Tajo Basin Research Articles

HRTEM evidences of Tajo Basin mineralogical complexity: Crystal chemistry and genetic relationship

In this study, a new genetic interpretation of the Mg-bentonite deposits from the Tajo Basin is given through a high-resolution transmission electron microscopy study. These bentonites, belonging to the Green Clays and Pink Clays lithostratigraphic units, are afforded by the sum of processes occurring during the weathering of parent rocks and the evolution of the materials by the transformation of phyllosilicates in the sedimentary environment. The primary phyllosilicates progressively change their microstructure and crystal chemistry, resulting in very complex clay minerals assemblages. The Green Clays are relatively enriched in Al, Fe, and K, whereas Pink Clays are enriched in Mg and Si, corresponding to almost pure trioctahedral smectites. Although the point analysis of the particles showed a continuous compositional variation that evidences their genetical relationship, they were statistically classified in groups that represented the evolution from the primary phyllosilicates (dioctahedral and trioctahedral micas and chlorites) to the final products comprise very low-charge saponite and scarce sepiolite. The intermediate steps in this transformation included the following: 1) particles of structural formulas with an excess of octahedral cations that were interpreted as hydroxy-interlayer minerals and 2) random mixed-layers of illite/smectite progressively poorer in illitic component as the more evolved particles. Green Clays correspond to the state of transformation to smectites where partially transformed detrital components were still predominant, corresponding to more proximal facies, whereas Pink Clays represented most evolved stages in the mineral transformation. The alternation of Green and Pink Clay levels was related to climatic changes with alternation of wetter and drier periods.

Seismic structure and composition of the southern central Iberian crust: The ALCUDIA wide angle seismic reflection transect

The nature of the crust beneath central Iberia was estimated by a wide-angle seismic reflection/refraction transect, ALCUDIA-WA, which sampled the southern half of the Variscan Central Iberian Zone, covered in the north by the Cenozoic Tajo Basin. The shot gathers recorded by vertical component sensors revealed well defined P- and S-wave phases. These arrivals were modeled by an iterative forward approach providing 2D crustal models showing variations in the velocity distribution with upper crustal P- and S-wave velocities increasing northwards. The lower crust P-wave velocities are homogeneous along the profile while the S-wave velocities slightly increase northwards. The Moho is placed at 32 km depth in the southern edge of the profile, deepening northward down to 35 km beneath the Tajo Basin. The Poisson's ratio, calculated from P- and S-wave velocities, varies along the profile at upper crustal depths. The highest values are located below the Mora and Pedroches batholiths. These resulting physical properties can serve to constrain the crustal composition by comparing them with laboratory measurements on rock samples. Our results suggest that the upper crust in the southern and central segments of the ALCUDIA profile is made up of low-grade metasedimentary rocks, while the northern segment is dominated by igneous rocks, in agreement with the surface geology. Separated by a sharp boundary located between 12 km (south) and 18 km (north) depth, the lower crust is more homogeneous and shows low Poisson’ ratios compatible with a rather felsic composition. However, outstanding lamination described in coincident vertical incidence data indicates some degree of intercalation with mafic components.

Influence of Hydrogeochemistry on Tunnel Drainage in Evaporitic Formations: El Regajal Tunnel Case Study (Aranjuez, Spain)

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

What can seismic noise tell us about the Alpine reactivation of the Iberian Massif? An example in the Iberian Central System

Abstract. The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750–800 m, and the Tajo Basin to the south, lying at 450–500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5–4 Hz, stations placed at ∼ 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny.

Little Ice Age, Palaeofloods and human adaptation on the Jarama River (Tajo Basin, Central Spain) from documentary proxy data

This research assesses the close relationship between river history and human adaptation by combining the study of the migration of channels on the floodplain, the temporal distribution of floods, and human adaptation to the fluvial environment during the Little Ice Age (LIA) period on the Jarama River section situated between the mouths of two tributaries, the Henares and Manzanares. The methodology consists of the employment of abundant documentary records from the 14th to 19th centuries related to the response of society to hydrological dynamics within changing river patterns. The management and delimitation of land ownership, along with the readjustments and modifications therein, allow the inference of the changes that have taken place in the river throughout history. These changes include meander cut-offs, the abandonment of a channel fragment and aggradation in the alluvial plain, all of them located in different areas within the study area and with different historical timeframes. A relationship exists between changes in fluvial dynamics and the times of the greater abundance of floods. An initial change in the alluvial plain occurred in the Middle Ages as a result of the abandonment of the medieval channel and the creation of a new channel. The second change occurred between the 15th and 17th centuries and affected the properties on the right-hand bank of the river. Since the 18th century, the abandonment of and reduction in meanders and the aggradation at the Manzanares-Jarama mouth have created a new alluvial plain of the river. The different phases of the LIA defined herein coincide with much of the palynological and dendrochronological research conducted in other areas of the southwestern fringe of Europe. From the historical point of view, critical changes appear to be associated with some LIA phases. Furthermore, the progressive transformation of communal lands into public or private property could be promoted by the intense floods recorded since the 15th century. The Maunder and Dalton Minimums occurred together with an increase in the area assigned for agriculture on the alluvial plain; this land use type continued to grow during the 19th and 20th centuries.

Lithospheric image of the Central Iberian Zone (Iberian Massif) using global-phase seismic interferometry

Abstract. The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau in two sectors – the northern Duero Basin and the Tajo Basin to the south. The topography of the area is highly variable with the Tajo Basin having an average altitude of 450–500 m and the Duero Basin having a higher average altitude of 750–800 m. The Spanish Central System is characterized by a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures during the Alpine orogeny. The high topography is, most probably, the response of a tectonically thickened crust that should be the response to (1) the geometry of the Moho discontinuity, (2) an imbricated crustal architecture, and/or (3) the rheological properties of the lithosphere. Shedding some light on these features is the main target of the current investigation. In this work, we present the lithospheric-scale model across this part of the Iberian Massif. We have used data from the Central Iberian Massif Deformation (CIMDEF) project, which consists of recordings of an almost-linear array of 69 short-period seismic stations, which define a 320 km long transect. We have applied the so-called global-phase seismic interferometry. The technique uses continuous recordings of global earthquakes (>120∘ epicentral distance) to extract global phases and their reverberations within the lithosphere. The processing provides an approximation of the zero-offset reflection response of a single station to a vertical source, sending (near)-vertical seismic energy. Results indeed reveal a clear thickening of the crust below the Central System, resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust–mantle boundary is mapped as a relatively flat interface at approximately 10 s two-way travel time except in the Central System, where this feature deepens towards the NW reaching more than 12 s. The boundary between the upper and lower crust is well defined and is found at 5 s two-way travel time. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13 and 18 s, and probably related to the Hales discontinuity.

Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites.

Structure of an intraplate fold-and-thrust belt: The Iberian Chain. A synthesis

The Iberian Chain is a complex intraplate fold-and-thrust belt resulting from the convergence between the Eurasian, Iberian and African plates during the late Eocene to the Miocene. The main trend of its contractionalstructures is NW-SE, but E-W, NE-SW and N-S-trending structures are also present. The boundaries of the chain with its surrounding foreland basins are always thrusts. The North-Iberian Thrust separates thechain from the Ebro Basin to the North, while the Serrania de Cuenca Thrust makes the SE boundary of the chain, separating it from the Tajo Basin and La Mancha foreland areas. Between these thrusts, thecontractional structure is basement-involved, while South of the Serrania de Cuenca Thrust only Mesozoic and Cenozoic rocks are involved in the thrust-system, detached in the evaporitic Triassic materials. Twoparts can be differentiated considering the major structure of the chain. The western and central areas hold two major anticlinoriums separated by the Almazan Synclinorium. East of the Teruel Depression, E-WstrikingN-verging thrusts in the North, and NW-SE-striking S-verging thrusts in the center and South are the dominant structures.The crust thickened during the Cenozoic contraction generating a mean crustal thickening of about 5km. The horizontal shortening obtained from cross-sections is 32km, and from a density-gravity section of 57.5km.These two values may be considered end values.The relief of the Iberian Chain has a strong areal coincidence with the contractional structures and the thickened crust, indicating that they are genetically related.

Geochemistry and Biomarker Analysis of the Bentonites from Esquivias (Toledo, Spain)

The Tajo Basin is one of the richest in Mg-clays known around the world. Mg-bentonites, kwon as pink clays and green clays, alter in the Intermediate Unit of the Miocene sediments. In this work, a new approach to the genesis of these bentonites is performed by studying for the first time the biomarkers present in these clays in relation to the mineralogy and geochemistry, as well as using discriminatory criteria between green and pink clays. Samples were collected at a quarry of Mg-bentonites, in the proximities of Esquivias (Toledo, Spain). Mineralogical characterization and semi-quantification (X-ray diffraction (XRD)) allowed a well-defined classification according to the mineralogical content of the samples to be established, differentiating four associations. Geochemical analyses are clearly linked to the mineralogy and provide criteria to differentiate the genesis of the materials studied. In this regard, green clays are interpreted as having a more detrital character than pink clays, which present a more authigenic character. Biomarkers (n-alkanes and n-alkanoic acids) were studied, not showing a clear link with the mineralogy as in the case of the geochemistry, but providing interesting information about the origin and degradation of the organic matter. Pink clays have higher contents in biomarkers than green clays, providing a discriminative criterion.

Identification and classification of mineralogical associations by VNIR-SWIR spectroscopy in the Tajo basin (Spain)

41 soil samples were collected at the Tajo Basin (Spain), in an area where Mg-rich clays are benefitted, whit the aim of studying their spectral response in the Visible, Near Infrared (VNIR) – Short Wave Infrared (SWIR) range (350–2500 nm) in terms of mineralogical composition and exploring the possibility of using these data as the basis of a geological mapping through hyperspectral imaging in this wavenumber interval in future research. The samples, belonging to nine different stratigraphic units, were characterized by X-Ray diffraction and VNIR – SWIR laboratory reflectance spectroscopy. The mineralogical associations are formed by complex mixtures of carbonates, gypsum, quartz, feldspars, illite, and smectites in variable proportions depending on the stratigraphic unit. The samples were classified into different groups and subgroups according to their spectral response. The resulting groups allow to extrapolate certain type-spectra to different mineralogical associations corresponding to the stratigraphic units sampled within the area of study. This work is of upmost importance for future works through remote-sensing techniques using VNIR – SWIR imaging of the area. The classification of the samples in different groups, according to their spectral response, and their attribution to the different stratigraphic units sampled, according to their mineralogical content, could help improve the geological mapping of the area of study as well as detecting deposits of Mg-rich clays of economic interest.

Exploring the distribution of groundwater Crustacea (Copepoda and Ostracoda) to disentangle aquifer type features—A case study in the upper Tajo basin (Central Spain)

AbstractOne of the most challenging questions in the assessment of groundwater ecosystem health is whether assemblages of groundwater biota can be used reliably as biomarkers. In this study, we aimed to (a) explore the diversity, distribution, and ecological composition of groundwater Crustacea, Copepoda, and Ostracoda communities from six aquifers in Central Spain and (b) relate the structure of the species assemblages to the aquifers' hydrogeological conditions, habitat features, and hydrochemistry. The datasets were simultaneously collected from 24 boreholes drilled in six unconfined aquifers from the upper part of the Tajo catchment. Our results show that the assemblages are primarily influenced by the specific hydrogeological conditions of the aquifer, determined by groundwater flow, supply of organic matter from the surface, and habitat features, whereas the aquifer's hydrochemistry has only a marginal effect. The assemblages from the Tertiary detrital aquifer were the most diverse, containing a mixture of stygobiont and nonstygobiont species distributed preferentially in the recharge area of the aquifer, characterized by medium hydraulic conductivity, high surface input and relatively high water renewal. The Quaternary alluvial aquifer type was found to have a moderate richness with several hyporheic dwellers, indicating an active surface/groundwater exchange with the adjacent stream channel. In contrast, the carbonate aquifer type was less diverse but markedly distinct owing to the high occurrence of stygobionts. Our results provide a step forward in exploring the groundwater biodiversity of aquifers in Spain and towards incorporating an ecological perspective into overall assessments of groundwater status.

Granulometrical, mineralogical and geochemical characterization of loess deposits in the Tajo Basin

Loess research has the merit of enabling reconstructions of Pleistocene sedimentation dynamics in many parts of the world. However, there is still very few information regarding the occurrence of loess deposits in the Mediterranean area, even though such records may provide a unique opportunity to investigate landscape evolution for a period for which terrestrial archives are very rare in this region. This paper presents the first results of investigations on a loess sequence in the middle Tajo Valley in central Spain. Findings from detailed granulometrical, mineralogical, geochemical, and grain morphological analyses help to give a first overview on character and composition of these deposits. Very high levels of carbonates (∼60%), but also of gypsum, both to large extents of primary origin, indicate the incorporation of material derived from marls and limestone. Furthermore, we found evidence that allows deduction of possible loess proveniences more precisely. Dolomite contents of up to 20% indicate that the Iberian Range might have been an important source area of loess sediments. The fact that these uplands are located to the east seems to be opposed to the common assumption of prevailing west winds for glacial periods. The studied sequence (Paraiso profile) is one of seven sections that have been investigated as part of a programme to reconstruct Upper Pleistocene landscape dynamics in central Spain. In this context, the detailed characterisation of sediment properties is crucial for discussing loess proveniences and sedimentary environments.

The structure and nature of the Moho beneath Central Iberia

The Moho is the most conspicuous feature in the ALCUDIA deep normal incidence and wide-angle seismic reflection datasets acquired across the Central Iberia Zone. This discontinuity appears to be sub-horizontal with a slight dip toward the center of the Iberian Peninsula, beneath the Tajo Basin. Densely spaced wide-angle seismic reflection data reveal conspicuous PmP and SmS reflections in the shot records. These reflections, arriving over a 1.5s time window and characterized by a relatively low frequency content, are used to infer the internal structure and characteristics of this crustal boundary in an effort to place constraints on its nature beneath the studied area. The wide-angle shot records were processed in order to generate low-fold stacks that reveal gradual deepening of Moho PmP phases from 10.2s TWT (~31km) in the Central Iberian Zone to 11.8s TWT (~36km) beneath the Tajo Basin. The Moho seismic signature was the main objective of a series of 1-D and 2-D synthetic modeling simulations. Reflectivity modeling was used as the 1-D modeling approach and an elastic finite difference scheme was used for the 2-D modeling. The Moho can be considered to be a self-similar/fractal heterogeneous media with a bimodal velocity distribution, alternating crustal and mantle values, with horizontal correlation lengths that range between 1 and 4km and vertical correlation lengths that range from 0.2 to 1km. The depth of this boundary is most probably the result of late to post-variscan re-equilibration processes affecting a previously deformed and laminated lower crust. The mechanisms that took part in this process might have differed to the north and south of the sampled Central Iberian Zone, being more thermally induced to the north, near the Central System. Processes leading to the layered structure of the Moho boundary, either tectonic or magmatic, should be further investigated.

Lithospheric velocity model across the Southern Central Iberian Zone (Variscan Iberian Massif): The ALCUDIA wide-angle seismic reflection transect

A P wave seismic velocity model has been obtained for the Central Iberian Zone, the largest continental fragment of the Iberian Variscan Belt. The spatially dense, high-resolution, wide-angle seismic reflection experiment, ALCUDIA-WA, was acquired in 2012 across central Iberia, aiming to constrain the lithospheric structure and resolve the physical properties of the crust and upper mantle. The seismic transect, ~310 km long, crossed the Central Iberian Zone from its suture with the Ossa-Morena Zone to the southern limit of the Central System mountain range. The energy generated by five shots was recorded by ~900 seismic stations. High-amplitude phases were identified in every shot gather for the upper crust (Pg and PiP) and Moho (PmP and Pn). In the upper crust, the P wave velocities increase beneath the Cenozoic Tajo Basin. The base of the upper crust varies from ~13 km to ~20 km between the southernmost Central Iberian Zone and the Tajo Basin. Lower crustal velocities are more homogeneous. From SW-NE, the traveltime of PmP arrivals varies from ~10.5 s to ~11.8 s, indicating lateral variations in the P wave velocity and the crustal thickness, reflecting an increase toward the north related with alpine tectonics and the isostatic response of the crust to the orogenic load. The results suggest that the high velocities of the upper crust near the Central System might correspond to igneous rocks and/or high-grade metamorphic rocks. The contrasting lithologies and the increase in the Moho depth to the north evidence differences in the Variscan evolution.

Thenardite after mirabilite deposits as a cool climate indicator in the geological record: lower Miocene of central Spain

Abstract. Salt deposits are commonly used as indicators of different paleoclimates and sedimentary environments, as well as being geological resources of great economic interest. Ordinarily, the presence of salt deposits is related to warm and arid environmental conditions, but there are salts, like mirabilite, that form by cooling and a concentration mechanism based on cooling and/or freezing. The diagenetic transformation of mirabilite into thenardite in the upper part of the lower Miocene unit of the Tajo basin (Spain) resulted in the largest reserves of this important industrial mineral in Europe. This unit was formed in a time period (~18.4 Ma) that, in other basins of the Iberian Peninsula, is characterized by the existence of particular mammal assemblages appropriate to a relatively cool and arid climate. Determining the origin of the thenardite deposits as related to the diagenetic alteration of a pre-existing mirabilite permits the establishment and characterization of the sedimentary environment where it was formed and also suggests use as a possible analog with comparable deposits from extreme conditions such as Antarctica or Mars.

Structures and geometries of the Tajo Basin crust, Spain: Results of a magnetotelluric investigation compared to seismic and thermal models

The Tajo Basin and Betic Mountain Chain in the south central region of the Iberian Peninsula were chosen for investigation in the first phase of the magnetotelluric (MT) component of the PICASSO (Program to Investigate the Convective Alboran Sea System Overturn) project. The MT results provide information about the electrical conductivity distribution in previously unprobed subsurface regions, as well as complimenting and enhancing results of prior geological and geophysical investigations thereby enabling the definition of a petrological subsurface model and a comprehensive understanding about the tectonic setting. Two-dimensional (2-D) inversion of the MT data provides enhanced insight into Iberian subsurface geology in the crust. The most striking features of the final model are (i) a distinct vertical interface within the Variscan basement beneath the center of the Tajo Basin that is spatially associated with the boundary between regions with and without substantial Alpine deformation, and (ii) a middle to lower crustal conductive anomaly that can be related to remnants of asthenospheric intrusion in connection with Pliocene volcanic events in the Calatrava Volcanic Province. For the latter, effects of hydrous phases are inferred that may originate from dehydration processes within the subducting slab beneath Alboran Domain and Betic Mountain Chain.

The thermal state and strength of the lithosphere in the Spanish Central System and Tajo Basin from crustal heat production and thermal isostasy

In this work we have modeled the thermal structure of the lithosphere of the Spanish Central System and the Tajo Basin, and their implications for lithospheric strength. For this, we have used refined heat-producing elements (HPE) values to obtain new estimates of heat production rates in the Spanish Central System and Tajo Basin areas, which have been used joined to the relation between topography and thermal structure of the lithosphere to calculate the best-fit surface heat flows in the study area. Moreover, we have implemented a temperature-dependent thermal conductivity (appropriate for olivine) for the lithospheric mantle to improve the calculations of temperature profiles in the mantle. The geotherms so obtained, together with the implementation of a new rheological law for the upper lithospheric mantle, have been used to calculate refined estimations of the strength and effective elastic thickness of the lithosphere. We have obtained surface heat flow values of 84mWm−2 and ∼82mWm−2 for the Spanish Central System and the Tajo Basin, respectively. The thermal state of the lithosphere affects mantle temperatures, and hence may be playing an important role in the uplift and maintenance of the Spanish Central System.

El valor del uso del agua en el regadío de la cuenca del Segura y en las zonas regables del trasvase Tajo-Segura

This study calculates the use value of water in the irrigated agriculture of the Segura basin and in the irrigated areas served from the Tajo-Segura transfer. Water is valued using a non-linear mathematical programming model that allocates water and irrigated land among crop activities in each of the 64 Water Demand Units of the basin. The marginal and average value of water for the basin are 0,52 €/m3 and 0,81 €/m3 respectively, with marked differences between areas. Irrigation in the Segura basin generates an average annual farm net margin of 879 million €/year, whereas the average annual value of resources transferred from the Tajo basin has been conservatively estimated at 169 million Euros.

Morphological and ecological characterization of Batrachospermales (Rhodophyta) in the Jarama Basin, Iberian Peninsula

Five populations of freshwater red algae were investigated between February 2008 and September 2009 in four segments of the Jarama River Basin (Tajo Basin), Iberian Peninsula, between 40-41◦ N, 3-4◦ W, at 700 to 1200 m altitude. Three species were documented (Batrachospermum gelatinosum, Lemanea fluviatilis and Paralemanea catenata) and information was collected about includes their morphology and the physical and chemical characteristics of the water. All the taxa have been reported previously, but the present work includes the first detailed morphological description of red algae in the region and their ecological preferences. The waters in these study sites are cool to temperate (5-17 ◦C), acid to circumneutral (pH 6.3-7.5) and with a low ion concentration (specific conductivity 77-270 μS cm−1). Two groups were distinguished on the basis of nutrient concentration. The first group, which included B. gelatinosum and L. fluviatilis, is found in clean water with low nutrient concentration, while the second group, which included P. catenata, occurred in nutrient-rich water. Gametophytes of L. fluviatilis and P. catenata were present in all seasons, with the highest percentage cover in autumn and winter corresponding to high current velocity and low water temperature. However, gametophytes were longest, and spermatangial sori and carposporophytes were most abundant in spring when current velocity was low and water temperature was high. The distribution of Batrachosermales from the Jarama Basin showed a strong affinity with temperate regions of central Europe and floras of other continents.

Effective elastic thicknesses of the lithosphere in the Central Iberian Peninsula from heat flow: Implications for the rheology of the continental lithospheric mantle

The traditional view of the rheology of the continental lithosphere, sometimes known as the “jelly sandwich model”, consists of a strong upper crust, a weak lower crust, and a strong upper lithospheric mantle. Some authors argue, however, that the lithospheric mantle is weak and contributes little to the total strength and the effective elastic thickness of the lithosphere; this weakness is claimed to be due to the mantle being wet or subjected to temperatures higher than usually believed. This paper uses the relationship between rheology of the lithosphere and heat flow to calculate theoretical effective elastic thicknesses for three regions of the central Iberian Peninsula (the Duero Basin, the Spanish Central System and the Tajo Basin), taking into account the contribution of the crust and the lithospheric mantle, for dry and wet rheologies. We found that a wet peridotite rheology for the lithospheric mantle is generally consistent with independent (based on Bouguer coherence or flexural modeling) estimates of the effective elastic thickness for the study area, whereas a dry peridotite rheology cannot be reconciled with them. Moreover, the contribution of the mantle to the bending moment of the lithosphere, and therefore to both the effective elastic thickness and the total strength of the lithosphere, is important, and it may even be the dominant contribution. Therefore, the jelly sandwich model may be considered valid for the central Iberian Peninsula.