Caracterización paleomagnética de procesos deformacionales en cuencas intraplaca (Alto Atlas Central): diapirismo, compresión e intrusiones ígneas

El uso de las remagnetizaciones inter-plegamiento suponen una herramienta idónea para el estudio de cuencas intraplaca invertidas, cuya geometría extensional está modificada por la compresión, y la presencia de este tipo de remagnetizaciones puede ser usada como control geométrico al momento de la adquisición de la remagnetización, siempre que sendos estados de deformación (el previo y el posterior a la remagnetización) sean coaxiales. La aplicación de las técnicas basadas en círculos menores a la remagnetización cretácica (portada por magnetita) presente en el Alto Atlas Central (Marruecos) permite esclarecer algunos aspectos de la evolución de la cuenca, tales como la datación relativa de la foliación tectónica presente en el área, o la importancia de los procesos halocinéticos e ígneos en la generación de las estructuras. Por otro lado, el estudio de las fábricas magnéticas de las calizas remagnetizadas ha permitido esclarecer algunos aspectos sobre el crecimiento de los granos de magnetita.Inter-folding remagnetizations are a useful to analyze inverted basins, whose extensional geometry was overprinted during compression. If both deformation stages are coaxial, this kind of remagnetizations can be used as geometric control at the remagnetization occurrence. The Jurassic carbonates of the Central high Atlas (Morocco) show an inter-folding remagnetization carried by magnetite. Using the small circle tools, the presence of this widespread remagnetization allow to shed light in some geological aspect about the Central High Atlas evolution, as the relative dating of the cleavage present in the area, or the role of halokinesis and igneous intrusion in the development of the characteristic structures present in the Atlas. On the other hand, the analysis of the magnetic fabrics carried by the remagnetized carbonates gives some clues about the growth of the magnetite grains that carry the remagnetization

Evidence of remagnetized red-beds in the Middle Atlas (Morocco)

Se ha realizado un estudio paleomagnético en el límite entre el Atlas Medio Plegado y el Atlas Medio Tabular, en el entorno de los sinclinales de Skoura y Tighboula y el anticlinal de Boulemane. La finalidad de este trabajo es tratar de reconocer una remagnetización que afecte a los materiales sedimentarios de dicha área. Para ello se han realizado diferentes test de estabilidad: (i) dos test del pliegue, uno en el anticlinal de Boulemane muestreando cinco estaciones paleomagnéticas en calizas jurásicas, y otro en el sinclinal de Tighboula, con tres estaciones en capas rojas del Cretácico Inferior; (ii) un test del conglomerado en un nivel basal del Cretácico. Los resultados de dichos test indican que en capas rojas la componente característica es una remagnetización sinpliegue, mientras que la señal magnética en las calizas es débil y no permite aislar ninguna componente paleomagnética. La similitud en el comportamiento paleomagnético de las capas rojas (propiedades de la magnetización remanente natural, probable dirección NNW de la remagnetización, polaridad normal sistemática) con la observada en cuencas de similares características del Alto Atlas podrían indicar que ambas remagnetizaciones están relacionadas.A paleomagnetic study has been carried out in the boundary between the Folded Middle Atlas and the Tabular Middle Atlas, around Skoura and Tighboula synclines and Boulemane anticline. The goal of this work is to test the existence of a remagnetization affecting the sedimentary rocks in this area. For this purpose different stability tests were done: (i) two fold tests, one in the Boulemane anticline by studying five paleomagnetic sites located in Jurassic limestones, and the other in the Tighboula syncline in three sites from Cretaceous red-beds; (ii) a conglomerate test was done sampling a Cretaceous basal level and the overlying red-beds. The results of these tests show a synfolding remagnetization in the redbeds, whereas the magnetic signal of the limestones is too weak and it is not possible to isolate a magnetic component. Red-beds shows similar paleomagnetic properties than in other basins of the High Atlas (properties of the natural remanent magnetization, a probably NNW trend of the remagnetization and a systematic normal polarity), which could indicate a relationship between both.Proyecto CGL2012-38481 de la DGICyT, MINECO y por fondos FEDER de la Unión Europea

The carriers of AMS in remagnetized carbonates. Insights for remagnetization mechanism and basin evolution

Magnetic fabrics are usually studied to unravel the evolution of sedimentary basins, mainly focusing the attention in paramagnetic minerals. However, since basins are sometimes affected by burial-related chemical remagnetizations, magnetic fabrics can also be carried by authigenic ferromagnetic minerals related to remagnetization processes. Consequently, the study of the different types of fabrics can give complementary and valuable information about the evolution of sedimentary basins. Here, we explore, in the Jurassic carbonates of the Central High Atlas (Morocco), the role in magnetic fabrics of authigenic magnetite that grew during the Cretaceous (ca. 100 Ma) widespread remagnetization event. Magnetic fabrics are studied in 53 sites using the anisotropy of the magnetic susceptibility measured at room temperature (RT-AMS) and comparing results with sub-fabrics that alternatively enhance the paramagnetic and the ferromagnetic signal. Furthermore, an innovative analysis is proposed, comparing the magnetic fabrics before and after bedding correction (the common procedure) with fabric orientation after partial bedding correction. We use the paleomagnetic information to reconstruct the attitude of bedding at the remagnetization time and to restore the magnetic fabrics at this time. The performed analysis allows interpreting RT-AMS in terms of the contribution of different subfabrics, and the relationship between these, tectonic processes and the magnetic mineralogy. Four RT-AMS types are defined: T1 is carried by superparamagnetic magnetite that grew during the remagnetization stage and shows a horizontal lineation parallel to the extension direction at this time; T3 and T4 are carried by paramagnetic minerals and show compressive fabrics with the magnetic lineation parallel to intersection (bedding-cleavage) lineation; finally, T2 shows a mix between ferrimagnetic and paramagnetic fabrics.MINECO (Spanish Ministry of Economy and Competitiveness) cofinanced by the ERDF (European Union) (research projects CGL2012-38481 and CGL2016-77560)

Magnetic extractions and electronic microscopy observations in Jurassic remagnetized carbonates

IX Congreso Geológico de España, Huelva, 12-14 de septiembre, 2016El estudio de la remagnetización en rocas carbonatadas viene realizándose durante los últimos 40 años, tanto por medio del análisis de sus propiedades magnéticas como tratando de realizar observaciones por medio de microscopía electrónica (SEM/TEM). Los resultados obtenidos con el primer análisis han proporcionado numerosos datos y hoy en día sabemos que generalmente la remagnetización es portada por magnetita. Ésta es de tamaño nanométrico generada durante la diagénesis, correspondiéndose con una remagnetización química. Sin embargo, los numerosos intentos de observación de dichos cristales por medio de SEM/TEM siempre han sido infructuosos y los cristales observados siempre presentan tamaños dentro del rango multidominio. En un nuevo intento de observación directa de dichos cristales mediante microscopía electrónica, hemos realizado nuevos ensayos sobre extractos magnéticos en calizas jurásicas remagnetizadas de las cuencas del Alto Atlas (Marruecos), Cameros y Vasco-Cantábrica (España) según las últimas técnicas propuestas en la literatura. Las propiedades magnéticas de los diferentes subproductos provenientes del proceso de extracción indican una pérdida de material magnético durante el mismo, principalmente las partículas de grano más fino (granos de tamaño monodominio y superparamagnético). Igualmente, mediante SEM/TEM únicamente han podido observarse cristales de magnetita multidominio.Since the last 40 years the analysis of remagnetized carbonates is under debate, by studying their magnetic properties and by using electronic microscopy (SEM/TEM). Results obtained from the first analyses allowed to infer that remagnetization is carried generally by nanometric magnetite and generated during the diagenesis, therefore it corresponds to a chemical remagnetization. However, several attempts to observe these magnetites by SEM/TEM were unsuccessful and in all cases the observed magnetite was in the range of multidomain size. In a new attempt to observe these crystals by electronic microscopy we did new magnetic extracts (according the last techniques proposed in the literature) in Jurassic remagnetized limestones of the High Atlas (Morocco), Cameros and Basque-Cantabrian (Spain) basins. Magnetic properties of the different sub-products of the extracts show a lost of magnetic material during the procedure, mostly of the smallest size (superparamagnetic and single-domain size). Likewise, only multi-domain magnetite grains were observed by SEM/TEM.proyecto CGL2012-38481 de la DGICyT, MINECO y fondos FEDER de la Unión Europea, así cómo por el programa de financiación de la NSF (EEUU) al Institute for Rock Magnetis

Extensional vs. compressional deformation in the Central High Atlas salt province: a paleomagnetic approach

In this paper we address the problem of the distinction between diapiric, salt-driven and compressional structures, using the outstanding example of the Central High Atlas (Morocco). A remagnetized component carried by magnetite has been isolated in 32 new paleomagnetic sites. It is characterized by: maximum unblocking temperatures around 450 °C, syn-folding behavior and normal polarity. These 33 mean paleomagnetic directions were analyzed together with other 68 from published works around the study area to construct a robust paleomagnetic dataset along a cross-section perpendicular to the main structures. The remagnetization direction (n: 100, Dec: 332.2°, Inc: 34.5°, η: 6.2°, ξ: 2.0°, A/n: 6.427°) and the paleo-dip of beds (the attitude of the beds at the remagnetization occurrence) were calculated through small circle methods. The remagnetization can be dated as ca. 100 Ma. Because of its occurrence between the extensional and compressional periods, this remagnetization offers the possibility of restore the basin to its pre-inversion geometry. Comparison between present-day and pre-inversion structure allows discriminating three different evolutionary patterns: (i) thrusted and welded salt-walls mainly structured during the extensional stage (Ikkou ridge) with steep limbs close to the salt-wall core. (ii) Jurassic salt-walls with weaker deformation, restricted to the areas adjacent to the structure (Tadaghmamt and Timedouine); in this case, Cenozoic compression is limited to welding of the salt-walls and buttressing of the sedimentary sequences against faults. (iii) salt-rollers gently initiated during the Jurassic (Toumliline diapir), thrusted during the Cenozoic compression. Results show the importance of salt tectonics both during extension and compression, as well as the control of the compressional features by the inherited extensional structures. The performed restorations prove that paleomagnetism is a useful, independent tool to obtain palinspastic restorations and to separate, and quantify, the imprint generated during the basinal stage from the inversional features.MINECO (Spanish Ministry of Economy and Competitiveness) cofinanced by the ERDF (European Union) (research projects CGL2012-38481 and CGL2016-77560

Analysing non-coaxial folding effects in the Small Circle Intersection method

The Small Circle (SC) tools analyse the stereographic tracks (small circles) followed by the palaeomagnetic vectors during folding processes. Working with interfolding and synfolding remagnetizations, the Small Circle Intersection (SCI) method allows finding the best solution of grouping that should correspond with the remagnetization direction. Once this is known, it is possible to determine the magnetization age as well as the degree of bed tilting at this moment. The SC tools are based on some assumptions, among which the coaxiality between the different deformation events is the one addressed in this work (i.e. absence of vertical axis rotations, VARs, or differential horizontal axis rotations, dHARs). This assumption is based on the necessity of knowing the rotation axis for folding after the acquisition of the remagnetization, and SC tools consider the bedding strike as this axis, something that is only accomplished under coaxial folding. In order to explore how non-coaxiality affects the solutions derived from the SC methods, we first (i) identify the variables that control these errors through simple models that only consider two theoretical palaeomagnetic sites, after that it is possible (ii) to derive the mathematical relationships between them. Finally, we (iii) simulate errors derived from the use of SC tools using a population of 30 palaeomagnetic sites recreating different possible scenarios with VARs and dHARs in nature.Research financed by the projects DR3AM- CGL2014-55118 and CGL2016-77560-C2 from the Spanish Ministry of Science (MINECO) and by the Applied Geology (GeoAP-E0117R) and Geotransfer groups of the Government of Aragon, as well as by the project BU235P18 (Junta de Castilla y Leon, Spain) and the European Regional Development Fund (ERD). It has also benefited from the MAGIBER-II network (CGL2017-90632-REDT) funded by the Ministry of Science, Innovation and Universities

Chronostratigraphy and new vertebrate sites from the upper Maastrichtian of Huesca (Spain), and their relation with the K/Pg boundary

The transitional-continental facies of the Tremp Formation within the South-Pyrenean Central Unit (Spain) contain one of the best continental vertebrate records of the Upper Cretaceous in Europe. This Pyrenean area is therefore an exceptional place to study the extinction of continental vertebrates across the Cretaceous/Paleogene (K/Pg) boundary, being one of the few places in Europe that has a relatively continuous record ranging from the upper Campanian to lower Eocene. The Serraduy area, located on the northwest flank of the Tremp syncline, has seen the discovery of abundant vertebrate remains in recent years, highlights being the presence of hadrosaurid dinosaurs and eusuchian crocodylomorphs. Nevertheless, although these deposits have been provisionally assigned a Maastrichtian age, they have not previously been dated with absolute or relative methods. This paper presents a detailed stratigraphic, magnetostratigraphic and biostratigraphic study for the first time in this area, making it possible to assign most vertebrate sites from the Serraduy area a late Maastrichtian age, specifically within polarity chron C29r. These results confirm that the vertebrate sites from Serraduy are among the most modern of the Upper Cretaceous in Europe, being very close to the K/Pg boundary.Spanish Ministry of Economy and Competitiveness (grant numbers CGL2014-53548-P, CGL2015-64422-P and CGL2017-85038-P), cofinanced by the European Regional Development Fund; and by the Department of Education and Science of the Aragonese Government (grant numbers DGA groups H54 and E05), cofinanced by the European Social Fund (ESF). The paleomagnetic study was possible thanks to the complementary grants (beneficiaries of FPU, grant number CGL2010-16447/BTE: Brief Stays and Temporary Transfers, year 2015) supported by the Spanish Ministry of Culture, Education and Sports; and the Laboratory of paleomagnetism of the University of Burgos (Spain). Eduardo Puértolas Pascual is the recipient of a postdoctoral grant (SFRH/BPD/116759/2016) funded by the Fundação para a Ciência e Tecnologia (FCT-MCTES)

Evaluation of the potential mobility of metals at industrial wastes in an urban environment (barrio de la Almozara, Zaragoza)

El cierre en 1979 de la Industrial Química de Zaragoza dejó los residuos industriales de tostación de piritas en el subsuelo del actual barrio de La Almozara (Zaragoza). Estos residuos, de carácter granular y constituidos por óxidos de Fe y Fe-Ti, poseen elevadas concentraciones en Tl, As, Mo, Cu, Sb, Ag, Pb y Be, que superan ampliamente los niveles genéricos de referencia. La interacción de estos residuos con agua provoca soluciones con pH=3,2, dando lugar a una movilización elevada de Cu, Zn, Cd, Mn y Co. Sin embargo, cuando estos residuos están mezclados con material granular de construcción, las soluciones resultantes de la interacción mantienen un pH neutro y la movilización elemental es muy inferior, siendo solo relevante para Se y Mo. Los resultados obtenidos demuestran el potencial riesgo de contaminación del medio hidrogeológico que supone la presencia de las escorias en el subsuelo y su alta dispersabilidad eólicaPyrite roasting wastes coming from a former industry closed in 1979 are still present at the subsoil of La Almozara neighborhood (Zaragoza, Spain). These granular wastes are mainly composed of Fe- and Fe-Ti-oxides, also having high Tl, As, Mo, Cu, Sb, Ag, Pb, and Be content that far exceed the generic reference levels. When these waste materials interact with water, they produce acid solutions with pH=3,2, resulting in a high mobilization of Cu, Zn, Cd, Mn, and Co. However, when wastes are mixed with granular construction materials, leachates showed neutral pH and chemical mobilization was much lower being only significant for Se and Mo. The results here obtained demonstrate the potential risk for hydrogeological contamination posed by the presence of these wastes in the subsoil and the high eolic dispersability of such material

Characterizing the Source of the Eastern Galicia Magnetic Anomaly (NW Spain): The Role of Extension in the Origin of Magnetization at the Central Iberian Arc

The Eastern Galicia Magnetic Anomaly is the best studied anomaly of the Central Iberian Arc. This is due to its location, on the Lugo-Sanabria gneiss dome, and to the fact that its source rocks crop out in the Xistral Tectonic Window. Multiple studies of this anomaly have been carried out, but still, new results keep on shedding light on its understanding. This paper presents the first results on rock magnetic analyses, natural remanent magnetization, anisotropy of the magnetic susceptibility, X-ray diffraction, and stable isotopes geochemistry carried out on the source rocks of this anomaly. Results suggest that magnetization responds to the increase in oxygen fugacity underwent by rocks affected by late Variscan (330-300 Ma) extensional tectonics. Extensional detachments were the pathways that allowed the entrance of fluids that led to syntectonic crystallization of magnetite and hematite in metasediments and inhomogeneous S-Type granitoids derived from their partial melting. Accordingly, magnetization is not linked to lithologies, but to extensional structures developed in the late Carboniferous/earliest Permian, during the Kiaman reverse superchron. Systematic reverse magnetic remanence exhibited by hematite-bearing samples confirms the age of the magnetization and adds complexity to the interpretation of the anomaly. Understanding the EGMA contributes to the interpretation of other anomalies existing in the CIA, also located on thermal domes. The observed extension-related magnetization probably affected most of the NW Iberian Massif, thus hindering the study of previous tectonics by paleomagnetic techniques. This work aims to provide new hints to interpret magnetic anomalies located in extensional tectonic contexts worldwide.Projects SA065P17 and BU235P18, funded by the Regional Castilla-León Government, (2) Salamanca University through different lines of funding related to its support to research groups program, (3) projects CGL2016-78560-P and CGL2016-77560 of the Spanish Ministry of Economy, Industry and Competitiveness, and (4) project PID2019-108753GB-C21/AECI/10.13039/501100011033 of the Agencia Estatal de Investigación