Flexural deformation controls on Late Quaternary sediment dispersal in the Garo-Rajmahal Gap,NW Bengal Basin     

Jean-Louis Grimaud  Celine Grall  Steven Goodbred  Michael S. Steckler  Ryan Sincavage  Jennifer L. Pickering  Chris Paola  Leonardo Seeber  Md. Saddam Hossain 《Basin Research》2020,32(5):1242-1260

Subsurface deformation is a driver for river path selection when deformation rates become comparable to the autogenic mobility rate of rivers. Here we combine geomorphology, soil and sediment facies analyses, and geophysical data of the Late Quaternary sediments of the central Garo-Rajmahal Gap in Northwest Bengal to link subsurface deformation with surface processes. We show variable sedimentation characteristics, from slow rates (<0.8 mm/year) in the Tista megafan at the foot of the Himalaya to nondeposition at the exposed surface of the Barind Tract to the south, enabling the development of mature soils. Combined subsidence in the Tista fan and uplift of the Barind Tract are consistent with a N-S flexural response of the Indian plate to loading of the Himalaya Mountains given a low value of elastic thickness (15–25 km). Provenance analysis based on bulk strontium concentration suggests a dispersal of sediment consistent with this flexural deformation—in particular the abandonment of the Barind Tract by a Pleistocene Brahmaputra River and the current extents of the Tista megafan lobes. Overall, these results highlight the control by deeply rooted deformation patterns on the routing of sediment by large rivers in foreland settings.  相似文献   

Introduction     

Jenna E. Beletic  James W. Beletic  Paola Amico 《Experimental Astronomy》2005,19(1-3):1-3

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A model for the viscosity of rhyolite as a function of H₂O-content and pressure: A calibration based on centrifuge piston cylinder experiments     

Paola Ardia  Daniele Giordano 《Geochimica et cosmochimica acta》2008,72(24):6103-6123

The Newtonian viscosity of synthetic rhyolitic liquids with 0.15-5.24 wt% dissolved water was determined in the interval between 580 and 1640 °C and pressures of 1 atm and 5-25 kbar. Measurements were performed by combining static and accelerated (up to 1000g) falling sphere experiments on water-bearing samples, with high temperature concentric cylinder experiments on 0.15 wt% H₂O melts. These methods allowed viscosity determinations between 10² and 10⁷ Pa s, and cover the complete range of naturally occurring magmatic temperatures, pressures, and H₂O-contents for rhyolites.Our viscosity data, combined with those from previous studies, were modeled by an expression based on the empirical Vogel-Fulcher-Tammann equation, which describes viscosities and derivative properties (glass transition temperature T_g, fragility m, and activation volume of viscous flow Va) of silicic liquids as a function of P-T-X_(H2O). The fitted expressions do not account for composition-dependent parameters other than X_(H2O) and reproduce the entire viscosity database for silicic liquids to within 3.0% average relative error on log η (i.e. std. error of estimate of 0.26 log units).The results yield the expected strong decrease of viscosity with temperature and water content, but show variable pressure dependencies. Viscosity results to be strongly affected by pressure at low pressures; an effect amplified at low temperatures and water contents. Fragility, as a measure for the deviation from Arrhenian behavior, decreases with H₂O-content but is insensitive to pressure. Activation volumes are always largely negative (e.g., less than −10 cm³/mol) and increase strongly with H₂O-content. Variations in melt structure that may account for the observed property variations are discussed.  相似文献   

Distrubution of Dissolved and Particulate Iron, copper and Manganese in the Shelf waters of the Ross sea (Antarctica)     

Carmela Ianni  Paola Rivaro  Roberto Frache 《Marine Ecology》2002,23(S1):210-219

Abstract. During the austral summer 1997–98, within the framework of the activities of the Climatic Long-term Interaction for the Massbalance in Antarctica (CLIMA) Project of the Italian National Program for Antarctic Research (PNRA) in the Ross Sea, measurements were conducted to focus on the role of dissolved iron, copper and manganese as micronutrients, and on their distribution in suspended particulate matter in different water masses. Sampling was carried out in two selected shelf areas, both important for formation and mixing processes of the water bodies.
Metal data were evaluated together with physical measurements and classical chemical parameters such as oxygen and nutrients.
In both the studied areas, the distribution of dissolved metals along the waste column confirmed their micronutrient behaviour, showing depletion where phytoplanktonic activities occurred.
The trend of particulate metals underlined the scavenging phenomena along the water column and presented an interesting correlation at intermediate depths with the amount and origin of suspended matter.  相似文献   

The Vema Transverse Ridge (Central Atlantic)     

Kastens  Kim  Bonatti  Enrico  Caress  David  Carrara  Gabriela  Dauteuil  Olivier  Frueh-Green  Gretchen  Ligi  Marco  Tartarotti  Paola 《Marine Geophysical Researches》1998,20(6):533-556

Transverse ridges are elongate reliefs running parallel and adjacent to transform/fracture zones offsetting mid-ocean ridges. A major transverse ridge runs adjacent to the Vema transform (Central Atlantic), that offsets the Mid-Atlantic Ridge by 320 km. Multibeam morphobathymetric coverage of the entire Vema Transverse ridge shows it is an elongated (300 km), narrow (<30 km at the base) relief that constitutes a topographic anomaly rising up to 4 km above the predicted thermal contraction level. Morphology and lithology suggest that the Vema Transverse ridge is an uplifted sliver of oceanic lithosphere. Topographic and lithological asymmetry indicate that the transverse ridge was formed by flexure of a lithospheric sliver, uncoupled on its northern side by the transform fault. The transverse ridge can be subdivided in segments bound by topographic discontinuities that are probably fault-controlled, suggesting some differential uplift and/or tilting of the different segments. Two of the segments are capped by shallow water carbonate platforms, that formed about 3–4 m.y. ago, at which time the crust of the transverse ridge was close to sea level. Sampling by submersible and dredging indicates that a relatively undisturbed section of oceanic lithosphere is exposed on the northern slope of the transverse ridge. Preliminary studies of mantle-derived ultramafic rocks from this section suggest temporal variations in mantle composition. An inactive fracture zone scarp (Lema fracture zone) was mapped south of the Vema Transverse ridge. Based on morphology, a fossil RTI was identified about 80 km west of the presently active RTI, suggesting that a ridge jump might have occurred about 2.2 m.a. Most probable causes for the formation of the Vema Transverse ridge are vertical motions of lithospheric slivers due to small changes in the direction of spreading of the plates bordering the Vema Fracture Zone.  相似文献   

Late Pleistocene vertebrate-bearing deposits at San Teodoro Cave (North-Eastern Sicily): Preliminary data on faunal diversification and chronology     

Laura Bonfiglio  Daniela Esu  Gabriella Mangano  Federico Masini  Daria Petruso  Michele Soligo  Paola Tuccimei   《Quaternary International》2008,190(1):26

This paper deals with the chronology and the possible correlations among levels of different excavated areas in the Pleistocene vertebrate-bearing deposits at the large San Teodoro Cave (North-Eastern Sicily). Two trenches have been excavated along the eastern side of the cave, located at a distance from the entrance, respectively, of 8 m (α trench) and 28 m (β trench) and at different depths. Lithological features, biometrical data from small mammals and ecological data from molluscs point to similar environmental conditions for the α trench deposits and those located along the eastern wall of the cave in the eastern part of the β trench. The same evidence, and the taphonomic features of large mammals, points to different environmental conditions and perhaps to different ages for the deposits located in the western part of the β trench. The survival of elephants in Sicily up to 32,000 years ago is a new significant result of the ²³⁰Th/²³⁴U dating carried out from a concretionary stratum from the β trench and represents the youngest elephant survival in the western Mediterranean islands.  相似文献   

Fractal analysis of mingled/mixed magmas: an example from the Upper Pollara eruption (Salina Island, southern Tyrrhenian Sea, Italy)     

Rosanna De Rosa  Paola Donato  Guido Ventura   《Lithos》2002,65(3-4):299-311

Upper Pollara eruption products (13 ka, Salina Island, Italy) include both homogeneous and heterogeneous pumices resulting from mixing/mingling processes between an HK andesite and a high-SiO₂ rhyolite. Representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling/mixing structures. Image analysis techniques are applied and eight grey color ranges (classes) are extracted from high-resolution scans of pumice. Class 1 (lighter colors) and class 8 (darker colors) show end-member glass compositions, i.e. HK andesite and high-SiO₂ rhyolite, respectively. These two classes show spot- to cluster-like morphological structures. Intermediate classes show an HK dacitic to rhyolitic composition and a banding- to fold-like morphology. Fractal analysis by box-counting of the boundary pattern of eight grey classified images is performed over a length scale of 0.028–1.8 cm. Fractal dimension D is between 1.01 and 1.84. Coupled fractal analysis and geochemical data reveal that D increases as the degree of magma interaction (homogenization) increases. This feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection. We conclude that the increase of D observed in the Upper Pollara samples reflects the transition from fractal mixing to homogenization. End-member magmas (HK andesite and high-SiO₂ rhyolite) represent isolated mixing regions, while homogenized magmas represent active mixing regions. In the analyzed pumices, isolated and active mixing regions coexist at scales between 10⁻⁴ and 10⁻² m. Morphological and compositional features of the Upper Pollara pumices result from turbulence.  相似文献   

δO of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater     

Antonio Longinelli  Paola IacuminMichele Ramigni 《Earth and Planetary Science Letters》2002,203(1):445-459

Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ¹⁸O values of the diagenetic water within the range of meteoric waters, the δ¹⁸O(SiO₂) yield temperatures in agreement with the apparent secondary origin of this phase. The δ¹⁸O(CO₃²⁻) range, with a certain continuity, between −10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ¹⁸O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ¹⁸O(PO₄³⁻) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ¹⁸O(PO₄³⁻) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ¹⁸O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.  相似文献   

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment     

Thomas Backhaus  Rolf Altenburger  sa Arrhenius  Hans Blanck  Michael Faust  Antonio Finizio  Paola Gramatica  Matthias Grote  Marion Junghans  Wiebke Meyer  Manuela Pavan  Tobias Porsbring  Martin Scholze  Roberto Todeschini  Marco Vighi  Helge Walter  L. Horst Grimme 《Continental Shelf Research》2003,23(17-19):1757

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.  相似文献   

Moisture sources to the 2010–2012 anomalous wet season in northern South America     

Paola A. Arias  J. Alejandro Martínez  Sara C. Vieira 《Climate Dynamics》2015,45(9-10):2861-2884

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