Catodoluminiscencia de carbonatos lacustres pérmicos de los Pirineos Occidentales: un modelo de cementación temprana en paleoacuíferos meteóricos asociados a lagos

Cathodoluminescence of Permian lacustrine carbonates from the Westem Pyrenees: a model for early cementation in meteoric aquifers associated with lakes. We present here a case-study of early diagenetic cementation in Permian lacustrine lithofacies (Aragón-Béarn and Basque Country Basins, western Pyrenees). Cathodoluminescence zoning in calcite cements shows a general non-luminescent-bright luminescent-dull luminescent sequence which we interpret as a result of the transition from the vadose and oxic phreatic environments to the progressively reducing phreatic ground waters. Vadose features and non-lumines-cent cements predominate in the more  pedogenically altered andlor subaerially exposed facies. The very early timing of the whole sequence and the differences in cementation among lacustrine, palustrine and alluvial plain facies emphasize the dependence of the aquifers on sedimentary subenvironments and lake level changes. The Permian model here described is applicable to early cementation in meteoric aquifers related to shallow, carbonate lakes. Our data agree with the well-known control of Fe and Mn contents on the cathodolurninescence of calcites and dolomites and the uncertainties of a quantitative relationship between chernical composition and luminescence. The proposed sensitizer role for Mg needs further testing

A 1400-years flood frequency reconstruction for the Basque country (N Spain): Integrating geological, historical and instrumental datasets

We present the first reconstruction of past flood events variability in the Basque Country and Western Ebro Basin (Northern Spain) integrating instrumental hydrological datasets (last 20 years), documentary archives (last 700 years) and Lake Arreo (655 m a.s.l.) sedimentary paleoflood record (last 1400 years). In this lake, allochthonous coarse and fine detrital layers (CDL and FDL respectively) intercalated within endogenic laminites were identified and interpreted as high- and moderate-energy flood events. The interplay between human activities and hydroclimate variability has controlled the deposition of these flood layers. Gauged data for the last 20 years suggest that floods are typically generated by heavy rainfall events on saturated soils after several days of continuous rainfall. These events occur mostly during the cold season (Oct–May). The reconstructed frequency of high-magnitude flood events from the lake record is coherent with the historical cold-season floods from Basque rivers. The lowest flood frequency took place during the 6–7th and 10–15th centuries, while higher flood frequency occurred during the 8–9th centuries and the last 500 years. Fluvial and lacustrine paleoflood records and documentary evidence show abrupt and large increases in extreme flood frequency during the termination of the Little Ice Age (1830–1870 CE) and mid to late 20th century, both periods of Rapid Climate Change (RCC). The significant increase in flood frequency observed during RCC suggests that a similar pattern could be expected in the near future with the ongoing global warming.</p

Progress in Detection and Projection of Climate Change in Spain since the 2010 CLIVAR-Spain regional climate change assessment report

The Iberian Peninsula region offers a challenging benchmark for climate variability studies for several reasons. It exhibits a wide variety of climatic regimes, ranging from wet Atlantic climates with annual precipitation around 2000 mm, to extensive semiarid regions with severe hydrological stress, to even cold alpine environments in some isolated areas

Perforación profunda en el lago de Chalco: Reporte técnico

En este artículo se presenta un resumen de las actividades realizadas para la recuperación de la totalidad de la secuencia lacustre del lago de Chalco. Mediante estudios geofísicos se determinó la distribución y espesor de los sedimentos lacustres con base en lo cual se seleccionó el sitio de perforación. Con datos de los espectros H/V de sísmica pasiva se hizo un mapa de isofrecuencias que definieron una región con sedimentos lacustres y material volcánico granulado de hasta 300 m de espesor. El uso de métodos electromagnéticos mostró cambios en la resistividad eléctrica relacionados con variaciones en la composición de la columna sedimentaria; entre 100 – 120 m de profundidad hay un primer aumento en la resistividad asociado al incremento de materiales volcaniclásticos, y entre 330 – 400 m de profundidad un segundo aumento asociado a la presencia de coladas de basalto. Fueron perforados tres pozos con recuperación continua, llegando a profundidades de 420 m en el pozo A, 310 m en el B y 520 en el C. Durante el trabajo de perforación se tomaron muestras para el análisis geomicrobiológicos y de metagenómica. Durante el proceso de perforación se recuperó un total de 1152 m de sedimentos con una profundidad máxima de 520 m. El porcentaje de recuperación de la columna sedimentaria varió entre 88 a 92 % en los tres sondeos. Los resultados del análisis de susceptibilidad magnética en las tres secuencias indica que los primeros 260 m son sedimentos lacustres, entre 260 y 300 m los sedimentos son más gruesos y debajo de los 300 m son predominantemente volcaniclásticos. El análisis de la secuencia sedimentaria del lago de Chalco de los últimos ~300000 años, permitirá documentar y ampliar el conocimiento acerca de la variabilidad climática de la zona, la historia paleoambiental, la historia del cierre de la cuenca, el desarrollo del sistema lacustre y la recurrencia de la actividad volcánica en la cuenca. Además, el estudio de las propiedades físicas de esta secuencia sedimentaria es importante para la modelación de la propagación de ondas sísmicas y de la estructura de la cuenca, así como para mejorar la capacidad de modelación del proceso de subsidencia del terreno que experimenta esta región. This paper presents a short description of the coring operations undertaken to recover the full lacustrine sedimentary sequence from Chalco. Geophysical techniques were used to determine the distribution and thickness of the sediments in order to select the drilling site. Resonance frequencies determined from H/V spectral ratios were used to determine an area where lake sediments reached 300 m thickness. Electromagnetic survey showed two changes in electric resistivity which were related to changes in sediment composition, the first from 100 to 120 m, related to an increase in volcanoclastic sediments and the second from 330 to 400 m related to the presence of a basaltic flows. Three wells were drilled with continuous recovery, reaching depths of 420 m in well A, 310 in B and 520 in C. Samples for geomicrobiological and metagenomics studies were collected during drilling operations. A total of 1152 m of core sediments were recovered reaching a maximum depth of 520 m. Recovery percentages were between 88 and 92 % in the three wells. Magnetic susceptibility analyses in the three sequences show that the first 260 m are mostly lake sediments, between 260 and 300 m sediments are coarser and below 300 m they are mostly volcaniclastic. Analysis of the sedimentary sequence of Lake Chalco that covers the last ~300000 years will allow documenting and extending the knowledge of climate variability in area, the paleoenvironmental history, basin closure history, lacustrian system development and volcanic activity recurrence. Studies of the physical properties of this sequence will be important for seismic propagation and basin structure modeling, and also will improve modeling of the subsidence process that this region experiences

A millennium-long perspective of flood-related seasonal sediment yield in Mediterranean watersheds

International audienceMediterranean mountains have been extremely vulnerable to land degradation and soil erosion due to climate factors (summer hydric stress, high storminess) and the long history of human pressure on these terrestrial ecosystems. The short-time span of instrumental monitoring datasets limits our ability to obtain a full depiction of the long-term drivers controlling flood intensity and frequency and soil erosion in Mediterranean watersheds. Here we have applied a novel methodology based on detailed microfacies analyses on annually-laminated (varved) lacustrine sediments to reconstruct floods and seasonal sediment yield and denudation rates in a mountainous Mediterranean watershed during the last 2775 years. The sediment yield reconstruction in this study agrees reasonably well with soil erosion rates from Pyrenean experimental watersheds supporting the validity of this methodology to assess the soil erosion and sediment production from a long-term perspective. The comparison with instrumental precipitation datasets demonstrates the different seasonal sensitivity of sediment yield to heavy rainfall magnitudes mostly depending on soil moisture conditions, soil and regolith erodibility and vegetation cover. During periods of reduced human impact in the watershed, the seasonal maxima in sediment production occurred in autumn, which corresponds to the season with more frequent and intense heavy rainfall in the region. The highest soil erosion rates occurred during periods with higher human impact in the watershed due to sustained burning, overgrazing and cereals cultivation that modified the seasonal sediment yield distribution, with the highest sediment production happening in winter. The most significant periods of increased sediment yield occurred during the Middle Ages (1168–1239 CE) and the 19th century (1844–1866 CE) due to an interplay between increased frequencies and magnitudes of heavy rainfall and intensive agropastoral activities in the lake's watershed. This study highlights the potential of seasonally-resolved archives to adequately evaluate the environmental drivers and mechanisms controlling flood dynamics and soil erosion at decadal to centennial time-scales in areas with strong seasonality

A 1400-years flood frequency reconstruction for the Basque country (N Spain): Integrating geological, historical and instrumental datasets

International audienc

A 22,000 14C year BP sediment and pollen record of climate change from Laguna Miscanti (23°S), northern Chile

Lake sediments and pollen, spores and algae from the high-elevation endorheic Laguna Miscanti (22°45′S, 67°45′W, 4140 m a.s.l., 13.5 km2 water surface, 10 m deep) in the Atacama Desert of northern Chile provide information about abrupt and high amplitude changes in effective moisture. Although the lack of terrestrial organic macrofossils and the presence of a significant 14C reservoir effect make radiocarbon dating of lake sediments very difficult, we propose the following palaeoenvironmental history. An initial shallow freshwater lake (ca. 22,000 14C years BP) disappeared during the extremely dry conditions of the Last Glacial Maximum (LGM; 18,000 14C years BP). That section is devoid of pollen. The late-glacial lake transgression started around 12,000 14C years BP, peaked in two phases between ca. 11,000 and <9000 14C years BP, and terminated around 8000 14C years BP. Effective moisture increased more than three times compared to modern conditions (∼200 mm precipitation), and a relatively dense terrestrial vegetation was established. Very shallow hypersaline lacustrine conditions prevailed during the mid-Holocene until ca. 3600 14C years BP. However, numerous drying and wetting cycles suggest frequent changes in moisture, maybe even individual storms during the mid-Holocene. After several humid spells, modern conditions were reached at ca. 3000 14C years BP. Comparison between limnogeological data and pollen of terrestrial plants suggest century-scale response lags. Relatively constant concentrations of long-distance transported pollen from lowlands east of the Andes suggest similar atmospheric circulation patterns (mainly tropical summer rainfall) throughout the entire period of time. These findings compare favorably with other regional paleoenvironmental data

Sediment and heavy metals flows recorded across an altitudinal transect in the central Pyrenees for the last 2 millennia P-4254

International Union For Quaternary Research, Dublin, 25th and 31st July 2019. -- http://www.inqua2019.org