Central Po Plain Research Articles

Multi‐source detrital contributions in the Po alluvial basin (northern Italy) since the Middle Pleistocene. Insights into sediment accumulation in intermediate sinks

AbstractIntegrated stratigraphic‐compositional studies on alluvial successions provide a valuable tool to investigate the provenance of detritus in multi‐source systems. The Po Plain is an intermediate sink of the Po‐Adriatic source‐to‐sink system, fed by rivers draining two orogens. The Alps are characterized by extensive outcrops of plutonic‐metamorphic and ultramafic rocks to the north‐west and of Mesozoic carbonates to the east (Southern Alps). The Northern Apennines, to the south, are dominated by sedimentary successions. The Po River flows from the Western Alps to the Adriatic Sea, interacting with a dense network of transverse tributaries that drain the two orogens. Stratigraphic, sedimentological and compositional analyses of two 101 and 77.5 m‐long cores, recovered from the Central Po Plain, reveal the stacking of three petrofacies, which reflects distinct provenance and configurations of the fluvial network. A South‐Alpine sedimentary input between MIS 12 and MIS 10 is testified by petrofacies 1, characterized by carbonate‐ and volcanic‐rich detritus from rocks exposed in the Southern Alps. A northward shift of the Po River of more than 30 km is marked by a quartz‐feldspar and metamorphic‐rich detritus (petrofacies 2), similar to modern Po River sands. This dramatic reorganization of the fluvial network likely occurred around MIS 9–MIS 8 and is possibly structurally controlled. A further northward shift of the Po River and the onset of Apennine sedimentation in the Late Holocene is revealed by petrofacies 3, rich in sedimentary lithics from the Apennine successions. The results of this study document how compositional analysis, if framed in a robust stratigraphic picture, may provide clues on the evolution of multi‐source alluvial systems.

Pollen and Molecular Biomarkers from Sedimentary Archives in the Central Po Plain (N Italy): Assessing Their Potential to Deepen Changes in Natural and Agricultural Systems

This paper proposes to improve the information provided by biological indicators from sedimentary archives by integrating biomolecular techniques and botanical skills. This study represents a first proposal for combining pollen and biomolecular markers to detect land use and improve knowledge of past environmental change drivers. The specific aim of the research is to verify the relationship between miliacin (a pentacyclic triterpene methyl ether, usually interpreted as a broomcorn millet biomarker) and Panicum pollen in three near-site stratigraphic sequences of the Terramara S. Rosa di Poviglio (Po Plain, N Italy). The three cores span the last ~15,000 years and potentially record the beginning of Panicum miliaceum cultivation attested in the area since at least the Bronze Age within the Terramare culture. Despite the fact that Panicum pollen grains were rare in the spectra and miliacin was barely detectable in most of the 31 samples selected for biomolecular analyses, their combined evidence testifies to the local presence of the plant. Panicum pollen and sedimentary miliacin suggest the adoption of millet crops during the Recent Bronze Age by the Terramare culture, when climatic instability led to the diversification of cereal crops and the shift to drought-tolerant varieties.

Correction to: High frequency attenuation of S waves in alluvial deposits of the central Po Plain (northern Italy)

Correction to: High frequency attenuation of <i>S</i> waves in alluvial deposits of the central Po Plain (northern Italy)

High frequency attenuation of S waves in alluvial deposits of the central Po Plain (northern Italy)

SUMMARY Estimation of local seismic response plays a key role in assessing local seismic hazard and particularly in the design of shaking scenarios. Modelling local seismic response involves knowing of the shear wave velocity (VS) and quality factor (QS) profiles for the site in question. The many techniques that have been developed to assess VS in surface deposits produce reliable measurements of VS, but these rarely correspond to direct measurements of QS. The latter is often considered through damping measures from laboratory tests on small-scale soil samples, which can provide information primarily on intrinsic attenuation, neglecting the contribution of scattering effects. In this paper, using seismic recordings obtained at the surface and in boreholes at 100 m depth, we estimate an average value of QS of some characteristic alluvial deposits of the Po Plain (northern Italy). Data come from a microseismic network which sampled an almost uniform lithology in the central Po Plain and consisted of three surface and four borehole stations with an interstation distance of about 2 km. The average value of QS of the shallowest 100 m of the sedimentary strata, QS,100, is estimated by considering: (1) the high-frequency attenuation of seismic waves due to propagation through the corresponding stratigraphy and (2) the interference between incident and surface-reflected waves observed at borehole stations. We parametrize the first through $\Delta k_{0_{ {100}}}$, the difference between the values of the spectral decay parameter kappa (k) estimated at the surface and at the boreholes depth, respectively. We use the second in order to compute VS,100, the time-averaged VS referred to the uppermost 100 m stratigraphy. We obtain: $\Delta k_{0_{ {100}}} = (11 \pm 3)\,$ ms, ${V_{S,100}} \, =\, (309\, \pm \, 11)\,$ m s−1 and ${Q_{S,100}} \, =\, 31 \pm 10$. At the surface, the estimated values of the site-specific kappa, k0, are found to range from 75 to 79 ms. As expected, these results are in good agreement with studies performed in other sites characterized by sandy or clayey lithologies, and can be usefully used in site response analysis at sites where the rigidity is mainly controlled by lithostatic pressure.

Constraining a bioavailable strontium isotope baseline for the Lake Garda region, Northern Italy: A multi-proxy approach

The evidence of prehistoric long-distance exchange networks in northern Italy is overwhelming, attested by several finds of non-local raw materials in Bronze Age pile-dwelling settlements of Lake Garda and eastern Po plain, like amber beads and bronze artefacts. Metals are dispersed throughout Bronze Age Europe from mining communities within the Alpine regions, and possibly local artefacts, like the Peschiera-type daggers, are known from archaeological records throughout Europe. This positions the region as part of organized networks of trade and communication connecting prehistoric Europe from north to south. This, however, does not in itself indicate a similar long-distance mobility of prehistoric individuals. To investigate individual, human provenance and mobility, the strontium (Sr) isotope methodology compares strontium isotope analysis of human remains to bioavailable strontium isotope baselines characterizing the regions of interest. We present here environmentally based, multi-proxy (water, soil leachates and plants) Sr baselines from the Lake Garda region. Our results show two separate baselines, roughly corresponding to the geographical distribution of rock types and erosional products thereof. One baseline is valid for the Lake Garda region, where Mesozoic carbonates are a dominant surface-near strontium source, and for the central Po plain north of River Po. We constrain this to 87Sr/86Sr = 0.7088 ± 0.0014 (2σ; n = 44) when including 9 compatible samples reported previously. The second Sr-baseline is valid for Alpine areas dominated by magmatic (basalts excluded) and metamorphic bedrock around the Fersina valley. We constrain this to 87Sr/86Sr = 0.7146 ± 0.0058 (2σ; n = 22) when including 11 compatible samples reported in previous studies. The baselines are compatible with previously reported results of other Sr proxies such as snails, archaeological fauna, and agricultural soils and products from the region.

Interplay of Holocene surface faulting and climate in the Central Po Plain, Italy

AbstractUnderstanding the recent events marking the late Quaternary history of the Po Plain (N-Italy) is of overriding importance to decipher the record of depositional versus erosional phases, and their interplay with climatic, tectonic, and human forcing. We reconstructed the structural setting and chronostratigraphy of a Holocene succession crosscut by a thrust fault located south of Montodine (Cremona, Italy) within the Po Plain. The fault shows a maximum displacement up to one meter. Radiocarbon dating fixes a minimum age of 11.9 cal ka BP for the postglacial river entrenchment and constrains the fault movement age between 5.9 and 3.4 cal ka BP. Undeformed Late Medieval coarse gravels cover the faulted succession. Due to the outcrop position, lying above the buried frontal thrusts of the Southern Alps and North Apennines, we propose that faulting results from secondary surface effects induced by seismic shaking. We discuss two main mechanisms, both related to lateral spreading, that can result in the formation of reverse faults close to the surface. The Soncino area, recording one of the strongest historical earthquakes of the central Po Plain (1802), is considered as a possible source for seismic shaking. The results of this study are a contribution for the assessment of the potential seismic hazard in one of the most populated regions of Europe.

Preliminary analyses of an innovative soil improving system by sand/gravel injections–Geotechnical and geophysical characterization of a first test site

Several soil improving systems are available to increase the geotechnical properties of low resistance soils and increase the stability of overlaying constructions. Most of the already available methods make use of injections of more compacted material inside the ground, like: micro-piles, sand compaction piles, stone columns or grouting. Most of these solutions requires vibrations and rotary drilling, which could compromise soil properties and overlaying building integrity. Recently an innovative soil improving system by injections of a sand/gravel mixture was developed by Novatek® through mechanical preload of the mixture by compression adopting a hydraulic jack. The advantage of this last system with respect to available methods is the absence of vibrations and rotary drilling operations. In this study, the application of this system is documented in a first trial test site in the central Po plain (Italy). Description of the system and of the executed injections are reported. Characteristics of the ground before and after injections are compared, using both geotechnical and geophysical tests, in order to evaluate the system performances, which were also ascertained with direct verification through an explorative trench. The first results reported, even if for limited application depths, highlight the good potentialities of the improving system with respect to the increase of geotechnical parameters in the treated soil.

Different sources of convergent patterns in the Alps

AbstractThe diffusion of particle-verbs in Rhaeto-Romance and Italo-Romance dialects is surveyed on the basis of a selection of 13 AIS maps presenting the responses to 12 input sentences referring to different events. Particle-verbs are more frequent in the coding of motion than non-motion events. The geographic diffusion appears to be biased towards the Central and the Eastern Alps and the Central Po Plain. The distribution of particle-verbs is shown to correlate with the presence of systems of topographical deixis and to result from processes of language shift from Romance to Germanic in the mountains. Diffusion in the plain has resulted from inter-dialectal contact along cross-Alpine trade routes.

Assessment of liquefaction potential in the central Po plain from integrated geomorphological, stratigraphic and geotechnical analysis

Large portions of the highly populated central Po Plain in northern Italy are susceptible to major liquefaction–induced ground failure and resulting damage, as illustrated by the 2012 Mw 5.6–5.8 earthquake sequence. Our work presents a comprehensive geomorphological, stratigraphic and geotechnical dataset from a 1012 km2 study area in the alluvial plain, analysed through the integration of different methodologies. For hazard reduction planning, we qualitatively and quantitatively assess liquefaction potential by the identification of three discrete geomorphological domains. Each geomorphological domain has variable Late Pleistocene to Holocene geological evolution, geotechnical characteristics and thus liquefaction susceptibility, as deduced from interpretation of three 25–m deep continuous cores and calculation of liquefaction potential based on the geotechnical analysis of 239 cone penetration tests (CPTs). For land use planning, we present this information at various map scales consistent with inherent uncertainties of data availability. The investigation procedures and geological–geotechnical interpretations may be applicable to similar liquefaction–prone areas elsewhere.

Possible Multiple Sources of the Strong 1117 Po Plain Earthquake, Inferred from the Plio-Quaternary Evolution of the Northern Adriatic Area

The strongest documented seismic disaster ever occurred in the Po Plain area (January 3, 1117, M = 6.5) involved significant damage over a large zone. The genetic mechanism of such an event, most probably caused by more than one earthquake, is still an object of debate. Above all, the sources so far proposed cannot account for significant features of the observed macroseismic field. In this work, we suggest that the damage in the Verona zone was caused by the activation of a fault in the Lessini tectonic district, while damage in the central Po Plain may be related to a thrust fault located beneath the Giudicarie belt. The effects felt in northern Tuscany might derive from the seismic activation of the presumed SW-ward buried prolongation of the Giudicarie fault. The presence of such transpressional lithospheric discontinuity in the Adriatic domain since the upper Miocene and its reactivation (Pliocene-Pleistocene) as a thrust zone is mainly suggested by an accurate analysis of the observed deformation pattern in the central Mediterranean region. The proposed Giudicarie source may also help to explain the damage observed in the central Po Plain on December 25, 1222, which is not compatible with the seismic sources so far proposed.

Early Neolithic Settlement of the Po Plain (Northern Italy)

Around the mid-19th century, several groups of archaeologists active in northern Italy discovered a few sites characterized by the presence of ‘hut-floors’ or ‘pit-dwellings’ (fondi di capanna), which they attributed to a well-defined period of their Stone Age sequence. Research in the central Po Plain of Lombardy was resumed in the 1970s, allowing one to attribute some of the older discoveries to the Early Neolithic Vhò cultural aspect. The scope of the excavations, which started on one of the Vhò di Piadena sites in 1974, was to interpret the function of the previously discovered features, establish their radiocarbon chronology, and compare the finds with those of the Fiorano culture distributed across the eastern regions of the Po Plain. The main goal of this paper is to provide an international audience with novel information about one of the still poorly known Early Neolithic cultural aspects of northern Italy, namely that of the Vhò.

Late-Holocene Human Resilience in a Fluvial Environment: A Geoarchaeological Dataset for the Central Po Plain (N Italy)

This paper presents a dataset collected and constructed as part of a PhD research project in Environmental Sciences. Applying a multidisciplinary approach that combines archaeological and geomorphological data, this project aimed to reconstruct the Late Holocene landscape evolution in the Central Po Plain (Italy). The dataset was collected digitising the information retrieved from various sources such as scientific literature, regional databases and terrain surveys. In particular, the geoarchaeological data consist of a record of 761 archaeological sites and a soil map reporting the different sediment types of the area. Natural and anthropogenic landscape features developed by human-environmental interplay are organised in paleochannels, watercourses and channelisation. This dataset represents one of the first open-access data collection available in Italy and can be reused by any researchers working in fluvial landscape studies.

Geomorphology of the central Po Plain, Northern Italy

ABSTRACT A micro-relief map (1:90,000 scale) and a geomorphological map (1:25,000 scale) of the central sector of the Po Plain (northern Italy) are presented. The geomorphological map represents fluvial and anthropogenic landforms as well as the distribution of the textures of superficial alluvial deposits. It resulted from the integration of different study methods, including remote sensing data analysis, field surveys and grain size analysis of superficial deposits. The micro-relief map was a fundamental tool for identifying many inconspicuous landforms. The geomorphological map can provide local authorities with useful information for correct territorial management and planning, in particular for seismic and flood hazard assessment.

Correction to: Estimating the Potential of Archaeo-historical Data in the Definition of Geomorphosites and Geo-educational Itineraries in the Central Po Plain (N Italy)

The authors’ family names/first names have been inverted.

Estimating the Potential of Archaeo-historical Data in the Definition of Geomorphosites and Geo-educational Itineraries in the Central Po Plain (N Italy)

Alluvial plains represent preferable areas for human settling for their suitability to agriculture activities, and many studies strengthen the interpretation of floodplains as complex human–water systems. The Late Holocene development of the Central Po Plain has a long-lasting connection with anthropogenic activities. In the study area, human land and water management, in association with different Late Holocene climate phases, deeply affected the geomorphological evolution of the Central Po Plain. The geomorphological and archaeomorphological features detected in this study represent valuable datasets of information about the evolution of this portion of the Po Plain in the Late Holocene. This paper aims to quantify the potential of archaeological and historical data in contextualising the anthropogenic geomorphological features and reconstructing how man affected the natural geomorphological processes. Through a multi-disciplinary approach that combines archaeomorphological and geomorphological investigations, we identify visible and invisible landforms developed in four different historical periods, and that corresponds to potential “geoarchaeomorphosites”. In the study area, the modern landscape consists of a cultural palimpsest of four different palaeolandscape layers characterised by peculiar landforms. After an in-depth analysis of present and past geomorphic features deriving from the reciprocal interaction between human and floodplain dynamics since Prehistory, this study suggests geoconservation and valorisation practices. Finally, starting from potential geoarchaeomorphosites, four geo-educational itineraries are proposed to promote future geotourism projects of the area.

The Impact of Late Holocene Flood Management on the Central Po Plain (Northern Italy)

Fluvial environments have always played a crucial role in human history. The necessity of fertile land and fresh water for agriculture has led populations to settle in floodplains more frequently than in other environments. Floodplains are complex human–water systems in which the mutual interaction between anthropogenic activities and environment affected the landscape development. In this paper, we analyzed the evolution of the Central Po Plain (Italy) during the Medieval period through a multi-proxy record of geomorphological, archaeological and historical data. The collapse of the Western Roman Empire (5th century AD) coincided with a progressive waterlogging of large floodplain areas. The results obtained by this research shed new light on the consequences that Post-Roman land and water management activities had on landscape evolution. In particular, the exploitation of fluvial sediments through flood management practices had the effect of reclaiming the swamps, but also altered the natural geomorphological development of the area. Even so, the Medieval human activities were more in equilibrium with the natural system than with the later Renaissance large-scale land reclamation works that profoundly modified the landscape turning the wetland environment into the arable land visible today. The analysis of fluvial palaeoenvironments and their relation with past human activities can provide valuable indications for planning more sustainable urbanized alluvial landscapes in future.

Geophysical characterization of liquefaction-prone areas: The Quistello test site, central Po Plain, Northern Italy

A geophysical conceptual model for sites prone to seismic liquefaction is presented, introducing a geophysical protocol to characterize the liquefaction proneness. Three parameters are used to characterize homogeneous units: vs, a proxy of the geotechnical classes of soils, vp related to the saturation degree and vp/vs ratio, related to the liquefaction geophysical susceptibility. A layer is geophysically susceptible to liquefaction when it meets the following criteria: a) vs< 270 m/s and 1300 <vp< 1800 m/s; b) vp/vs> 5.The model has been tested and validated in the Quistello site, where liquefaction occurred during the 2012 Emilia earthquake. The validation of the proposed geophysical model for liquefaction susceptibility against the geotechnical one, calculated from CPTU, indicates the reliability of the proposed approach. This approach was extended to other sites affected by the 2012 seismic swarm. The study demonstrates that the geophysical susceptibility to liquefaction could be an indicator to support microzonation studies concerning the liquefaction proneness of extended areas.

An electrostratigraphic cross-section across the central Po plain: bearings on subsurface geology and hydrostratigraphy

A 72-km-long N–S cross-section was surveyed with direct current resistivity soundings through the Quaternary clastic infill of the Apennine foredeep in the Po plain of Lombardy (Northern Italy). The aims are (1) to test the potential of DC resistivity methods at the regional scale; (2) to draw the electrostratigraphic picture of the basin fill, down to the pre-Quaternary substratum; (3) to refine and test the methodology and concepts of hierarchic electrostratigraphy at the basin scale; (4) to contribute to characterize the regional hydrostratigraphy of a relevant hydrogeological basin. 163 resistivity-versus-depth profiles with a maximum investigation depth of 450 m were obtained from vertical electrical soundings. To draw the electrostratigraphic cross-section, the polarity of the resistivity contrast across resistivity interfaces (i.e. resistive over conductive layers or vice versa) was considered and the discontinuities were correlated according to the persisting pattern from north to south. Doing so, the hierarchic assemblage of four major electrostratigraphic boundaries and the five intervening groups of electrostratigraphic units (EsUs) was established. The resulting picture was compared to the available subsurface reconstructions from the literature, using the 1-D borehole data only to check the geophysical image at some random sample sites. The results show that the electrostratigraphic picture captures the geological and hydrostratigraphic complexity of the subsurface of the basin comparing well with the available direct subsurface geological and hydrostratigraphic reconstructions. At the regional scale of the cross-section, two hierarchic orders of EsUs and correlative boundaries could be drawn (first-order groups and second-order individual EsUs), while the lowermost third-order rank, the electrolayer, is recognized at the single-VES sites only.

Decoupled geomorphic and sedimentary response of Po River and its Alpine tributaries during the last glacial/post-glacial episode

The complex geomorphic and sedimentary evolution of the central Po Plain (northern Italy) during the last 30 ky was reconstructed through the integration of stratigraphic, geomorphological, geochemical and radiocarbon data. A key element of the Late Pleistocene stratigraphy is a 20 km-wide channel-belt sand body, with its top at a depth of ~13 m, fed by the Po River. Whereas the southern boundary of the Po fluvial channel belt coincides with a sharp lithological contact with floodplain muds, its northern boundary is an erosional (sand-on-sand) surface that was traced tentatively in the subsurface with the aid of sediment provenance (Po versus Alpine) proxies and radiocarbon data. Stratigraphic and geomorphological features testify to a decoupled sedimentary and geomorphic response of the Alpine and Po River systems to climate change in the last 30 ky. Contemporaneous Po River incision and Alpine rivers aggradation occurred at the onset of the Last Glacial Maximum (LGM). In contrast, Po River aggradation and Alpine rivers entrenchment took place during early deglaciation. The Holocene stratigraphy records the overall aggradation and northward migration of the Po River, with the consequent erosion of distal Alpine LGM deposits and formation of a fluvial scarp parallel to the Po River course. Late Pleistocene and Holocene climate change influenced river dynamics controlling (i) the balance between sediment supply and water discharge, through glacier and vegetation dynamics, and (ii) the rate of sea-level fall/rise. Apennine, Alpine and Po river systems responded in distinct ways to climate forcing due to the influence of local factors. Lithology, drainage area and mean elevation of river catchments, as well as river and valley gradients, determined the type of sedimentary response (e.g., aggradation versus degradation). This study shows that a combined geomorphic and stratigraphic approach focusing on the geometric relations between exposed and buried features can provide valuable information about the evolution of a fluvial system and its controlling factors.

Micromorphology and site formation processes in the Castrum Popilii Medieval Motte (N Italy)

This paper presents the results of the geoarchaeological study of a medieval motte known in historical documents as “Castrum Popilii” (Poviglio, Northern Italy). The Castrum Popilii motte, for its particular environmental characteristics, represents an exceptional case study for the Early Medieval Age in Po Valley. In 1989 an archaeological rescue excavation revealed an exceptionally well-preserved stratigraphic sequence at the northern side of the Santo Stefano church. The study of the archaeological materials and thin soil sections collected during this campaign, integrated with geoarchaeological observations, allowed the reconstruction of the natural and anthropogenic processes involved in the formation of the Santo Stefano di Poviglio stratigraphy sequence. The area also referred to as “Santo Stefano di Poviglio”, exposed the eastern limit of the medieval motte, characterizes by a sequence of occupation deposits, living floors, and wooden structural remains dated between the late 9th and the 11th centuries AD.The micromorphological study of this archaeological site led to developing a new hypothesis about the use of lime-based plaster in the construction of domestic living floors in a rural early medieval village in Central Po Plain. The sealing of the sequence due to the construction of a stone stronghold in the 15th century, combined with waterlogging, preserved the deposit from reworking by bioturbation and later human activities. On the other hand, water stagnation influenced a series of post-depositional migration and accumulation of iron–manganese and phosphatic features. The geoarchaeological tools applied in this study allowed to maximize the data collected in a rescue situation in 1989 highlighting new information about the genesis and development of Castrum Popilii medieval motte.