Análisis de la fábrica magnética en modelos analógicos de arcillas

Este estudio presenta el análisis de la fábrica magnética en una serie de modelos analógicos realizados con arcillas rojas comerciales. A partir de la disgregación de la arcilla en agua y su posterior decantación conseguimos reproducir la adquisición de una fábrica magnética deposicional (geometría oblata del elipsoide magnético con el eje mínimo de susceptibilidad perpendicular al plano de depósito). En un modelo de deformación de desgarre (experimento de Riedel), la lineación magnética se dispone paralela a la dirección de estiramiento. En el modelo de acortamiento, la lineación magnética se orienta perpendicular a la dirección de acortamiento. Los resultados obtenidos ponen de manifiesto el gran potencial de la arcilla roja comercial para ser utilizada en este tipo de modelos analógicos, así como su capacidad de registrar una fábrica magnética coherente en cada caso. This study shows the magnetic fabric analysis applied to several analogue models developed with common commercial red clays. By dispersing the clays in water and after allowing their subsequent decan-tation, we were able to reproduce the acquisition of a depositional magnetic fabric (oblate geometry of the magnetic ellipsoid with the minimum susceptibility axis perpendicular to the deposit plane). In a strike-slip deformation model (Riedel experiment), magnetic lineation is parallel to the stretching direction. In the shortening model, magnetic lineation orients perpendicular to the shortening direction. The obtained results illustrate the great potential of these commercial red clays to be used in this type of analogue models, as well as their capacity to register a coherent magnetic fabric in each case

La agricultura marginal como fuente de sedimentos en el Pirineo Central

[Resumen] La agricultura cerealista ha ocupado grandes extensiones en los valles pirenaicos, en exposiciones solanas por debajo de 1600 m de altitud. En este artículo se estudia el papel de la agricultura tradicional en la producción de sedimentos y la degradación del paisaje. Por medio de parcelas experimentales puede afirmarse que la agricultura itinerante y el barbecho han dado lugar a pérdidas de suelo muy elevadas y explican la pedregosidad superficial de mu.chas laderas. En el caso de la agricultura itinerante (articas), la quema de matorral y la incorporación de cenizas al suelo como fertilizante no contribuía a mejorar sustancialmente la calidad de los suelos.[Abstract] Cereal cropping has occupied large extent in the Pyrenean valleys, on sunny aspects under 1.600 m a.s.l. In this paper the role of traditional farming on sediment yield and landscape degradation is studied. By means of experimental plots the authors conclude than shifting agriculture an fallow land have caused great soil losses and explain the surface stoniness in many hillslopes. In the case of shifting agriculture, the burning of the shrub cover and the use of ashes as fertilizer did not contribute to improve the quality of soil

Tethyan versus Iberian extension during the Cretaceous period in the Eastern Iberian Peninsula: insights from magnetic fabrics

This work investigates how anisotropy of magnetic susceptibility (AMS) recorded the strain related to the Early Cretaceous extensional processes in synrift sediments of the Maestrat basin (eastern Spain). Forty-two sites, distributed throughout the Lower Cretaceous sequence with dominant gentle dips, were sampled. Minerals contributing to the AMS are mainly phyllosilicates. The parallelism between magnetic and sedimentary foliation seems to indicate that a primary (synsedimentary and early diagenetic) magnetic fabric was preserved at 84% of sites. Consequently, preferred orientations of magnetic lineations are interpreted to record the effect of extensional processes coeval with sedimentation and diagenesis during this period. At these 35 sites, two main magnetic lineation orientations are found, delimiting two large domains: a NE–SW orientation prevailing in the NW sector of the basin (parallel to the extension direction of the Iberian basin), and NW–SE to NNW–SSE orientations to the SE (parallel to the extension direction controlling the western Tethys margin). Directional variability demonstrates that the Maestrat basin is located at the boundary between two domains (Iberian and Tethyan) undergoing different plate-scale extensional processes. The subsequent Cenozoic tectonic inversion affected the synsedimentary magnetic fabrics at only a few sites at the borders of the basin, where compressive features are more developed

Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)

Determining transport direction in thrusts is one of the main issues to study deformation and to achieve reliable balanced cross-sections reconstruction of inverted basins and thrust systems. Anisotropy of Magnetic Susceptibility provides a tool to study deformation in fault rocks through the relationships between the magnetic susceptibility ellipsoid and deformational structures. The Cameros-Demanda Thrust (N Spain) shows a relatively simple history, with an average N-directed movement during the Cenozoic, and provides the possibility of determining the relationships between magnetic fabrics and transport directions in thrusts. The outcropping rocks are Mesozoic limestones in the hangingwall of the main thrust and Cenozoic conglomerates and Albian sandstones and coal in its footwall. Illite crystallinity and organic matter maturity indicate P-T conditions on the order of....The study of AMS in fault rocks (more than 400 samples distributed in 25 sites with fault gouge, breccia and microbreccia) in the Cameros thrust and its comparison with kinematic indicators (foliation, S/C structures and slickenside striations) indicates, in spite of the a priori simple relationships inferred from thrust geometry, a complex history of movements, changing from top-to-the-NW to top-to-the-NE along the history of Cenozoic thrusting. The transport direction is either oblique to the magnetic lineation and perpendicular to the strike of magnetic foliation, and can be checked with shear structures observed in thin sections and other kinematic indicators. The results obtained indicate that AMS can give clues about the transport direction in thrusts depending on the particular structures developed in each studied area

Panorámicas para un corte de la vertiente surpirenaica en la zona de estructuras oblicuas de Aínsa – Valle del Cinca

En la vertiente meridional de los Pirineos, la franja comprendida entre las latitudes 0º9’30’’O y 0º26’30’’E, que tiene su eje en torno al valle del río Cinca, tiene caracteres peculiares en su estructura: la dirección de los pliegues y cabalgamientos se aparta de la dirección pirenaica dominante..

The Sediment Green-Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin

Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard-generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate-related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high-resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox-sensitive sedimentary U/Th generally co-varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B-derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet-alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high-resolution paleoceanographic records that circumvent the traditionally laborious methodology.publishedVersio

Deep submarine infiltration of altered geothermal groundwater on the south Chilean Margin

Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V JOIDES Resolution Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.publishedVersio

A deletion at Adamts9-magi1 Locus is associated with psoriatic arthritis risk

Objective: Copy number variants (CNVs) have been associated with the risk to develop multiple autoimmune diseases. Our objective was to identify CNVs associated with the risk to develop psoriatic arthritis (PsA) using a genome-wide analysis approach. Methods: A total of 835 patients with PsA and 1498 healthy controls were genotyped for CNVs using the Illumina HumanHap610 BeadChip genotyping platform. Genomic CNVs were characterised using CNstream analysis software and analysed for association using the χ2 test. The most significant genomic CNV associations with PsA risk were independently tested in a validation sample of 1133 patients with PsA and 1831 healthy controls. In order to test for the specificity of the variants with PsA aetiology, we also analysed the association to a cohort of 822 patients with purely cutaneous psoriasis (PsC). Results: A total of 165 common CNVs were identified in the genome-wide analysis. We found a highly significant association of an intergenic deletion between ADAMTS9 and MAGI1 genes on chromosome 3p14.1 (p=0.00014). Using the independent patient and control cohort, we validated the association between ADAMTS9-MAGI1 deletion and PsA risk (p=0.032). Using next-generation sequencing, we characterised the 26 kb associated deletion. Finally, analysing the PsC cohort we found a lower frequency of the deletion compared with the PsA cohort (p=0.0088) and a similar frequency to that of healthy controls (p>0.3). Conclusions: The present genome-wide scan for CNVs associated with PsA risk has identified a new deletion associated with disease risk and which is also differential from PsC risk

Decrypting magnetic fabrics (AMS, AARM, AIRM) through the analysis of mineral shape fabrics and distribution anisotropy

The fieldwork was supported by the DIPS project (grant no. 240467) and the MIMES project (grant no. 244155) funded by the Norwegian Research Council awarded to O.G. O.P.'s position was funded from Y-TEC.Anisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X-ray micro-computed tomography to directly compare mineral shape-preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and > 50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: the magnetite and the amphibole shape fabrics and the magnetite spatial distribution. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P’ = 1.079). If shape fabrics and/or magnetite distribution are non-coaxial, the resulting AMS is weakly anisotropic (P’ = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first-order implications for the interpretation of petrofabrics using magnetic methods.Publisher PDFPeer reviewe