Characterisation of a Pleistocene debris-avalanche deposit in the Tenteniguada Basin,Gran Canaria Island,Spain     

Alejandro Lomoschitz  Javier Hervás  Jorge Yepes  Joaquín Meco 《Landslides》2008,5(2):227-234

We studied a large debris-avalanche deposit of Pleistocene age in the Tenteniguada Basin, Gran Canaria Island, Spain. This deposit, which is well preserved because it is mostly covered by basanite lava flows, has distinctive matrix and block facies, hummocky topography and internal structures typical of debris avalanches. However, neither syneruptive lavas nor some characteristic features of volcanic debris-avalanche deposits, such as a stratovolcano edifice or a horseshoe-shaped crater, are present. The occurrence of internal features characteristic of volcanic avalanche deposits could be attributed to the volcanic materials involved in the movement rather than to the triggering of the avalanche during a volcanic eruption. The conditioning factors are shown to be associated with specific structural and hydrological conditions, such as the presence of old volcanic domes, strength reduction of the rocks, effective stress decrease, active gully erosion and water table rise during Pleistocene humid episodes. We finally suggest that the possible triggering factor of the avalanche was a neighbouring volcanic or tectonic earthquake.  相似文献   

Plant macrofossil assemblages from surface sediment represent contemporary species and growth forms of aquatic vegetation in a shallow Mediterranean lake     

Jorge García-Girón  Camino Fernández-Aláez  Alejandro Nistal-García  Margarita Fernández-Aláez 《Journal of Paleolimnology》2018,60(4):495-509

Macrofossils are known as a useful tool in reconstructing their original plant communities. However, most studies have been focused on comparing the composition and distribution of living plant communities and their remains in temperate lakes. Mediterranean shallow lakes have been historically far less studied and little is known about the relationships between Mediterranean macrophyte communities and their remains. The aim of our study is to assess how contemporary aquatic macrophyte communities are represented by their sedimentary remains in terms of composition, distribution and concordance between the contemporary and the subfossil assemblages in a procrustean superimposition space, and to determine which surface sediment cores, collected along a depth gradient, may represent best the whole-lake macrofossil assemblage. These analyses were carried out for both species and macrophyte growth forms (submerged hydrophytes, floating-leaved hydrophytes, helophytes and charophytes) in order to check which of the two (species and growth forms) were represented best by their macro-remains. The most abundant present-day species (Myriophyllum alterniflorum DC. and Potamogeton trichoides L.) were under-represented while Characeae and some floating-leaved hydrophytes (Polygonum amphibium L. and Ranunculus peltatus Schrank) were over-represented in sedimentary samples. Additionally, macro-remains of submerged hydrophytes and helophytes were generally found in the central areas and in close proximity to contemporary vegetation, whereas floating-leaved hydrophytes distributed close to the near-shore. Notwithstanding some disparities between contemporary vegetation and their macrofossil assemblages, we found a good agreement between present-day and sedimentary datasets for both species and macrophyte growth forms. Furthermore, our study suggests that sediment cores from deep areas are more likely to represent best the whole-lake macrofossil assemblage because of their high diversity, equitability and heterogeneity. We conclude that aquatic macrophyte subfossils from the central areas of the basin can be a very useful tool in tracking the species composition and structure of the original macrophyte communities in shallow Mediterranean lakes. Additionally, when considering the use of macro-remains to reconstruct the composition and structure of macrophyte growth forms, we recommend a multicore approach that uses transects running from the shore to the lake center.  相似文献   

Spatial and temporal variation of picoplanktic cyanobacteria population in a density stratified estuary,and the introduction of a cellular gradient number     

Alejandro Carrillo  Pablo Huq  Mari C. Pérez  José M. Redondo 《Estuarine, Coastal and Shelf Science》2008

Spatial and temporal variations in the distribution of the marine picoplanktic cyanobacteria population and mixing conditions were found in the Ebro River estuary outflow to the Mediterranean Sea in Spain. Six sampling surveys were undertaken between July 1999 and February 2000 for distances up to 15 km from the river mouth. Measurements were taken of flow velocity, salinity, temperature, depth and picocyanobacteria (PCB) abundances. Gradient Richardson (Rig) and Reynolds (Re) numbers were determined to evaluate hydrodynamics. In summer, large values of Rig arise from the small flow rates, and small values of velocity shear between the surface fresh water layer and the bottom saline layer; conversely, in winter the large flow rates and attendant large velocity shears between the layers give rise to small values of Rig. Flow conditions in the fall are an intermediate case between the summer and winter cases. Vertical abundance distributions were resolved through the river water, interfacial region, and the bottom salt wedge; longitudinal gradients of PCB abundances were also resolved. Seasonal differences in the PCB abundance values were observed. Analysis of cell numbers (C) showed that the variable dC/dS, the dependence of cell number upon salinity gradient (dS) was critical. A non-dimensional number; the cellular gradient number (Cg) is introduced. Cg has useful biological interpretations that can potentially be included in ecological modeling. For example, Cg = 1 pertains to perfect adaptability of the organism to adjust to changing environmental conditions, whereas Cg = 0 describes total mortality. For a system with strong advection there is insufficient time for cells to adapt to the changing environment, and so those cell counts are unchanged. This is the case for the Ebro estuary in winter as advection of salinity (and hence PCB abundance) dominates the other loss processes for large flow rates.  相似文献   

Seismic attenuation of coda waves in the eastern region of Cuba   总被引：1，自引：0，他引：1  

Berta Biescas  Zulima Rivera  Jose Alejandro Zapata 《Tectonophysics》2007,429(1-2):99-109

Cuba's seismic attenuation had never been studied in detail. In this paper we present the results of the research on the seismic attenuation of Cuba's eastern zone based upon the information collected by the seismological Cuban network from 1998 to 2003. 581 earthquakes were selected from the Cuban catalogue to make this study. All of them, recorded by at least three seismic stations, had their epicenters located in the eastern Cuban region (19.3–22 N, 79–73 W), epicentral distances between 15 km and 213 km, their coda duration magnitudes ranging from 2 and 4.1 and their focal depths reaching up to 30 km. The seismic wave attenuation was studied using coda waves. The single scattering method proposed by Sato in 1977 was applied, the attenuation and frequency dependency for different paths and the correlation of the results with the geotectonics of the region are presented in this paper.The mean Q_c value calculated was Q_c = (64 ± 2)f^{0.84 ± 0.01}. The relatively low Q₀ and the high frequency dependency agree with the values of a region characterized by a high tectonic activity. The Q_c values of seven subregions of eastern Cuba were calculated and correlated with the geology and tectonics of the area.  相似文献   

Community structure and phenology of chironomids (Insecta: Chironomidae) in a Patagonian Andean stream     

Patricia Elizabeth García  Diego Alejandro An Surez 《Limnologica》2007,37(1):109-117

In this paper, we studied the assemblage of Chironomidae from headwaters of Ñireco stream by recording drifting pupal exuviae caught in the debris close to the shore. Samples were collected in three stations along 18 km of the stream every 2 weeks during spring–summer months and monthly during autumn–winter over a year. A total of 15949 exuviae were collected and 55 taxa were identified. The most abundant taxa were Cricotopus spp. with highest numbers of exuviae recorded in each station over the study period. Subfamily Orthocladiinae was the most abundant taxa, followed by Chironominae and Podonominae. The emergence period in the stream occurred between December 1998 and March 1999. Most of the dominant and frequent species were univoltine. The emergence peaks at each sampling station occurred at the highest temperature of the water recorded.  相似文献   

The influence of halokinesis on prograding clinoforms: Insights from the Tiddlybanken Basin,Norwegian Barents Sea     

Luis Alberto Rojo  Dora Marín  Nestor Cardozo  Alejandro Escalona  Hemin Koyi 《Basin Research》2020,32(5):979-1004

Although the trajectory and geometry of clinoforms in different types of basins have been described in many studies, few studies discuss the influence of halokinesis on clinoforms in salt-related basins. In this study, we analyse the Lower Cretaceous clinoforms in the Tiddlybanken Basin, Norwegian Barents Sea to evaluate the impact of salt mobilization on the geometry and trajectory of clinoforms as well as its implications on sediment partitioning. To accomplish this objective, we use a multidisciplinary approach consisting of seismic and well-interpretation, 3D structural restoration, and forward stratigraphic modelling. The results show that salt mobilization affects prograding clinoforms by: (a) causing lateral variations in progradation rates, resulting in complex palaeogeography, (b) increasing slope angles, which affect the equilibrium of the clinoform profile and can trigger slope-readjustment processes and (c) producing lateral and temporal variations in accommodation space, leading to different clinoform trajectories, stacking patterns and reservoir distribution along the basin. Forward stratigraphic modelling shows that in salt-related basins and other tectonically active basins, the isolated use of conventional methods for clinoform analysis might lead to potential interpretation pitfalls such as misinterpretation of trajectories and overestimation of foreset angles, which can have negative consequences for exploration models.  相似文献   

Erosional and depositional contourite features at the transition between the western Scotia Sea and southern South Atlantic Ocean: links with regional water-mass circulation since the Middle Miocene     

Lara F. Pérez  F. Javier Hernández-Molina  Federico D. Esteban  Alejandro Tassone  Alberto R. Piola  Andrés Maldonado  Benedict Preu  Roberto A. Violante  Emanuele Lodolo 《Geo-Marine Letters》2015,35(4):271-288

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User-centered road network traffic analysis with MobilityDB     

Mahmoud Sakr  Esteban Zimányi  Alejandro Vaisman  Mohamed Bakli 《Transactions in GIS》2023,27(2):323-346

Performance indicators of road networks are a long-lasting topic of research. Existing schemes assess network properties such as the average speed on road segments and the queuing time at intersections. The increasing availability of user trajectories, collected mainly using mobile phones with a variety of applications, creates opportunities for developing user-centered performance indicators. Performing such an analysis on big trajectory data sets remains a challenge for the existing data management systems, because they lack support for spatiotemporal trajectory data. This article presents an end-to-end solution, based on MobilityDB, a novel moving object database system that extends PostgreSQL with spatiotemporal data types and functions. A new class of indicators is proposed, focused on the users' experience. The indicators address the network design, the traffic flow, and the driving comfort of the motorists. Furthermore, these indicators are expressed as analytical MobilityDB queries over a big set of real vehicle trajectories.  相似文献   

Impact of sediment-induced stratification and turbulence closures on sediment transport and morphological modelling   总被引：1，自引：0，他引：1  

Laurent O. Amoudry  Alejandro J. Souza 《Continental Shelf Research》2011,31(9):912-928

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Effects of sugar cane monocultures on origin and characteristics of dissolved organic matter in the Manguaba lagoon in northeast Brazil     

Berit Brockmeyer  Alejandro Spitzy 《Organic Geochemistry》2011,42(1):74-83

Brazil has extensive sugar cane monocultures, which significantly alter hydrogeochemical material fluxes. We studied dissolved organic matter (OM) fluxes in the Manguaba lagoon-estuary system, which drains a sugar cane monoculture-dominated hinterland and discharges into the Atlantic coastal ocean. The OM fluxes into the lagoon originate from baseflow, field runoff and sugar cane factory effluents. In the study, dissolved organic carbon (DOC) concentration, δ¹³C DOC and UV absorbance were analysed along a freshwater-seawater salinity gradient that encompasses river (DOC 9-11 mg l⁻¹, δ¹³C −22.2‰ to −25.5‰); lagoon (4-11 mg l⁻¹, −20.5‰ to −24.8‰); estuary (3-9 mg l⁻¹, −22.6‰ to −25.3‰) and coastal waters (1.64 mg l⁻¹, −21‰) with different intra-seasonal runoff conditions. We used the carbon isotope data to quantify the sugar cane derived DOC. Where river water meets brackish lagoon water, substantial loss of DOC occurs during rainy conditions, when suspended sediment from eroded fields in the river is very high. During dry weather, at much lower suspension levels, DOC increases, however, presumably from addition of photolysed resuspended sedimentary OM. In the estuary, mixing of DOC is strictly conservative. Ca. 1/3 of riverine DOM discharged into the lagoon has a sugar cane source. Within the lagoon on avg. 20% of the bulk DOM is comprised of sugar cane DOM, whereas during heavy rainfall the amount increases to 31%, due to intensified drainage flow and soil erosion. In the estuary, 14-26% is of sugar cane origin. The sugar cane-derived component follows the mixing patterns of bulk DOM.  相似文献