Exploring the potential of tree-ring chronologies from the Trafoi Valley (Central Italian Alps) to reconstruct glacier mass balance

Two tree-ring chronologies of stone pine ( Pinus cembra L.) and two of Norway spruce ( Picea abies Karst.) were constructed on the basis of data from three high-altitude sites in the Trafoi Valley (Central Alps, Italy) to test tree species sensitivity to climate at different sites and to explore the potential of the two species for reconstructing the mass balance of two glaciers in the same region (the Careser and Hintereis glaciers). Influence of climate on tree-ring growth and on glacier mass variations was tested by means of Pearson's correlation and response functions. At highest altitude sites, both species appeared to be sensitive to July temperatures, while stone pine also showed higher sensitivity than Norway spruce to previous winter precipitation. Comparing the dendrochronological and glaciological series, stone pine showed higher negative correlations with glacier mass balance series than Norway spruce. These different relationships reflect different species responses to climate, and stone pine is potentially useful in reconstructing past glacier mass balance in the Central Alps. Extreme climatic events induce different and even contrasting responses of tree-ring growth and glacier mass variations and may therefore bias tree-ring-based glacier mass balance reconstructions.     

Application of numerical modelling to a case of compaction-driven dolomitization: a Jurassic palaeohigh in the Po Plain, Italy

Dolomitization of a carbonate platform can occur at different times and in different diagenetic environments, from synsedimentary to deep burial settings. Numerical simulations are valuable tools to test and select the model that, among different hypotheses compatible with field and geochemical data, best honour mass balance, kinetic and thermodynamic constraints. Moreover, the simulation can predict the distribution of the dolomitized bodies in the subsurface and evaluate porosity changes; valuable information for the oil industry. This study is the first attempt to reproduce and investigate the compaction dolomitization model. The diagenetic study of the Jurassic carbonate basin and palaeohigh system of the Po Plain indicates that the carbonates of the palaeohighs were dolomitized by basin compaction fluids. The main goal of the simulations is to evaluate the origin and evolution of the dolomitizing fluids and to provide insights regarding the distribution of the potential reservoir‐dolomitized bodies in the Po Plain. The modelling process is subdivided into two steps: basin modelling and reactive transport modelling. The SEBE3 basin simulator (Eni proprietary) was used to create a three‐dimensional model of the compacting system. The results include compaction fluid flow rate from the basin to the palaeohigh, compaction duration and a determination of the total amount of fluid introduced into the palaeohigh. These data are then used to perform reactive transport modelling with the TOUGHREACT code. Sensitivities on dolomite kinetic parameters suggest that dolomitization was an efficient process even at low temperatures, with differences mainly related to the dynamics of the process. Fluid composition is one of the main constraints, the sea water derived compaction fluid is proven to be efficient for dolomitization due to its relatively high Mg content. Simulations also confirmed that permeability is the most important factor influencing fluid flow and, consequently, the dolomite distribution in the formation. Permeable fractured zones have a strong influence, diverting the dolomitizing fluids from their normal path towards overlying or lateral zones. Moreover, the simulations showed that, after dolomite replacement is complete, the dolomitizing fluids can precipitate dolomite cement, causing over‐dolomitization, with related localized plugging effects in the zone of influx. Mass balance calculations indicate that in the dolomitization compaction model, the amount of compaction water fluxed from the basin to the carbonate is the main constraint on dolomitization efficiency. This observation implies that the ratio between the volume of the basin undergoing compaction and the volume of the palaeohigh is a limiting factor on the final size of the dolomitized bodies. An isolated palaeohigh could be an ideal site for pervasive replacement dolomitization due to the large volume of compaction fluids available compared with the carbonate rock volume. In the case of large platforms, the more permeable margin lithofacies are the most likely sites for compaction model dolomitization. The combined use of a basin simulator and reactive transport modelling has proved to be a successful method to verify model reliability and it provides insights into the volumetric distribution of diagenetic products.     

Sequence stratigraphy in the context of rapid regional uplift and high‐amplitude glacio‐eustatic changes: the Pleistocene Cutro Terrace (Calabria,southern Italy)

The Cutro Terrace is a mixed marine to continental terrace, where deposits up to 15 m thick discontinuously crop out in an area extending for ca 360 km² near Crotone (southern Italy). The terrace represents the oldest and highest terrace of the Crotone area, and it has been ascribed to marine isotope stage 7 (ca 200 kyr bp ). Detailed facies and sequence‐stratigraphic analyses of the terrace deposits allow the recognition of a suite of depositional environments ranging from middle shelf to fluvial, and of two stacked transgressive–regressive cycles (Cutro 1 and Cutro 2) bounded by ravinement surfaces and by surfaces of sub‐aerial exposure. In particular, carbonate sedimentation, consisting of algal build‐ups and biocalcarenites, characterizes the Cutro 1 cycle in the southern sector of the terrace, and passes into shoreface and foreshore sandstones and calcarenites towards the north‐west. The Cutro 2 cycle is mostly siliciclastic and consists of shoreface, lagoon‐estuarine, fluvial channel fill, floodplain and lacustrine deposits. The Cutro 1 cycle is characterized by very thin transgressive marine strata, represented by lags and shell beds upon a ravinement surface, and thicker regressive deposits. Moreover, the cycle appears foreshortened basinwards, which suggests that the accumulation of its distal and upper part occurred during forced regressive conditions. The Cutro 2 cycle displays a marked aggradational component of transgressive to highstand paralic and continental deposits, in places strongly influenced by local physiography, whereas forced regressive sediments are absent and probably accumulated further basinwards. The maximum flooding shoreline of the second cycle is translated ca 15 km basinward with respect to that of the first cycle, and this reflects a long‐term regressive trend mostly driven by regional uplift. The stratigraphic architecture of the Cutro Terrace deposits is the result of the interplay between regional uplift and high amplitude, Late Quaternary glacio‐eustatic changes. In particular, rapid transgressions, linked to glacio‐eustatic rises that outpaced regional uplift, favoured the accumulation of thin transgressive marine strata at the base of the two cycles. In contrast, the combined effect of glacio‐eustatic falls and regional uplift led to high‐magnitude forced regressions. The superposition of the two cycles was favoured by a relatively flat topography, which allowed relatively complete preservation of stratal geometries that record large shoreline displacements during transgression and regression. The absence of a palaeo‐coastal cliff at the inner margin of the terrace supports this interpretation. The Cutro Terrace provides a case study of sequence architecture developed in uplifting settings and controlled by high‐amplitude glacio‐eustatic changes. This case study also demonstrates how the interplay of relative sea‐level change, sediment supply and physiography may determine either the superposition of cycles forming a single terrace or the formation of a staircase of terraces each recording an individual eustatic pulse.     

Fault array evolution in extensional basins: insights from statistical analysis of gravel deposits in the Cecina River (Tuscany,Italy)

Two statistical analyses of gravel clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, Italy) have been combined to unravel changes in the palaeo‐drainage system. Data from 16 outcrops were collected and 6400 clasts described. Facies analysis, micro‐palaeontology and macro‐palaeontology and petrographic characteristics of the gravel deposits have highlighted the presence of three allostratigraphic units. Clast lithology is the main discriminator among these units. Cluster and principal component analyses of the 6400 clasts have improved understanding of the stratigraphy of the Lower Pleistocene deposits and constrain the re‐routing of the lower palaeo‐Cecina River from a supposedly south‐east to north‐west direction to the present east to west direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic units were abandoned in the Lower Pleistocene, when the re‐routing of the Cecina River caused the capture of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of normal faults sub‐parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull‐apart basin, which is now exploited by the Cecina River. This study illustrates the value of lithological analyses of gravel deposits for understanding the tectonic evolution of an area.     

Fluid and Element Cycling in Subducted Serpentinite: a Trace-Element Study of the Erro-Tobbio High-Pressure Ultramafites (Western Alps, NW Italy)

The oceanic serpentinization of peridotites and the influenceof such an alteration on element cycling during their subductiondewatering are here investigated in a mantle slice (Erro–Tobbioperidotite), first exposed to oceanic serpentinization and laterinvolved in alpine subduction, partial dewatering and formationof a high-pressure olivine + titanian-clinohumite + diopside+ antigorite assemblage in the peridotites and in veins. Previouswork indicates that high-pressure veins include primary brines,representing a residue after crystallization of the vein assemblageand containing recycled oceanic Cl and alkalis. To reconstructthe main changes during oceanic peridotite serpentinizationand subsequent subduction, we analysed samples in profiles fromserpentinized oceanic peridotites to high-pressure serpentinites,and from high-pressure ultramafites to veins. Here we presentresults indicating that the main features of the oceanic serpentinizationare immobility of rare earth elements (REE), considerable waterincrease, local CaO decrease and uptake of trace amounts ofSr, probably as a function of the intensity of alteration. Srentered fine-grained Ca phases associated with serpentine andchlorite. Trace-element analyses of mantle clinopyroxenes andhigh-pressure diopsides (in country ultramafites and veins),highlight the close similarity in the REE compositions of thevarious clinopyroxenes, thereby indicating rock control on thevein fluids and lack of exotic components carried by externallyderived fluids. Presence of appreciable Sr contents in vein-formingdiopside indicates cycling of oceanic Sr in the high-pressurefluid. This, together with the recognition of pre-subductionCl and alkalis in the vein fluid, indicates closed-system behaviourduring eclogitization and internal cycling of exogenic components.Diopside and Ti-clinohumite are the high-pressure minerals actingas repositories for REE and Sr, and for high field strengthelements (HFSE), respectively. The aqueous fluid equilibratedwith such an assemblage is enriched in Cl and alkaline elementsbut strongly depleted in REE and HFSE (less than chondrite abundances).Sr is low [(0·2–1·6) x chondrites], althoughselectively enriched relative to light REE. KEY WORDS: eclogite facies; fluid; trace elements; serpentinite; subduction     

Depositional systems,composition and geochemistry of Triassic rifted‐continental margin redbeds of the Internal Rif Chain,Morocco

The Middle to Upper Triassic redbeds at the base of the Ghomaride and Internal ‘Dorsale Calcaire’ Nappes in the Rifian sector of the Maghrebian Chain have been studied for their sedimentological, petrographic, mineralogical and chemical features. Redbeds lie unconformably on a Variscan low‐grade metamorphic basement in a 300 m thick, upward fining and thinning megasequence. Successions are composed of predominantly fluvial red sandstones, with many intercalations of quartzose conglomerates in the lower part that pass upwards into fine‐grained micaceous siltstones and massive mudstones, with some carbonate and evaporite beds. This suite of sediments suggests that palaeoenvironments evolved from mostly arenaceous alluvial systems (Middle Triassic) to muddy flood and coastal plain deposits. The successions are characterized by local carbonate and evaporite episodes in the Late Triassic. The growth of carbonate platforms is related to the increasing subsidence (Norian‐Rhaetian) during the break‐up of Pangea and the earliest stages of the Western Tethys opening. Carbonate platforms became widespread in the Sinemurian. Sandstones are quartzose to quartzolithic in composition, testifying a recycled orogenic provenance from low‐grade Palaeozoic metasedimentary rocks. Palaeoweathering indices (Chemical Index of Alteration, Chemical Index of Weathering and Plagioclase Index of Alteration) suggest both a K‐enrichment during the burial history and a source area that experienced intense weathering and recycling processes. These processes were favoured by seasonal climatic alternations, characterized by hot, episodically humid conditions with a prolonged dry season. These climatic alternations produced illitization of silicate minerals, iron oxidation and quartz‐rich red sediments in alluvial systems. The estimated burial temperature for the continental redbeds is in the range of 100 to 160 °C with lithostatic/tectonic loading of ca 4 to 6 km. These redbeds can be considered as regional petrofacies that mark the onset of the continental rift valley stage in the Western Pangea (Middle Triassic) before the opening of the western part of Tethys in the Middle Jurassic. The studied redbeds and the coeval redbeds of many Alpine successions (Betic, Tellian and Apenninic orogens) show a quite similar history; they identify a Mesomediterranean continental block originating from the break‐up of Pangea, which then played an important role in the post‐Triassic evolution of the Western Mediterranean region.     

ON THE ELECTRICAL BEHAVIOUR OF A POLARIZABLE SAMPLE STUDIED BY THE NORMALIZED TIME-INTEGRAL AND BALLISTIC METHODS*

In this paper the experimental data obtained studying the decay of a sample of pisolitic bauxite both by a ballistic method and the normalized time-integral procedure are compared. This comparison allowed me to note two peculiarities. First, the apparent capacitance of the sample, as well as its normalized time-integral, seems to show a characteristic behaviour within the same interval of the charging time. Secondly, while the apparent capacitance plotted versus time (measured from the energization interruption instant) appears to assume values which seem to tend towards asymptotic value of the apparent capacitance, it is to be noted instead that in these circumstances the relative normalized time integral shows no tendency to reach any limiting value.     

INFLUENCE OF CLIMATE AND CLIMATE ANOMALIES ON NORWAY SPRUCE TREE-RING GROWTH AT DIFFERENT ALTITUDES AND ON GLACIER RESPONSES: EXAMPLES FROM THE CENTRAL ITALIAN ALPS

Climate change and climate anomalies are inducing strong variations in the high‐mountain environment, driving the responses of physical and biological systems differently. This paper assesses tree‐ring growth responses to climate for two Norway spruce (Picea abies (L.) Karst.) sites at different altitudes from an Ortles‐Cevedale Group (OCG; internal zones of the Central Italian Alps) valley site and reports some examples of climate impact on glacier dynamics in the OCG in recent decades. Growth–climate relationships between tree‐ring chronologies and meteorological data were established by means of Pearson's correlation and response functions. In the high‐altitude chronology we found a strong signal of July temperatures, whereas the low‐altitude chronology also contained a signal of summer precipitation. Climate anomalies occurring in these months proved to influence tree growth at the two sites differently. In summer 2003 extreme climatic conditions established over Europe and the Alps, strongly affecting physical and biological systems. Spruce responses to the climate anomaly of 2003 were more evident with a one‐year lag. The high‐altitude site profited from the warmer growing season, whereas trees at the low‐altitude site experienced water stress conditions and their growth was strongly inhibited also in the following year. Glacier mass loss in the OCG in 2003 was the highest since yearly measurement started. The examples reported confirm the strong and even divergent variations affecting the Alpine environment, induced by recent climate change.     

Farola Monte Hermoso: Fission-track Dating of Darwin's mammals deposit in Argentina

The Montehermosan Land Mammal Age has been etablished by fission-track dating of the mammal deposit of Farola Monte Hermoso. The fossil bones were found in the lowest part of the outcrop, consisting of fluvially derived clay and silt. The erosional surface between the lowest portion and the overlying aeolian sands is charcterised by a compact unit of rounded volcanic glass shards; a second fresh volcanic ash level is about 1 m above. EDS analyses and fission-track age analyses were performed on the two levels. The age determined for the lower volcanic ash level, 1.7 ± 0.4 Ma, is a minimum age for the Chapadmalalan mammal assemblage and a maximum age for the Uquian mammal assemblage in the Bonaerense area.