption of the flowstone. Previous data permit changes in precipitation to be identified as one of the major limiting factors for the growth of this flowstone, probably in a period including MISs 13-10. The more significant lithological features of the flowstone as well as the vegetal and climate signatures suggest that its development principally represents a response to global events including teleconnections active between the Mediterranean and the Atlantic circulation, with minor contribution from local factors.