Benthic foraminifera as a key to delta evolution: A case study from the late Holocene succession of the Po River Delta

ABSTRACT: Benthic foraminifera from stratigraphically expanded, late Quaternary prodelta successions of the Po Delta plain reveal small-scale paleoenvironmental variations within lithologically homogeneous deposits formed under conditions of rapid sedimentation (ca. 6 cm/yr). A detailed paleoenvironmental reconstruction was obtained comparing benthic foraminifera with shallow-water assemblages from the modern Po Delta. The integration with sediment geochemistry and radiocarbon dates was also tested to detect short time-scale delta dynamics controlled by autogenic factors. Core 7 records the development of an inner-shelf environment (interval A), replaced by a prodelta with strong fluvial influence, shown by the sharp increase in Ammonia tepida and Ammonia parkinsoniana (interval B). These taxa are replaced by Aubignyna perlucida (interval C) which indicates a major mouth shift (Ficarolo avulsion). Subsequent abrupt increases in A. tepida and A. parkinsoniana document a step-like progradation of the Po di Goro delta lobe (intervals D and E). In the seaward Core 1, possible minor mouth shifts are recorded by a sharp increase in A. tepida and A. parkinsoniana, paralleled by Cr/Al2O3 depletion. The upper portion of both prodelta successions includes stacked flood layers formed near the river mouth, as indicated by scarce A. tepida and A. parkinsoniana.