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Hinterland basins are low-lying and often heavily populated areas at the back of orogenic belts which have significant economic and infrastructural importance. The tectonic-stratigraphic and regional characterisation of hinterland basins is fundamental for evaluating their subsurface utilisation and potential geohazards.This study focuses on the origin and development of the Tuscan hinterland basins of the Northern Apennines. These basins have been associated with a compressional regime lasting until the Late Pliocene-Pleistocene during which out-of-sequence thrusts and back-thrusts in the inner portion of the chain accommodated the compressive stress accumulated in the frontal zones. An alternative interpretation considers the evolution of these basins in an extensional regime as an effect of large-scale back-arc processes or gravitational collapse of thickened crust following the Apennine orogeny since the Early Miocene. In this tectonic regime, the basins have been interpreted as graben, half-graben or bowl-shaped basins evolving into graben.Our work aims to determine the tectonic-sedimentary evolution of the Valdera-Volterra Basin through the analysis of ~271.8 km of 2D seismic reflection profiles and wireline logs from two exploration wells. The Valdera-Volterra Basin basin is an NW–SE oriented depocenter ~60 km long ~30 km wide filled with a clastic succession of Miocene-Pleistocene fluvial-lacustrine to marine deposits up to ~2 km thick.The analysis has revealed a polyphased tectonic history of the basin with a Messinian-Zanclean compressional phase deforming the basin-infill as indicated by seismic imaging of synformal geometries and strongly tilted unconformities. Such deformation is tentatively associated with E/NE vergent blind thrusts and SW vergent blind back-thrusts. During the Piacenzian, the activity of normal border faults and the presence in their hanging wall of associated sedimentary wedges thickening towards NE suggest an extensional phase following the earlier Messinian-Zanclean compression. Broad folding of the shallow Piacenzian units in the hangingwall of the normal faults suggests the occurrence of mild positive inversion at the end of the Piacenzian/Lowermost Pleistocene?.This tectonic history has been associated with crustal shortening in the Northern Apennines hinterland, accommodated by thrusting, that occurred discontinuously until the end of the Pliocene/Lowermost Pleistocene?. The formation of the border faults during the Piacenzian has been related to a prolongated phase of tectonic quiescence that led to the collapse of the sedimentary pile and the Pre-Neogene substrate. In this setting, the positive inversion occurred at the end of the Piacenzian/Lowermost Pleistocene? represents the last compressive event related to crustal shortening.

Although Pliocene palaeosols can supply palaeoclimate information and help to disentangle stratigraphic reconstructions, soils are sparsely represented in global datasets for Pliocene climate. Pliocene was characterised by global mean annual temperatures 2–4 °C warmer than today, representing an analogue for future climate prevision. We aimed, thus, to investigate palaeosols as suitable archives for reconstructing geomorphic processes, ecosystems and climate patterns in the Pliocene.We compared the palaeosol record stored in Zanclean and Piacenzian successions locate in central and southern Tuscany, respectively. Palaeosol morphological features observed in the field were used for the sequence-stratigraphic interpretation. To qualitatively evaluate soil development, we considered the time needed to attain various soil properties. Pedogenetic processes and the intensity of weathering were also quantified by applying a range of proxies based on geochemical analyses. Climofunctions based on major element ratios were used to estimate mean annual palaeoprecipitation (MAP). Carbon and oxygen isotopes analysis were performed on carbonate nodules, to verify their pedogenic origin and as a proxy for palaeovegetation and palaeotemperatures.Though all soils are unconformities in the record, the rank and type of unconformity were defined in detail, to precisely place the soil formation time within the sedimentary sequence and to correlate soil-forming intervals with general environmental changes. Then, soil characteristics were interpreted, considering the geomorphological setting reconstructed by the stratigraphic and sedimentological analysis.The Zanclean-age soils represent a presumably long-time span, likely a few thousand years, and exhibit strong redoximorphic features such as low-grade plinthite, suggesting that they developed in intervals of humid climate. The mid Piacenzian-age soils represent rhythmic and short intervals of pedogenesis, which correlate to sea level highstands. The main characteristics of palaeosols are due to clay shrink-swell properties (vertic) and carbonate translocation (calcic). Calcic features were interpreted as recording the duration of pedogenesis and thus of the sedimentary hiatuses, suggesting a range of development from 1,000 to 10,000 years. These soil features and the isotopic proxies converge towards indicating a highly seasonal rainfall pattern. This inference matches the sedimentological facies, which point to sediment transport and deposition from highly laden flood flows, recalling the sedimentary dynamics of seasonal fluvial systems. The hypothesis of a very high degree of rainfall seasonality would match well with existing palaeoclimatic records for the Mediterranean Middle Pliocene Warm Period (MPWP), and could shed light on certain unusual features in such records.Comparing soils developed in the Early and in the Late Pliocene, the MAP estimates confirm the differences in climate condition which likely led to the divergent pedogenesis pathways. Furthermore, the palaeotemperatures estimated from the oxygen isotopic composition of pedogenic carbonates within Piacenzian calcic horizons, point to values matching the modelled temperatures for the MPWP.

Mercury dispersion in the Paglia and Tiber river catchments (Central Italy) from the abandoned Monte Amiata mining district has long been documented (Rimondi et al., 2019, and references therein). However, there are comparatively fewer data on fluxes of the metal across the basin to the Tyrrhenian sea. The only published estimates (Rimondi et al., 2014) refer to the first 40 km of the Paglia River between Abbadia San Salvatore and Allerona Scalo. They reported highly variable total (dissolved + suspended particulate) Hg loads, up to 34 g/day, strongly depending on river discharge. We report here unpublished data from a sampling campaign of September 2014 (Millacci, 2016), that included three samples along the Tiber river. The data refer to low flow conditions at the end of the dry season. As expected, loads progressively increase with discharge from 1-5 g/day near the source of the Paglia river to about 100 g/day in the city of Rome. There is an anomalous value of 220 g/day just south of the Alviano dam (near Orvieto): a possible explanation is a release of Hg-rich sediments from the dam during maintenance operations.Millacci G. (2016) – Unpublished thesis (Laurea magistrale) in Geological sciences, Università di FirenzeRimondi V., et al. (2014) – Environmental Science and Pollution Research, 21:5575–5585Rimondi V., et al. (2019) - Environmental Pollution 255, 113191

Pliocene has a key role in assessing future climate impact and specifically, the mid-Piacenzian is considered the most recent period in Earth’s history in which temperatures reached values similar to those predicted for the end of the 21st century, about 2°–3°C warmer globally on average than today. Palaeopedology offers a great potential for elucidating high resolution, deep time palaeoclimate records. Thus, we aimed to investigate palaeosols as suitable archives for reconstructing surface processes, paleo-ecosystem structures and local- to global-scale paleoclimate patterns in the Pliocene.A favourable opportunity to study soils developed in the Early and in the Late Pliocene was provided on two alluvial sediments in Tuscany (Central Italy). Piacenzian palaeosol-stratigraphic sequences were compared with previously known Zanclean stratigraphic records. A multi-proxy approach, combining stratigraphic and paleopedological evidence, was adopted to produce more robust palaeoenvironmental insights. Field observations were related with quantitative techniques based on geochemical and isotopic analysis, to evaluate pedogenic processes, past-climate and palaeovegetation.Pedological evidence of two contrasting environments were present at the two sequences. Strong redoximorphic features such as low-grade plinthite were observed in the Zanclean-age soil, suggesting that these soils evolved in humid palaeoclimate in a time span of a few thousand years. On the other hand, the Piacenzian-age soils of central Tuscany represented rhythmic and short intervals of pedogenesis, connected with sea level highstands. The best developed palaeosols show very well-expressed Calcic horizon. Pedogenic carbonates are typically associated with well-drained soil profiles in sub-humid, semi-arid and arid climates characterized by relatively low rainfall and high evapotranspiration. This suggest that Mediterranean-type rainfall patterns may have prevailed in the warmest intervals of Late Pliocene. The studied Piacenzian soils with carbonates were weak- to moderated-developed based on the characteristics of carbonate accumulation that are II and III stage moving from the ancient to the recent ones, suggesting a range of development from 103 to 104 years.The estimates of the mean annual precipitation (MAP), based on weathering indices (CIA-K) and geochemical climofunctions, further allowed us to solidly inferred that substantial differences in climate conditions leaded to the divergent pedogenesis pathways, even considering the large difference in time as a factor (about one order of magnitude) between the two outcrops.