Thirty years (1988-2018) of advances in the knowledge of the structural evolution of the south-central Pyrenees during the Cenozoic collision, a summary

La cadena Pirenaica ha atraído una gran atención, lo que ha producido una gran cantidad de artículos científicos y tesis doctorales sobre las relaciones de la estructura-sedimentación durante la colisión. En años recientes, la aplicación de técnicas geofísicas y geoquímicas han permitido cuantificar (en ocasiones de manera cualitativa) los procesos que han estado activos durante la convergencia de las placas Ibérica-Euroasiática desde el Santoniense tardío hasta el Mioceno. Esta convergencia produjo una cadena de dirección ONO-ESE estrecha, de ~ 1000 km de longitud que se extiende desde el Golfo de León hasta el margen de Galicia. La parte centro-occidental del Pirineo ístmico es donde se centra este trabajo, donde se agrupa un resumen de los trabajos realizados en las últimas tres décadas (1988-2018). El agrupamiento se centra en las técnicas utilizadas a lo largo de estos años: cortes geológicos compensados, limitaciones a partir de anomalías magnéticas del fondo oceánico, gravimetría…, que contribuyen a calcular el acortamiento que se ha producido durante la convergencia; datos geoquímicos que proporcionan información sobre paleotemperaturas y edades de levantamiento/exhumación, paleomagnetismo y fábricas magnéticas que permiten calcular rotaciones de eje vertical, edades de sedimentos sintectónicos y la deformación de las rocas; y modelos analógicos que apuntan factores que influyen en el desarrollo de la deformación. Se han añadido unos comentarios breves sobre los estadios pre-convergencia y sobre la evolución post-orogénica de la cuenca de antepaís del Ebro. Finalmente se muestra un resumen con la cronología más relevante sobre la actividad de los distintos cabalgamientos y la exhumación de la parte interna de la cadena. A pesar de la gran cantidad de datos, aún queda por resolver la aparente inconsistencia entre algunos de ellos. The Pyrenean Chain has drawn an extensive attention which has produced a plethora of research papers and doctoral theses about the structure-sedimentation relationships, and in recent years, geophysical and geochemical techniques have allowed quantifying the processes active during the convergence of Iberian-Eurasian plates from late Santonian to Miocene times. This convergence produced a WNW-ESE striking, narrow asymmetric chain of ~1000 km in length from the Gulf of Lion to the Galicia margin. The west-central part of the Pyrenean isthmus is the focus of this work, where a summary of some of the last 30 years’ publications are grouped by technique(s): geological balanced cross-sections and geophysical constraints from oceanic magnetic anomalies, gravimetry…, which contribute to calculate shortening; geochemical data that provide information about paleotemperatures and ages of uplift; paleomagnetism and magnetic fabrics which allow calculating vertical axis rotations, dating syntectonic sediments and getting information about the strain in rocks; and analog models and their input in the understanding of the Pyrenean deformation. Short comments about the pre-convergence stages and post-orogenic evolution of the Ebro foreland basin are also included. Finally, a chronostratigraphic chart with a summary of the main events (activity of thrust sheets and uplifted areas) is shown. Despite many data have been collected, some inconsistencies are not yet resolved

The case of a southern European glacier which survived Roman and medieval warm periods but is disappearing under recent warming

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

The Use of Magnetic Susceptibility as a Technique to Measure the Impact of Wildfires on Archaeological Heritage

Wildfires are one of the main threats of natural areas and often fires can affect protected or heritage areas and properties, in which the preservation requirements demand the use of non-destructive techniques (NDTs). The magnetic susceptibility is an NDT that provides information on the mineralogical composition of the materials but has never been applied to the evaluation of fires. Here, we combine laboratory with field analysis to test the applicability of the magnetic susceptibility for the assessment of the impacts of wildfires. The laboratory results showed an increase in the magnetic susceptibility with the temperature, more evident in the samples heated to 600 °C and above. The in situ measures revealed a spatial variation in the magnetic susceptibility, which was related to the behaviour of the fire in the area. The samples were later analysed with other magnetic destructive techniques that were used to confirm the mineralogical processes that occurred in the materials. The increase in the susceptibility values were due to the formation of iron oxides. The destructive analysis also showed the presence of minerals such as hematite and magnetite in the samples. Overall, the study allowed a first approach to test the magnetic susceptibility as a simple and fast way to measure the impacts of wildfires

A Paleomagnetic Inspection of the Paleocene-Eocene Thermal Maximum (PETM) in the Southern Pyrenees

Magnetic properties of rocks can be useful for determining paleoenvironmental changes. A dramatic climate change that occurred in the Paleocene-Eocene Thermal Maximum (PETM) modified the environment and, hence, the magnetic properties recorded in the sediments. New paleomagnetic data from marine records of the PETM in the Southern Pyrenean zone displays a variation of the magnetic parameters in four different sections. The magnetic signal reveals a positive excursion of magnetic values starting before the onset of the marly interval of La Faja de las Flores Mb (beginning of the PETM record, Ilerdian) in the Carriata section with a maximum value in the marly interval. A similar magnetic signal is observed in the Bujaruelo section (~10 km south of Carriata at PETM times) that is related directly to the marly interval of Faja de las Flores Mb. However, towards the south, the PETM interval does not appear in the sedimentary record; therefore, in the southern Gallisué section, no magnetic excursion occurs. In the southernmost-studied Entremón section, a positive magnetic excursion occurs in a thin marly interval unrelated to the PETM, and in two lower intervals of the column. All sections were later subjected to deformation during the pyrean orogeny and the three northernmost sections in the regional cleavage front, where pressure solution and remagnetizations have been described. A post-folding remagnetization component is found in the three northern sections

Reducción de la resistencia por aumento de la temperatura en una granodiorita de una zona arqueológica afectada por incendios

Los incendios suponen una de las mayores causas de destrucción del Patrimonio Natural y Cultural. El aumento brusco de temperatura durante un incendio provoca la reducción de la resistencia mecánica de las rocas. El presente trabajo evalúa los efectos mecánicos generados por las altas temperaturas en una granodiorita relacionada con el yacimiento arqueológico de El Berrueco (Ávila – Salamanca). Los resultados muestran un descenso en las propiedades mecánicas del material, que es menor hasta 400oC y catastrófico y penetrativo a partir de 600oC

Datación magnetostratigráfica de la molasa Surpirenaica (Fm Uncastillo, Oligoceno-Mioceno)

The Uncastillo Fm crops out along the southern boundary of the External Sierras, which represents the southernmost limit of the Pyrenean Range. Three tectosedimentary units related to tectonic pulses have been previously differentiated in this formation. The sedimentary evolution of the Uncastillo Fm is mainly related to the tightening of the WNW-ESE Santo Domingo anticline in the External Sierras during Chattian-Aquitanian times and records the younger tectonic movement of the south Pyrenean sole thrust. The Uncastillo Fm represents the change to overall southwardflowing alluvial and fluvial systems from overall west-northwest-flowing fluvial systems (Campodarbe Fm). Recent magnetostratigraphic results from the underlying Campodarbe Fm shift to younger ages (from chron 10r to 7r) the top of the Campodarbe Fm in the proximal area of the fluvial system (Luesia fan). In order to check that reassignment and refine the age of the Uncastillo Fm, a new magnetostratigraphic study has been conducted in laterally equivalent deposits that represent middle-distal areas located to the east of the Luesia fan. These deposits consist of mudstones with interbedded sandstones. These finer grain size sediments allow for a magnetostratigraphic sampling in the Fuencalderas section of ~1300 m, which complete the chronostratigraphic frame of the last tectonic pulses of the Pyrenean Range.Trabajo financiado por los proyectos SEROS (CGL 2014-55900-PL), DR3AM (CGL2015- CGL2014-55118) y Grupos Geotransfer y Análisis de Cuencas de la Universidad de Zaragoza. Es una contribución del Institut de Recerca Geomodels y del Grup de Geodinàmica i Anàlisi de Conques (2014SGR467).Peer Reviewe

Multi-episodic remagnetization related to deformation in the Pyrenean Internal Sierras

The Internal Sierras (IS) in the southern margin of the Western and Central Axial Zone (Southern Pyrenees) are affected by a syn-orogenic remagnetization that provides information to reconstruct deformation geometries at the time of acquisition of magnetization. Furthermore, the IS structure changes strike along its structural trend, from ∼N120 to 130°E in the western and eastern margins to ∼N070–090°E in the central part. Palaeomagnetic techniques have been used to (i) accurately define the timing of remagnetization with regard to deformation and (ii) determine if the along-strike trend variation in the IS was induced by deformation and thrust emplacement during the Pyrenean compression or, on the contrary, was the result of a primary orientation controlled by structures inherited from pre-orogenic times. From 23 new palaeomagnetic sites, collected in Upper Cretaceous marls and marly limestones, two meaningful and stable palaeomagnetic components were resolved, principally carried by magnetite: (1) a lower-temperature component (B) that unblocks between 200 °C and 325–400 °C and (2) a higher-temperature component (C) that has been successfully isolated by means of combined thermal (up to 400 °C) and AF demagnetization (generally up to 50–100 mT). The B component is a late remagnetization that post-dates folding and emplacement of basement thrust sheets in the IS (mainly the Gavarnie thrust). It supports small but statistically significant clockwise rotations in the western part of the IS (from +18 to +26°). These rotations can be attributed to the westwards shortening decrease in the thrust system below the Gavarnie unit that results from its along-strike structural change, with a higher number of basement thrusts to the east. The C component has been interpreted as an early remagnetization, based on the results of conglomerate and fold tests. This component predates basement thrusting and is diachronous across the study area: reverse and normal polarities dominate in the eastern and western margins of the IS, respectively. New and previous palaeomagnetic data point out that curvature in the IS is probably a primary feature and the along-strike change in their trend could be interpreted as the result of basement geometrical features inherited from Variscan, Late Variscan or Mesozoic times. A complex, multi-episodic remagnetization probably related to burial and deformation processes occurred during Eocene times

Strain variations in a seismogenic normal fault (Baza Sub-basin, Betic Chain): Insights from magnetic fabrics (AMS)

AMS and structural analysis are here applied to study the deformed zone associated with a large-scale, active normal fault in the central Betic Cordillera (Spain), namely the Baza fault system, to determine: i) the kinematics of structures and their relation with fault zone architecture and segmentation degree, ii) the correlation between deformational structures and the different types of magnetic fabrics and iii) the evolution of magnetic fabrics patterns, from sedimentary to shear-related, associated with normal faults. Five outcrops (969 samples) were analysed along the fault trace, which shows different degrees of segmentation along strike and strong localization of deformation along narrow fault zones. A first, main set of magnetic fabric data corroborates the normal kinematics of the Baza fault, showing magnetic lineations parallel to the dip-slip, transport direction. A second, secondary set of magnetic lineations, is parallel to the intersection lineation, and can be related to less intense deformation in the fault rocks. Furthermore, a detailed study (523 samples) of a trench excavated across the fault zone, where two fault splays tend to coalesce in a linkage relay zone indicates that i) lithology and distance to fault planes are two factors that control the development of extension-related magnetic fabrics in weakly deformed sediments, ii) the development of shear-related fabrics in fault zones entails the mechanical rotation of minerals, iii) different orientation of magnetic lineations are related to different intensity of bulk deformation and iv) magnetic lineation is useful to define local deviations of deformation axes produced by changes in the local extension direction (from fault-perpendicular to fault-parallel extension) in the linkage zone between adjacent fault splays