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Tartaj P.,CSIC - Institute of Materials Science | Morales J.,Laboratorio Of Estudios Cristalograficos Iactcsic Ugr | Fernandez-Dlaz L.,Complutense University of Madrid | Fernandez-Dlaz L.,Institute Geociencias CSICUCM
Crystal Growth and Design | Year: 2015

Mineralization studies on calcium sulfates when compared to those on phosphates and carbonates are relatively rare despite the economic relevance of these sulfates. A series of recent findings, however, have renewed the interest in calcium sulfate mineralization. These studies, similar to those on calcium carbonates and phosphates, have shown a richer than previously thought scenario especially at the nanoscale. Here, we intentionally use confinement reactors with fast exchange rates (organically/inorganically functionalized reverse micelles) to rapidly establish pathways relevant to calcium sulfate mineralization in solution (including long-term stabilization). Furthermore, we rationalize all the results on the basis of an adsorption model with solubility inputs for inorganic additives. Thus, the typical bassanite nanofibers involving oriented attachment are observed either at weak-adsorption conditions or in the presence of less soluble inorganic dopants. At strong adsorption conditions, nanofibers are no longer observed, and long-term stabilization of nanobassanites is chemically possible if calcium/carboxylate bridging bonds are established during the first stages of nucleation and growth (aliquots after 30 min are similar to 24 h and remain preserved after 5 months). The results here presented are thus important, as they suggest specific conditions for the stabilization of biogenic bassanites. Furthermore, our results suggest that when oriented attachment is no longer energetically favored at intermediate stages (presence of rounded nanoparticles instead of nanorods), gypsum crystallization still can occur from small nanobassanites, however, through a classical dissolution-recrystallization mechanism. © 2015 American Chemical Society.

Gonzalez P.J.,Complutense University of Madrid | Gonzalez P.J.,University of Western Ontario | Fernandez J.,Complutense University of Madrid | Fernandez J.,Institute Geociencias CSICUCM
Geology | Year: 2011

In unconsolidated, heterogeneous aquifer systems, low rates of pore-pressure diffusion of applied effective stresses due to the drainage of thick, low-permeability, clay-rich layers with time constants of decades to centuries cause delayed, residual permanent compaction and land subsidence. Current application of satellite differential radar interferometry (DInSAR-differential interferometric synthetic aperture radar) to estimate aquifer hydraulic properties (compressibility and/or storage) in these systems is limited by the temporal availability of synthetic aperture radar data (1992-present). In this paper we study the degree of aquifer compaction due to water extraction using DInSAR through an example in southeast Spain. Ground deformation data indicate large-scale deformation and in particular the discovery of the highest rates of groundwater-related land subsidence recorded in Europe (>10 cm/yr), affecting the Guadalentín River basin (>200 km2), the largest tributary of the Segura River. Modeling of the ground surface time series of the Guadalentín Basin indicates that deformation is mainly driven by nonlinear time-delayed flow processes in the underlying aquifer. After a drought period (1990-1995), the aquifer responded with an exponential decay of the land subsidence (lasting ~8 yr), suggesting transient groundwater pore-pressure flow. We show that multitemporal satellite radar interferometry analysis and its modeling can be a stimulating way to study nonlinear soil mechanics and groundwater fl ows at aquifers. A deeper understanding of such processes could help the management of water resources and land subsidence of unconsolidated coastal and Quaternary alluvial aquifers in a highly evolving climate region (the Mediterranean Sea and elsewhere). © 2011 Geological Society of America.

Borruel-Abadia V.,Institute Geociencias CSICUCM | Lopez-Gomez J.,Institute Geociencias CSICUCM | De la Horra R.,Complutense University of Madrid | Galan-Abellan B.,Complutense University of Madrid | And 6 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Until recently the climate of the Early-Middle Triassic at low latitudes was broadly considered as generally temperate-warm with no major climate oscillations. This work examines the climate of this period through a detailed study of the sedimentary, plant, soil and mineral records of continental rocks (Buntsandstein facies) in eastern Iberian basins. Our findings indicate temporal climate variations for these near equator (10°-14°N) regions and unveil the significance of such variations in the southern Laurasian domain. The climate of Iberia's Early Triassic was mainly dominated by alternating brief (<. 0.4. ma) arid and semi-arid climate periods, with two main arid periods documented at the end of the Smithian and middle Spathian. However, an initial short subhumid to semi-arid period was also observed in the late Spathian. Remarkably, this latter period appears just after an unconformity related to the tectonically induced Hardegsen Event in western Europe. It is also of interest that this short subhumid climate period is concurrent with the beginning of faunal and floral recovery in the basins examined. The Early Triassic ended again with a short very arid period. Although the beginning of the Anisian (Aegean) was represented by alternating arid and semi-arid to subhumid intervals, during the Bithynian and Pelsonian clearly wetter climates are recorded by the succession consisting of alternating semi-arid to semi-humid intervals. This general tendency was interrupted by three short but marked intervals, two humid intervals in the late Bithynian, and one arid period near the Bithynian/Pelsonian boundary. Iberia was crossed by prominent irregular highs separating marked corridors or isolated areas. This palaeogeography, prevailing since Variscan tectonics, clearly conditioned dominant climates and their geographical distribution. No clear climate belts developed in these conditions. However, isolated internal climate zones separated by elevated areas are identified. This palaeogeographic configuration and the low latitudinal position of Iberia determined central Iberia highs in the southernmost border of Laurasia, beyond which more humid conditions clearly extended towards the equator reaching the present-day Moroccan Meseta and Argana Basin. © 2015 Elsevier B.V.

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