Timing and mechanisms of sediment accumulation and pedogenesis: Insights from the Po Plain (northern Italy)

The relationships between pedogenetic processes and fluvial-coastal dynamics in the Po Plain have been reconstructed through sedimentological analysis and correlation of ca. 170 core data chronologically constrained by 376 radiocarbon dates. Vertically stacked, weakly developed paleosols within Upper Pleistocene and Holocene mud-prone strata testify to intermittent pedogenesis, periodically interrupted by overbank sedimentation. Individual paleosols are laterally traceable for tens of km and exhibit A-Bk-Bw, A-Bk or A-Bw profiles. Stratigraphically ordered 14C calibrated ages from A organo-mineral horizons testify to slow aggradation during 4–6 thousand years-long exposure periods. Burial ages, with an error of few centuries, are provided by plant debris at the top of A horizons. Millennial-scale climate oscillations and glacio-eustasy are the main drivers of the pedo-sedimentary evolution of the area during the last 50 kyr. Upper Pleistocene paleosols (P1-P3) developed in well-drained floodplain environments, during relatively warm periods. Paleosol burial occurred during colder phases. High-sediment-supply during the Last Glacial Maximum hindered pedogenesis and led to the accumulation of 3–10 m-thick overbank strata. Widespread soil development (paleosol PH) occurred at the end of Last Glacial Maximum, following the retreat of Alpine glaciers and the afforestation of Apennine drainage basins. At distal locations, paleosol PH was progressively buried under estuarine sediments during the Holocene phases of post-glacial sea-level rise. Beyond the area of marine influence, burial ages of paleosol PH change from a place to another without specific spatial trends and reflect upstream fluvial sedimentation dominated by avulsions and deposition of spatially restricted alluvial units. Holocene (H1−H2) paleosols show a poor correlation potential and laterally variable degree of maturity that reflect avulsive sedimentation patterns and crevassing. This paper provides insights on the timing and mechanisms of formation and burial of weakly-developed paleosols. The outcomes of this research are applicable to similar Quaternary alluvial systems, and may help interpreting ancient paleosol-bearing successions.