Search

This study examines the first precisely dated and temporally highly resolved speleothem record from Iberia that reconstructs the Oldest Dryas (OD). The onset of cold conditions in the study area, contemporary with the beginning of Heinrich Stadial 1, is recorded at 18.13 ± 0.08 ka, with a pronounced drop of 6.1‰ in δ13C in 250 years. Henceforth, stadial conditions depict a period of instability in the Atlantic Meridional Overturning Circulation, peaking in freshwater input from iceberg melting during Heinrich Event 1. Anomalies in the δ18O of the stalagmite attributed to such a freshwater event are found from 16.17 to 15.89 ka. Such absolute dates given to the onset of the OD in Iberia and to the main iceberg discharges are reliable anchor points for non-absolute chronologies. Two periods are identified in the OD: OD-a (18.13–16.17 ka) is characterized by wet conditions and a faster growth rate, and OD-b (15.89–14.81 ka) exhibits relative dryness and a slower growth rate. The sudden release of fresh water is considered to be the reason for the disruption of rainfall patterns in eastern Iberia. The present study also highlights the existence of heterogeneous and complex hydrological conditions during the OD in Iberia when both Atlantic and Mediterranean realms are considered.

The utility of the Mg/Ca elemental ratio of calcite ((Mg/Ca)calcite) as a temperature indicator in continental carbonate deposits is a matter of debate due to the different results obtained by diverse authors. In this study, we aimed to test the reliability of the (Mg/Ca)calcite in fluvial carbonates. We selected the recent tufa stromatolite records of four rivers on the Iberian Peninsula for the trace element analysis based on six-monthly sampling. Previous sedimentary and hydrological studies on these fluvial basins provided the information for this work. The water temperature estimates for the stromatolite (Mg/Ca)calcite substantially differed from the measured water temperatures in most of the studied cases. We thus assessed other factors that participate in the control of the Mg partitioning between water and calcite. The correction of the detrital Mg content yielded water temperatures that matched the measured ones in one of the rivers. The (Mg/Ca)water, water discharge and calcite precipitation rates may also occasionally influence the (Mg/Ca)calcite. The six-month behaviour of some of these parameters could interfere with the relationship between the (Mg/Ca)calcite and water temperature. According to these results, and their comparison with other non-marine carbonates, the wide variety of parameters that are involved in the (Mg/Ca)calcite limit it as a geochemical thermometer in continental sedimentary environments.

We provide first insights into the speleogenesis of Ejulve cave (Teruel province, Iberian Range, NE Spain) by studying cave morphologies and cave deposits, combined with regional geomorphological and hydrothermal observations. Three main hydrogeomorphic evolutionary stages can be distinguised to explain the origin and evolution of the Ejulve endokarstic system. Cave pattern and cave solutional features (calcite vein fillings, tubes with rising ceiling cupolas, pendants and cusps, spongework and micro-corrosion features) suggest that the cave generated in a phreatic environment by ascending water. Cave morphologies and regional hydrothermal springs in this region suggest, but not prove, the involvement of thermal waters and related convection and condensation-corrosion mechanisms in the origin of the cave. Subsequently, the cave underwent a change to epigenic conditions driven by denudation, as a result of regional uplift. Once the karstic system was exhumated, carbonate speleothems formed in a vadose environment. Mineralogical, petrographic, isotopic and chronological (U-series dating) analyses of carbonate speleothems (i.e. stalagmites, flowstones, botryoids, spars, acicular crystals and farmed carbonate) are provided. Calcite, high-Mg calcite and aragonite are the most common minerals, whereas columnar, dendritic, micrite, mosaics and fans are the main fabrics. Mean δO values of − 7.3‰ and δC values of − 9.1‰ indicate carbonate precipitation from meteoric waters without a hydrothermal origin. Carbonate deposits formed at least since 650 ka BP. Our study suggests that hydrothermal fluid flow may explain, although the evidences are not fully conclusive, the speleogenesis of this cave., We acknowledge the predoctoral research Grant from the Government of Aragón (B158/13) and CTM2013-48639-C2-2-R (OPERA) and CGL2016-77479-R (SPYRIT) projects for funding. Fernando Gázquez was financially supported by the “HIPATIA” research program of the University of Almeria.

A 12-year study (2000–2012) of the stable isotopes of recent fluvial tufas has been performed in the Monasterio de Piedra Natural Park (River Piedra, NE Iberian Peninsula), an area of Mediterranean climate with intense tufa deposition since the Pleistocene. The biannual monitoring of the tufa calcite δ13C and δ18O signatures and of the water δ18O value has demonstrated a clear seasonal pattern for the tufa-calcite oxygen isotope composition, with less negative values for cool periods, which is consistent with regional temperature oscillations. The tufa calcite δ13C values only occasionally exhibit a pattern, which is inconclusive and opposite to the δ18O clear pattern. The water δ18O signature has a distinct seasonal pattern, also opposite to the tufa-calcite δ18O clear pattern. The temperature calculations from the tufa-calcite δ18O values and average water δ18O values agree with the seasonal pattern of measured water temperatures, with a mean difference of 2.3 °C between the calculated and measured temperatures. The anomalous values recorded for both the water and the tufa-calcite oxygen isotope composition during a two-year period are characterized by smoothing of the seasonal variations of the tufa calcite and by reversal of the water pattern. There is also an increase in the differences between the measured and estimated temperatures. The detected anomaly is roughly synchronous with a change in the isotopic signature of the regional precipitation δ18O values. This contribution demonstrates that tufas in this depositional and climatic context are good indicators of seasonal temperature oscillations, and that tufas can also record other interannual environmental changes such as variations in the isotopic composition of precipitation. These results can be extrapolated to ancient tufa systems developed in similar contexts, which would expand the potential of tufas as high-resolution records of paleoenvironmental conditions.

The transition between extensional and compressional-driven magnetic fabrics in sedimentary rocks is explored in this paper through the study of an example of the Basque-Cantabrian basin. In the area where extensional structures prevail and no superimposed deformation is observed, except for gentle large-scale folds, the magnetic fabric is interpreted as extensional, in consistency with mesostructural (tension gashes) and macrostructural (large-scale faults) data. Compressional tectonic fabrics are unequivocally interpreted in the area with cleavage development related to the buttressing of the syn-rift sequence against faults located near the northern basin margin. In this area, kmax is oriented according either to the intersection lineation or the dip direction of cleavage planes. In the area located in-between, where no macroscopic evidence of either compression or extension exist, there is a transitional fabric between compressional (resulting from the modification during inversion of a previous sedimentary or extensional fabric) and extensional (inherited from the extensional stage) magnetic fabrics that correlate with subtle evidences at the microscopic scale (pressure shadows, deformation and re-orientation of nodules). Therefore, the magnetic fabric is revealed as an exceptionally sensitive marker of deformation in sedimentary rocks. This transition in the magnetic fabric occurs within a length of 6.25 km along the cross-section that correlates with a thickness of 200 m of the stratigraphic pile. These results indicate that even in the absence of clear structural markers of compressional deformation, extensional magnetic fabrics can be only interpreted when there is a minimum separation (in the vertical or the horizontal) to the cleavage front. © 2012 Elsevier Ltd., The authors thank Sylvia Gracia for her help in measuring with the KLY3S susceptibility metre. This study has been financed by the research project CGL2009-08969 of the MICINN (Spanish Ministry of Science and Innovation). BOU acknowledges the “Juan de la Cierva Postdoctoral Program” from the MCINN. G. Borradaile and an anonymous reviewer are thanked for their constructive comments that help to improve the manuscript.

δ 13 C and δ 18 O of recent, continuous tufa records, obtained during a monitoring period spanning 3 to 13 years, are compared with the corresponding, known environmental conditions. Three rivers in NE Iberia (located along a 200-km N–S transect) are used for this comparison. The isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales, focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions, which is important to past climate studies based on isotopic data. The calculation of the actual isotopic fractionation coefficients, and the comparison with the literature-derived coefficients, demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature. The difference between mean measured water temperature (Tw) and mean calculated Tw (based on δ 18 O calcite and measured δ 18 O water ) is less than 2.7 °C. Tendencies of these calculated Tw are similar to the regional air temperature (Tair) tendencies through time, in particular in the case of the 13-year record, although certain deviations exist over shorter time spans. The best agreement between measured and calculated Tw and between δ 18 O calcite -based Tw tendencies and Tair tendencies corresponds to the tufa stromatolite facies. Differences between the δ 18 O calcite records of the three rivers cannot be attributed to temperature changes, but to the varying influences of groundwater inputs and isotopic rainfall composition in each river. Without considering these parameters, δ 18 O calcite -based Tw calculations yield inaccurate results when comparing the study sites. δ 13 C calcite values do not exhibit distinct patterns over time, and δ 13 C calcite variations are likely caused by local processes that do not reflect general environmental changes. These findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems, particularly when differences between the isotopic signatures of deposits exist in the same region.

A paleomagnetic study has been carried out on a waterlaid detrital sedimentary sequence of ~240cm thick within the Seso Cave System (West-Central Pyrenees). In these sediments, seven charcoal samples were dated using 14C AMS ranging from 2080 to 650calyrBP (130BC-1300AD). Two levels of human occupation of the cave have been recognized by ceramics associated to the Iberian Period and to the Roman Period, respectively. The detrital sedimentary sequence is made of autochthonous (piping detached material from the Eocene marls host rock inside of the cavity) and allochthonous (stream transported sediments from the outside) sediments. The autochthonous material (first 100cm), made of fine grain laminated sediments (lutites and marls) corresponds to pond facies; the allochthonous material (190-240cm) is made of lutites and sands and corresponds to stream facies, and both facies are mixed from 100 to 190cm. The increase in sedimentation rate towards the end of the sequence (stream facies) points to an intensification of the alluvial activity as a possible consequence of a more arid climate during the Medieval Climate Anomaly. For the paleomagnetic study, 44 discrete cylindrical samples were taken along the detrital sequence. The values of the natural remanent magnetization and magnetic susceptibility are significantly lower in the pond sediments than in the stream sediments. The declination and inclination of the paleomagnetic characteristic component (sister samples analyzed by both alternating field and temperature demagnetizing procedure) of each depth point is compared to the Spanish archeomagnetic catalog and available geomagnetic models (ARCH3k.1, CALS3k.4, CALS10k.1b and SCHA.DIF.3K) in order to determine the accuracy of these sediments recording the Earth's magnetic field. Results suggest that these sediments poorly record the Earth's magnetic field, however, paleomagnetic inclination shows similar results between both demagnetizing methods and the inclination is well recorded especially in the younger stream facies. The lack of archeological remains with absolute dates from 925 to 1545calyrBP in the Iberian paleomagnetic secular variation reference curve has prevented, up to now, the study of that time period. Therefore, the inclination data from the Seso Cave deposit is the first record of the Iberian paleomagnetic secular variation during most part of the Medieval time, and they are closer to the inclination values of one geomagnetic model (CALS10k.1b). © 2014 Elsevier B.V., BOU acknowledges the JAEdoc Programme of CSIC, partly financed by the European Social Fund. All authors thank the financial support of the Instituto de Estudios Altoaragoneses, of the projects CGL2009-10455/BTE, HIDROPAST CGL2010-16376 (MICINN and FEDER), ORDESA (Autonomous Organism of National Parks), and the PaleoQ Group (Universidad de Zaragoza-Gobierno de Aragón). We are also indebted to Jaume Mas-Moiset and Xavier Fuertes from the Grup d'Espeleologia de Badalona (GEB) for the cartography of the cave system and field support. Dr. José Luis Peña-Monné and Dr. Fernando Pérez-Lambán are acknowledged for the classification and comments of pottery remnants. We are indebted to GEOMAGIA50, which is a database that comes with a web interface intended to give users easy access to archeomagnetic data (Donadini et al., 2006 and Korhonen et al., 2008). Comments and suggestions from two anonymous reviewers are deeply acknowledged.

22 páginas, 6 figuras, 1 tabla, This work presents a palaeoenvironmental interpretation of the Upper Pleistocene–Holocene sedimentary sequence recorded in the Valsalada saline wetland system (Monegros, Central Ebro Basin). This morphosedimentary system developed on karstified, gypsiferous bedrock and was mainly fed by local saline groundwater. Based on geomorphological, sedimentological, palynological and radiocarbon data, three depositional units have been differentiated: 1) a lacustrine unit, which accumulated under cold/cool and humid environmental conditions at 41–40 kyr cal BP, 2) a fluvial unit that was deposited under arid climatic conditions with cold episodic periods from 14 to 3.5 kyr cal BP, and 3) an alluvial slope unit associated with arid climate with human influence during the Late Roman Period (1.5 kyr cal BP). The morphosedimentary evolution of the Valsalada system is strongly influenced by the geomorphic setting (small catchment with karstic depressions and low gradient slopes on gypsum), the hydrological availability (runoff and groundwater discharges) related to climate variability during the Late Pleistocene–Holocene, and the human activities developed in the area during historical times. The response of the Valsalada system displays a low sensitivity to short-term climatic changes but responds to major long-term climatic conditions, improving the regional paleoenvironmental picture of the Late Quaternary in NE Spain., This work was supported by projects CGL2006-08973/BTE, CGL2009-10455/BTE, CGL2009-07992 and CSD2007-00067 of the Spanish Government and the European Regional Development Fund. This is a contribution by PaleoQ, GCC and Cuencas Sedimentarias Continentales groups (Aragón Regional Government). We are grateful to the anonymous reviewers for their helpful comments.