Contributo preliminare allo studio della macroflora del bacino lacustre "villafranchiano" di Steggio (Prealpi Venete, Italia settentrionale)

Abstract

Excavations in the "villafranchian" Steggio deposits (Treviso) have revealed a number of allochthonous plant remains enclosed in paleolake sediments. The macrofossils are especially abundant in the lowermost layers of the succession consisting of muddy sand and gravel deposited by the interdistributary channels of an alluvial fan. They are essentially coalified wood remains (branches, stem and root fragments), fruits, seeds and leaves. Seventy wood remains were xilotomically analysed; preservation is quite good but in some cases the microscopical decay processes contributed difficulties to systematic identification. Most of the specimens belong to the Pinaceae, except for a few badly preserved fragments which have the typical dicotyledonous wood. The following genera have been identified: Abies, Picea, Tsuga and Pinus "haploxylon". The preliminary examination of the paleocarpological content shows the presence of arboreal and shrubby angiosperms (Carya, Carpinus, Corylus, Rubus...). Further data are expected from the study of the carpoflora. The preliminary results indicate some interesting features of the Steggio flora, which is generally characterized by deciduous elements and conifers common in the mesic forests of the European Piio-Pleistocene, with Asian-American affinities (Tsuga, Carya). This forest probably was vegetating on piedmont slopes and drier areas surrounding the basin. A floristic similarity is noticed between the Italian sequences of Leffe and Stirone River and the Steggio succession.