Climatic signature of cyclic fluvial architecture from the Quaternary of the central Po Plain, Italy

Abstract

Detailed investigation of middle-upper Quaternary deposits from central Po Plain was carried out on the basis of integrated sedimentological and pollen analyses of a 114 m-long core, and stratigraphic correlations of well data. Stratigraphic architecture of alluvial strata beneath modern Po River reveals distinctive cyclic changes in lithofacies and channel stacking patterns. Each cycle includes basal, silt–clay overbank deposits with thin and lenticular fluvial-channel sands, with upward transition to increasingly amalgamated and more laterally extensive fluvial-channel sand bodies. Lower cycle boundaries, corresponding to the top of laterally extensive fluvial complexes, are locally associated with organic-rich, paludal clays. Pollen records show distinctive cyclic changes that parallel facies architecture. Overbank deposits in the lower parts of cycles are invariably associated with forest expansions. These indicate that major phases of channel abandonment and widespread floodplain aggradation took place at the onset of warm-temperate (interglacial) climatic conditions. The middle portions of cycles record transition to pollen associations diagnostic of glacial periods. Lack of pollen data from sandy facies prevents climatic characterization of laterally extensive fluvial bodies in the upper parts of cycles. On the basis of the overall stratigraphic framework, internal facies architecture and distinctive pollen attributes, the cycles identified in the subsurface of the study area are interpreted to fall in the Milankovitch (100 ka) band, and inferred to be correlative with the transgressive–regressive sequences recently recognized in the coeval successions of the Po coastal plain.