Short-term under-ice variability of prokaryotic plankton communities in coastal Antarctic waters (Cape Hallett, Ross Sea)     

Mauro Celussi  Alessandro Paoli  Erica Crevatin  Andrea Bergamasco  Francesca Margiotta  Vincenzo Saggiomo  Serena Fonda Umani  Paola Del Negro 《Estuarine, Coastal and Shelf Science》2009,81(4):491-500

During the 2006 Italian Antarctic expedition a diel sampling was performed close to Cape Hallett (Ross Sea) during the Austral summer. Under-ice seawater samples (4 m) were collected every 2 h for 28 h in order to estimate prokaryotic processes' variability and community structure dynamics. Prokaryotic and viral abundances, exoenzymatic activities (β-glucosidase, chitinase, lipase, alkaline phosphatase and leucine aminopeptidase), prokaryotic carbon production (³H-leucine incorporation) and community structure (Denaturing Gradient Gel Electrophoresis – DGGE fingerprints) were analysed. Results showed that the diel variability of the prokaryotic activity followed a variation in salinity, probably as a consequence of the periodical thawing of sea ice (driven by solar radiation and air temperature cycles), while negligible variation in viral and prokaryotic abundances occurred. The Bacterial and Archaeal community structures underwent an Operational Taxonomic Units (OTUs) temporal shift from the beginning to the end of the sampling, while Flavobacteria-specific primers highlighted high variations in this group possibly related to sea ice melting and substrate release.  相似文献   

Sedimentology,architecture, and sequence stratigraphy of coarse-grained,submarine canyon fills from the Pleistocene (Gelasian-Calabrian) of the Peri-Adriatic basin,central Italy     

Claudio Di Celma  Gino CantalamessaPetros Didaskalou  Paola Lori 《Marine and Petroleum Geology》2010

The Plio-Pleistocene stratigraphic record of the Peri-Adriatic basin (eastern central Italy) is well exposed along the uplifted western margin of the basin and consists of a series of coarse-grained slope canyon fills encased in a thick succession of hemipelagic mudstones. This study deals with the detailed sedimentology, stratal architecture, and sequence-stratigraphic interpretation of two of these submarine canyon-fills (namely CMC1 and CMC2) exposed at Colle Montarone. These strata contain widespread evidence of gravity-driven sedimentation processes, with high- and low-density turbidity currents, slumps and cohesive debris flows being responsible for most of the sediment transport and deposition. Beds are organised into four recurrent lithofacies, each corresponding to a specific deep-water depositional element: (i) clast-supported conglomerates (channel complexes); (ii) thin-bedded sandstones and mudstones (levee-overbank); (iii) very thinly-bedded mudstones (tributary channels); (iv) pebbly mudstones and chaotically bedded mudstones (mass-transport complexes).  相似文献   

Cooling and exhumation history of deep‐seated and shallow level,late Hercynian granitoids from Calabria     

Alfredo Caggianelli  Giacomo Prosser  Aldo Del Moro 《Geological Journal》2000,35(1):33-42

The thermal and exhumation history of late Hercynian granitoids from Calabria (Sila and Serre massifs) has been studied using thermobarometry and radiometric age determinations. The uplift and erosion which followed contractional tectonics of Tertiary age exposed in Calabria a nearly complete section of the Hercynian crust. Field data, constrained by igneous thermobarometrical data, have enabled us to draw simplified crustal profiles. In both the Sila and Serre massifs, granitoids make up the intermediate portions of the crustal sections and are stacked as tabular intrusions for up to 13 km cumulative thickness. Shallow granitoids are characterized by a weak fabric, mostly developed in the magmatic stage, whereas deep‐seated granitoids display a strong fabric developed in the magmatic state and, with decreasing temperatures, in the subsolidus state. The intrusive bodies were emplaced at 300–290 Ma, at a time when the Calabrian crust was undergoing extensional tectonics and crustal thinning. The subsequent post‐Hercynian evolution is recorded by Rb‐Sr dates of micas and fission track ages of zircon and apatite obtained from granitoids emplaced at different depths. A decrease in Rb‐Sr and fission track ages is observed as depth of emplacement increases. Data on the post‐Hercynian geological evolution of Calabria were used to model in three stages the cooling and exhumation history of deep‐seated and shallow granitoids. The first stage, in Permian to Triassic times, was characterized by slow erosion. It was followed by a second stage of extensional tectonics in Jurassic times. The third stage was exhumation during the Apenninic Orogeny. The model has generated two P–T–t arrays, one for deep‐seated and the other for shallow granitoids of the Serre massif. The T–t paths suggest that the dates of micas, zircon and apatite are cooling ages. They also show that deep‐seated granitoids remained at temperatures above the brittle–plastic transition for a long time, whereas shallow granitoids cooled rapidly. Distinct P–T–t paths explain why deep‐seated and shallow granitoids display different fabric and microstructural features. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Petrology of basic and intermediate orogenic granitoids from the Sila Massif (Calabria,southern Italy)     

A. Caggianelli  A. Del Moro  G. Piccarreta 《Geological Journal》1994,29(1):11-28

Hercynian gabbroic, dioritic and tonalitic rocks crop out in the neighbourhood of Rovale (Sila Grande, Calabria). They make up a crude rectangular outcrop with the western part consisting of gabbroic rocks and the eastern of dioritic and tonalitic rocks. They come into contact with medium to high grade metapelites on the western side and with heterogeneous granodiorites on the other sides. In the gabbroic body both opx ± ol bearing cumulates and amphibole differentiates occur and are characterized by the widespread presence of brown pargasite. Sporadic magmatic to subsolidus corona textures between olivine and plagioclase or orthopyroxene and plagioclase can be observed and their preservation clearly suggests a post-tectonic emplacement for the gabbroic magma. Diorites and tonalites display hypidiomorphic textures free of olivine and orthopyroxene and bearing green Mg-hornblende. The granitoids, on the basis of chemical data, display orogenic features of the continent-continent collision type. The gabbroic rocks have high Al tholeiitic composition and fractionation of orthopyroxene and plagioclase played an important part in their evolution. The Rb/Sr isochron method did not give a precise emplacement age for the granitoids as a whole. Initial ⁸⁷Sr/⁸⁶Sr ratios (at 290 Ma) are higher in the gabbroic body (0.7091–0.7095) than in diorites and tonalites (0.7083–0.7092). Thus gabbroic rocks appear more displaced than diorites and tonalites towards crustal isotopic composition. The eNd data seem to confirm this feature, thus suggesting that the gabbroic rocks and diorites derived from distinct mantle magma batches. Interestingly, small isotropic gabbroic masses occur within the diorites and show general features that allow them to be considered as possibly parental with respect to the host diorites. The evolution to the dioritic composition might have occurred through fractionation and minor mixing with a more acidic component such as the northern granodiorites. Geochemical, Sr and Nd isotopic data indicate a scenario of a composite plutonic body formed by distinct magma batches of mixed crust and mantle origin.  相似文献   

Liquefaction triggering in silty sands: effects of non-plastic fines and mixture-packing conditions     

Gobbi  Stefania  Reiffsteck  Philippe  Lenti  Luca  d’Avila  Maria Paola Santisi  Semblat  Jean-François 《Acta Geotechnica》2022,17(2):391-410

Acta Geotechnica - During recent seismic events, such as 2010 Darfield and 2016 Ecuador earthquakes, widespread liquefaction has been observed in sand deposits with silt content. Nevertheless, the...  相似文献