UPPER CARBONIFEROUS TO TRIASSIC TERRESTRIAL PALYNOFLORAS OF SARDINIA: BIOSTRATIGRAPHIC, PALEOCLIMATOLOGIC AND PALEOPHYTOGEOGRAPHIC IMPLICATIONS

The Late Palaeozoic (Stephanian - Permian) and Triassic terrestrial palynofloras of Sardinia provide an invaluable tool for reconstructing the evolution of these successions. Several sedimentary environments are represented, whose depositional conditions were governed by the post-collisional extensional tectonics of the Hercynian Chain, followed by the opening of the Tethys during Middle Triassic. Depositional settings include continental environments, mainly lacustrine and alluvial plain, marginal marine, shallow normal marine and coastal sabkhas. A non-conformity at the base and several erosional unconformities distinguish the Upper Carboniferous, Lower and Upper Permian, and the Triassic successions. The Permian and Triassic palynostratigraphic framework provides reliable dating and subdivision of time intervals for Sardinia, independent of the lithofacies changes between the northern and southern part of the region and gives an interesting picture of the terrestrial microfloral evolution in the Sardinia terrain. Palynological spectra are distinctly different and they clearly reflect paleoclimatic and paleogeographic conditions. Of the Upper Pennsylvanian palynofloras a significative component is represented by the zonate camerate spores like Cristatisporites and Densosporites and among the megaspores Zonalesporites and Valvisisporites; Triquitrites, Savitrisporites and Calamospora for the azonate triletes; the coniferous pollen and prepollen grains are subsidiary. Lower Permian palynofloras are instead dominated by Voltziales and Caytoniales pollen grains, and Crucisaccites, Gondwanopollis, Lueckisporites and others notably characterize the assemblages. The taxonomic diversity, high in the assemblages of Early Permian, remarkably decrease in those of the late Early Permian, preannouncing extreme climate conditions that southern Europe was undergoing. A very long erosional phase took place during Late Permian and Early Triassic. The Anisian and mainly Ladinian marine transgression re-established wet conditions, the floras became rich in higrophytic elements up to when the extensive deposition of gypsum in supratidal marine and inland sabkhas saline mudflats produced major changes in land vegetation.