Continental Sequence Stratigraphy: the Quaternary Succession of the Po Basin (Italy) and its Relation to Coeval Coastal Deposits

Abstract

Late Quaternary depositional systems of the Po Plain exhibit distinct, predictable and chronologically constrained facies patterns that are useful as modern analogs for interpreting the ancient record. Proximal segments of alluvial successions are characterized by a complex succession of floodplain clays and fluvial-channel sand bodies. The distal portions, on the other hand, record the transition from alluvial clay deposits to swamp, lagoonal and marine-influenced facies associations, the internal configuration of which has been predominantly neglected. This Ph.D. thesis focuses on the Late Pleistocene-Holocene succession of the Po Plain, providing firstly a stratigraphic analysis of paleosols with a focus on their lateral traceability, and then a millennial-scale subdivision of the coastal succession. The stratigraphic architecture of the Late Pleistocene fluvial succession consists of non-pedogenized alluvial strata in alternation with weakly developed paleosols spanning intervals of time of a few thousand years, and genetically related to coeval aggradationally-stacked channel-belt bodies. Two prominent paleosols were recognized and mapped: one developed at the onset of the Last Glacial Maximum (LGM), and the less developed Younger Dryas (YD) paleosol, reflecting different duration and magnitude of these two cooling events. Above the YD paleosol, the Holocene depositional history of the Po coastal plain was reconstructed through stratigraphic correlation of eight parasequences, small-scale packages bounded by marine flooding surfaces and their equivalents, developed on millennial time scales. Parasequences document how climatic variations may affect the fluvial environment over short time scales: eustasy appears to be a dominant control on stratigraphic architecture of Early Holocene parasequences, whilst parasequence development in Middle to Late Holocene deposits appears to have been controlled dominantly by autogenic processes during the generalized phase of sea-level stabilization. High-accommodation fluvial settings can respond to sea-level fall with very minor or no degradation, leading to aggradationally stacked channel-belt sand bodies, in lieu of well-defined paleovalley systems.