Picea+ Tsuga pollen record as a mirror of oxygen isotope signal? An insight into the Italian long pollen series from Pliocene to Early Pleistocene

Abstract

Chronostratigraphic control is of substantial importance for palynological studies carried out both on continental and marine sequences. Long pollen records provide an opportunity to examine the response of the vegetation to glacial/interglacial climate changes, and the integration of pollen data with different datasets (biostratigraphic – foraminifers and nanoplankton, δ 18O and magnetostratigraphic data) results in a reliable chronostratigraphic control. Unfortunately, long pollen records with multi-datasets are uncommon, and lack of such integration could generate misinterpretations in chronostratigraphic assignment of the sedimentary successions in which only pollen data are available. To specify the chronostratigraphic placement of sedimentary successions controlled by palynological data solely, an alternative approach is proposed in this paper. The procedure is very simple and practical, being based on the combination of Picea and Tsuga pollen data resulting in a new pollen profile to be visually compared to δ 18O signals from reference sites. Picea and Tsuga are two of the main conifer forest taxa in Italian sedimentary successions of Pliocene to Early Pleistocene age, and their pollen-types can be unambiguously identified at the microscope. Moreover, Picea and Tsuga are elements of peculiar ecological demands, being very responsive to the variations of temperature ( Picea) and precipitation ( Tsuga). As temperature and precipitation are also the main climatic parameters which drive the expansion and retreat of ice-caps, by comparing the profile of the stacked Picea+ Tsuga pollen curve to δ 18O curves from reference sites, a visual resemblance between each other, if present, could be used for chronostratigraphic implications. In order to test and discuss the validity of this approach, the Italian long pollen series of Pliocene–Early Pleistocene age (with Picea and Tsuga concurrently present) are considered in this study.