Geology, ore deposits and hydrothermal venting in Bahía Concepción, Baja California Sur, Mexico     

Antoni  Camprubí  Carles  Canet  Augusto A.  Rodríguez-Díaz  Rosa M.  Prol-Ledesma  David  Blanco-Florido  Ruth E.  Villanueva  Abigail  López-Sánchez 《Island Arc》2008,17(1):6-25

Abstract Bahía Concepción is located in the eastern coast of the Baja California peninsula and it is shaped by northwestern–southeastern normal faults. These are associated with a 12–6 Ma rifting episode, although some have been reactivated since the Pliocene. The most abundant rocks correspond to the arc related Comondú Group, Oligocene to Miocene, which forms a mainly calc‐alkaline volcanic and volcaniclastic sequence. There are less extensive outcrops of sedimentary rocks, lava flows, domes and pyroclastic rocks of Pliocene to Quaternary ages. The Neogene volcanism in the area indicates a shift from a subduction regime to an intraplate volcanism related to continental extension and the opening of an oceanic basin. The Bahía Concepción area contains numerous Mn ore deposits, being the biggest at El Gavilán and Guadalupe. The Mn deposits occur as veins, breccias and stockworks, and are composed by Mn oxides (pyrolusite, coronadite, romanechite), dolomite, quartz and barite. The deposits are hosted in volcanic rocks of the Comondú Group and, locally, in Pliocene sedimentary rocks. Thus, the Mn deposits formed between the Middle Miocene and the Pliocene. The mineralized structures are associated with Miocene northwestern–southeastern fault systems, which are analogous to those associated with the Cu‐Co‐Zn‐Mn deposits of El Boleo. The Bahía Concepción area also bears subaerial and submarine hot springs, which are associated with the same fault systems and host rocks. The submarine and subaerial geothermal manifestations south of the bay are possibly related with recent volcanism. The geothermal manifestations within the bay are intertidal hot springs and shallow submarine diffuse venting areas. Around the submarine vents (5–15 m deep, 87°C), Fe‐oxyhydroxide crusts with pyrite and cinnabar precipitate. In the intertidal vents (62°C), aggregates of opal, calcite, barite and Ba‐rich Mn oxides occur covered by silica‐carbonate stromatolitic sinters. Some 10–30 cm thick crustiform veins formed by chalcedony, calcite and barite are also found close to the vents. The hydrothermal fluids exhibit mixed isotopic compositions between δ¹⁸O‐enriched meteoric and local marine water. The precipitation of Ba‐rich Mn oxides around the vent sites could be an active analog for the processes that produced Miocene to Pliocene hydrothermal Mn‐deposits.  相似文献   

Chronology and paleoenvironmental interpretation of talus flatiron sequences in a sub‐humid mountainous area: Tremp Depression,Spanish Pyrenees     

Carles Roqué  Rogelio Linares  Mario Zarroca  Joan Rosell  Xavier M. Pellicer  Francisco Gutiérrez 《地球表面变化过程与地形》2013,38(13):1513-1522

Talus flatirons are debris‐covered relict slopes, disconnected from the source area, which are relatively common in arid and semi‐arid areas. Talus flatiron sequences record the alternation of accumulation and incision phases. These chronosequences may be used for infer temporal changes in the morphogenetic processes acting on the slopes as well as information on the local paleoclimatic history. Talus flatiron sequences developed in the Tremp Depression, eastern Spanish Pyrenees, are analysed from the geomorphological, chronological and paleoenvironmental perspective. The two groups of relict slopes differentiated by means of detailed geomorphological mapping have been dated by optically stimulated luminescence (OSL) and radiocarbon dating at 25–20 kyr (S3) and 5·4–1·7 cal kyr (S2). The talus flatiron group S3 is correlated with a fluvial terrace of the Noguera Pallaresa River (c. 23 kyr bp ). The comparison of the ages obtained in the Tremp Depression with chronologies published for talus flatiron sequences in semi‐arid areas and other paleoclimatic proxies suggests that the aggradation phases in the slopes occurred during periods with higher humidity and vegetation cover. The chronological differences observed between semi‐arid Spain and the Tremp Depression may be partly related to the more humid climate of the latter mountain area. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Artificial macrophytes as fish habitat in a Mediterranean reservoir subjected to seasonal water level disturbances     

Luciano N. Santos  Angelo A. Agostinho  Carles Alcaraz  Joaquim Carol  Alejandra F. G. N. Santos  Pablo Tedesco  Emili García-Berthou 《Aquatic Sciences - Research Across Boundaries》2011,73(1):43-52

Artificial macrophytes were experimentally deployed in Boadella Reservoir (NE Spain) and assessed for fish use throughout the first 3 months of the 2007 summer drawdown. In total, 1,832 individuals of seven fish species were recorded through visual censuses, with introduced perch Perca fluviatilis being the prevalent species. Fish richness and abundance were significantly higher in artificial macrophytes than in rocky shores and sandy beaches, displaying a unimodal variation through time. P. fluviatilis, Rutilus rutilus and Abramis brama were significantly more abundant in artificial macrophytes than in the other two naturally submersed habitats, where no individuals of these species were recorded. The abundances of Squalius laietanus, Lepomis gibbosus, Micropterus salmoides and Cyprinus carpio were overall greater in artificial macrophytes than in rocky shores but displayed significant habitat × time interactions. A decrease in predation risk was apparently the key-factor of the intensive use of artificial macrophytes by small fish (≤100 mm TL) in Boadella Reservoir, since most species reduced drastically or completely the use of submerged structures when body size increased. This study demonstrates that adding artificial structures mimicking aquatic macrophytes can be an interesting tool to mitigate the adverse effects of water level fluctuations on fish assemblages in structure-less and homogeneous ecosystems, and to understand the mechanisms affecting habitat use and species replacement.  相似文献   

Sustainability of Mediterranean Deltaic and Lagoon Wetlands with Sea-Level Rise: The Importance of River Input     

John Day  Carles Ibáñez  Francesco Scarton  Didier Pont  Philippe Hensel  Jason Day  Robert Lane 《Estuaries and Coasts》2011,34(3):483-493

We report on a decadal trend of accretionary dynamics in the wetlands of several northwestern Mediterranean deltas and a lagoon system, all of them with high rates of wetland loss. Wetland vertical accretion and surface elevation change were measured at 55 riverine, marine, and impounded sites in four coastal systems: the Ebro delta, Spain; the Rhône delta, France; and the Po delta and Venice Lagoon, Italy. Vertical accretion and elevation change ranged between 0 and 25 mm year^?1 and were strongly correlated. The highest rates of elevation gain occurred at riverine sites where vertical accretion was highest. We conclude that areas with high sediment input, mainly riverine, are the only ones likely to survive accelerated sea-level rise, especially if recent higher estimates of 1 m or more in the twenty-first century prove to be accurate. This is the first study where the importance of river input on wetland survival has been demonstrated at a decadal time scale over a broad geographical area.  相似文献   

Qualitative study of the planar isosceles three-body problem     

Carles Simó  Regina Martinez 《Celestial Mechanics and Dynamical Astronomy》1987,41(1-4):179-251

We consider the particular case of the planar three body problem obtained when the masses form an isosceles triangle for all time. Various authors [1, 2, 12, 8, 9, 13, 10] have contributed in the knowledge of the triple collision and of several families of periodic orbits in this problem. We study the flow on a fixed level of negative energy. First we obtain a topological representation of the energy manifold including the triple collision and infinity as boundaries of that manifold. The existence of orbits connecting the triple collision and infinity gives some homoclinic and heteroclinic orbits. Using these orbits and the homothetic solutions of the problem we can characterize orbits which pass near triple collision and near infinity by pairs of sequences. One of the sequences describes the regions visited by the orbit, the other refers to the behaviour of the orbit between two consecutive passages by a suitable surface of section. This symbolic dynamics which has a topological character is given in an abstract form and after it is applied to the isosceles problem. We try to keep globality as far as possible. This strongly relies on the fact that the intersection of some invariant manifolds with an equatorial plane (v=0) have nice spiraling properties. This can be proved by analytical means in some local cases. Numerical simulations given in Appendix A make clear that these properties hold globally.  相似文献   

Analysis of some degenerate quadruple collisions   总被引：1，自引：1，他引：0  

Carles Simó  Ernesto Lacomba 《Celestial Mechanics and Dynamical Astronomy》1982,28(1-2):49-62

We consider the trapezoidal problem of four bodies. This is a special problem where only three degrees of freedom are involved. The blow up method of McGehee can be used to deal with the quadruple collision. Two degenerate cases are studied in this paper: the rectangular and the collinear problems. They have only two degrees of freedom and the analysis of total collapse can be done in a way similar to the one used for the collinear and isosceles problems of three bodies. We fully analyze the flow on the total collision manifold, reducing the problem of finding heteroclinic connections to the study of a single ordinary differential equation. For the collinear case, from which arises a one parameter family of equations, the analysis for extreme values of the parameter is done and numerical computations fill up the gap for the intermediate values. Dynamical consequences for possible motions near total collision as well as for regularization are obtained.Paper presented at the 1981 Oberwolfach Conference on Mathematical Methods in Celestial Mechanics.Dedicated to Prof. Szebehely on the occasion of his sixtieth birthday.  相似文献   

Response scenarios for the deltaic plain of the Rhône in the face of an acceleration in the rate of sea-level rise with special attention to<Emphasis Type="Italic">Salicornia</Emphasis>-type environments     

Didier Pont  John W. Day  Philippe Hensel  Evelyne Franquet  Frank Torre  Patrick Rioual  Carles Ibànez  Eric Coulet 《Estuaries and Coasts》2002,25(3):337-358

One of the most critical problems facing many deltaic wetlands is a high rate of relative sea-level rise due to a combination of eustatic sea-level rise and local subsidence. Within the Rhône delta, the main source of mineral input to soil formation is from the river, due to the low tidal range and the presence of a continuous sea wall. We carried out field and modeling studies to assess the present environmental status and future conditions of the more stressed sites, i.e.,Salicornia-type marshes with a shallow, hypersaline groundwater. The impacts of management practices are considered by comparing impounded areas with riverine areas connected to the Rhône River. Analysis of vegetation transects showed differences between mean soil elevation ofArthrocnemum fruticosum (+31.2 cm),Arthrocnemum glaucum (+26.5 cm), bare soil (+16.2 cm), and permanently flooded soil (?12.4 cm). Aboveground and belowground production showed that root:shoot ratio forA. fruticosum andA. glaucum was 2.9 and 1.1, respectively, indicating more stressful environmental conditions forA. glaucum with a higher soil salinity and lack of soil drainage. The annual leaf litter production rate of the two species is 30 times higher than annual stem litter production, but with a higher long-term decomposition rate associated with leaves. We developed a wetland elevation model designed to predict the effect of increasing rates of sea-level rise on wetland elevation andSalicornia production. The model takes into account feedback mechanisms between soil elevation and river mineral input, and primary production. In marshes still connected to the river, mineral input decreased quickly when elevation was over 21 cm. Under current sea-level rise conditions, the annual amount of riverine mineral input needed to maintain the elevation of the study marshes is between 3,000 and 5,000 g m^?2 yr^?1. Simulations showed that under the Intergovernmental Panel on Climate Change best estimate sea-level rise scenario, a mineral input of 6,040 g m^?2 yr^?1 is needed to maintain marsh elevation. The medium term response capacity of the Rhône deltaic plain with rising sea level depends mainly on the possibility of supplying sediment from the river to the delta, even though the Rhône Delta front is wave dominated. Within coastal impounded marshes, isolated from the river, the sediment supply is very low (10 to 50 g m^?2 yr^?1), and an increase of sea-level rise would increase the flooding duration and dramatically reduce vegetation biomass. New wetland management options involving river input are discussed for a long-term sustainability of low coastal Mediterranean wetlands.  相似文献   

A dynamical equivalent to the equilateral libration points of the earth-moon system     

Carles Díez  Àngel Jorba  Carles Simó 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):13-29

Consider the Earth-Moon-particle system as a Restricted Three Body Problem. There are two equilateral libration points. In the actual world system, those points are no longer relative equilibrium points mainly due to the effect of the Sun and to the noncircular motion of the Moon around the Earth. In this paper we present the problem as a perturbation of the RTBP and we look for the dynamical equivalent of L _4,5. It turns out to be a quasiperiodic orbit. It is obtained for a simplified model but the procedure to obtain it is general and can be carried out with an additional computational effort.  相似文献   

Sedimentological and palaeohydrological characterization of Late Pleistocene and Holocene tufa mound palaeolakes using trenching methods in the Spanish Pyrenees          下载免费PDF全文

Xavier M. Pellicer  Juan Pablo Corella  Francisco Gutiérrez  Carles Roqué  Rogelio Linares  Domingo Carbonel  Mario Zarroca  Jesús Guerrero  Xavier Comas 《Sedimentology》2016,63(6):1786-1819

Lakes developed in the inner depressions of tufa mounds are rare geomorphic features and still poorly understood. Sedimentation in this unusual type of endorheic lake with a very restricted catchment area is highly sensitive to environmental and hydrological changes. The Isona tufa mound complex, north‐eastern Iberian Peninsula, is associated with the discharge zone of a confined artesian aquifer and comprises 11 tufa mounds consisting of an annular rimstone enclosing a central depression filled with lake deposits. Data gathered from trenches excavated in four palaeolakes located within three different morphostratigraphic units permitted a precise analysis of the geometrical characteristics and stratigraphic relationships of the deposits and provided a sedimentation model for the Late Quaternary infilling of the spring‐fed lakes. The work illustrates that trenches allow a precise characterization of the stratigraphic arrangements, lateral facies changes and deformation structures, which are not apparent in studies relying solely on borehole records, and facilitate sampling for dating and geochemical analyses. The five sedimentary facies described represent different evolutionary stages of the lakes, including: (i) carbonate‐rich palustrine deposits probably related to periods with strong hydrological seasonality; (ii) massive highly bioturbated organic ooze; (iii) banded organic carbonate‐rich facies associated with an increase in the regional effective moisture; (iv) fine‐grained quartz‐rich aeolian/slope‐wash sediments; and (v) colluvial facies deposited following the desiccation of the lakes located at higher altitudes. Geochemical and sedimentological analyses of the lacustrine sequences provided information on the palaeohydrological evolution of the Isona tufa mound complex and the palaeoenvironmental conditions of the area over the last 28 ka. Radiometric dating suggests that deposition occurred simultaneously at ca 22 ka in palaeolakes situated at different elevations. A drop in the piezometric level prompted by the opening of springs at lower altitudes probably caused the deactivation of the upper springs and the desiccation of the lakes. Arid conditions prevailed in the area during the Late Glacial and the early Holocene (28·0 to 8·5 ka bp ). More humid conditions recorded from 8·5 to 4·2 ka and again since 1·7 ka are in accordance with palaeoenvironmental reconstructions available in the Western Mediterranean since the Last Glacial Maximum.  相似文献   

Evaluation of trenching,ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization          下载免费PDF全文

Domingo Carbonel  Verónica Rodríguez  Francisco Gutiérrez  James P. McCalpin  Rogelio Linares  Carles Roqué  Mario Zarroca  Jesús Guerrero  Ira Sasowsky 《地球表面变化过程与地形》2014,39(2):214-227

This paper explores the suitability and advantages of combining the trenching technique with geophysical surveys [ground penetrating radar (GPR) and electrical resistivity tomography (ERT)] for sinkhole characterization in a mantled karst area. The approach is applied to two active sinkholes concealed by anthropogenic deposits and formed by contrasting subsidence mechanisms; collapse and sagging. The ERT section acquired across the collapse sinkhole images the clayey fill of the depression as an obvious low resistivity area, showing the approximate location of the sinkhole edges. Spatially dense GPR surveys provide information on the position of the boundaries of the concealed subsidence structures and their three‐dimensional (3D) internal geometry, revealing the dominant subsidence mechanism. We illustrate the impact of several factors on the quality of the GPR data such as sinkhole size, nominal frequency of the antennas, antenna shielding, and the presence of backfilled excavations and above‐surface objects. Trenches provided detailed information on the subsurface structure of the sinkhole, subsidence magnitude, partitioning of the strain, and the position of the sinkhole edges, especially when they are deep enough and excavated across the central sector and perpendicular to the boundaries. The stratigraphic and structural relationships observed in the trench were then used to infer the spatial evolution of the sinkholes (e.g. enlargement), their kinematic behavior (episodic versus progressive), and to differentiate discrete subsidence events and their associated magnitude. Numerical dates were used to estimate average subsidence rates and the recurrence of subsidence events. Such integrated data sets may be used as an objective basis to forecast the future behavior of potentially damaging sinkholes and to assess the associated hazard and risk. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献