Soil erosion susceptibility assessment and validation using a geostatistical multivariate approach: a test in Southern Sicily

A certain number of studies have been carried out in recent years that aim at developing and applying a model capable of assessing water erosion of soil. Some of these have tried to quantitatively evaluate the volumes of soil loss, while others have focused their efforts on the recognition of the areas most prone to water erosion processes. This article presents the results of a research whose objective was that of evaluating water erosion susceptibility in a Sicilian watershed: the Naro river basin. A geomorphological study was carried out to recognize the water erosion landforms and define a set of parameters expressing both the intensity of hydraulic forces and the resistance of rocks/soils. The landforms were mapped and classified according to the dominant process in landsurfaces affected by diffuse or linear water erosion. A GIS layer was obtained by combining six determining factors (bedrock lithology, land use, soil texture, plan curvature, stream power index and slope-length factor) in unique conditions units. A geostatistical multivariate approach was applied by analysing the relationships between the spatial distributions of the erosion landforms and the unique condition units. Particularly, the density of eroded area for each combination of determining factors has been calculated: such function corresponds, in fact, to the conditional probability of erosion landforms to develop, under the same geoenvironmental conditions. In light of the obtained results, a general geomorphologic model for water erosion in the Naro river basin can be depicted: cultivated areas in clayey slopes, having fine-medium soil texture, are the most prone to be eroded; linear or diffuse water erosion processes dominate where the topography is favourable to a convergent or divergent runoff, respectively. For each of the two erosion process types, a susceptibility map was produced and submitted to a validation procedure based on a spatial random partition strategy. Both the success of the validation procedure of the susceptibility models and the geomorphological coherence of the relationships between factors and process that such models suggest, confirm the reliability of the method and the goodness of the predictions.     

Holocene climate variability in Sicily from a discontinuous stalagmite record and the Mesolithic to Neolithic transition

Fabric and stable isotopic composition of a Holocene stalagmite (CR1) from a cave in northern Sicily record changes in paleorainfall in the early Holocene. High δ¹³C stable isotope values in the calcite deposited from ca. 8500 to ca. 7500 yr ago are interpreted as reflecting periods of high rainfall. The wet phase was interrupted by two periods of multi-century duration characterized by relatively cool and dry winters centered at ca. 8200 and ca. 7500 yr ago, highlighted by low δ¹³C and δ¹⁸O values. A high variability of δ¹³C values is recorded from ca. 7500 to ca. 6500 yr ago and indicates that the transition from a pluvial early Holocene to the present-day climate conditions was punctuated by decadal-scale periods of relatively dry winters. In northern Sicily, the traditional elements of the Neolithic appear at ca. 7700 yr ago. It is possible that changes in rainfall influenced the passage from hunter-gathering to farming and sheep-herding economies.     

Initiation and development of pull-apart basins with Riedel shear mechanism: insights from scaled clay experiments

Typical pull-apart structures were created in scaled clay experiments with a pure strike-slip geometry (Riedel type experiments). A clay slab represents the sedimentary cover above a strike-slip fault in the rigid basement. At an early stage of the development of the deformation zone, synthetic shear fractures (Riedel shears) within the clay slab display dilatational behaviour. With increasing basal displacement the Riedel shears rotate and open further, developing into long, narrow and deep troughs. The shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes. At a more evolved stage, synthetic segments (Y-shears) parallel to the basal principal fault develop and accommodate progressive strike-slip deformation. The Y-shears connect the tips of adjacent troughs developed from the earlier Riedel shears, resulting in the typical rhomb-shaped structures characteristic for pull-apart basins. The Strait of Sicily rift zone, with major strike-slip systems being active from the Miocene to the Present, comprises pull-apart basins at different length scales, for which the structural record suggests development by a mechanism similar to that observed in our experiments.     

Landslide hazard in the Nebrodi Mountains (Northeastern Sicily)

The eastern sector of the Nebrodi Mountains (NE Sicily), a part of the Apenninic-Maghrebian orogenic chain, is characterized by an high landslide hazard. The village of S. Domenica Vittoria, which lies in the area, has been particularly affected by various landslide phenomena, with resulting damage to buildings and infrastructure.The rocks outcropping in the area belong to the Cretaceous Monte Soro Flysch; they consist of an alternation of argillaceous and calcareous beds at the base and argillaceous and quartzarenitic beds at the top. The lithotechnical characteristics of the formation and the steepness of the slopes in the area lead to an elevated instability, as testified by the widespread occurrence of sub-vertical arcuate cliffs (landslide scarps) and sub-horizontal areas (landslide terraces), typical of a landslide-controlled morphology. From a kinematics point of view, the observed phenomena can be referred to multiple rotational slides, flows, and complex landslides, often with a retrogressive development and enlargement. Triggering causes lie principally in the intense rainfalls that determine the decay of the geomechanical properties of the terrain and supply discontinuos groundwater circulation that is evident in seasonal springs. Human activity, such as the construction of roads and buildings on steep slopes and dispersal of water from supply systems and sewers has a significant impact as well.Due to the instability of the area, expansion of the village, which is already limited by the morphological conditions, is made difficult by the high hazard level, especially in the areas at higher elevations, where the principal landslide scarps are located, and even more on the rims of the scarps. Considering the high hazard level, S. Domenica Vittoria has been inserted by the National Geological Service among the sites in Sicily to be monitored by means of a GPS network. The survey carried out along the entire slope hosting the village has furnished the base for geological and geomorphological knowledge needed for the planning of the network, to identify the areas at landslide risk, where parts of the village lie, including the areas of expansion of the village, the main roads, and a portion of the Favoscuro river bed.     

典型小陆块海相成钾机理——以西西里微陆块钾盐矿床为例

中国大陆是由多个小陆块经多期次离散碰撞拼合而成,而"小陆块是否能成大钾"一直是国内钾盐研究领域关注的科学问题。文章剖析了意大利西西里微陆块的典型海相钾盐矿床形成条件与机理,为中国小陆块成钾研究提供借鉴。在晚中新世墨西拿盐度危机(Messinian Salinity Crisis)最盛期(5.60~5.55 Ma),西西里岛的卡尔塔尼塞塔盆地聚集了高达2亿t的钾盐镁矾矿。通过对卡尔塔尼塞塔盆地钾盐矿的赋存地层格架、矿体特征、成矿模式和机理进行梳理和总结,指出该矿床呈层状赋存于地中海"再沉积下石膏组"的原生石盐岩中,形成于深水、分层的常年性盐湖环境;晚中新世中地中海碰撞挤压的构造活动导致卡尔塔尼塞塔盆地强烈挠曲下凹,形成多个次级成矿凹陷;次级凹陷接受海水的周期性补给;在墨西拿盐度危机最盛期,由于气候变冷变干、直布罗陀海峡关闭、海平面急剧下降,远离补给源的次级凹陷变得更加封闭,从而在5万年的极短时间内经强烈蒸发,聚集为大规模钾盐矿。西西里微陆块尽管陆块小、盆地小,但在满足封闭构造_干旱气候_充足物源三要素耦合的特定时期内,同样形成了大型钾盐矿床。因此,西西里微陆块的钾盐成矿实例证明海相小陆块同样具有形成大型钾矿床的潜力,这对中国海相小陆块汇聚区的找钾工作具有重要的借鉴意义。     

GEOMORPHOLOGY AND KINEMATICS OF THE CONTURRANA ROCKSLIDE-DEBRIS FLOW (NW SICILY)

The Conturrana rockslide-debris flow involved a mass of almost 22 × 10⁶ m³ of well indurated breccia with a plastic basal layer. The original rock mass slid initially along a listric slip surface — which required the rupture of the mass itself by internal shearing and caused the formation of a horst-and-graben morphology — and attained a high speed. Then part of the mass fell from a morphological step, and moved about 800 m forward. In this landslide, the morphological and morphometrical examination — which is also based on a reconstruction of the pre-landslide topography — indicates that mobility was rather low when related to volume and to the control exerted by local morphology. The event might have been induced by an earthquake in the 4th century.     

Mascali,Mount Etna Region Sicily: An Example of Fascist Planning During the 1928 Eruption and Its Continuing Legacy

The 1928 eruption of Etna, Sicily, although the largest such event this century, has not been studied in detail. In this paper the nature of the eruption, the destruction it caused – including the complete devastation of the town of Mascali (pre-eruption population 2,000) – and emergency responses of the authorities to it are reviewed in the context of fascist politics and planning priorities. It is contended that, although at one level the response to the 1928 eruption was successful, at another fascism merely continued and enhanced a reactive, propitiatory approach to hazard mitigation. We argue that this legacy was not successfully overcome until the middle of the nineteen eighties. Finally contemporary Italian moves towards a more proactive approach to disaster planning, both generally and in the context of Etna, are discussed.     

Petrogenesis of tourmaline rocks associated with Fe-carbonate–graphite metapelite, metabasite and strata-bound polymetallic sulphide mineralisation, Peloritani Mountains, Sicily, Southern Italy

Tourmalinite and tourmaline-rich rocks associated with Fe-carbonate–graphite phyllite, strata-bound polymetallic sulphide deposits, metabasite and marble were studied, for information on the mechanism of tourmaline formation in the pre-Hercynian low-grade metamorphic sequence of the Mandanici Unit in the Peloritani Mountains of Sicily, southern Italy. The major and trace element compositions of the tourmaline rocks suggest the existence of a sedimentary protolith with pre-metamorphic black shale and bedded chert. Boron was interpreted to be accumulated in a restricted sedimentary basin, between platform carbonate formations, with abundant organic matter and Fe–Al–Ti-rich laterite–bauxite soil-derived clastic supply, under a continental volcano-tectonic extensional regime accompanied by a local convective hydrothermal system along faults. Petrographic, crystal–chemical and δ¹¹B isotopic data are compatible with a model of marine sediment dewatering at temperatures below 200 °C, which caused the removal of boron from clay. Metamorphism led to the development of tourmaline in an Al–Ti-rich environment, in equilibrium with other minerals such as ilmenite, albite and muscovite. The upper temperature of metamorphism (almost 375 °C), estimated on the basis of δ¹¹B, fits geothermometric results from Δ¹³C_{carbonate–graphite} on associated rocks. The estimated value of δ¹¹B in the tourmalinite protolith, − 7.5‰ , is also compatible with continental-derived Al-rich sediments.