Glaucony from the Cretaceous of the Sierra de Guadarrama (Central Spain) and its application in a sequence-stratigraphic context   总被引：1，自引：0，他引：1  

Alessandro Amorosi  Roberto Guidi  Ramon Mas  Elisa Falanga 《International Journal of Earth Sciences》2012,101(2):415-427

Detailed sedimentological and geochemical analyses of Upper Cretaceous glaucony-bearing deposits from the middle portion of the Castro de Fuentidueña Formation, in Central Spain, enable identification of a multiphase history of glaucony accumulation. Despite its relatively high maturity (K₂O > 7%), glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock (generally <10%), suggesting remobilization from a different source. The remarkable thickness of the glaucony-bearing horizons, concurrently with concentration of glaucony in laminae, small size, and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains. In contrast, authigenic glaucony from the overlying offshore clays exhibits higher abundance (up to 45%) and lower maturity (K₂O < 7%) and is interpreted to have formed in situ. Allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation. The green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third-order depositional sequence. Maximum concentration of autochthonous glaucony is recorded at the transition from tidal-influenced to offshore deposits: this glaucony, which is relatively less evolved due to lower time available for maturation, is interpreted to reflect the turnaround from transgressive to highstand conditions, marking the condensed section of the depositional sequence. As postulated by previous sequence-stratigraphic models, this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract (TST), while the condensed section (CS) typically hosts autochthonous glaucony. Contrary to the existing literature, however, this study shows that glaucony from the TST may be even more mature than glaucony from the CS, if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains. Identification of spatial and temporal characteristics of glaucony, thus, is critical to a reliable sequence-stratigraphic interpretation of the glaucony-bearing deposits.  相似文献   

Reconstruction of annual winter rainfall since A.D.1579 in central-eastern Spain based on calcite laminated sediment from Lake La Cruz     

Lidia Romero-Viana  Ramon Julià  Martin Schimmel  Antonio Camacho  Eduardo Vicente  M. Rosa Miracle 《Climatic change》2011,107(3-4):343-361

We present the first winter (December to March) rainfall reconstruction based in a novel proxy, the thickness of annual calcite laminations preserved in Lake La Cruz (central–eastern Spain). A previous calibration analysis between laminae thickness and the instrumental data series (1950 to present) indicated a highly significant correlation with winter rainfall. Therefore this study attempts the winter rainfall reconstruction since the onset of laminations (1579 a.d.) by means of the calibration function previously developed. The verification analysis between inferred annual values and earlier instrumental data (1859–1949) confirms the suitability of this novel proxy and the reliability of the series reconstructed. The reconstructed series show the fluctuating character of winter rainfall in the western Mediterranean area; interdecadal dry periods alternated with wetter periods following, in a board sense, the pattern recorded by documentary sources in other regions of the Iberian Peninsula. At present times regional winter rainfall anomalies are highly correlated with the phase of the North Atlantic Oscillation (NAO). However the time series analysis showed the dominance of nonstationary components at high frequencies of the climate signal over the last four centuries suggesting that the connection between winter rainfall and the NAO has not been stable over time and also other modes of variability, not only NAO, may have conditioned winter rainfall variability.  相似文献   

Land use change and resource management in the Jnane Mas valley (Khenifra,Middle Atlas,Morocco)     

Brahim Akdim  Ramon Julia  Mohamed Laaouane 《Geography and Natural Resources》2011,32(1):87-94

The purpose of this paper is to bring into light the landscape change and natural resources management in the Moroccan Middle Atlas across centuries. The pastoral way of life prevailed for many centuries. However, following the results of this research, evidence of important socioeconomic changes and resources use is found. Ancient agricultural activities, as well as the exploitation of the forest and even mineral resources have been growing activities over time. The survey shows that the agricultural activity has existed for several centuries as indicated by terraces and encrusted travertine channels used for irrigation. The landscapes and the ways of resources use are therefore in continuous change. The increasing needs in water and agriculture for demographic and climatic reasons (the dry periods in summer or periodic droughts) generated because of intensive over-exploitation of resources. The vegetation degraded facing human pressure (the pastoral activities, the coal of wood making, the lime manufacturing, etc.). Field observations show that irrigation has been used in this domain, for several centuries. Travertine channels, encrusted in the valleys of Jnane Mas and Arougou, illustrate these ancient uses of water resources for agriculture irrigation.  相似文献   

Growth and grazing rate dynamics of major phytoplankton groups in an oligotrophic coastal site   总被引：1，自引：0，他引：1  

Andrés Gutiérrez-Rodríguez  Mikel Latasa  Renate Scharek  Ramon Massana  Gemma Vila  Josep M. Gasol 《Estuarine, Coastal and Shelf Science》2011

There has been more attention to phytoplankton dynamics in nutrient-rich waters than in oligotrophic ones thus requiring the need to study the dynamics and responses in oligotrophic waters. Accordingly, phytoplankton community in Blanes Bay was overall dominated by Prymnesiophyceae, remarkably constant throughout the year (31 ± 13% Total chlorophyll a, Tchl a) and Bacillariophyta with a more episodic appearance (20 ± 23% Tchl a). Prasinophyceae and Synechococcus contribution became substantial in winter (Prasinophyceae = 30% Tchl a) and summer (Synechococcus = 35% Tchl a). Phytoplankton growth and grazing mortality rates for major groups were estimated by dilution experiments in combination with high pressure liquid chromatography and flow cytometry carried out monthly over two years. Growth rates of total phytoplankton (range = 0.30–1.91 d⁻¹) were significantly higher in spring and summer (μ > 1.3 d⁻¹) than in autumn and winter (μ ∼ 0.65 d⁻¹) and showed a weak dependence on temperature but a significant positive correlation with day length. Microzooplankton grazing (range = 0.03–1.4 d⁻¹) was closely coupled to phytoplankton growth. Grazing represented the main process for loss of phytoplankton, removing 60 ± 34% (±SD) of daily primary production and 70 ± 48% of Tchl a stock. Chla synthesis was highest during the Bacillarophyceae-dominated spring bloom (Chl a_synt = 2.3 ± 1.6 μg Chl a L⁻¹ d⁻¹) and lowest during the following post-bloom conditions dominated by Prymnesiophyceae (Chl a_synt = 0.23 ± 0.08 μg Chl a L⁻¹ d⁻¹). This variability was smoothed when expressed in carbon equivalents mainly due to the opposite dynamics of C:chl a (range = 11–135) and chl a concentration (range = 0.07–2.0 μg chl a L⁻¹). Bacillariophyta and Synechococcus contribution to C fluxes was higher than to biomass because of their fast-growth rate. The opposite was true for Prymnesiophyceae.  相似文献   

Regional and species specific sexual reproductive patterns of three zooxanthellate scleractinian corals across the Eastern Tropical Pacific          下载免费PDF全文

Jeimy D. Santiago‐Valentín  Susan B. Colley  Peter W. Glynn  Amilcar L. Cupul‐Magaña  Ramon A. López‐Pérez  Fabián A. Rodríguez‐Zaragoza  Francisco Benítez‐Villalobos  Eric Bautista‐Guerrero  Denisse A. Zavala‐Casas  Alma P. Rodríguez‐Troncoso 《Marine Ecology》2018,39(2)

Sexual reproduction of zooxanthellate scleractinian corals in the Eastern Tropical Pacific (ETP) is influenced by the interactive effects of regional and local oceanographic conditions, as well as a variety of other environmental factors. Differences in spatial and temporal gamete development and reproductive patterns of three widespread scleractinian corals of this region—Pocillopora damicornis (branching colony morphology, characterized as hermaphrodite broadcaster), Pavona gigantea (massive colonies, characterized as gonochoric broadcaster/sequential co‐sexually hermaphroditic) and Porites panamensis (encrusting colonies, characterized as gonochoric brooder)—were evaluated at local and regional scales across the ETP. This area extended from the Gulf of California (24°N) to the southern coast of Ecuador (–1°S), including offshore islands, using existing data pooled from prior studies. Predictive models were employed based on environmental variables: sea surface temperature, daylight hours, diffuse attenuation co‐efficient at 490 nm and photosynthetically active radiation. Datasets were extracted from satellite images ( https://oceancolor.gsfc.nasa.gov ) and analysed using WAM_STATIST ver. 6.33® software to obtain monthly average data from each site. The spatial (region, sub‐region and site) and seasonal (wet, dry) variation in reproductive activity (% colonies with gametes) differed among the three species; significant interactions were season × sub‐region for P. damicornis, season × site (sub‐region) for P. gigantea, and season × site for P. panamensis, for which sub‐region was not considered as a factor. The predictive models also suggest that gamete production/maturation of P. damicornis and P. gigantea is influenced by local differences in sea surface temperature and daylight hours. Porites panamensis was not correlated with any environmental variable examined. Variations in local and regional reproductive developmental patterns are likely an acclimatization response by each species imposed by the timing and duration of local stressor events. This analysis has provided insights into the diverse local and regional physical drivers that affect species responses and acclimatization in sexual reproduction across the ETP.  相似文献   

Characterizing the dead time of the ECLAIRs camera on board the mission SVOM     

A. Bajat  O. Godet  J.-L. Atteia  S. Maestre  D. Rambaud  V. Waegebaert  C. Amoros  S. Bordon  S. Delaigue  M. Galliano  B. Houret  K. Lacombe  P. Mandrou  W. Marty  R. Pons  P. Ramon 《Experimental Astronomy》2018,46(2):337-356

French (CNES) and Chinese (CNSA) space agencies collaborate to build the SVOM (Space-based multi-band Variable Object Monitor) mission due to be launched in 2021 to study gamma-ray bursts and high-energy transients. The SVOM prime instrument, ECLAIRs, will detect and localize GRBs autonomously as well as provide a spectral and temporal characterization of the GRB prompt emission. ECLAIRs is expected to detect around 200 GRBs during the 3 year nominal lifetime of the mission. ECLAIRs is a wide-field (\(\sim 2 \text {sr}\)) coded mask camera with a detection plane made of 8 independent sectors of 800 Schottky CdTe detectors working in the 4-150 keV energy range. Each sector is connected to independent readout electronics. In this paper, we focus on the study of the temporal performance and we estimate how dead time will affect bright transient lightcurves. We discuss the analytical model based on simulations over a large range of source count rates on a dedicated test bench. We show that dead time will not significantly affect ECLAIRs data, even for the brightest GRBs (3.7% of lost counts for a count rate of 10⁵ counts.s^??1 over the detection plane in the energy range 4?150 keV) and our model can nicely correct the parts of the lightcurves which are the most affected by dead time effects for very bright GRBs.  相似文献   

Angular momenta in binary systems     

Ramon Julian Quiroga  Luiz Paulo Ribeiro Vaz 《Astrophysics and Space Science》1988,146(1):99-137

The correlations angular momentaL to massesM are studied for different types of spectroscopic binaries. The functionsL=AM ^b have the coefficientb with the values expected from a Keplerian mechanics, but the valuesA(q, T), A(q, a), A(q, v), associated tob=5/3, 3/2, and 2, respectively, are given (statistically speaking) by multiples or submultiples of discrete values of: the mass ratiosq, the semi-major axesa, periodsT, and velocitiesv of the reduced mass. This indicates the existence of a discrete unit of actionL=(1/2)×potential energy xperiod. Postulates about equivalent states of angular momenta for different orbital parameters are introduced, being this coherent with the analysis of the up-to-date data. Among other examples of the application of such equivalence postulates, we haveL(M) (W-type of the WUMa systems)L(M) (main group of the Algol binaries). The quantum units of action seen here are equivalent to those seen in the solar system in one of our previous works. From comparisons with galaxies and single stars, it is evidence that there is not an unique universal functionL=AM ^b, when the fine structure of the relation is analysed: each type of object has its own coefficients,A, b. It sems to be that there are an upper and a lower limit for all the possible functions. The upper limit isL=A _gM^5/3, withA _g1 associated to periodsT Hubble time, and the lower limit isL=GM ^2/c, with 1. The existence of the upper limit can be investigated with studies of pairs of galaxies, and the lower limit can be tested with analysis of single G, K, M stars. The quantical hypothesis introduced here can be checked definitely, when available larger samples of data with low errors, with similar quality as the selected list of almost 80 eclipsing binaries (mainly detached systems) analysed here.  相似文献   

Evaluation of the recharge processes and impacts of irrigation on groundwater using CFCs and radiogenic isotopes in the Silao-Romita basin, Mexico     

Axel Horst  Jürgen Mahlknecht  Broder J. Merkel  Ramon Aravena  Yann R. Ramos-Arroyo 《Hydrogeology Journal》2008,16(8):1601-1614

The recharge processes in the overexploited aquifer of the Silao Romita basin, central Mexico, were investigated by means of gaseous tracers (chlorofluorocarbons, CFCs) and radioactive isotopes (C-14, tritium). CFC concentrations varied between 0.06 and 12 pmol/l (CFC-11), 0.03 and 1.7 pmol/l (CFC-12), and <0.01 and 0.23 pmol/l (CFC-113). CFC concentrations are controlled by irrigation return flow which became apparent by the comparison with tritium. Tritium activities ranged from 0 to 3.5 TU. The calculated mean residence times of 70 to more than 300 years are considerably lower than the ages estimated based on the CFCs data. These data showed that CFCs were not appropriate for groundwater dating in this particular area but the CFCs were suitable as a qualitative measure of the magnitude of irrigation return flow which proved to be a significant source of recharge in the irrigated areas. Radiocarbon activities were in the range of 6–109 pmC. Carbon-13 values varied between –11.9 and –7.2‰ VPDB. Modelling of carbon isotopes with NETPATH along a plausible flow path reveals considerable influences of exchange with soil CO₂ and carbonate dissolution. Radiocarbon data indicate, at least in one case, the existence of groundwaters with residence times of more than 10,000 years.  相似文献   

Properties of theβ pictoris disc deduced from optical imaging polarimetry     

Ramon D. Wolstencroft  S. M. Scarrott  T. M. Gledhill 《Astrophysics and Space Science》1995,224(1-2):395-398

The asymmetries in the brightness structure and levels of polarization between the two sides of the Pic disc are discussed. The possibility of these differences being caused by a planet, or planets, within the circumstellar disc is investigated.  相似文献