The last 40 ka evolution of the Central Po Plain between the Adda and Serio rivers

Abstract

We reconstructed the geological evolution and the history of the fluvial network in the central part of the Po Plain in Lombardy, northern Italy, since the Middle Würm. We focused on evidences of dissection and incision of former rivers into the large outwash fans originating from piedmont glaciers of the southern Alps in the Last Glacial Maximum. The studied area is located between the Po River and the Alps north of the Adda/Serio river confluence, around the town of Crema. Morphometric analysis and stratigraphic investigation were carried out, supported by palaeobotany, sand petrography and radiometric dating. The obtained stratigraphic framework is presented by cross sections and by a geological map. During the Middle Würm, an alluvial fan of the Adda River oriented NWN-SSE occupied the area, feeding south and west the Romanengo hill. A substantial reorganisation of the fluvial network occurred during the Last Glacial Maximum. Since 32-30 ka cal. BP, the area was fed by two outwash rivers, originated from the Adda and the Oglio piedmont glaciers, both characterised by a prevalent southward drainage, 160°-170° S in the LGM. After the LGM the fan-head was dissected by trunk channels and, at the downslope fan limit, the southward flow shifted to a southeastern direction. Thereafter, major dissection and downcutting occurred in the Lateglacial, confining the major rivers into large alluvial corridors, further shaped by lateral erosion during the Holocene. The Late Holocene history of the Serio River is marked by fluvial floods during the late Roman Age, and by a capture of the lower reach by the Adda River. The geomorphological evidence supports the historically inferred age assignment of the diversion to 12th-14th c. AD. (Marchetti, 1990(Marchetti, , 2002. fig. 10 à fig. 12) fig. 11 et fig. 13A) D'un point de vue méthodologique, on a préparé un DTM détaillé en se servant des points cotés de la Cartographie Technique de la Région Lombardie (fig. 2). La succession stratigraphique a été décrite sur le terrain à partir de plusieurs affleurements et carottes, dont les plus intéressantes ont été soumises aux analyses radiocarbone, palynologiques et minéralogiques (sables). 14 dates AMS ont été obtenues sur plantes terrestres, calibrées avec CALIB à partir de la courbe de calibration IntCal09 (Reimer et al., 2009 ; tab. 2) et indiquées dans le texte « cal. BP ». Certains vestiges archéo-logiques présents dans les dépôts ont été examinés, étant donné qu'ils peuvent fournir des indices chronologiques utiles. L'analyse palynologique s'est faite sur 400 grains. Les plantes aquatiques et de marais ont été exclues de la somme pollinique. Le diagramme pollinique intègre la séquence de tourbes et de tourbes sableuses déposées dans le marais de Mosi di Crema (fig. 9), quelques données polliniques sur échantillons isolés, prélevés dans les dépôts lacustres de Cresmiero, et la séquence fluvio-palustre de Ripalta Guerina (tab. 5). Pour chacun des 13 échantillons de sables étu-diés, 400 points ont été comptés avec la méth...

Northern richness and cryptic refugia: phylogeography of the Italian smooth newtLissotriton vulgaris meridionalis

“…Pinus sylvestris , P. mugo , Picea abies and Larix decidua ) and even temperate trees (i.e. Corylus avellana , Quercus deciduous , Tilia spp., Ulmus spp., Fraxinus excelsior , Carpinus spp., Abies alba and Fagus sylvatica ) would have survived during the LGM in north‐eastern Italy and in the central Po plain in small, environmentally favourable sites (Monegato et al ., ; Amorosi et al ., ; Kaltenrieder et al ., ; Pini, Ravazzi & Donegana, ; Monegato et al ., ; Ravazzi et al ., ). This palaeoenvironmental scenario for northern Italy, with scattered pockets of (micro)environmentally suitable habitats dispersed in a matrix of unsuitable environments for temperate species, echoes the well‐known pattern of northern ‘cryptic’ refugia previously discovered in central‐eastern and northern Europe (Stewart & Lister, ; Willis & van Andel, ; Stewart et al ., ; Schmitt & Varga, ).…”

Human settlement and vegetation-climate relationships in the Greenland Stadial 5 at the Piovesello site (Northern Apennines, Italy)

“…The forest cover of the Po Plain in this time span is recorded in the AP (arboreal pollen) from the Lake Fimon record in the south-eastern Italian foreland (Wick, 2000; Monegato et al, 2011; Ravazzi et al, in prep., Fig. 1 and 12, panel A) and the Casaletto Ceredano site (Ravazzi et al, 2012; Deaddis et al, 2017, Fig. 1).…”

“…The location of the Piovesello and of the other Gravettian sites cited in the text is shown. 1) Grotte de L’Observatoire cave; 2) Riparo Mochi rockshelter; 3) Grotta delle Arene Candide cave; 4) Casaletto Ceredano pollen record (Ravazzi et al, 2018); 5) Berceto paleolake pollen record; 6) Grotta Rio Secco cave; 7) Grotta Broion cave; 8) Lake Fimon pollen record; 9) Bilancino; 10) Fonte delle Mattinate; 11) Grotta Paglicci cave; 12) Grotta della Cala and Grotta La Calanca caves.

Figure 2Digital Terrain Model and simplified geological setting (according to Elter et al, 1997, with updatings) of the northern watershed of the Mount Ragola-Camolara Massifs. The Gravettian site of Piovesello is shown.

…”

Papia civitas gloriosa: urban geomorphology for a thematic itinerary on geocultural heritage in Pavia (Central Po Plain, N Italy)

“…The series of Holocene valleys, one entrenched inside the other, within which the rivers Po, Ticino, Adda, Oglio, etc. flow, are the result of this activity (Ravazzi et al, 2012). Alternating phases of erosion and deposition also took place during the Holocene.…”