Suchergebnisse

Environmental magnetic proxies were analyzed in a relatively monotonous, ~25.3m thick alluvial sedimentary sequence drilled in the Añavieja Basin (NE Spain). Results from the core AÑ2 suggest that the concentration dependent magnetic parameters mainly reflect variations in the content of detrital magnetite, sourced in the catchment rocks and soils of the basin, via changes in the dynamics of alluvial fans due to temperature changes in the northern hemisphere during the Late Pleistocene. The correspondence between the magnetic proxies and the temperature variations in the North Atlantic region (NGRIP curve) indicates that higher (lower) concentrations and finer (coarser) magnetite grains coincide with warm (cold) periods. We propose that during cold periods, a sparser vegetation cover favored the incoming of higher energy runoff bearing coarser sediments to the basin that are relatively impoverished in magnetite. In contrast, during warm periods, the wider distribution of the vegetation cover associated with the lower runoff energy lead to finer, magnetite-richer sediment input to the basin. Maghemite, presumably of pedogenic origin, appears to be present also in the studied alluvial sediments. Further studies are necessary to unravel its palaeoclimatic significance ; This study has been supported by research projects CGL2009-09165/BTE and CGL2009-08969, funded by the Ministerio de Ciencia e Innovación from Spain and FEDER UZ 2008-CIE-12. The Groups "Análisis de cuencas sedimentarias continentales" (E-28), "Geotransfer" and "Geomorfología y Cambio Global" (E-68) of the Aragón Government Fondo Social Europeo also supported the study. Q. Liu thanks support from the Chinese Academy of Sciences

A new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from −18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth. ; This work is part of the project CGL2017-84901-C2-2-P funded by MCIN/AEI/10.13039/501100011033 and "ERDF A way of making Europe" and project PID2020-114273GB-C22 funded by MCIN/AEI/10.13039/501100011033 from Spanish Ministry of Science, Innovation and Universities. Seequent has provided us the GM-SYS module of the Oasis Montaj. The authors acknowledge the contribution of José María Llorente and Agustin González for the acquisition of the gravity data. We thank to Aigüestortes National park and Alt Pirineu Natural park their logistic support. We thank anonymous reviewer for improving the content in the manuscript. This study represents a contribution to GeoAp Research Group (E01-20R) (Aragón Government). ; Peer reviewed