Weathering, mineralogical evolution and soil organic matter along a Holocene soil toposequence developed on carbonate-rich materials   总被引：2，自引：0，他引：2  

Markus Egli  Christian Merkli  Giacomo Sartori  Aldo Mirabella  Michael Pltze 《Geomorphology》2008,97(3-4):675-696

A toposequence of Holocene soils located between 1100–2400 m asl in the Italian Alps served as the basis for the following analyses: the weathering of limestone and dolomite, the calculation of mass balances, understanding the formation of pedogenic Fe and Al, the determination of soil mineral and clay mineral reactions and transformation and the measurement of accumulation and stabilisation mechanisms of soil organic matter. Leaching of carbonates is most intense at the lower elevations, although calcite and dolomite have a higher solubility at low temperatures. The pCO₂ in the soil is higher at lower elevations and weathering is driven mainly by carbonic acids. At higher elevations, organic acids appear to determine the mineral transformations and weathering reactions to a greater extent. This suggests that two very different weathering regimes (carbonic and organic acid weathering) exist along the toposequence. The transformation of mica into vermiculite is the main process in both the clay and fine-earth fraction. Weathering of silicate minerals started even before the carbonates had been completely removed from the soils. The transformation mechanisms of silicate minerals in the A and O horizon at higher elevations was at least as intensive as that at the climatically warmer sites. The neoformation of pedogenetic clays at climatically cooler sites was slightly greater than that at the warmer sites. However, the formation rate of secondary Fe and Al phases was more pronounced at lower elevation, which means that this process seemed to be driven dominantly by carbonic acid (weathering of primary minerals). Soil organic matter (SOM) abundance in the mineral soil is nearly 15 kg/m² at all sites and, surprisingly, no climate-driven effect could be detected. In general, the preservation and stabilisation of SOM was due to poorly crystalline Al and Fe phases and vermiculite, regardless of some variations in the composition of the parent material (varying calcite/dolomite ratio).  相似文献   

The role of climate and vegetation in weathering and clay mineral formation in late Quaternary soils of the Swiss and Italian Alps   总被引：2，自引：0，他引：2  

Markus Egli  Aldo Mirabella  Giacomo Sartori 《Geomorphology》2008,102(3-4):307-324

Interactions between climate and soil remain ambiguous, particularly when silicate weathering and clay mineral formation and transformation rates are considered in relation to global climate changes. Recent studies suggest that climate affects weathering rates much less than previously thought. Here we show that the climate in the central European Alps has a significant, but indirect, influence on the weathering of soils through vegetation. The pattern of element leaching and mineral transformations is not only due to precipitation and temperature. Element leaching was greatest in subalpine forests near the timberline; weathering is lessened at higher and lower altitudes. Vegetation, therefore, contributes significantly to weathering processes. The highest accumulation of organic matter was found in climatically cooler sites (subalpine range) where the production of organic ligands, which enhance weathering, is greatest. Patterns of smectite formation and distribution had strong similarities to that of the elemental losses of Fe and Al (R = 0.69; P < 0.01) or base cations (R = 0.58; P < 0.05). Higher precipitation rates and the production of organic chelating compounds in the soil promoted the appearance of smectites. The relationship between climate, element leaching (Fe, Al, Ca, Mg, K, Na), and smectite formation is strongly nonlinear and driven by the podzolisation process, which is more pronounced near the timberline because of the bioclimatic constellation. Climate warming will probably, in the future, lead to a decrease in SOM stocks in the subalpine to alpine range because of more favourable conditions for biodegradation that would also affect weathering processes.  相似文献   

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

Philippe Rossi  Giacomo Oggiano  Alain Cocherie 《Comptes Rendus Geoscience》2009,341(2-3):224-238

A 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.  相似文献   

Late orogenic collapse and thermal doming in the northern Gondwana margin incorporated in the Variscan Chain: A case study from the Ozieri Metamorphic Complex, northern Sardinia, Italy     

Leonardo Casini  Giacomo Oggiano   《Gondwana Research》2008,13(3):396-406

A branch of the South European Variscan chain is noticeably exposed in Sardinia. The early stage of collision between the Northern Gondwana margin and the Armorica Terrane Assemblage (ATA) generated syn-metamorphic folding and thrusting. The evidences of such deformation are well preserved in the nappe zone, a structural domain characterized by stacking of different tectonic units under metamorphism of Barrovian greenschist facies. A late, post-nappe, shortening, under retrograde metamorphic conditions, gave rise to wide, upright, N120–N160 trending antiforms that control the trend of the chain. The structural analysis of the Ozieri Metamorphic Complex (OMC) shows evidence of an important phase of late-Variscan extensional tectonics. Deformation results in, the formation of oppositely dipping, normal shear zones, which developed at upper and middle structural level along the limbs of major regional antiforms causing fabric reactivation, crustal thinning, and exhumation of the OMC core. Within the OMC, the activity of the shear zones was coeval with HT-LP metamorphism as suggests the occurrence of syn-kinematic cordierite + andalusite ± sillimanite + biotite. Whereas syntectonic dykes and a tonalite body in the deeper part of the OMC indicate that early emplacement of melt along shear zones and/or in the antiform hinges possibly supplied the heat for the anomalous thermal gradient and triggered the exhumation of a core complex-like structure.  相似文献   

Real time monitoring of structures in task force missions: the example of the Mw = 6.3 Central Italy Earthquake, April 6, 2009     

M. Picozzi  R. Ditommaso  S. Parolai  M. Mucciarelli  C. Milkereit  M. Sobiesiak  D. Di Giacomo  M. R. Gallipoli  M. Pilz  M. Vona  J. Zschau 《Natural Hazards》2010,52(2):253-256

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Exact density–potential pairs from the holomorphic Coulomb field     

Luca Ciotti  Giacomo Giampieri † 《Monthly notices of the Royal Astronomical Society》2007,376(3):1162-1168

We show how the complex-shift method developed by Appell to study the gravitational field of a point mass (and used in electrodynamics by, among others, Newman, Carter, Lynden-Bell, and Kaiser to determine some remarkable properties of the electromagnetic field of rotating charged configurations) can be extended to obtain new and explicit density–potential pairs for self-gravitating systems departing significantly from spherical symmetry. The rotational properties of two axisymmetric baroclinic gaseous configurations derived with the proposed method are illustrated.  相似文献   

A note on the tidally induced potential of a satellite in eccentric orbit     

Giacomo Giampieri 《Icarus》2004,167(1):228-230

A planetary body moving on an eccentric orbit around the primary is subject to a periodic perturbing potential, affecting its internal mass distribution. In a previous paper (Rappaport et al., 1997, Icarus 126, 313), we have calculated the periodic modulation of the gravity coefficients of degree 2, for a body on a synchronous orbit. Here, the previous analysis is extended by considering also non-synchronous orbits, and by properly accounting for the apparent motion of the primary due to the non uniform motion along the elliptical orbit. The cases of Titan and Mercury are briefly discussed.  相似文献   

Modelling the lithospheric rheology control on the Cretaceous rifting in West Antarctica     

Marco Bonini  Giacomo Corti  Chiara Del Ventisette  Piero Manetti  Genene Mulugeta  Dimitrios Sokoutis 《地学学报》2007,19(5):360-366

Small‐scale analogue models were used to investigate the process of Cretaceous orthogonal extension in the West Antarctic Rift System. The models considered the transition from the East Antarctic Craton to a weaker lithosphere, and the results support previous hypotheses about the strong control exerted by lateral variations in lithospheric structures on the process of extension. Strain was mostly accommodated at the boundary between the two types of lithosphere, with a relative uplift of the cratonic block which remained essentially undeformed. Conversely, the weaker lithosphere showed wide‐rifting style geometry, locally associated with core complex‐like structures. In agreement with the natural prototype, this tectonic scenario led to a long‐lasting extension without continental break‐up, and to the absence of relevant surface magmatism.  相似文献   

Occurrence of palygorskite and sepiolite in upper Paleocene–middle Eocene marine deep sediments of the Lagonegro Basin (Southern Apennines—Italy): Paleoenvironmental and provenance inferences     

Francesco Cavalcante  Claudia Belviso  Mario Bentivenga  Saverio Fiore  Giacomo Prosser 《Sedimentary Geology》2011,233(1-4):42-52

A mineralogical and geochemical study of clay lithologies and a biostratigraphic analysis of the carbonates from the deep-sea Lagonegro Basin (Southern Apennines—Italy) have been carried out to deduce in general the provenance of clay sediments and their paleoenvironmental conditions and particular to recognize the signature of the Paleocene–Eocene climatic global warming. The analysed succession comprising a wide stratigraphic interval of the Sannio Unit, spanning between Albian to the upper Oligocene–lower Miocene, is exposed near Accettura and Stigliano villages. Eighteen clay samples were analysed by XRD, XRF, SEM, TG-DTA. Their age was framed by biostratigraphic analyses carried out on carbonate sediments. Mineral assemblage of the clay sediments includes quartz, carbonates (calcite and dolomite), feldspars (plagioclase and k-feldspars), hematite, randomly illite/smectite mixed layers with a low illite percentage, kaolinite, discrete illite–muscovite, chlorite, palygorskite and sepiolite. The low illite percentage in randomly illite/smectite mixed layers indicates low diagenetic conditions for the studied successions. These features are unique for the Cretaceous–Tertiary successions of the Lagonegro domain and are particularly significant for the preservation of the native mineralogical assemblage useful to determine the provenance and paleoenvironmental conditions of the clayey sediments. Palygorskite and sepiolite are concentrated in the upper Paleocene–middle Eocene stratigraphic interval and particularly in the upper part of the early Eocene—lower part of the middle Eocene (biozone of Blow P 9–12). Clay sediments rich in palygorskite and sepiolite show a higher P₂O₅ amount and a lower kaolinite percentage, compatible with warm and arid climatic conditions typical of the global warming event well recorded in the southern tethyan margin. Likely palygorskite and sepiolite formed in lagoonal environment in nearby carbonate platform margins and then they were transported into the Lagonegro Basin as indicated by the well developed habitus of palygorskite. During the Paleogene the Lagonegro Basin and the nearby carbonate platforms represented a key sector the southern paleodomains of the Tethys. The discovery of these minerals gives a contribution to the reconstruction paleoenvironmental conditions of the Tethian paleo-margin during the early–middle Eocene.  相似文献   

A Hercynian suture zone in Sardinia : geological and geochemical evidence     

Beatrice Cappelli  Luigi Carmignani  Francesca Castorina  Anselmo Di Pisa  Giacomo Oggiano  Riccardo Petrini 《Geodinamica Acta》2013,26(1-2):101-118

Abstract

The Hereynian basement of Northern Sardinia consists of two main teetonometamorphic complexes : the Southern Paleozoic Low to Medium Grade Metamorphic Complex (LMGMC) and the Northern (Precaimbrian ?) High Grade Metamorphic Complex (HGMC). These complexes are separateli bu the “Posada-Asinara Line” which is a several kilometer-wide mylonitie belt consisting of micaschist. parag-neiss and quartzite that cuts across all Northern Sardinia and contains scattered hodies of amphibolites with granulile and eclogite facies relies.

Major element composition of ampbibolites indicates they were derived from metamorphosed basalts of tholciitie affinity. REE and the relative abundances of HKS elements strongly suggest an oceanic basaltie prololith (N- and T-typc MORB). A whole-rock Sm-Nd isochron for the amphibolite protoliths yields an age of ea. 960 Ma.

The Northern Sardinia basement can he interpreted as a continental collisional zone with the “Posada-Asinara Line” representing a suture zone squeezed between a crustal nappe (HGMC), which represents the overthrust continental margin. and (he inner portion of the Varisean orogenie wedge, which represents the underthrust continental margin with its Paleozoic cover (LMGMC).

Geological and geochemical evidence indicate that the “Posada-Asinara Line” may he considered as part of the South European Hereynian Suture Zone.  相似文献