[1] Samples rich in organic matter were collected from boreholes in the southern part of the Po Plain (Italy), a rapidly subsiding sedimentary basin. New 14 C dates, obtained from these samples, and 14 C data from the literature allowed for the evaluation of the rates of natural subsidence in the area. These range from 0 to 5 mm/yr. Most areas show rates around 1 and 2 mm/yr. The obtained subsidence rates are comparable with burial rates obtained from archaeological data. These data are interpreted in terms of long-term (related to tectonics and geodynamics) and short-term (glacial cycle) processes. It is concluded that approximately 50% of the subsidence rates are related to tectonics, geodynamics and sediment load/compaction while the other half is controlled by ice melting. The effects of the glacial cycle through time are discussed. It is shown that the southeastern Po Plain generally behaves as a far-field area in relation to the high-latitude ice caps. Deviations from this behavior observed in the northeastern part of the Po Plain are tentatively interpreted as the effects of ice formation and melting in the Alps during the last glacial cycle.Components: 6485 words, 7 figures, 1 table.

No abstract

No abstract

The Po River Basin, where accumulation and preservation of thick sedimentary packages are enhanced by high rates of tectonic subsidence, represents an ideal site to assess the relations between vertical changes in stratigraphic architecture and sediment accumulation rates. Based on a large stratigraphic database, a markedly contrasting stratigraphy of Late Pleistocene and Holocene deposits is reconstructed from the subsurface of the modern alluvial and coastal plains. Laterally extensive fluvial channel bodies and related pedogenically modified muds of latest Pleistocene age are unconformably overlain by Holocene overbank fines, grading seaward into paralic and nearshore facies associations. In the interfluvial areas, a stiff paleosol, dating at about 12.5-10 cal ky BP, marks the Pleistocene-Holocene boundary. Across this paleosol, aggradation rates (ARs) from 16 radiocarbondated cores invariably show a sharp increase, from 0.1-0.9 mm year À1 to 0.9-2.9 mm year À1 . Comparatively lower Pleistocene values are inferred to reflect fluvial activity under a low-accommodation (lowstand and early transgressive) regime, whereas higher ARs during the Holocene are related to increasing accommodation under late transgressive and highstand conditions. Holocene sediment accumulation patterns vary significantly from site to site, and do not exhibit common trends. Very high accumulation rates (20-60 mm year À1 ) are indicated by fluvial channel or progradational delta facies, suggesting that extremely variable spatial distribution of Holocene ARs was primarily controlled by autogenic processes, such as fluvial channel avulsion or delta lobe switching. Contrasting AR between uppermost Pleistocene and Holocene deposits also are reported from the interfluves of several coeval, alluvial-coastal plain systems worldwide, suggesting a key control by allogenic processes. Sediment accumulation curves from adjacent incised valley fills show, instead, variable shapes as a function of the complex mechanisms of valley formation and filling.

No abstract