On the role of the Hercynian and Alpine thrusts in the Upper Paleozoic rocks of the Central and Eastern Pyrenees

Abstract

The structure of the Pyrenean pre-Hercynian rocks involved in the “Axial Zone” antiformal stack, results from the association of Hercynian cleavage-related folds and Hercynian and Alpine thrusts. Some of these Alpine and Hercynian thrusts separate thrust sheets in which Upper Paleozoic rocks, Devonian and pre-Hercynian Carboniferous, exhibit different lithostratigraphy and internal structure.

In order to know both, the original Devonian facies distribution and the structural characteristics, the effects of the Alpine and the Hercynian thrusts must be considered. If a conceptual restored cross-section is constructed taking into account both the Alpine and Hercynian thrusts, a different Devonian facies distribution is achieved. Devonian carbonatic successions were originally located in a northernmost position, whereas sequences made by alternations of slates and limestones lie in southernmost areas. Moreover, a N-S variation of the Hercynian structural style appears. In the northern units thrusts are synchronous to folding development and they are the most conspicuous structures. In the intermediate units, thrust postdate cleavage-related folds, and in the southernmost units several folding episodes, previous to the thrusts, are well developed.

We present some examples which enable us to discuss the importance of the Hercynian and Alpine thrusts in the reconstruction of the Pyrenean pre-Alpine geology.     

Laboratory set-up for studying ices at the MIR and FIR region

H₂O, CO and CO₂ ices are condensed on carbonaceous and silicate dust grains in dense interstellar clouds and circumstellar environments. The presence of these ices is inferred by analysing their infrared (IR) spectra. The upcoming Herschel space observatory (HERSCHEL) and ground-based astronomy project (ALMA) will provide new spectral data in the unexplored far infrared (FIR) and sub-millimetre range. In our laboratory we are developing instrumentation to study ices at IR region. One of the key components of our laboratory is a silicon composite bolometer in our IFS. This detector allows us to obtain spectra with a sensitivity much greater than that obtained with a standard deuterated triglycine sulphate (DTGS) detector working at room temperature and under vacuum conditions. We plan to collect mid infrared (MIR) and FIR spectra of simple ices and their mixtures and compare these with observational data. It is also planned to do a systematic laboratory study of the effects that ultraviolet (UV) photolysis and thermal annealing have on the ice band profiles and their structure.     

Consequences of Uncertainties in CO<Subscript>2</Subscript> Density for Estimating Net Ecosystem CO<Subscript>2</Subscript> Exchange by Open-path Eddy Covariance

Errors in the estimation of CO₂ surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85, (2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements of absolute CO₂ density (ρ _c ). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to reliably report ρ _c and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ _c in a semi-arid climate with large sensible heat fluxes (H _s ) and (wet) mineral deposition. When ρ_c is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO₂ uptake.     

The role of the Río de la Plata bottom salinity front in accumulating debris

The Río de la Plata, one of the most important South American estuarine environments, is characterized by a bottom salinity front that generates an ecotone between the river and the estuary. Based on bottom trawls and costal sampling we describe the distribution, types, and amount of debris found in the bottom and shoreline across this front. Plastics and plastic bags were the main debris types in both areas. Concentrations of total debris upriver the front were always significantly higher than downriver the front showing that the front acts as a barrier accumulating debris. Moreover, a large part of debris end ups accumulated in the coastal area upriver the frontal position. This area is particularly sensitive because the coastline encompasses an UNESCO Man and the Biosphere Reserve and a Ramsar site, and due to the ecological significance of the front for many valuable species.     

Characterisation of streamflow regimes in central Spain, based on relevant hydrobiological parameters

The biotic composition, structure, and function of aquatic, wetland, and riparian ecosystem depend largely on the hydrological regime (Poff, N.L., Ward, J.V., 1990. Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns. Can. J. Fisheries Aquat. Sci. 46, 1805–1818; Richter, B.D., Baumgartner, J.V., Wiginton, R., Braun, D.P., 1997 How much water does a river need? Freshwater Biol. 37, 231–249). Available flow data for many rivers in the world can be used to validate these ecological theories. There is a demand for studies that use hydrological indices to establish criteria, which serve to group together regime types at a local level. Once this has been done, these hydrologically similar groups can be used to identify communities of living organisms that are linked to specific aspects of the river's behaviour.

An approach to characterise flow regimes in the river network of the Tagus basin in Spain is presented. The river Tagus (río Tajo) is one of the seven major rivers of the Iberian peninsula. All hydrological data were acquired from the measurements made in the Tagus basin, at 25 gauging stations. Twelve variables were derived for each gauged site to describe variability and predictability of average streamflow conditions, and to describe the frequency, timing and intensity of high flow and low flow extremes.

A hierarchical clustering routine was used to identify similar groups of rivers as defined in terms of similar characteristics of their streamflow regime. The variables were also examined with simple correlations to determine if multicollinearity occurred, in order to reject redundant parameters or to identify similar behaviour trends between pairs of parameters. Some parameters have shown a tendency to increase or decrease along the east–west axis, suggesting that some of the studied characteristics may have a geographical cause.

Cluster analysis, with the values of the 12 parameters, reveals two main groups, each of which splits into two main subdivisions. One of these subgroups contains six rivers with similar characteristics, can be considered to be ‘classic regular rivers’, the stations in this first subgroup are mostly situated geographically close to each other. At the other end, we have found a subgroup, with a high variation of flows over the year and high flood flows; these rivers are highly irregular rivers with great changes. This regular–irregular gradient found between the groups is similar to that observed by others authors (Poff, N.L., Allan J.D., 1995. Functional organization of stream fish assemblages in relation to hydrological variability. Ecology 76, 606–627), and strong associations have been documented with compositions of populations and probably reflect differences in other similar important environmental factors.     

Groundwater arsenic distribution in South-western Uruguay

This is the first specific information regarding arsenic distribution of groundwater in SW Uruguay. Twenty-eight wells were sampled on the aquifers of Mercedes, Raigón and Chuy in five localities. The pH, specific conductivity and temperature were determined in the field. The hydrochemical characterization (major and trace elements) was carried out by both inductively coupled plasma-optical emission spectrometry and inductively coupled plasma-mass spectrometry. The occurring arsenic concentrations exceed the recommended threshold for drinking water of the World Health Organization (10 μg/l of As) in 22 samples, with more than 50 μg/l of As in two cases. The median, minimum and maximum concentrations were 0.1, 16.9 and 58.0 μg/l of As, respectively. The studied aquifers present a horizontal and a vertical variation of the concentrations as a whole as well as individually. The highest values were observed in the Mercedes Aquifer in the areas near the Uruguay River.