Analisi petrografica di alcuni campioni ceramici rinvenuti nella tomba 2 di Iloi-Ispiluncas: [appendice C]

Tra i materiali ceramici rinvenuti nel corso dello scavo della tomba 2, sono stati selezionati dieci elementi rappresentativi delle produzioni fittili caratteristiche delle diverse fasi culturali durante le quali la sepoltura era in uso. Scopo dell'analisi è stato sia la verifica delle stime sulla quantità e sulla natura degli inclusi dei materiali, condotte in base al solo esame macroscopico durante la fase di classificazione dei pezzi, sia l'osservazione delle eventuali variazioni sul piano della tecnologia e dell'approvvigionamento delle materie prime nel corso dei differenti periodi documentati

Outline of the Variscan basement of Sardinia

In Sardinia a quasi-complete section of the southern branch of the Variscan orogenic belt crops out, characterized by non-metamorphosed to high-grade rocks, whose age ranges from Early Cambrian to Early Carboniferous, and that are involved in a complex polyphase deformation. The main result of the Variscan orogeny in Sardinia is a tectono-metamorphic partition with, from north to south: an Inner Zone, with medium to high grade metamorphism, thrusted over a Nappe Zone, with green schist metamorphism that overthrusted a Foreland Zone affected by very low grade regional metamorphism. The pre-Variscan succession is well exposed in the Foreland and Nappe zones where four main synthemes can be recognized: i) a Lower Cambrian to Lower Ordovician terrigenous and carbonatic succession deposited in the Gondwana passive margin, sealed by an angular unconformity related to the Sardic Phase, ii) a Middle-Upper Ordovician magmatic complex, both intrusive and effusive, probably related to an Andean-type plate convergence, iii) a terrigenous to carbonatic succession from Late Ordovician to Early Carboniferous, again related to a passive margin evolution; iv) finally a flyschoid Culm-like succession accredited to Early Carboniferous

Lo Sfruttamento delle falde freatiche nelle coltri detritiche superficiali come riserve idriche sussidiarie in regioni granitiche

The study of some catch-basins upstream to some headwaters has been carried out on the southern slope of the «Monti di Alà» chaine. The characteristics of some springs with a scarse flow have been also investigated. The data obtained allow us to frame the various source areas as gravity springs. The interception of the underground flows operated by some draining trenches has permitted, in a further moment, a considerable increase of flow, compared with the natural one. In consideration of this result, the catch basins consisting of surficial detrital sheet coming from the alteration of granites, assume a certain significance as subsidiary water reserve in some areas lacking in good aquifers as the granitic domains

Low Entalpy Geothermal Suitability of North Sardinia (Italy)

Abstract Heat flow density over Sardinia is relatively high. Tertiary geodynamics and radiogenic heating from the Variscan batholith are the possible concurrent causes. Major anomalies were thought confined to the Tertiary basins, where 180 mW/m2 are reported. New data ascertain that the occurrence of the hottest thermal springs does not mirror these basins, as they pour out from Variscan granites. Hence the high thermal flow from the basins can result from basin-wide heat redistribution by hot "granite" water flowing laterally in shallow aquifers. This scenario is particularly favourable for low-medium enthalpy fluids exploitation as well as for geoexchange

Geologia e giacimentologia delle argille nella regione Bonu Ighinu

L'area di Bonu Ighinu, in cui è situata la grotta di Sa Ucca de Su Tintirriolu, occupa la fascia occidentale di un'ampia fossa tettonica ad andamento meridiano, nota in letteratura come "Rift Sardo", sviluppatasi a partire dall'Oligocene e riempita a più riprese da prodotti vulcanici di affinità calco-alcalina, costituiti da andesiti, trachiandesiti, riedaciti in facies ignimbritica e da altri prodotti di natura piroclastica. Tale attività effusiva si manifestò fino al Miocene medio; a partire da questo periodo la "fossa" fu interessata da una trasgressione marina che depositò calcari di ambiente neritico e, con l'approfondirsi del mare miocenico, marne più o meno arenacee. Nel Pliocene e nel Quaternario l'area, già emersa nel Miocene superiore, fu sottoposta a smantellamento e fu sede di un nuovo recente vulcanismo caratterizzato da basalti "intraplacca" ad affinità alcalina. Sempre nel Quaternario più recente prese forma l'attuale assetto geo-morfologico dell'area, caratterizzato da aree pianeggianti, in corrispondenza dei basalti e delle aree calcaree mioceniche, variamente incise dagli affluenti di sinistra del Temo

REEs and other critical raw materials in Cretaceous Mediterranean-type bauxite: the case of the Sardinian ore (Italy)

Mediterranean-type bauxite deposits in Sardinia formed during the Upper Cretaceous (Cenomanian–Turonian) due to the emergence of the south European margin of the Alpine Tethys in an area affected by monsoonal climate. The deposits were controlled by the structural frame formed in a transpressive tectonic regime and unconformably overlie carbonate rocks of different age and composition, which led to the formation of different bauxite types. In general, in the Sardinian bauxite deposits, boehmite is the main Al-phase, kaolinite is the main Si-rich mineral, and hematite as well as goethite are the Fe-rich phases. Secondary authigenic anatase and detrital rutile control the Ti contents. Eu/Eu* anomalies show that the bauxite types were derived from the Variscan basement. However, there are differences in Al2O3 and SiO2 contents, which suggest there was localised variability in the extent of epigenetic replacement of kaolinite by boehmite. R-mode factor analysis suggests that most critical raw materials (as defined by the devoted European Union working group), such as Sc, Ga, Nb, Hf, Ta, and W, covary with Al2O3 contents. In the Si-poor bauxite, these metals of economic interest are likely controlled by boehmite, whereas in the Si-rich bauxite they are mostly controlled by weathering-resistant minerals. Rare earth element (REE)-rich minerals, including fluorocarbonates and cerianite, are concentrated in the basal, illuvial horizon, especially in the silica-rich bauxite (ΣREE = 1006–2034 ppm). Cerianite formation required Ce oxidation, whereas fluorocarbonate formation involved mobilisation of trivalent REEs and further fluoride complexation. Both REE-rich mineral phases precipitated under alkaline pH conditions near to the carbonate bedrock. Our evaluation of the critical raw materials distribution in the Sardinian bauxite, coupled with the “economic importance” and “supply risk” parameters, indicate the ore contains large amounts of metals characterised by a “supply risk”, such as light and heavy REEs, and metals of “economic importance”, such as V and W. In this way, the Sardinian bauxite deposits could be reconsidered as a potential source of critical raw materials

Hydrogeological and geophysical investigations for groundwater in the Arumeru District (Northern Tanzania)

Due to water shortage, in the wards of Ngarenanyuki and Oldonyosambu (Arumeru District, Northern Tanzania), the per capita daily water consumption is 8 liters as.average, The avaleability goes down to 3-4 liters in the dry seasons when most of the population cannot resort to seasonal ponds or streams and so it is compelled to concentrate around the few perennial water points. This datum is quite far from the Millennium Goal objectives that foresee a quantity of at least 20 l/d/p (litres per day per person) for the Development Countries population, within 2015. Problems are also related to water quality, in particular, the high concentration of fluoride that characterises the waters in East Africa Rift System

A restored section of the “southern Variscan realm” across the Corsica–Sardinia microcontinent

International audienceA complete section of the southern realm of the Variscan orogenic belt can be restored in the Corsica–Sardinia segment. Northern Corsica exposes a nonmetamorphosed Palaeozoic succession lying on Panafrican mica schist related to a microcontinent (most likely Armorica or from a microcontinent from the Hun superterrane) that had drifted away directly from Gondwana. These formations are thrust over the Variscan Internal Zone composed mainly of anatectic high-grade Palaeozoic formations that crop out from central Corsica to northern Sardinia; the metamorphic peak of the eclogite remnants has been dated at c. 420 Ma. The Variscan Internal Zone interpreted here as a collision zone, and also the Eovariscan suture, was intruded in Corsica by Mg–K granite from 345 to 335 Ma. The thrust of this Internal Zone onto the stack of parautochthonous nappes in central Sardinia is cross-cut by the Posada Asinara dextral shear zone. To the south, parautochthonous nappes overthrust the North-Gondwana margin which displays a possible Panafrican basement topped by an Iglesiente–Sulcis nonmetamorphic/anchimetamorphic Palaeozoic succession

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

A multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations, was aimed at locating a source of safe groundwater for a district of northern Tanzania, within the western branch of the East Africa Rift Valley, where water shortage is common and much of the surface water carries unacceptable levels of dissolved fluoride. The 440 km2 study area lies in the northern part of Arumeru district and is dominated by Mt. Meru (4565m a.s.l.). The local climate is semi-arid, with distinct wet and dry seasons. Four hydrogeological complexes were identified, occurring within different volcanic formations, either alone or superimposed upon one another. The groundwater flow system was interpreted from the spatial distribution of the springs, combined with a lithology- and geometry-based reconstruction of the aquifers. The dominant pattern consists of a multi-directional flow from the higher elevations in the south towards the lower areas in the north, but this is complicated by structures such as grabens, faults, lava domes and tholoids. After the identification of the major fluoride source, an interference pattern between groundwater and high fluoride surface water was drawn. Finally, vertical electrical soundings were performed to define the location of aquifers in regions where release of fluoride was prevented. The methodological approach for the prospecting of safe water in a semi-arid, fluoride polluted region was validated by the drilling of a 60m deep well capable of supplying at least 3.8 l/s of low fluoride, drinkable water

Hydrogeology and hydrogeochemistry of an alkaline volcanic area: the NE Mt. Meru slope (East African Rift – Northern Tanzania)

The objective of this study is to analyze the geochemical conditions associated with the presence of fluoride (F−) in the groundwater of an area of Northern Tanzania. The studied aquifers are composed of volcanic rocks such as phonolitic and nephelinitic lavas, basalts, lahars of various ages and mantling ash. Sedimentary rocks consisting of fine-grained alluvial and lacustrine deposits occur as well. Samples collected from springs, borehole and surface water, during two monitoring surveys, were analyzed for the various physico-chemical and isotopic parameters. The geochemical composition of water is typically sodium bicarbonate. High values of F− (up to 68 mg l−1) were recorded. The highest values of fluoride agreed with the highest values of pH, sodium and bicarbonate. Dissolution of major ions, exchange processes and precipitation of Ca2+ from supersaturated solutions joined with the local permeability and hydraulic gradients, control the fluoride mobilization and the contamination of the area