Effect of block rotation on the pitch of slickenlines     

Shunshan S. Xu  Ángel F. Nieto-Samaniego  Susana A. Alaniz-Álvarez  Luis Germán Velasquillo-Martínez 《Central European Journal of Geosciences》2011,3(1):29-36

Rotation of faults or pre-existing weakness planes produce two effects on the slickenlines of fault planes. First, the rotation leads to changes in the pitch of slickenlines. As a result, the aspect of the pre-existing fault may change. For example, after rotation, a normal fault may show features of an oblique fault, a strike-slip fault, or a thrust fault. Second, due to rotation, stress states on the fault planes are different from those before the rotation. As a consequence some previous planes may be reactivated. For an isolated plane, the reactivation due to rotation can produce new sets of slickenlines. With block rotation, superimposed slickenlines can be generated in the same tectonic phase. Thus, it is not appropriate to use fault-slip data from slickenlines to analyze the stress tensor in a region where there is evidence of block rotation. As an example, we present the data of slickenlines from core samples in the Tunich area of the Gulf of Mexico. The results wrongly indicate that the calculated stress tensor deviates from the far-field stress tensor.  相似文献   

Inter- and intra-estuarine fish assemblage variability patterns along the Portuguese coast     

Susana França  Maria José Costa  Henrique N. Cabral 《Estuarine, Coastal and Shelf Science》2011

Estuaries along the Portuguese coast differ considerably in terms of their structure, geomorphologic and hydrologic characteristics. They play an important ecological role for different fish species, namely acting as important nursery areas. The fish assemblages of nine estuaries of the Portuguese coast were investigated in order to evaluate their main inter- and intra-estuarine variability patterns. Fish sampling surveys were conducted in May and July 2006, covering the full estuarine gradient. The different saline areas in each estuary were mapped using a Geographic Information System and fish assemblages’ were described and compared using a functional guilds approach. Generalized linear models were used to relate fish species richness to geomorphologic, hydrologic and environmental characteristics of the estuaries considered and correspondence analyses were performed to evaluate similarities in fish assemblages’ structure. At a large scale, river flow was the most important factor explaining the variability in species richness in estuaries along the Portuguese coast. At a regional scale, different abiotic factors explained the occurrence and abundance of fish species in the estuaries. Nonetheless, the overall role of the estuary was strongly related with the dominant saline zone within each estuary.  相似文献   

Distribution and contribution of major phytoplankton groups to carbon cycling across contrasting conditions of the subtropical northeast Atlantic Ocean     

Andrés Gutiérrez-Rodríguez  Mikel Latasa  Susana Agustí  Carlos M. Duarte 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(11):1115-1129

The relation between trophic regime and phytoplankton composition and function in oceanic systems is well accepted in oceanography. However, the relative dynamics and carbon cycling contributions of different phytoplankton groups across gradients of ocean richness are not fully understood. In this work we investigated phytoplankton dynamics along two transects from the NW African coastal upwelling to open-ocean waters of the north Atlantic subtropical gyre. We adopted a pigment-based approach to characterize community structure and to quantify group-specific growth and grazing rates and associated carbon fluxes. Changes in pigment cell concentration during the incubation experiments due to photoadaptation were corrected to obtain reliable rates. The oceanic region was dominated by Prochlorococcus (PRO) (45±7% of total chlorophyll a) while diatoms dominated in upwelling waters (40±37%). Phytoplankton grew faster (μ=0.78±0.26 d⁻¹) and free of nutrient limitation (μ/μ_n=0.98±0.42) in the coastal upwelling region, with all groups growing at similar rates. In oceanic waters, the growth rate of bulk phytoplankton was lower (μ=0.52±0.16 d⁻¹) and nutrient limited (μ/μ_n=0.68±0.19 d⁻¹). Diatoms (0.80±0.39 d⁻¹) and Synechococcus (SYN) (0.72±0.25 d⁻¹) grew faster than Prymnesiophyceae (PRYMN) (0.62±0.26 d⁻¹) and PRO (0.46±0.18 d⁻¹). The growth rates of PRO and SYN were moderately nutrient limited (μ/μ_n=0.81 and 0.91, respectively), while the limitation for diatoms (μ/μ_n=0.71) and PRYMN (μ/μ_n=0.37) was more severe. Microzooplankton grazing rate was higher in upwelling (0.68±0.32 d⁻¹) than in oceanic waters (0.37±0.19 d⁻¹), but represented the main loss pathway for phytoplankton in both systems (m/μ=0.90±0.32 and 0.69±0.24, respectively). Carbon flux through phytoplankton, produced and grazed, increased from offshore to coastal (∼2 to ∼200 μg C L⁻¹ d⁻¹), with diatoms dominating the flux in the upwelling region (52%) while PRYMN (40%) and PRO (30%) dominated in the open ocean.  相似文献   

Holocene sea-surface temperature variability in the Chilean fjord region     

Magaly Caniupán  Frank Lamy  Carina B. Lange  Jérôme Kaiser  Rolf Kilian  Helge W. Arz  Tania León  Gesine Mollenhauer  Susana Sandoval  Ricardo De Pol-Holz  Silvio Pantoja  Julia Wellner  Ralf Tiedemann 《Quaternary Research》2014

Here we provide three new Holocene (11–0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50–53°S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past ~ 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During the mid-Holocene, pronounced short-term variations of up to 2.5°C and a cooling centered at ~ 5 cal ka BP, which coincides with the first Neoglacial glacier advance in the Southern Andes, are recorded. The latest Holocene is characterized by two pronounced cold events centered at ~ 0.6 and 0.25 cal ka BP, i.e., during the Little Ice Age. These cold events have lower amplitudes in the offshore records, suggesting an amplification of the SST signal in the inner fjords.  相似文献   

Constraints regarding gold deposition in episyenites: the Permian episyenites associated with the Villalcampo Shear Zone, central western Spain     

Francisco Javier López-Moro  María Candelas Moro  Susana María Timón  María Luisa Cembranos  Juan Cózar 《International Journal of Earth Sciences》2013,102(3):721-744

The Villalcampo Shear Zone (around 307 Ma) shows second-order shear zones (420–390 °C) with gold ore bodies hosted by episyenites, which consist of albite episyenites (albitites) and albite-Kfs episyenites, both types with different contents in sulphides and gold. Mass transfer modelling supports higher fluid/rock ratios in albitites than in albite-Kfs episyenites. The study of worldwide barren and gold-bearing episyenites reveals abundant sulphides in the latter as a distinguishing feature. The electrochemical processes at the surface of sulphide would have enhanced gold precipitation, sulphides working as a gold trap. A complex fluid history occurred in gold ore bodies hosted by episyenites, although in essence, it was similar to quartz-sealed faults hosting late Variscan gold deposits: (a) an early fluid equilibrated with the metamorphic pile with sulphides or with a metamorphic fingerprint, resulted in a sulphide deposition and (b) a shallower fluid reservoir of meteoric origin provided gold deposition. In contrast to earlier claims regarding episyenite fluid flow, a down temperature and probably an upwards fluid flow are proposed for the episyenitization process, also in keeping with the early stages of fluid flow in quartz-sealed faults. Fluid inclusions in albite confirm that the striking coupled quartz leaching albitization processes occurred around 400 °C and 60 MPa, crosscutting the retrograde solubility field of silica and yielding a vuggy rock. Initially, albite, and later quartz and sulphide, filled the vugs from the same or a very similar fluid. Uraninites deposited during the albitization and probably the onset of the sulphide deposition afforded the same age (270 ± 12 Ma) as other Spanish episyenites, confirming a synchronous and a regional-scale process and ruling out a relationship with the granite cooling history (324 ± 11 Ma).  相似文献   

Impact of predation on the polychaete Hediste diversicolor in estuarine intertidal flats   总被引：1，自引：1，他引：0  

Susana Rosa  Jos Pedro Granadeiro  Catarina Vinagre  Susana Frana  Henrique N. Cabral  Jorge M. Palmeirim 《Estuarine, Coastal and Shelf Science》2008,78(4):655-664

In estuarine sediment flats benthic macroinvertebrates are intensively consumed by a variety of predators, such as aquatic birds and nekton (mostly fish and crustaceans). However, there is still a lack of conclusive studies that evaluate if this predation has a relevant impact on the populations of those invertebrates, which are a key element of the estuarine food chain. In the Tagus estuary we experimentally tested and quantified the impact of predation on the polychaete Hediste diversicolor, one of the most important prey for a variety of predators in many estuaries. Using an exclusion experiment, we compared the seasonal variation in the densities of H. diversicolor from February to November in sediment plots (1) available to both bird and nekton predators, (2) just to nekton, and (3) without predators. We also followed changes in the abundance of potential predators throughout the study. The lowest densities were systematically observed in the plots accessible to all predators, followed by those which excluded just birds, and finally by those that excluded all predators. The exclosures were in place for 9 months, at the end of which the average density of H. diversicolor in the plots protected from all predators was eight times greater than in those without any protection. These results demonstrate that predation had a major impact on the densities of H. diversicolor. The relative importance of bird and nekton predation varied along the study, and this seems to be determined by different peaks of abundance of the two types of predators. However, when present in high densities, birds and nekton seem to have a similar impact on H. diversicolor. Our results suggest that predation is a key factor on the population dynamics of H. diversicolor. In addition, the levels of predation that we observed suggest that this polychaete can be a limited resource, and this could have major ecological consequences for predators for which it is a key prey.  相似文献   

Growth and photosynthetic responses to copper stress of an invasive cordgrass, Spartina densiflora     

Mateos-Naranjo E  Redondo-Gómez S  Cambrollé J  Enrique Figueroa M 《Marine environmental research》2008,66(4):459-465

Spartina densiflora Brongn. is found in coastal marshes of south-west Spain, growing in sediments with between 300 and 3000mg Cu kg(-1) total soil DW (450-4500mg Cu kg(-1) supposing that the soil porosity is 0.5). An experiment was designed to investigate the effect of copper from 0 to 5000mgkg(-1) (64mmoll(-1)) on the photosynthetic apparatus and the growth of S. densiflora. We also determined total ash, copper, calcium, magnesium and phosphorous concentrations, as well as C/N ratio. S. densiflora survived to concentrations as high as 320mg Cukg(-1) DW in leaves, although excess of Cu diminished water use efficiency and Ca-, Mg- and P-uptake. Also, quantum efficiency of PSII, net photosynthetic rate, stomatal conductance and pigment concentrations declined with increasing external Cu. Finally, the decline in the photosynthetic function resulted in a biomass reduction of between 50 and 80% (for 600 and 5000mg Cu kg(-1), respectively).  相似文献   

Raman spectroscopic and scanning electron microscopic analysis of a novel biological colonisation of volcanic rocks     

Susana E. Jorge Villar  Howell G.M. Edwards 《Icarus》2006,184(1):158-169

A novel type of colonisation of a basaltic rock, collected on the Arctic island of Svalbard, Norway, during the AMASE expedition in 2004, was characterised using Raman spectroscopy and Scanning Electron Microscopy (SEM). The sample contains two different types of extremophile communities, one occurring behind a radial white crystallisation and the other occurring inside a dark vacuole. Several types of minerals and microbial colonies have been identified by both Raman spectroscopy and SEM analyses. It is the first time that photosynthetic communities have been documented to colonise the inside of dark basaltic rocks. Our discovery has important implications for planetary exploration because it extends the analytical capability and our understanding of microbial rock colonisations to subaerial volcanic outcrops and has wide implications towards the search for life in extraterrestrial planets. In this work we also demonstrate that the use of different laser wavelengths for Raman spectroscopic studies and complementary microscopic analysis are critical for a comprehensive organic and inorganic compound identification.  相似文献   

Constraining Theoretical Models with Astronomical and Geophysical Bounds     

Nidal Chamoun  Susana J. Landau  Hector Vucetich 《Astrophysics and Space Science》2003,283(4):595-600

We consider astronomical and geophysical bounds in order to test Kaluza-Klein like models and some particular models of Bekenstein's theory. Bounds on the free parameteres of the theories are obtained. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Factors and interactions controlling infiltration,runoff, and soil loss at the microscale in a patchy Mediterranean semiarid landscape     

Ángeles G. Mayor  Susana Bautista  Juan Bellot 《地球表面变化过程与地形》2009,34(12):1702-1711

In semiarid ecosystems, the transfer of water, sediments, and nutrients from bare to vegetated areas is known to be crucial to ecosystem functioning. Rainfall simulation experiments were performed on bare‐soil and vegetated surfaces, on both wet and dry soils, in semiarid shrub‐steppe landscapes of SE Spain to investigate the spatial and temporal factors and interactions that control the fine‐scale variation in water infiltration, runoff and soil loss, and hence the water and sediment flows in these areas. Three types of shrub‐steppe landscapes varying in plant community and physiography, and four types of plant patches (oak shrub, subshrub, tussock grass, and short grass mixed with chamaephytes) were studied. Higher infiltration and lower runoff and soil loss were measured on vegetation patches than on bare soils, for both dry and wet conditions. The oak‐shrub patches produced no runoff, while the subshrub patches showed the highest runoff and soil loss. Despite these differences among patch types, the influence of vegetation patch type on the variables analysed was not significant. The response of bare soil surfaces clearly varied between landscape types, yet the differences were only relevant under dry soil conditions. Stone cover, particularly the cover of embedded stones, and crust cover, were the key explanatory variables for the hydrological behaviour of bare soils. The study documents quantitatively how bare soils and vegetation patches function as runoff sources and runoff sinks, respectively, for a wide range of soil moisture conditions, and illustrates that landscape‐type effects on bare‐soil runoff sources may also exert an important control on the site hydrology, while the role of the vegetation patch type is less important. The effects of the control factors are modulated by antecedent soil moisture, with dry soils showing the most contrasting soil water infiltration between landscapes and surface types. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献