Pollen and macrofossil analyses of Pliocene lacustrine sediments (Salto river valley, Central Italy)

The study of two sedimentary records sampled in the fluvio-lacustrine succession of high Salto river valley (Rieti, central Italy) was originated in the frame of the Geomorphologic Map of Italy (APAT, 2008) field survey and improved with a multidisciplinary approach addressed to a better knowledge of the Plio-Pleistocene continental environments of central Apennines. The two successions are associated to different sedimentary facies, with lateral heteropic relations: the deposits cropping out at Marano de' Marsi are thought to represent deposition in the distal portion of a lacustrine delta, while those of Borgorose took place in a frankly lacustrine environment. The sediment succession from Marano de' Marsi (11 m) was sampled from an outcrop, the one from Borgorose (24.5 m) from a drillhole. Palaeomagnetic investigations carried out on both sediment records indicate a normal magnetic polarity and very low magnetic susceptibility values. In the record from Marano de' Marsi section, gymnosperm pollen is prevailing. Four main and short angiosperm arboreal pollen oscillations can however be observed, the oldest of which more marked. The gymnosperms are mainly represented by Pinus haploxylon type, Pinta sylvestris type, Cedrus, Picea, Abies, Cathaya, Tsuga, Taxodium type. Among angiosperms the dominant taxa, some of which at present extinct in Italy, are Quercus, Zelkova, Ulmus, Carya and Pterocarya. The presence of pollen of subtropical taxa as Nyssa, cfr. Rhoiptelea, Liquidambar, Engelhardia is worth to be mentioned. The investigation was integrated also by a preliminary study of macrofossils. Fossil impressions with some organic matter of angiosperm and gymnosperm leaves and seeds/fruits were ascribed to Acer cfr. monspessulanum, Carpinus cfr. orientalis, Engelhardia, Fagus, Hedera, Liquidambar, Quercus, Rosa, Abies and Pinus. The 24.5 m long sediment core from Borgorose resulted very poor in pollen, with the same list of arboreal taxa, at present extinct in Italy, found at Marano de' Marsi, and a diagram was drawn only for the stretch of the core between 3 and 8.2 m. Gymnosperms (P. haploxylon type is dominant, and accompanied by P. sylvestris type, Picea, Taxodium type, Cedrus, and Tsuga) are always prevailing. The results obtained by this interdisciplinary investigation indicate that Marano de' Marsi and Borgorose successions can be possibly attributed to the Upper Pliocene (normal polarity Olduvai subchron) even if an older age, considering the present state of the art on Pliocene continental records, and the peculiarity of the site and of the region, cannot be excluded. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.