Análisis sedimentológico del embalse de Barasona, Huesca

[Resumen] La pérdida de capacidad debido al aterramiento es un grave problema en numerosos embalses. El pantano de Barasona, en la cuenca del Esera-Isábena, Pirineos Centrales, uno de los más antiguos de España, ha perdido un tercio de su 3 capacidad inicial (71 Hm ) desde su construcción en 1932. El estudio de 23 sondeos ha permitido caracterizar el sedimento,definir facies sedimentarias, reconstruir tridimensionalmente el relleno del vaso y proponer un modelo deposicional dominado por las fluctuaciones en el régimen de aporte de los ríos. Las variaciones en la composición mineralógica proporcionan información sobre áreas fuente y procesos de erosión y transporte en la cuenca. Correlacionando los niveles de limos arenosos con los episodios de avenidas, se ha construido una cronología preliminar que permitirá evaluar variaciones en la tasa de aporte de sedimentos al embalse y en la dinámica del sistema embalse-cuenca..[Abstract] Sediment deliver and consequent loss of water storage capacity aggravate reservoir management problems. The Barasona reservoir in the Esera-Isabena watershed, Central Pyrenees, is one of the oldest in Spain (1932) and has lost one 3 third of its initial water capacity (71 Hm ). In this study we analyze the composition of the infilling of the Barasona reservoir, identify sedimentary facies, and reconstruct the tri-dimensional geometry based on 23 cores. Sedimentary dynamics is mainly controlled by fluctuations in the river inflow. Changes in mineral composition inform of sediment provenance and transport processes in the catchment area. A preliminary chronology based on the identification of floods in the sedimentary record (sandy silt layers) will allow to investigate changes in the sediment yield and in the interaccions reservoir-catchment

Limnogeologúa de Laguna Chungará y cambio climático durante el Holoceno superior en el altiplano chileno septentrional

[Resumen] El estudio sísmico de la Laguna Chungará (69° 30' O, 18° 15'S, 4520 m. s.n.m, Altiplano chileno septentrional) y el análisis sedimentológico de varios sondeos ha permitido reconstruir la evolución de la sedimentación lacustre en el lago durante el Holoceno Superior. Se han identificado dos asociaciones de facies: i) litoral, más somera, compuesta por facies de turbera y in plataforma lacustre, más profunda, compuesta por facies con abundantes fragmentos de Characeae. Estas facies alternan en tres ciclos sedimentarios provocados por fluctuaciones en el nivel del lago. Estas variaciones hidrológicas en la laguna han sido causadas por cambios en el balance hídrico que a su vez reflejan importantes fluctuaciones climáticas durante el Holoceno Superior.[Abstract] We reconstruct the Late Holocene sedimentary history of Laguna Chungará (69° 30' W, 18° 10'5, 4520 m.a.s.l., northern Chilean Altiplano) based on high resolution seismic profiling and sedimentologic analyses of cores. Two sedimentary facies associations have been defined and interpreted: n macrophytedominant littoral, composed of black muds with macrophyte remains and peaty muds, and in Characeae-dominant lacustrine self, composed of gray muds and sands with abundant Characeae remains. The two facies associations define three cycles caused by oscillations in the lake level from shallower (macrophyte) to deeper (Characeae) conditions. Changes in the hydrology of Laguna Chungará reflect variations in the effective moisture (precipitation - evaporation) in the Altiplano during the Late Holocene

Hacia una enseñanza universitaria participativa y no jerarquizada : desarrollo de un método activo-solidario. Un ejemplo en la enseñanza de la Petrología

Presentamos una experiencia didáctica realizada en la Universidad de Zaragoza con el alumnado de tercero de Ciencias Geológicas, en un curso cuatrimestral de Petralogía de Rocas Sedimentarias y Metamórficas. Pretendemos demostrar que es posible una enseñanza de calidad en la que una mayoría de los estudiantes desarrollen el máximo de sus potencialidades.We want to presente a didactic experiment wich was carried put for a term in a course on "Exogenous and Metamorphic Rock petrology" within the third tear of Geological Studies. Our experiment tries to show the likeliness of a kind of university studies where students can have a greater share and therefore develop their full potentiality

Hacia una enseñanza universitaria participativa y no jerarquizada : desarrollo de un método activo-solidario. Un ejemplo en la enseñanza de la Petrología

Presentamos una experiencia didáctica realizada en la Universidad de Zaragoza con el alumnado de tercero de Ciencias Geológicas, en un curso cuatrimestral de Petralogía de Rocas Sedimentarias y Metamórficas. Pretendemos demostrar que es posible una enseñanza de calidad en la que una mayoría de los estudiantes desarrollen el máximo de sus potencialidades.We want to presente a didactic experiment wich was carried put for a term in a course on "Exogenous and Metamorphic Rock petrology" within the third tear of Geological Studies. Our experiment tries to show the likeliness of a kind of university studies where students can have a greater share and therefore develop their full potentiality

Late Holocene climate variability in the southwestern Mediterranean region: an integrated marine and terrestrial geochemical approach

A combination of marine (Alboran Sea cores, ODP 976 and TTR 300 G) and terrestrial (Zoñar Lake, Andalucia, Spain) geochemical proxies provides a high-resolution reconstruction of climate variability and human influence in the southwestern Mediterranean region for the last 4000 years at inter-centennial resolution. Proxies respond to changes in precipitation rather than temperature alone. Our combined terrestrial and marine archive documents a succession of dry and wet periods coherent with the North Atlantic climate signal. A dry period occurred prior to 2.7 cal ka BP – synchronously to the global aridity crisis of the third-millennium BC – and during the Medieval Climate Anomaly (1.4–0.7 cal ka BP). Wetter conditions prevailed from 2.7 to 1.4 cal ka BP. Hydrological signatures during the Little Ice Age are highly variable but consistent with more humidity than the Medieval Climate Anomaly. Additionally, Pb anomalies in sediments at the end of the Bronze Age suggest anthropogenic pollution earlier than the Roman Empire development in the Iberian Peninsula. The Late Holocene climate evolution of the in the study area confirms the see-saw pattern between the eastern and western Mediterranean regions and the higher influence of the North Atlantic dynamics in the western Mediterranean

The History of the El Niño - Southern Oscillation according to lacustrine and marine sediments

El gran impacte que El Niño — Oscil·lació del Sud (ENSO) té en la nostra societat industrialitzada ha esperonat la comunitat científica d'arreu a entendre quins són els mecanismes físics que el controlen, així com clarificar quina ha estat la seva història. El registre sedimentari de sensors naturals, com els llacs o la mar, ha permès reconstruir la història de l'ENSO. En aquest article, els autors donen una visió sintètica de la història d'aquest fenomen climàtic al llarg dels darrers quatre milions d'anys.The large impact of the El Niño – Southern Oscillation (ENSO) in our industrial society has spurred the scientific community to understand the physical processes that trigger this climate phenomenum and to elucidate its history. The sedimentary record of natural sensors, such as lakes and seas, was used to reconstruct the history of the ENSO and to obtain a comprehensive history of this climate phenomenon throughout the last 4 million years

Andean drought and glacial retreat tied to Greenland warming during the last glacial period

Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America

Andean drought and glacial retreat tied to Greenland warming during the last glacial period

Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America

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

U-Th dating of lake sediments: Lessons from the 700 ka sediment record of Lake Junín, Peru

Deep sediment cores from long-lived lake basins are fundamental records of paleoenvironmental history, but the power of these reconstructions has been often limited by poor age control. Uranium-thorium (U-Th) dating has the potential to fill a gap in current geochronological tools available for such sediment archives. We present our systematic approach to U-Th date carbonate-rich sediments from the ∼100 m drill core from Lake Junín, Peru. The results form the foundation of an age-depth model spanning ∼700 kyrs. High uranium concentrations (0.3–4 ppm) of these sediments allow us to date smaller amounts of material, giving us the opportunity to improve sample selection by avoiding detrital contamination, the greatest factor limiting the success of previous U-Th dating efforts in other lake basins. Despite this advantage, the dates from 174 analyses on 55 bulk carbonate samples reveal significant scatter that cannot be resolved with traditional isochrons, suggesting that at least some of the sediments have not remained closed systems. To understand the source of noise in the geochronological data, we first apply threshold criteria that screen samples by their U/Th ratio, reproducibility, and δ²³⁴U_(initial) value. We then compare these results with facies types, trace element concentrations, carbonate and total organic carbon content, color reflectance, mineralogy, and ostracode shell color to investigate the causes of open system behavior. Alongside simulations of the isotopic evolution of our samples, we find that the greatest impediment to U-Th dating of these sediments is not detrital contamination, but rather post-depositional remobilization of uranium. Examining U-Th data in these contexts, we identify samples that have likely experienced the least amount of alteration, and use dates from those samples as constraints for the age-depth model. Our work has several lessons for future attempts to U-Th date lake sediments, namely that geologic context is equally as important as the accuracy and precision of analytical measurements. In addition, we caution that significant geologic scatter may remain undetected if not for labor intensive tests of reproducibility achieved through replication. As a result of this work, the deep sediment core from Lake Junín is the only continuous record in the tropical Andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates