Giovanni Sarti

Palaeogeographic and palaeoclimatic evolution of the Po Plain from 150-ky core records

Integrated sedimentological and micropalaeontological (foraminifers, ostracods, pollen) analyses of eight continuously cored boreholes, up to 140 m deep, reveal the depositional history and the palaeoclimatic evolution of southeastern Po Plain (northern Italy) over the last 150 ky. Age assignments are supported by the chronostratigraphic sequence framework calibrated by radiocarbon and pollen data, allowing detailed correlation with the oxygen-isotope record. Facies analysis (including identification of 12 distinct microfossils associations) and detailed stratigraphic correlations across several tens of km document a cyclic sedimentation pattern (including continental, coastal and shallow-marine deposits), which defines two transgressive–regressive sequences, deposited over the last two interglacial–glacial cycles. Two prominent stratigraphic markers, corresponding to wedge-shaped coastal sand bodies, are recorded between 0–30 and 100–125 m core depths. These sedimentary bodies were deposited during the two major transgressive pulsations and subsequent sea-level highstands of the last 150 ky, assigned to the Holocene and the Tyrrhenian (oxygen-isotope Substage 5e), respectively. The stratigraphic architecture of post-Substage 5e deposits shows consistent patterns of coastal evolution with changing sea-level position. Lowering of sea level between 125 and 70 ky (onset of Substages 5d and 5b, and Stage 4) resulted in extensive and repeated basinward shifts of facies, which can be observed across closely spaced unconformity surfaces associated to alluvial plain sedimentation (falling-stage systems tract). The general phase of sea-level fall was punctuated by short transgressive phases (Substages 5c, 5a and Stage 3 interstadials), which led to widespread deposition of organic-rich (lagoonal and swamp) deposits. Upper Stage 3 and Stage 2 deposits (lowstand systems tract) are replaced across a significant part of the study area by a hiatal surface. Holocene interglacial deposits are characterized by a retrogradational stacking pattern of coastal plain and littoral facies (transgressive systems tract), reflecting invariably the landward migration of a barrier–lagoon–estuary system. Subsequent highstand deposition (highstand systems tract) was characterized by extensive progradation of wave-influenced deltas and strandplains. The two major transgressive surfaces, of Tyrrhenian and Holocene age, are considerably easier to identify than the other key surfaces for sequence stratigraphic interpretation. The lowermost transgressive deposits display a pollen signature diagnostic of warm climate (interglacial) periods, showing wide forest development and relatively high pollen concentrations. By contrast, the deposits overlying the unconformable surfaces related to successive phases of sea-level fall are fingerprinted by pollen spectra dominated by Pinus and non-arboreal pollen types, with very low pollen concentrations, reflecting the onset of a stable cold climate vegetation characteristic of stadial to fully glacial conditions. The good match between facies architecture, pollen distribution and global sea-level evolution strongly suggests that Late Quaternary sedimentation in the Po Basin developed under a predominantly glacio-eustatic control. Stratigraphic architecture of the Po Basin thus can provide a useful analog for interpretation and correlation in the stratigraphic record of very rapid glacio-eustatic (fourth-order) cycles, with frequencies of about 100 ky.

Facies Architecture and Latest Pleistocene-Holocene Depositional History of the Po Delta (Comacchio Area), Italy

Integrated sedimentological and micropaleontological study of 16 cores and 137 piezocone penetration tests, approximately 40 m deep, in the Comacchio area enables the documentation of the depositional history of southeastern Po Plain in the last 30 ka, in response to fluctuating sea level. Sedimentation within an alluvial plain was the dominant feature across the entire study area during the pronounced sea level fall that culminated in the Last Glacial Maximum. Thin lowstand fluvial sediments form the lower part of a shallow incised valley above the Last Glacial Maximum unconformity, whereas a characteristic paleosol separates the last glacial alluvial plain deposits from the overlying postglacial deposits in the interfluves. Transgressive and highstand deposits show a well‐developed stacking pattern of retrogradational (coastal plain and estuarine) and progradational (deltaic) facies. Detailed reconstruction of transgressive paleogeography shows evolutionary features that can be useful for refined interpretation of coeval and ancient analogs. At relatively early stages of transgression (10.5–9 ka B.P.), sedimentation in a coastal plain was restricted to the incised valley, whereas nondeposition and pedogenesis took place on the interfluves. With rising sea level (9–6 ka B.P.), a wave‐dominated, barred estuary developed in the former topographic low. At peak transgression, after filling up of the estuarine systems with coastal, back‐barrier sediments, wide areas outside the valleys were flooded, aggradation extended onto the interfluve unconformity, and a shallow marine depositional environment developed across most of the study area. The depositional history during the subsequent highstand phase was dominated by progradation of the early Po Delta and reflects the complex interplay between high‐frequency sea level fluctuations, climate, subsidence, and autocyclic processes.

Inverse to normal magnetic fabric transition in an Upper Miocene Marly Sequence from Tuscany, Italy

The magnetic susceptibility fabric of an upper Miocene marly sequence exposed along the Morra creek (Tuscany, Italy) changes from inverse (maximum susceptibility axis sub-perpendicular to bedding) to normal from the bottom to the top of the section. The change is gradual, with the presence of anomalous magnetic susceptibility fabrics at some levels. The anhysteretic remanence anisotropy is always normal throughout the sequence. The changes in the magnetic fabric seem to be controlled by sedimentological variations, with the inverse susceptibility fabric related to the abundance of iron-bearing carbonates in the lower part of the section. In the upper part of the section subtle changes in the detrital inputs in the basin, and particularly a larger contribution of clayey and ferrimagnetic particles, turned the susceptibility fabric to a normal type.

On the displacement of marked pebbles on two coarse-clastic beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy)

The aim of the investigation was to define the mechanisms of sediment transport in the swash zone of microtidal coarse-clastic beaches in the very short term by evaluating the displacement rates of marked pebbles under low-energy wave conditions. Tests were performed at two sites (Marina di Pisa, Ligurian Sea, and Portonovo, central Adriatic Sea) to check the consistency of the data over a range of different grain sizes. Two recovery campaigns were carried out at both sites, one 6 h and the other 24 h after the injection. During the experiments wave action was at a minimum (wave heights never exceeded 0.3 m). The results show that 20% of pebbles ranging in diameter from 30–90 mm moved significantly (more than 0.5 m) already 6 h after the injection, with some tracers being lost (3%). After 24 h, 40% of the pebbles were significantly displaced and 10% were lost. The preferential downslope movement of tracers, which suggests that coarse sediment movement under low-energy conditions is mainly controlled by gravity processes enhanced by steep beachface slopes, represents the novelty of the results reported here. It would appear that swash processes on low-energy beaches cause a significant rate of pebble displacement through the destabilization induced by wave uprush and backwash. Despite the microtidal range, the position of the mean water level plays a major role in changing the beach level at which swash processes can actually trigger pebble movement. The results of this study show that considerable, and mostly seaward-directed, coarse sediment transport takes place even during short fair-weather periods.

An RFID Based System for the Underwater Tracking of Pebbles on Artificial Coarse Beaches

Coastal erosion represents one of the most significant environmental emergencies, due to the fact that it affects locations distributed all over the world, including tourist sites and urban centers. Several solutions have been studied during the last years, including the use of gravel beaches as shore protections against the effects of waves. These solutions seem to provide a good protection, but efficient studies on the movement of sediments are very difficult to be performed due to the absence of effective technical solutions. In this article we propose the use of RFID automatic identification technology to keep trace of single pebbles shifting on a gravel beach. The tracking operations are made possible in the sea as well as on the beach providing a tool to perform accurate and global studies on the dynamics of artificial coarse beaches for what concerns both its under and outside water sectors.

In situ abrasion of marked pebbles on two coarse-clastic beaches (Marina di Pisa, Italy)

In this paper pebbles marked by passive integrated transpon ders from two artificial coarse-grained beaches at Marina di Pisa (Tuscany, Italy) were analyzed in order to measure the in situ abra sion rate. The beaches (Cella 7 and Barbarossa) were set up in 2006 as a form of coastal protection. They are both composed of pebbles (30-to-90 mm diameter) and bounded longshore by huge groynes. They differ in length (250 m and 110 m respectively) and in the prese nce of an additional defense structure, a submerged breakwater 50 m off the coastline, at Cella 7. The aim of the study is to reckon the abrasion rate of individual pebbles and evaluate abrasion differen ces of pebbles released on Cella 7 and on Barbarossa. The RFID technology (Radio Frequency Identification) was used to track the pebbles due to its reliability and limited costs. The tracers were released on the beaches in March 2009 along closely-spaced crossshore transects. The recovery campaign was carried out in May 2009. A total of 127 pebbles was detected, 83 of which were recov ered. Huge beach reworking during the storms determined high burial rates and consequently the loss of a definite amount of tracers. The pebbles that were recovered showed a significant increase in roundness, in particular the tracers that were released on Bar barossa. The average pebble weight loss measured at Cella 7 was slightly lower, which means lower mobilization rate at this site rather than at Barbarossa. The resulting values are significant considering the short time frame of the research (two months) and the limited energy of the storms occurred during the experiment.

The role of sediment grain size, mineralogy, and beach morphology on plant communities of two Mediterranean coastal dune systems

Coastal dune ecosystems are characterized by a strong relationship between abiotic and biotic factors. The aim of the study is to identify the abiotic factors that mostly affect distribution and composition of plant dune communities along the coast-to-inland gradient, focusing the attention on sediment grain-size parameters, mineralogy, and dune morphology. The research was carried out on two coastal dune systems belonging to protected areas in the Mediterranean Basin, specifically in Northern and Southern Tuscany (Italy). Grain-size analysis, X-ray powder diffraction, topographic surveys, and floristic data recording were carried out along 11 transects perpendicular to the shoreline; the portion of the beach investigated is comprised within the foreshore and the backdune area. The analyses revealed some differences between the two coastal dune systems in terms of sediment parameters, mineralogy, and dune topography. The differences are mainly ascribed to the physical characteristics of the sites where the surveys were carried out. These data were matched with those provided by the vegetation sampling and then statistically processed by means of methods such as the Canonical Correlation Analysis (CCA), which showed that the mean grain-size is the most important abiotic factor that influences the composition of these coastal plant communities. These results might be considered to improve and optimize management and conservation programs for these ecosystems, since nowadays artificial dune reconstruction is a practice frequently used as a form of coastal protection.

Background levels of potentially toxic metals from soils of the Pisa coastal plain (Tuscany, Italy) as identified from sedimentological criteria

Identification of reliable background values of potentially toxic metals in sediments requires detailed integration of geochemical data with accurate sedimentological studies. Through analysis of 60 soil samples from the Pisa coastal plain, this study shows to what extent sediment provenance and facies characteristics may influence the natural distribution of potentially toxic metals (Cr, Ni, Cu, Zn, Pb) within alluvial and coastal sediments. Metals supplied to the alluvial plain are mostly concentrated within the finest sediment fraction (floodplain clays), while coarser crevasse and overbank deposits exhibit invariably lower metal contents. Beach-ridge sands display the lowest metal concentrations. Transport of ophiolitic detritus by the longshore drift may account for locally high Cr concentrations within beach deposits. Geochemical fingerprinting of individual facies associations in terms of natural metal contents results in the construction of a geologically-based geochemical map. This map offers a more reliable depiction of spatial distribution of background levels than interpolation techniques based uniquely upon statistical methods. Matching background values against metal concentrations from topsoil samples leads to the reliable assessment of the pollution status of Pisa coastal plain. Metal contents exceeding the threshold values designated for contaminated areas (Cr) simply reflect catchment geology, and are not the product of artificial contamination. On the other hand, anthropogenic disturbance may be detected even where metal contents (Pb, Cu) lie below the threshold values. The use of sedimentological criteria is presented here as a pragmatic tool to enhance predictability of natural metal contents in sediments, with obvious positive feedbacks for legislative purposes and environmental protection.

An Analysis of the Performances of Low Frequency Cylinder Glass Tags for the Underwater Tracking of Pebbles on a Natural Beach

In this paper we provide the results of a two months experimentation of Low Frequency RFID technology for the sediments tracking on a beach close to Ancona, Italy. For this experimentation, cylinder glass tags were used, modifying a previous solution based on the use of plastic disc tags. While the use of Low Frequency RFID as a technology to monitor the movements of sediments under and outside water on beaches subject to high coastal erosion phenomenons was already been tested before and described in previous papers, the use of glass tags was not introduced until this last experimentation due to the fragile nature of these devices that discouraged from their use. Anyway, their use was finally encouraged from the goods results obtained from laboratory test concerning their reading range and their ease of use. The results provided in this paper show that cylinder glass tags are probably the best solution for the tracking of pebbles movements.

GRAIN SIzE CHARACTERIzATION OF MODERN AND ANCIENT DUNES WITHIN A DUNE FIELD ALONG THE PISAN COAST (TUSCANy, ITALy)

In this paper, grain size analysis on a large number of samples from a dune field within the Migliarino - San Rossore - Massaciuccoli Regional Park has been carried out in order to define the textural characterization of modern and ancient dune ridges. More than 200 samples along five transects have been collected from the backshore, the active dunes and the steady dunes up to the last recognizable dune ridge. The samples have been dry-sieved and the obtained data have been processed electronically to achieve textural param - eters such as mean diameter and sorting. The results showed similar trends of the transects throughout the entire dune field. In particular, the grain size tends to decrease towards the most ancient dune ridges, showing a significant drop at the transi - tion between active and inactive areas. The drastic decrease might be related to a possible variation of River Arno sediment discharge occurred after the XVIII century.