Characterisation of the Nocturnal Boundary Layer at a Site in Northern Spain

The availability of well-calibrated meteorological data for a 10-month period on a 100-m tower has allowed a statistical study to be carried out of many boundary-layer variables. The analyses are restricted to nighttime conditions with stable stratification most of the time, allowing the checking of a number of similarity proposals and the quantifying of the frequency of the different nighttime regimes. We study in detail two typical nights at the site: one weakly stable and one with very strong stratification, highlighting the different aspects between the nights.     

Trace elements in high-S subbituminous coals from the teruel Mining District, northeast Spain

The elemental composition of high temperature ash (750°C) and forms of S were studied in 25 coal seams from the Escucha Formation (Middle Albian) in the Teruel Mining District, northeast Spain. The principal analytical method was ICP-MS, but ICP-ES was also used in the determination of some trace elements. The analytical data show wide ranges of trace element cotnents among the coal seams studied, even in the vertical profile of a single coal seam. These wide ranges of the trace element concentrations are attributed to both syngenetic and epigenetic processes.When a comparison was made between the average trace element contents of the Teruel Mining District coals, and those of the average content in worldwide coals, the Teruel coals show slightly higher concentrations of Be and U, and lower concentrations of Ba, Cd, Mn, Pb, Sr and Zr. Further, three main groups of trace elements were differentiated on the basis of the inorganic/organic association: (1) trace elements with inorganic affinity; Ba, Ce, Co, Cr, La, Mn, Ni, Rb and Zr. Between these, Ba, Ce, Cr and Rb show a well defined correlation with the clay mineral content, and Co and Ni with pyritic-S content; (2) trace elements with an intermediate (mixed) affinity; As, Cd, Cu, Dy, Er, Eu, Gd, Ge, Ho, Lu, Mo, Nd, Pb, Pr, Sb, Sm, Sr, Tb, Th, Tm, U, Yb and Zn. In this group, As, Cd, Cu, Ge, Mo, Th, U and Zn show a weak trend associated with the mineral matter and Sr with the organic matter; and (3) Be shows an organic affinity. The high mineral matter content (21.3% HTA) of the Teruel coals may account for the great number of elements with inorganic affinity. This classification represents a general trend, but the results show that the affinities of some trace elements (e.g. As, Sb and Zn) may vary from one coal seam to another in the Teruel Mining District.     

Nannofossils: the smoking gun for the Canarian hotspot

The origin of volcanism in the Canary Islands has been a matter of controversy for several decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of superheated mantle material. However, the debate has recently come to a conclusion following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which tell us about the age and growth history of the western‐most island of the archipelago. Light coloured, pumice‐like ‘floating rocks’ were found on the sea surface during the first days of the eruption and have been shown to contain fragments of pre‐island sedimentary strata. These sedimentary rock fragments were picked up by ascending magma and transported to the surface during the eruption, and remarkably retained specimens of pre‐island Upper Cretaceous to Pliocene calcareous nannofossils (e.g. coccolithophores). These marine microorganisms are well known biostratigraphical markers and now provide crucial evidence that the westernmost and youngest island in the Canaries is underlain by the youngest sediment relative to the other islands in the archipelago. This finding supports an age progression for the onset of volcanism at the individual islands of the archipeligo. Importantly, as fracture‐related volcanism is known to produce non‐systematic age‐distributions within volcanic alignments, the now‐confirmed age progression corroberates to the relative motion of the African plate over an underlying mantle plume or hotspot as the cause for the present‐day Canary volcanism.     

Le magmatisme basique filonien néoprotérozoïque de la boutonnière de Zenaga, Anti-Atlas central, Maroc: pétrologie, géochimie et signification géodynamique

Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P₂O₅, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding.     

Accuracy of GPS-derived relative positions as a function of interstation distance and observing-session duration

 Ten days of GPS data from 1998 were processed to determine how the accuracy of a derived three-dimensional relative position vector between GPS antennas depends on the chord distance (denoted L) between these antennas and on the duration of the GPS observing session (denoted T). It was found that the dependence of accuracy on L is negligibly small when (a) using the `final' GPS satellite orbits disseminated by the International GPS Service, (b) fixing integer ambiguities, (c) estimating appropriate neutral-atmosphere-delay parameters, (d) 26 km ≤ L ≤ 300 km, and (e) 4 h ≤T ≤ 24 h. Under these same conditions, the standard error for the relative position in the north–south dimension (denoted S _n and expressed in mm) is adequately approximated by the equation S _n =k _n /T ^0.5 with k _n =9.5 ± 2.1 mm · h^0.5 and T expressed in hours. Similarly, the standard errors for the relative position in the east–west and in the up-down dimensions are adequately approximated by the equations S _e =k _e /T ^0.5 and S _u =k _u /T ^0.5, respectively, with k _e =9.9 ± 3.1 mm · h^0.5 and k _u =36.5 ± 9.1 mm · h^0.5. Received: 5 February 2001 / Accepted: 14 May 2001     

Observational and Numerical Simulation Study of a Sequence of Eight Atmospheric Density Currents in Northern Spain

A sequence of eight atmospheric density current fronts occurred in consecutive days are identified and analyzed using micrometeorological time series and numerical simulations. Observations were collected in the context of the INTERCLE project, which took place from September 2002 to November 2003 at the CIBA (Research Centre for the Lower Atmosphere) site located over the northern Spanish plateau. Numerical simulations used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km). Both observations and simulations agree that the arrival of the density currents are characterized by a sharp change in temperature, wind velocity, wind direction and specific humidity and a source of intermittent turbulence. However, comparison between model and observations shows that the model predicts the intrusion of the density currents earlier than is observed. In addition, wavelet techniques applied to the data help distinguish the different scales present in the events, and therefore can reveal traces of gravity waves induced by the arrival of the density currents.     

An integrated thermodynamic mixing model for sphalerite geobarometry from 300 to 850°C and up to 1 GPa

An asymmetric, Margules-type, solid solution model was used to model the mixing behavior of Fe-Zn sphalerites. The model is based on an analysis of experimental results from fifteen independent data sources. After a careful, stepwise, analysis of the available runs, the solid solution model was constrained using a refined experimental database of 279 experiments which were simultaneously regressed to obtain the excess parameters and a general geobarometric equation. The model indicates that, when pressures are low, the value of γ_FeS^Sph, which is always greater than one, is higher at low FeS contents and an increase in temperature causes it to decline. However, for certain compositions γ_FeS^Sph values might be slightly less at low T than at high T. This behavior is corrected when pressure increases, regardless of the composition. The excess Gibbs free energy has positive values at any P&T while it is asymmetric. Pressure increases the value of the excess free energy. On the other hand, the Gibbs free energy of mixing is always negative, with a single minimum that tends to move towards Fe-poorer compositions as the pressure goes up. An increase in temperature leads to a more negative Gibbs free energy mixing function suggesting that increasingly Fe-poorer sphalerite would be expected at high temperatures and pressures. The application of the solid solution model to a selection of case-studies provided results which are consistent with independent pressure estimates. However, the pressure determinations for sphalerite + pyrite + pyrrhotite and sphalerite + pyrrhotite assemblages are very sensitive to uncertainties in the composition of the phases involved and, to a lesser extent, to temperature. The results of the application of the model to a field case (scheelite-mineralized Hercynian veins from the Central Pyrenees) were also consistent when compared with independent pressure-constraining silicate assemblages. Thus, the solid solution model described in this paper provides a workable framework with which to compute the pressures of the formation of rocks over a wide range of geological conditions.     

Subsistence practices in western Mediterranean Europe during the Final Gravettian. Zooarchaeological and taphonomic analysis of faunal remains from level D of Arbreda Cave (Serinyà, NE Iberian Peninsula)

During the Final Gravettian, the Reclau Caves (northeast Iberia) were intensively occupied by hunter-gatherer communities. The study of residential level D (c. 25.4–19.7 kyr bp ) of Arbreda Cave offers a new view of subsistence strategies of communities which inhabited the northeast of the Iberian Peninsula, a transition region between the steppe-tundra and the Iberian wooded steppe biomes, during Greenland Stadial 3. Presented here are the results of the zooarchaeological and taphonomic analysis of ungulate and carnivore remains recovered from level D. The study confirms that the faunal assemblage of this level was mainly brought there by humans. The zooarchaeological analysis indicates selective hunting based on the exploitation of familial groups of horses and deer, while other ungulate taxa appear to be infrequent. Hunter-gatherers frequented the site throughout the year, but more intensive use in spring is indicated by subadult sensu lato horses. There was extensive exploitation of ungulate carcasses: various butchery activities, marrow extraction, the use of bone as fuel and ‘less elaborate tools’ are documented. Carnivore canines were exploited to produce ornaments. The great dominance of horses reveals cold conditions and the expansion of open environments related to the chronology span of Greenland Stadial 3.