Reverse magnetic anomaly controlled by Permian igneous rocks in the Iberian Chain (N Spain)

Two important reverse dipolar magnetic anomalies in the Iberian Chain (Spain) are located over Permian igneous rocks. A detailed study of one of them, the Loscos magnetic anomaly, where the geological structure is well constrained, reveals that the source of the anomaly must be a reverse remanent magnetisation carried by igneous rocks, acquired during the period of the Kiaman reverse magnetic superchron. Magnetic and gravimetric detailed survey (with 50 new gravimetric measurements and 8 main magnetic profiles -six of them N–S and the rest E–Wwith a total length of 40km), together with a study of the petrophysical characteristics of igneous materials, data processing and interpretation (upward continuation, 2.5D modelling, etc.) allowed to characterize qualitatively the anomaly and its source. Two overlapping anomalies with different wavelength were identified, indicating the presence of a shallower strongly altered igneous body with heterogeneous magnetic properties, and a deeper, large igneous body, responsible for the main, long-wavelength anomaly

Diachronous folding and cleavage in an intraplate setting (Central High Atlas, Morocco) determined through the study of remagnetizations

Remagnetizations are common in intraplate basins. When remagnetizations occur at an intermediate stage between different tectonic processes, they can be used for paleo-geometrical reconstructions and relative dating of different structures. This has a particular interest in geological frameworks where other geological time markers are absent. In order to apply this methodology, it is necessary to calculate the regional remagnetization direction and subsequently to use this reference direction to restore the attitude of the beds at the moment of remagnetization acquisition. In this work, we use this methodology for dating a pervasive cleavage (whose time of formation is controversial) and the associated structures in the Central High Atlas (Morocco). Paleomagnetic directions from 64 sites were used to calculate the remagnetization direction (D = 330.9°, I = 35.1°, A/n = 6.107) which is coincident with the Albian-Cenomanian (ca. 100 M.a.) expected direction for NW Africa. This direction was used to restore the Mesozoic paleo-geometry of beds allowing us to analyze bedding orientation, cleavage and folding relationships between the present day and the Cretaceous geometry. After restoration we conclude that the development of cleavage post-dates remagnetization, being in relation with Cenozoic basin inversion. However, the paleo-geometry shows incipient folds at Cretaceous times, which can be related to an intra-Mesozoic compressional event

Emplacement and Deformation of Mesozoic Gabbros of the High Atlas (Morocco): Paleomagnetism and Magnetic Fabrics

A paleomagnetic and magnetic fabric study is performed in Upper Jurassic gabbros of the central High Atlas (Morocco). These gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults. These structures were reactivated as anticlines during the Cenozoic compressional inversion. Gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization, carried by magnetite, which has been interpreted as a primary component. This component shows an important dispersion due to postemplacement tectonic movements. The absence of paleoposition markers in these igneous rocks precludes direct restorations. A novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks. Paleomagnetic vectors are distributed along small circles with horizontal axes, indicating horizontal axis rotations of the gabbro bodies. These rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases. Due to the uncertainties inherent to this work (the igneous bodies recording strong rotations), interpretations must be qualitative. The magnetic fabric is carried by ferromagnetic (s.s.) minerals mimicking the magmatic fabric. Anisotropy of magnetic susceptibility (AMS) axes, using the rotation routine inferred from paleomagnetic results, result in more tightly clustered magnetic lineations, which also become horizontal and are considered in terms of magma flow trend during its emplacement: NW-SE (parallel to the general extensional direction) in the western sector and NE-SW (parallel to the main faults) in the easternmost structures

Aportaciones de la modelización analógica al estudio de la deformación intraplaca

Se han realizado modelos analógicos de sistemas frágil/dúctil dinámicamente dimensionados. Los experimentos consistieron en comprimir longitudinalmente un paquete de arena con un nivel basal de silicona que funciona como un nivel de despegue. Las condiciones en los límites se eligieron para analizar la influencia de la migración lateral del nivel dúctil, así como de la velocidad de deformación en el patrón de deformación resultante. Los resultados obtenidos indican que cuando el nivel dúctil migra lateralmente el mayor engrosamiento cortical no se produce en la zona más próxima al back-stop, sino que aparece desplazado hacia el interior del modelo. Dynamically scaled brittle/ductile analogue models have been performed. Experiments consisted of the compression of a sand-pack with a basal ductile layer of silicone putty acting as a décollement level. The boundary conditions were chosen to analyze the influence of the lateral migration of the ductile level and the strain rate on the deformational pattern. Results show that when the ductile level migrates laterally, the higher thickening is obtained far from the back-stop creating a high relief in the pro-wedge region

Nuevas aportaciones sobre la estructura de la terminación occidental del anticlinal Barbastro-Balaguer

En este trabajo se presenta el estudio estructural de la terminación occidental del anticlinal de Barbastro-Balaguer. Con base en una síntesis cartográfica, nuevos datos estructurales, la interpretación de perfiles de sísmica de reflexión y la reinterpretación parcial de varios sondeos profundos de la zona, se han elaborado dos cortes geológicos. Éstos, más un tercer corte de autores previos, permiten describir la estructura de la terminación occidental del anticlinal en tres sectores distintos. En el sector oriental, o de Calasanz, el anticlinal se desdobla en dos ramas, individualizando un sinclinal laxo entre ambas. En el sector central, o del Cinca, el flanco sur del anticlinal lo componen los materiales autóctonos de la Cuenca del Ebro y el flanco norte, la lámina basal de las Sierras Marginales se dispone sobre los yesos de la Fm. Barbastro y sus equivalentes terrígenos laterales. En el sector occidental, o de Bierge, un retrocabalgamiento enraizado en la Fm. Barbastro caracteriza la estructura. A pesar del control estructural, ciertas interpretaciones de la geología en profundidad tendrán que precisarse mediante la aplicación futura de técnicas geofísicas. In this work we present a structural study of the western end of the Barbastro-Balaguer anticline. We elaborated two new cross sections based on a geological map synthesis, new structural data, seismic reflection profiles interpretation and the reinterpretation of well log data. These two cross sections together with an already published one allow to describe the subsurface structure in three different sectors. In the eastern or Calasanz sector, the anticline splays into two branches that individualize a gentle syncline in between. In the central or Cinca sector, the southern flank is composed by Ebro Basin deposits whereas in the northern flank the basal Sierras Marginales thrust sheet lies onto the equivalent terrigenous facies of the Barbastro Fm. In the western or Bierge sector a backthrust rooted on the Barbastro Fm. characterizes the structure. Despite the proper structural control, several interpretations of the subsurface geology can be further constrained by means of the application of different techniques

Petrophysical properties in the Iberian Range and surrounding areas (NE Spain): 1-density

We introduce the first map of density data in Northeastern Spain which can help in the interpretation of gravimetric surveying. The background map is a simplified version of the Geode continuous geological cartography (scale 1:200.000) of the Iberian Range and Ebro basin. These maps are synthetic and homogeneous maps based on previous 1:50, 000 scale geological maps (MAGNA). The map uses the ETRS89 datum and UTM coordinates (30T northern zone) and covers an area of 140, 000 sq km. The compiled data shown in the map come from previous papers of the region (˜ 700 points) as well as from more than 800 additional points developed in the course of an exploratory project focused on the underground characterization of a potential CO2 reservoir in the so-called ‘Linking Zone''. The new data accomplish some basic criteria; they are accurately georeferenced and lithology, stratigraphic age and other technical details about the measurements (e.g. means and error) and methods are fully displayed

Primeros datos magnetoestratigráficos y nuevos yacimientos del Maastrichtiense superior en Huesca (sector noroccidental de la Cuenca de Tremp).

Las facies continentales de la Cuenca de Tremp contienen uno de los abundantes registros con vertebrados continentales del final del Cretácico en Europa. Esta área de los Pirineos es un lugar excepcional para estudiar la extinción de los vertebrados continentales en el límite Cretácico-Paleógeno (K-Pg) al ser uno de los pocos lugares de Europa con un registro sedimentario continuo de depósitos continentales del Campaniense superior al Daniense. En el entorno de Serraduy, localizado en el flanco noroeste del sinclinal de Tremp, se han recuperado abundantes restos de vertebrados en los últimos años, destacando la presencia de dinosaurios hadrosáuridos y crocodilomofos eusuquios. Sin embargo, aunque provisionalmente estos yacimientos se han situado en el Maastrichtiense superior, nunca habían sido datados con métodos absolutos o relativos. En este trabajo se exponen por primera vez los resultados preliminares de datación magnetoestratigráfica en este sector, permitiendo asignar estos yacimientos a una edad Maastrichtiense superior dentro de los crones C30n y C29r. Estos resultados confirmarían que los yacimientos de vertebrados del área de Serraduy son unos de los más modernos del Cretácico Superior de Europa estando muy cercanos al límite K-Pg. The continental facies of the Tremp Basin contain one of the best continental vertebrate record from the Upper Cretaceous of Europe. Therefore, this area of the Pyrenees is an exceptional place to study the extinction of continental vertebrates across the Cretaceous-Paleogene boundary (K-Pg) being one of the few places in Europe that has a continuous record of continental deposits ranging from the upper Campanian to Danian. The area of Serraduy, located on the northwest flank of the Tremp syncline, has reported abundant vertebrate remains in recent years, highlighting the presence of hadrosaurid dinosaurs and eusuchian crocodylomorphs. Nevertheless, although these deposits have been provisionally assigned as Maastrichtian, they never had been dated with absolute or relative methods. This paper presents for the first time the preliminary magnetostratigraphic dating results in this sector, allowing to assign these vertebrate sites to a late Maastrichtian age within the polarity chrons C30n and C29r. These results confirm that the vertebrate sites of the Serraduy area are among the most modern in the Upper Cretaceous of Europe, being very close to the K-Pg boundary

Reverse magnetic anomaly controlled by Permian Igneous rocks in the Iberian Chain (N Spain)

Two important reverse dipolar magnetic anomalies in the Iberian Chain (Spain) are located over Permian igneous rocks. A detailed study of one of them, the Loscos magnetic anomaly, where the geological structure is well constrained, reveals that the source of the anomaly must be a reverse remanent magnetisation carried by igneous rocks, acquired during the period of the Kiaman reverse magnetic superchron. Magnetic and gravimetric detailed survey (with 50 new gravimetric measurements and 8 main magnetic profiles -six of them N?S and the rest E?W- with a total length of 40km), together with a study of the petrophysical characteristics of igneous materials, data processing and interpretation (upward continuation, 2.5D modelling, etc.) allowed to characterize qualitatively the anomaly and its source. Two overlapping anomalies with different wavelength were identified, indicating the presence of a shallower strongly altered igneous body with heterogeneous magnetic properties, and a deeper, large igneous body, responsible for the main, long-wavelength anomaly

Evolution of the ridges of Midelt-Errachidia section in the High Atlas revealed by paleomagnetic data

New paleomagnetic data (43 sites) from Mesozoic sediments are contributed in this work, verifying the presence of a pervasive syntectonic Early Cretaceous remagnetization in the easternmost area of the Moroccan High Atlas. Using the small circle intersection method, we have calculated the characteristic remagnetization direction (Dec: 337.3, Inc: 38.4) that fits with a 100-Ma age, according to the Apparent Polar Wander Path of Africa. The paleomagnetic vectors of remagnetization are used to obtain the geometry during the remagnetization stage (100Ma) of one of the most renowned geological cross sections of the High Atlas, the Midelt-Errachidia profile. The partial restoration of the cross section at 100Ma allows us to determine the dips of the beds at the remagnetization stage in five structures (ridges or anticlines). Our results indicate that the five ridges that configure the Midelt-Errachidia profile were initiated to different degrees prior to wholesale compressive deformation during the Cenozoic. This configuration can be explained according to two different scenarios that we discuss in this paper: transpression and diapirism. The geological model obtained, both at present and at 100Ma, indicates the existence of a Mesozoic cover substantially decolled from the Paleozoic basement, what strongly contrasts with previously published transects of the same area

Polymorphism at High Molecular Weight Glutenin Subunits and Morphological Diversity of Aegilops geniculata Roth Collected in Algeria

A collection of 35 accessions of the tetraploid wild wheat Aegilops geniculata Roth (MM, UU) sampled in northern Algeria was evaluated for morphological and biochemical variability. Morphological and ecological analyses based on morphological traits and bioclimatic parameters, respectively, were assessed using principal component analysis (PCA). Accessions were differentiated by width characters, namely spike’s width, and a weak relationship between morphological traits and ecological parameters was found. Polymorphism of high molecular weight (HMW) glutenin subunits was carried on by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Among accessions analyzed, 27 alleles were identified at the two loci Glu-M1 and Glu-U1: resulting in twenty-nine patterns and a nomenclature was proposed. Two alleles at the Glu-U1 locus expressed a new subunit with a slightly slower mobility than subunit 8. These results provide new information regarding the genetic variability of HMW glutenin subunits, as well as their usefulness in cultivated wheat quality improvement