Middle to Late Pleistocene palaeoenvironmental evolution of the southeastern Alpine Valeriano Creek succession (northeastern Italy)

The Middle–Late Pleistocene alluvial and lacustrine succession of Valeriano Creek (southeastern Alpine foothills, 190 m a.s.l.) documents the environmental evolution of the piedmont plain before the onset of the Last Glacial Maximum (LGM). The sedimentary record was investigated by multidisciplinary stratigraphical and sedimentological studies coupled with petrographic and palaeobotanical analysis. A chronology has been provided by luminescence, radiocarbon dating and pollen biochronology. The succession developed at the valley mouth of a small catchment and is confined in the piedmont plain by the alluvial fans of major rivers. The oldest deposits were formed during a cold phase during the late Middle Pleistocene. This part of the piedmont plain was generally stable until Termination II, when it was trenched more than 15 m deep by watercourses. The infilling succession of the trench, mostly by low‐energy alluvial sediments interbedded with mire and peat deposits, documents, for the first time on the southern side of the Alps, the relationships between fluvial activity, vegetation and climate change at the foothills piedmont plain during late Marine Isotope Stage (MIS) 5. The stadial–interstadial climate forcing implies a local reorganisation of fluvial dynamics and of forest composition, although substantial plant cover persisted even during cooler stadials. In accordance with coeval alluvial and speleothem records from the northern side of the Alps, this environmental evolution supports a very restricted Alpine glaciation of the main fluvial catchments of the southeastern Alps during MIS 5a–d. Copyright © 2009 John Wiley & Sons, Ltd.     

Using 137Cs measurements to establish catchment sediment budgets and explore scale effects

Growing awareness of the wider environmental significance of fine sediment transport by rivers and associated sediment problems linked to sediment–water quality interactions, nutrient and contaminant transfer, and the degradation of aquatic habitats has resulted in the need for an improved understanding of the mobilization and transfer of sediment in catchments to support the development of effective sediment management strategies. The sediment budget provides a key integrating concept for assembling information on the internal functioning of a catchment in terms of its sediment dynamics by providing information on the mobilization, transfer, storage and output of sediment. One key feature of a catchment sediment budget is the relationship between the sediment yield at the catchment outlet and rates of sediment mobilization and transfer within the catchment, which is commonly represented by the sediment delivery ratio. To date, most attempts to derive estimates of this ratio have been based on a comparison of the measured sediment yield from a catchment with an estimate of the erosion occurring within the catchment, derived from an erosion prediction procedure, such as the Universal Soil Loss Equation (USLE) or its revised version, RUSLE. There is a need to obtain more direct and spatially distributed evidence of the erosion rates occurring within a catchment and to characterize the links between sediment mobilization, transfer, storage and output more explicitly. In this context, fallout radionuclides have proved particularly useful as sediment tracers. This paper reports the results of a study aimed at exploring the use of caesium‐137 (¹³⁷Cs) measurements to establish sediment budgets for three catchments of different sizes and contrasting land use located in Calabria, southern Italy. Long‐term measurements of sediment output were available for the catchments, and, by using the estimates of gross and net rates of soil loss within the catchments provided by ¹³⁷Cs measurements, it was possible to establish the key components of the sediment budget for each catchment. By documenting the sediment budgets of three catchments of different sizes, the study provides a basis for exploring the effects of scale on catchment sediment budgets and, in particular, the increasing importance of catchment storage as the size of the catchment increases. The results of this study demonstrate a reduction in the sediment delivery ratio from 98 to 2% as catchment area increases from 1·47 ha to 31·2 km². Copyright © 2010 John Wiley & Sons, Ltd.     

Constraining the onset of the Holocene “Neoglacial” over the central Italy using tephra layers

A study of six tephra layers discovered in different deposits between 1600 and 2700 m a.s.l. in the Apennine chain in central Italy allowed precise stratigraphic constraints on environmental and climatic changes between ca. 4.5 and 3.8 cal ka BP. Chemical analyses allowed the correlation of these tephra layers with the eruptions of Agnano Mt Spina (AMST) from Phlegrean Field and Avellino (AVT) from Somma–Vesuvius. Major environmental changes in the high mountains of the Central Apennines occurred just after the deposition of the AMST and predate the deposition of the AVT. At this time, renewed growth of the Calderone Glacier occurred, marking the onset of the Apennine “Neoglacial”. The presence of the AMST and AVT enabled us to make a precise, physical correlation with other archives in central Italy. Synchronization of records between sites showed that the period intervening the deposition of the AMST and AVT layers coincided with environmental changes that were not always exactly in phase. This highlights the fact that stratigraphic correlations using only radiocarbon chronologies (the most common method used for dating archives during the Holocene) could produce erroneous correlation of events, giving rise to oversimplified paleoclimatic reconstructions.     

The geothermal gradient of Io: Consequences for lithosphere structure and volcanic eruptive activity

We solve numerically the equations describing the transfer of heat through the lithosphere of Io by a mixture of conduction and volcanic advection as proposed by O’Reilly and Davies (O’Reilly, T.C., Davies, G.F. [1981]. Geophys. Res. Lett. 8, 313-316), removing the requirement that average material properties must be used. As expected, the dominance of advective heat transfer by volcanic eruptions means that Io’s geothermal gradient well away from volcanic centres is very small, of order 1 K km⁻¹. This result is independent of any reasonable assumptions about the radiogenic heating rate in the lithosphere. The lithosphere temperature does not increase greatly above the surface temperature until the base of the lithosphere is approached, except in limited areas around shallow magma bodies. As a consequence, solid volatile sulphur compounds mobilized by volcanic processes and re-deposited on the surface of Io commonly remain solid until they reach great depths as they are progressively buried by ongoing activity. For current estimates of the volcanic heat transfer rate, melting of SO₂ does not begin until a depth of ∼20 km and sulphur remains solid to a depth of ∼26 km in a 30 km thick lithosphere. Rising magmas can incorporate fluids from these deep sulphur compound aquifers, and we quantify the major influence that this can have on the bulk density of the magma and hence the resulting possible intrusion and eruption styles.     

Improvement of Disc Cutter Performance by Water Jet Assistance

This article deals with the problem of assisting disc cutters by means of high-velocity jets of water, with the aim of increasing the excavation rate while improving the working conditions, with particular reference to wear. The results of an experimental research undertaken at the Waterjet Laboratory of the University of Cagliari on a medium–hard abrasive rock clearly show that a higher removal rate is achieved owing to the weakening action of a jet directed on one side of the disc, causing deeper penetration. This outcome is interpreted on the basis of the scale formation model, which explains why smaller scales are obtained on the water jet’s side of the groove. Accordingly, it is suggested that the results can be further improved if the jet is directed ahead of the tool along the same path, since, in this way, larger scales can be produced on both sides.     

Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy)

An integrated study based on fluid inclusion, δ¹⁸O composition and structural analyses was carried out on a Pliocene fossil hydrothermal system, located to the South of the present active Larderello geothermal field, in the Boccheggiano-Montieri area. The study area is typified by mineralized cataclastic levels related to Late Oligocene–Early Miocene thrust surfaces, and to the following two generations of normal faults of Miocene and Pliocene ages, respectively. Within the damage zone of the Pliocene Boccheggiano fault, the mineralization is mainly made up of quartz and pyrite. Quartz + Pb–Zn sulfides, or quartz + Pb–Zn sulfides + fluorite + carbonates assemblages occur instead in the older cataclastic levels. Two generations of liquid-rich fluid inclusions were recognized in quartz and fluorite: the first one, with homogenization temperatures ranging between 172 and 331°C and salinity between 0.0 and 8.8 wt.% NaCl_equiv., records the early stage of hydrothermal activity. The second generation of fluid inclusions documents a later stage, with homogenization temperature from 124 to 288°C and salinity from 0.2 to 1.9 wt.% NaCl_equiv.. Fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and/or temperatures was a widespread process during the early stage, and that fluid temperatures decreased moving from the Boccheggiano fault toward the more distal and older cataclastic levels. The δ¹⁸O values of water in equilibrium with hydrothermal quartz, which range from −5.7 to −0.1‰, are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in δ¹⁸O through water–rock interaction, and/or with magmatically derived fluids. Results indicate that the damage zone of the Pliocene Boccheggiano fault represented the main channel for the flow of meteoric water, which was heated at depth, then mixed with high salinity fluids, and finally ascend to infiltrate along the older cataclastic levels. Our results, based on fluid inclusions, oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the Boccheggiano fault and the older cataclasites, which were thus hydraulically connected.     

Oligocene to Present kilometres scale subsidence and exhumation of the Ligurian Alps and the Tertiary Piedmont Basin (NW Italy) revealed by apatite (U–Th)/He thermochronology: correlation with regional tectonics

The Ligurian Alps segment of the Alpine–Apennine orogen in NW Italy is unconformably covered by Upper Eocene to Holocene sediments in the Tertiary Piedmont Basin (TPB) and Po Plain. These sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin. Apatite (U–Th)/He and fission track thermochronology shows that the orogen first subsided and was buried at >4 km from 30 to 26 Ma and began its exhumation thereafter. From 26 Ma to present, this upward movement was contemporaneous with subsidence in the northern TPB. The couple exhumation in the S and subsidence in the N migrated northwards through time. Vertical movements in the area are similar to those reconstructed in Corsica. In both cases, the onset of exhumation becomes younger away from the Ligurian‐Provençal basin and has little correlation with the opening of the surrounding oceanic basins.