Optically Stimulated Luminescence (OSL) of young palaeoflood sediments

Comunicación dada en el XIV Reunión Nacional de Cuaternario, 30 junio y 1-2 julio 2015, GranadaOptically Stimulated Luminescence (OSL) of young palaeoflood sediments): The challenge of accurately estimating the deposition age of incompletely-bleached samples in luminescence dating has motivated developments in both measurement and analysis methods over the last few years. In this study, we compare the behaviour of CAM and IEU models when applied to dose distributions from a sequence of eight recent (40-1000 yr) flash flood deposits, potentially affected by incomplete bleaching. These dose distributions were obtained from quartz single grains and quartz small multigrain aliquots (~30 grains). Comparison was made between the different measuring and analysing techniques applied. The most suitable method was assessed by comparison of these results with those available from independent age control. It is shown that the measurement of multigrain aliquots in combination with the minimum age model IEU on OSL dose distributions is appropriate for the accurate dating of young flash flood deposits.Peer reviewe

Estimación de la recarga en lechos fluviales mediante sondas TDR flexibles durante eventos de avenida (Río Andarax, Almería)

Acta de las VIII Jornadas de Investigación de la Zona no Saturada del Suelo (Córdoba, España - 2007)[ES] En este trabajo se describe la metodología y la instrumentación instalada en el cauce fluvial para la medida de la infiltración directa en la zona no saturada asociada a las crecidas en el río Andarax (Almería), y se presentan los datos preliminares registrados en el primer año de funcionamiento de la estación. El objetivo final de este seguimiento es cuantificar la recarga a largo plazo de los acuíferos aluviales someros, asociada a eventos de crecida. La estación de medida se localiza en las proximidades de la localidad de Gádor, y permite el registro de los contenidos de humedad en la zona no saturada mediante sondas TDR flexibles (15 en total) hasta los 10 m de profundidad. Igualmente, se dispone de sondas para el registro del niveles del agua superficial durante la crecida y de las variaciones del nivel piezométrico. Los resultados preliminares muestran claramente que la metodología utilizada permite obtener datos de infiltración en la zona no saturada del suelo de manera continua y en tiempo real con mínimas perturbaciones de suelo. El registro de un evento ocurrido el 7 de Enero de 2006, de duración estimada de 7 días y cuyo calado máximo se ha registrado en 7 cm, permite demostrar que el hidrograma de crecida tiene una respuesta clara en el contenido de humedad del suelo en el perfil estudiado, con aumentos de hasta el 5% de humedad en sondas a profundidades superiores a 9 m. Analizando los cambios ocurridos en el nivel freático podemos comprobar que los datos obtenidos en el perfil estudiado son extrapolables al conjunto de la zona no saturada y con ello elaborar una estimación de la recarga.[EN] This work describes the methodological procedure and the instrumentation installed to monitor the infiltration through the vadose zone associated with flood events of the Andarax River (Almeria). First, the preliminary data recorded in the station’s first functional year are presented and discussed. The final objective of this monitoring was to quantify the long-term shallow alluvial aquifer recharge related to flooding. The monitoring station is located near Gador, and records the moisture contents through the vadose profile using 15 flexible TDR probes (FTDR) reaching depths of 10 m. In addition, water surface and groundwater piezometric levels are recorded. The preliminary results clearly show that the methodology chosen permits the collection of real time and continuous infiltration data in the vadose zone with minimum soil disturbances. The 7 January 2006 event recorded, 7 days in length and whose maximum flood height recorded was 7 centimeters, demonstrated that the flood hydrograph gave a clear response in the soil moisture content of the profile studied, with increases in soil water content of up to 5% for soil depths below 9 meters. Analyzing the changes in the ground water level it is obvious that the infiltration data can be applied to the whole vadose zone and therefore the aquifer recharge can be estimated.Este trabajo se ha realizado con la financiación del Proyecto Europeo WADE (FloodWater recharge of alluvial Aquifers in Dryland Environments, contrato no. GOCE-CT-2003-506680), y del proyecto CICYT PALEOREC “Infiltración en lechos fluviales y recarga de acuíferos relacionadas con avenidas y paleocrecidas en ríos efímeros” (Proyecto CGL2005-01977/HID).Peer reviewe

New insights on the seismogenic potential of the Eastern Betic Shear Zone (SE Iberia): Quaternary activity and paleoseismicity of the SW segment of the Carrascoy Fault Zone

The Carrascoy Fault (CAF) is one of the main active faults that form part of the Eastern Betic Shear Zone, a 450 km fault system that accommodates most of the convergence between the Eurasian (Iberia) and Nubian plates in the Betic Cordillera, south Spain. Although the CAF represents a major earthquake threat to the nearby City of Murcia, studies on its Quaternary tectonics and seismogenic potential are scarce to date. We present evidence that supports the division of the CAF into two overlapping segments with contrasting tectonic structure, Quaternary activity, and landform control: a SW segment, characterized by a broad fold-and-thrust zone similar to the forebergs defined in the Gobi-Altai region, and a NE segment, characterized by a sharp mountain front controlled by strike-slip tectonics. We attribute the differentiation into these two segments to the stresses associated with topography, which in turn is a consequence of the shortening component, at the middle Pleistocene, after circa 217.4 ka. For the SW segment we infer the occurrence of 9 to 11, Mw 6.7 paleoearthquakes in the last 30.2 kyr, and a slip rate of 0.37 ± 0.08 m/kyr. We date the occurrence of the last surface rupture event after 2750 B.P., and we estimate an average recurrence period of major events of 3.3 ± 0.7 kyrThis work was supported by SISMOGEN (IGME, 2279) and FASEGEO (CGL2009-09726) research projects and a technical assistance of the Civil Protection Service of Murci

Devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last British-Irish Ice Sheet

This contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last British-Irish Ice Sheet, a task undertaken as part of a larger community-based project (BRITICE-CHRONO) that aims to improve understanding of the ice sheet's deglacial evolution. As accurate reconstructions depend on the quality of the available data, some form of assessment is needed of the reliability and suitability of each given age(s) in our dataset. We outline the background considerations that informed the quality assurance procedures devised given our specific research question. We describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty. When these criteria were applied to an existing database of all geochronological data relating to the last British-Irish Ice Sheet they resulted in a significant reduction in data considered suitable for synthesis. The assessed data set was used to test a Bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

Factors controlling rare earth element plus yttrium enrichment in Fe–Mn crusts from Canary Islands Seamounts (NE Central Atlantic)

Marine minerals are important because concentrate in their structure high contents of strategic and critical elements as rare earth elements. Forty-two samples from eight seamounts of Canary Islands Seamount Province (CISP) have been analyzed in order to evaluate their rare earth elements plus yttrium contents (REY). Highest contents of REY are related to hydrogenetic minerals and essentially Fe-vernadite (on average 3000 μg/g). Diagenetic minerals, on the other hand, show the lowest REY contents with an average content of 260 μg/g. These differences also depend on the growth rates, hydrogenetic minerals with growth rates between 0.5 and 5 mm/Ma allow the incorporation of more REY in their structure. REY contents in studied samples varies depending several factors associated with depth and location, shallowest samples presumably growth near or within the oxygen minimum zone are the most enriched with up to 3800 μg/g due to local enrichment of these elements and the slowest growth rate promoted by the reduced ambient conditions while deeper samples around 3000 m water depth show 2800 μg/g. Location also has a role in REY contents essentially due to the presence of different currents. Samples faced to north are exposed to the more oxygenated waters of the North Atlantic Deep Water and are depleted in REY if compared with deeper samples facing to south to the more oxic Antarctic Bottom Water. Finally, the case of study made on three different seamounts of the CISP show that Fe–Mn crusts from this area could provide on average 130 tons of hydrometallurgical recovered REY (based on 1 km2 areal crust coverage) together with interesting quantity of several other strategic and base elements as Mn, Co, Ni, Cu, V, Mo between others

Late immune response and chronic infection of vascular graft. A controversial diagnosis

La prevalencia de reacciones periprotésicas estériles en injertos vasculares es de aproximadamente un 0,8%. Son situaciones clínicas donde resulta difícil determinar si su origen reside en una infección por gérmenes de crecimiento lento o es secundario a un rechazo inmunológico al material o por una desestructuración del mismo. Revisamos y comentamos las principales características para distinguir ambas situaciones clínicas. Se aporta un ejemplo clínico que trata de un paciente con injerto vascular de Dacron y una colección de 6 años de evolución, estéril, que rodea el total de la prótesis y requiere su explante y sustitución por un nuevo injerto. En conclusión, ante los casos de reacciones periprotésicas tardías es obligado excluir la presencia de infecciones latentes, pero se recomienda profundizar en el estudio de la respuesta inmunológica frente a los materiales del injerto vascular.The prevalence of sterile perigraft reaction is approximately 0.8% in vascular grafts. To diagnose between an infection by germs of slow growth or a secondary reaction to an immune rejection of the material is difficult in this clinical situation. We review and discuss the main features to distinguish these two clinical possibilities. We report a patient case report with dacron vascular graft and a perigraft collection, sterile, around the total prosthesis which required explantation and replacement by a new graft. In conclusion, to cases of late periprosthetic reactions is required to exclude the presence of latent infections, but recommended further study of the immune response against vascular graft materials

Extreme Floods in Small Mediterranean Catchments: Long-Term Response to Climate Variability and Change

Climate change implies changes in the frequency and magnitude of flood events. The influence of climate variability on flooding was evaluated by an analysis of sedimentary (palaeofloods) and documentary archives. A 500-year palaeoflood record at Montilea River (657 km(2) in catchment area), eastern Spain, revealed up to 31 palaeofloods with a range of discharges of 20-950 m(3) s(-1), and with at least five floods exceeding 740-950 m(3) s(-1). This information contrasts with the available gauged flood registers (since year 1971) with an annual maximum daily discharge of 129 m(3) s(-1). Our palaeoflood dataset indicates flood cluster episodes at (1) 1570-1620, (2) 1775-1795, (3) 1850-1890, and (4) 1920-1969. Flood rich periods 1 and 3 corresponded to cooler than usual (about 0.3 degrees C and 0.2 degrees C) climate oscillations, whereas 2 and 4 were characterised by higher inter-annual climatic variability (floods and droughts). This high inter-annual rainfall variability increased over the last 150 years, leading to a reduction of annual maximum flow. Flood quantiles (>50 years) calculated from palaeoflood+gauged data showed 30%-40% higher peak discharges than those using only instrumental records, whereas when increasing the catchment area (1500 km(2)) the discharge estimation variance decreased to-15%. The results reflect the higher sensitivity of small catchments to changes on flood magnitude and frequency due to climate variability whereas a larger catchment buffers the response due to the limited extent of convective storms. Our findings show that extended flood records provide robust knowledge about hazardous flooding that can assist in the prioritization of low-regret actions for flood-risk adaptation to climate change

Palaeoceanographic implications of current-controlled sedimentation in the Alboran Sea after the opening of the Strait of Gibraltar

This study focuses on the Alboran Sea area (Westernmost Mediterranean), where a seismic analysis of the Pliocene and Quaternary stratigraphy was conducted in the Alboran Sea (Westernmost Mediterranean) using ~2000 profiles consisting of single and multi-channel seismic records. The seismic facies and architectural analysis of the deposits evidence the presence of bottom-current deposits (plastered, sheeted, elongated-separated and confined monticular drifts) and associated erosive features (terraces, scarps, moats and channels). Many of these deposits were previously considered to be open slope turbidite deposits which have now been reinterpreted as contourites.The contourite features have developed under the continuous influence of Mediterranean water masses, after the opening of the Strait of Gibraltar (roughly divided into light and dense Mediterranean waters), with plastered drifts dominating on the Spanish and Moroccan continental slopes, and sheeted drifts infilling the subbasins. The location and growth of contourite features have been mainly controlled by two main factors: i) tectonics, which has governed the relocation of the main pathways of the water masses; and ii) climate, which has influenced both water mass conditions and the depth of interfaces, as well as hinterland sediment sources, conditioning the morphoseismic characteristics of the drifts (facies and geometry) and terrace formation (dimensions). The mapping of the contourite facies through time has allowed defining three main scenarios for deep water circulation since the opening of the Strait of Gibraltar, which are: i) Atlantic Zanclean flooding; ii) the Pliocene sea, with two different stages caused by the progressive relocation of flow pathways; and iii) the Quaternary sea, with well defined characteristics and mostly stable flow pathways for the AW, and light and dense Mediterranean waters.This work lead us to consider the geologic framework characterizing the Alboran Sea may have played an important role in the interaction of the Mediterranean Waters before entering the Strait of Gibraltar, and thus in forming the MOW. Additionally, the results of this work may help in understanding the sedimentation in other Mediterranean margins affected by the same water masses and other partly land-locked basins with exchanges of waters over a confining sill

Timing and pace of ice-sheet withdrawal across the marine-terrestrial transition west of Ireland during the last glaciation

Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a−1) and reduced (8 m a−1) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets