The high-supply,current-dominated continental margin of southeastern South America during the late Quaternary     

Hendrik Lantzsch  Till J.J. Hanebuth  Cristiano M. Chiessi  Tilmann Schwenk  Roberto A. Violante 《Quaternary Research》2014

The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-¹⁴C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.  相似文献   

Raman and infrared study of hydroxyl sites in natural uvite,fluor-uvite,magnesio-foitite,dravite and elbaite tourmalines     

C. Fantini  M. C. Tavares  K. Krambrock  R. L. Moreira  A. Righi 《Physics and Chemistry of Minerals》2014,41(4):247-254

We present the Raman and infrared spectra of different tourmaline species in the spectral range associated with the hydroxyl stretching modes, investigated through polarized Raman spectroscopy. Different lineshapes are observed for the OH spectra in uvite, fluor-uvite, magnesio-foitite, dravite and elbaite samples, and can be related to the coordination of OH in the two different structural V[O(3)]- and W[O(1)]-occupied sites. Local arrangements around the two different OH sites were assigned, and different ion substitutions for these five tourmaline species were identified. Our work with polarized Raman spectroscopy revealed that OH-stretching modes are described by totally symmetric, irreducible representations.  相似文献   

Frictional Properties of a Low-Angle Normal Fault Under In Situ Conditions: Thermally-Activated Velocity Weakening     

André R. Niemeijer  Cristiano Collettini 《Pure and Applied Geophysics》2014,171(10):2641-2664

The Zuccale fault is a regional, low-angle, normal fault, exposed on the Isle of Elba in central Italy that accommodated a total shear displacement of 6–8 km. The fault zone structure and fault rocks formed at <8 km crustal depth. The present-day fault structure is the final product of several deformation processes superposed during the fault history. In this study, we report results from a series of rotary shear experiments performed on 1-mm thick powdered gouges made from several fault rock types obtained from the Zuccale fault. The tests were done under conditions ranging from room temperature to in situ conditions (i.e., at temperatures up to 300 °C, applied normal stresses up to 150 MPa, and fluid-saturated.) The ratio of fluid pressure to normal stress was held constant at either λ = 0.4 or λ = 0.8 to simulate an overpressurized fault. The samples were sheared at a constant sliding velocity of 10 μm/s for at least 5 mm, after which a velocity-stepping sequence from 1 to 300 μm/s was started to determine the velocity dependence of friction. This can be represented by the rate-and-state parameter (a–b), which was determined by an inversion of the data to the rate-and-state equations. Friction of the various fault rocks varies between 0.3 and 0.8, similar to values obtained in previous studies, and decreases with increasing phyllosilicate content. Friction decreases mildly with temperature, whereas normal stress and fluid pressure do not affect friction values systematically. All samples exhibited velocity strengthening, conditionally stable behavior under room temperature conditions and (a–b) increased with increasing sliding velocity. In contrast, velocity weakening, accompanied by stick–slips, was observed for the strongest samples at 300 °C and sliding velocities below 10 μm/s. An increase in fluid pressure under these conditions led to a further reduction in (a–b) for all samples, so that they exhibited unstable, stick–slip behavior at low sliding velocity. The results suggest that phyllosilicate-bearing fault rocks can deform by stable, aseismic creep at low, resolved shear stress and low shear rate conditions. An increase in fluid pressure or loading of stronger portions could lead to a runaway instability. The runaway instability might be limited in size because of (1) the fault heterogeneity, (2) the observed strengthening at higher sliding velocities, and (3) a co-seismic drop in pore-fluid pressure.  相似文献   

Tourmaline composition and boron isotopes record lateritic weathering during the Great Oxidation Event     

Alexandre Raphael Cabral  Tiago Henrique DeFerreira  Cristiano Lana  Marco P. de Castro  Glucia Queiroga 《地学学报》2021,33(1):46-55

Identifying evidence of oxidative weathering in the geological record is essential to trace the evolution of Earth's atmosphere oxygenation. Metamorphosed residues of lateritic weathering have been identified as two rock types in the 2.1‐Ga‐old Cercadinho Formation, Piracicaba Group, Quadrilátero Ferrífero of Minas Gerais. One is tourmaline–hematite–sillimanite–kyanite quartzite; the other is rutile–tourmaline–hematite–muscovite phyllite. Both rocks have abundant tourmaline with δ¹¹B values between about ?17‰ and ?13‰. The Cercadinho tourmaline is roughly parallel to the povondraite–“oxy‐dravite” join of meta‐evaporitic tourmaline, in its more aluminous segment, offset to higher contents of iron. These compositional and isotopic characteristics of the Cercadinho tourmaline indicate that continental evaporitic brines interacted with aluminium‐ and iron‐rich residues of lateritic weathering. The abundance of disseminated tourmaline, a mineral poorly reported from palaeosols worldwide, implies a boron‐rich brine overprint on the lateritic profile before the onset of metamorphism, reflecting a climatic change from humid to arid conditions in a continental setting. The recognition of lateritic weathering in the Cercadinho Formation contributes to the amount of evidence for increased levels of atmospheric oxygen between 2.22 and 2.06 Ga ago.  相似文献   

Angola seismicity     

Francisco António Pereira Neto  George Sand França  Cristobal Condori  Giuliano Sant’Anna Marotta  Cristiano Naibert Chimpliganond 《Journal of Seismology》2018,22(5):1113-1126

This work describes the development of the Angolan earthquake catalog and seismicity distribution in the Southwestern African Plate, in Angola. This region is one of the least seismically active, even for stable continental regions (SCRs) in the world. The maximum known earthquake had a magnitude of 6.0 M_s, while events with magnitudes of 4.5 have return period of about 10 years. Events with magnitude 5 and above occur with return period of about 20 years. Five seismic zones can be confirmed in Angola, within and along craton edges and in the sedimentary basins including offshore. Overall, the exposed cratonic regions tend to have more earthquakes compared to other regions such as sedimentary basins. Earthquakes tend to occur in Archaic rocks, especially inside preexisting weakness zones and in tectonic-magmatic reactivation zones of Mesozoic and Meso-Cenozoic, associated with the installation of a wide variety of intrusive rocks, strongly marked by intense tectonism. This fact can be explained by the models of preexisting weakness zones and stress concentration near intersecting structures. The Angolan passive margin is also a new region where seismic activity occurs. Although clear differences are found between different areas along the passive margin, in the middle near Porto Amboim city, seismic activity is more frequent compared with northwestern and southwestern regions.  相似文献   

Numerical simulation of the circulation and tropical teleconnection mechanisms of a severe drought event (2012–2016) in Northeastern Brazil     

de Medeiros  Felipe Jeferson  de Oliveira  Cristiano Prestrelo  Santos e Silva  Cl&#;udio Mois&#;s  de Ara&#;jo  Jo&#;o Medeiros 《Climate Dynamics》2020,54(9):4043-4057

Climate Dynamics - Large domains in regional climate models are known to provide a better representation of the mesoscale circulation and hence the precipitation field. To evaluate the model...  相似文献   

Toward semantics-aware annotation and retrieval of spatial data     

Cristiano Fugazza 《Earth Science Informatics》2011,4(4):225-239

The retrieval of spatial resources is typically hindered by the lack of exhaustive metadata, linguistic issues, multilingualism, and domain-related terminology mismatches. This paper describes an experimental attempt to set up a knowledge base that will serve as groundwork for harmonising domain knowledge from distinct thematic areas, to enable the semantics-aware annotation of resources, and to support the implementation of novel discovery techniques. Setting this up also required establishing a general work flow for translating ISO-compliant registries into SKOS/RDF data structures and enriching them with structural information. These steps are also presented. The validity of the approach is then evaluated by analysing various applications’ exploitation of the knowledge base in diverse use cases.  相似文献   

Medieval Dark Earth in an Active Alluvial Setting from the Uffizi Gallery Complex in Florence,Italy     

Cristiano Nicosia  Roger Langohr  Florias Mees  Antonia Arnoldus‐Huyzendveld  Jacopo Bruttini  Federico Cantini 《Geoarchaeology》2012,27(2):105-122

Archaeological excavations at the Biblioteca Magliabechiana, which is part of the Uffizi gallery complex in Florence (Tuscany, central Italy), exposed Dark Earth deposits between alluvial sediments of the nearby Arno River. The term Dark Earth refers to thick, dark colored, and seemingly homogeneous deposits occurring in urban settings throughout Europe, broadly dated to the post‐Roman period. The stratigraphic sequence of the Biblioteca Magliabechiana was investigated by integrating geomorphological, chronological, and archaeological information with micromorphological and soil analytical data. This combination of approaches resulted in the identification of an early phase of Dark Earth formation (7th century A.D.) during which the area was characterized by the accumulation of manure or night soil in wet peri‐fluvial conditions. After a phase of abandonment, Dark Earth accretion resumed (10th to early 11th century A.D.), at this stage due primarily to the dumping of domestic waste. Subsequent progressive abandonment of the area was followed by the deposition of alluvium, probably during the major flood of November 4, 1177. The present study demonstrates that Dark Earth is the outcome of strong bioturbation and human reworking acting on anthropogenic deposits and possibly on alluvial sediments.  相似文献   

Luminosity- and redshift-dependent quasar clustering     

Cristiano Porciani  Peder Norberg 《Monthly notices of the Royal Astronomical Society》2006,371(4):1824-1834

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The 2014 southeast Brazil austral summer drought: regional scale mechanisms and teleconnections     

Caio A. S. Coelho  Cristiano Prestrelo de Oliveira  Tércio Ambrizzi  Michelle Simões Reboita  Camila Bertoletti Carpenedo  José Leandro Pereira Silveira Campos  Ana Carolina Nóbile Tomaziello  Luana Albertani Pampuch  Maria de Souza Custódio  Lívia Marcia Mosso Dutra  Rosmeri P. Da Rocha  Amanda Rehbein 《Climate Dynamics》2016,46(11-12):3737-3752

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