Late Quaternary aggradation rates and stratigraphic architecture of the southern Po Plain, Italy

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.

Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy)

“…The burial of paleosol PH occurred diachronously in the coastal plain after 10 ka bp , when this exposure surface was progressively transgressed during the post‐MWP1B sea‐level rise (Bruno et al , 2017a). In the Bologna area, less continuous and less developed Holocene paleosols reflect increased accumulation rates after 10 ka bp (Bruno et al , 2017b). A buried soil, identified within eolian sediments (‘Usselo layer’; Hošek et al , 2017a), has been dated to the Allerød interstadial in several sites in northern Europe, with sparse dates around the YD and the early Holocene (Kaiser et al , 2009).…”

Three‐fold nature of coastal progradation during the Holocene eustatic highstand, Po Plain, Italy – close correspondence of stratal character with distribution patterns

“…New accommodation was continuously generated under relatively stable eustatic levels by: (i) tectonic subsidence, due to the flexure of the Adriatic plate beneath the Tyrrhenian plate (Carminati & Di Donato, ); augmented by (ii) sediment compaction (Teatini et al ., ). Modern subsidence rates for the Po Delta area are in the range of 3 to 4 mm year −1 , with substantially different values laterally as a function of subsurface lithology (Bruno et al ., 2017a; Vitagliano et al ., ). Sediment supply rates were likely influenced by changing climatic and land use conditions: flood activity in the southern Alps increased between 6 to 5 kyr bp and 3·4 to 2·4 kyr bp , northern European climate changed from Atlantic to Sub‐Boreal ( ca 5·2 kyr bp ) to Sub‐Atlantic ( ca 2·8 kyr bp ), and glaciers advanced and retreated globally and in the Alpine realm throughout this period (Table ; Mangerud et al ., ; Hormes et al ., ; Wirth et al ., ).…”

Early Holocene transgressive palaeogeography in the Po coastal plain (northern Italy)

“…In a source to sink perspective, the Po Plain, the Adriatic Sea and the surrounding mountain chains constitute a unique, complex system where sediment routing and dispersal is influenced by a wide array of allogenic (climate, eustasy and tectonics) and autogenic (local subsidence, lithology of the drainage areas and coastal dynamics) factors. The stratigraphic architecture of the area investigated in this work results from the combination of all of these factors (Amorosi et al ., ; Bruno et al ., ).…”