The chronology and rotational kinematics in the South-Eastern Jaca Basin (Southern Pyrenees): Las Bellostas section

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The significant difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Pico del Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust

Rotational kinematics of the southpyrenean basal thrust at the Sierras Exteriores Aragonesas: Magnetotectonic data

[ES] El estudio magnetotectónico de 32 estaciones localizadas, principalmente, en las margas de la formación Arguis a lo largo de las Sierras Exteriores Aragonesas (Pirineo Suroccidental) nos ha permitido caracterizar la estabilidad y el carácter primario de la magnetización registrada por estas rocas e interpretar las diferencias con el campo de referencia (Iberia estable) en términos de cinemática rotacional asociada al cabalgamiento basal surpirenaico en este sector. La estabilidad de la magnetización se fundamenta en la constancia de los intervalos de definición de las direcciones (300" - 425°C en el tratamiento térmico) y en la homogeneidad de los portadores magnéticos en las estaciones estudiadas (que siempre fueron fases de baja coercitividad, probablemente sulfuros y10 magnetita). Por otra parte, se puede demostrar que dicha magnetización se adquirió en el momento del depósito de las rocas (Eoceno medio) por varios motivos; la constancia de la inclinación magnética (47,3" +/- 1,7") y su similitud con la dirección de referencia; la existencia de inversiones y el test del pliegue positivo realizado con las estaciones del anticlinal del Pico del Águila; así como la congruencia entre la dirección de referencia (DEC=005", INC=51°, q5=6') y la calculada en la zona autóctona del sector occidental de las Sierras (DEC=005', INC=38', ag5=8 "). La interpretación de los datos paleomagnéticos en el contexto de la estructura deja patente la componente rotacional horaria de los cabalgamientos asociada a la formación de las Sierras Exteriores, observándose valores máximos de 42' en el sector occidental y de 30" en el central. Asimismo, la edad de dicha rotación parece migrar hacia el W (simultánea y anterior al depósito de la Fm. margas de Arguis, Priaboniense, en el sector central y simultánea al depósito de la Fm. Campodarbe, Sannoisiense-Stampiense, en el sector occidental) y se puede afirmar que ha habido rotación diferencial entre sectores adyacentes. Para explicar la no acumulación de las rotaciones es necesaria la existencia de estructuras de articulación que separarían zonas con diferente componente rotacional, como parece ocurrir en los anticlinales de Rasa1 y Anzañigo.[EN] The magnetotectonic analysis of 32 sites located along the External Sierras (mainly in Middle Eocene marls) shows the primary character of the magnetisation and pennits the differences between the paleovectors obtained to be interpreted as a result of the rotational kinematics of the southpyrenean floor thrust in the study area. The constancy of the directions of the defined unblocking intervals (300"-425°C for the thermal treatment) and the homogeneity of the magnetic carriers (these were always low coercitivity phases, probably sulphides andlor magnetite) prove the stability of the magnetisation. On the other hand, the primary character of the magnetisation (Middle Eocene) can be demonstrated by: a) the constancy of the magnetic inclination (47.3 +/- 1.7) and its similarity with the reference direction; b) the occurrence of reversals, and the positive result of the fold-test made in the Pico del Águila anticline; c) the consistency between the reference direction (DEC = 005", INC = 51°, a95=6 ") and the direction obtained for the authocthonous footwall (DEC = 005", INC = 38", a95= 8") which crops out in the western sector of the Sierras Exteriores thrust front. The interpretation of the paleomagnetic data within the External Sierras structural framework clearly shows that the kinematics of individual thrust sheets involves a clockwise component, at least during a period of their evolution. The maximum rotation values were found in the western and central sectors (42" and 30" respectively). The age of the rotation decreases towards the west along with the age of deformation of the cover rocks. Starting in late Priabonian the kinematics of the thrust front resulted in a lack of rotation in the central sector of the Sierras, while the western sector undenvent a clockwise rotation. The differential movement between both sectors gave rise to the development or reactivation of structures (i. e. Rasal-Anzáñigo anticlines) that articulated the deformation of adjacent zones with different rotational components.lEste trabajo ha sido financiado por una beca de la Institución Fernando el Católico (Dip. Prov. de Zaragoza) durante 1993 y una beca de Formación de Profesorado Universitario (M.E.C.) 1996- concedidas al primero de los firmantes, una beca CONA1 (DGA') concedida al segundo firmante, así como por los proyectos PB93-1218 DGICYT y una acción integrada Hispano-Austríaca (HU1995-0023). Ana Gómez del laboratorio de Paleomagnetismo de ICT "Jaume Almera" CSIC se encargó de buena parte de los análisis preliminares durante 1992. Carlos Sabariego (Saba) y Tomás Arauzo colaboraron en los muestreos. Todas las proyecciones estereográficas se realizaron utilizando el programa Stereonet (v. 4.9.5) de R. Allmendinger, a quien estamos muy agradecidos por su generosidad. La revisión de Jaume Dinarés fue especialmente provechosa.Peer reviewe

Systematics of Lutetian larger foraminifera and magneto-biostratigraphy from the South Pyrenean Basin (Sierras Exteriores, Spain)

A systematic description of the Eocene larger foraminifera recorded in the South Pyrenean Basin (Sierras Exteriores) is presented herein. The large dataset provided in this work includes Nummulites and Alveolina species, along with a variety of other porcellaneous and hyaline taxa with lesser biostratigraphic relevance. Most of the larger foraminifera described in this work correspond to the Lutetian (SBZ13 to SBZ16 biozones) interval, but late Ypresian (SBZ11, Cuisian) and early Bartonian (SBZ17) shallow benthic zones have also been identified. A new species, Idalinaosquetaensis, is described. The systematic revision of middle to late Lutetian alveolines led to a reassessment of Alveolinafusiformis and the finding of two new precursor forms, described as Alveolina aff. fragilis and Alveolina aff. elongata. The new taxa fill in the gap existing so far in the middle to late Lutetian alveolinid biostratigraphy. Despite not being exclusive to SBZ16, these forms provide realiable biostratigraphic information in facies where Nummulites are not present. This realibility lies on the correlation of Nummulitesand Alveolina biostratigraphic markers in the same sections and their calibration to the global time scale through magnetostratigraphy. Magnetostratigraphic calibration of described taxa is provided, along with an update of the SBZ calibration to the Geological Time Scale (Gradstein et al., 2012).&nbsp

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

Systematics of Lutetian larger foraminifera and magneto-biostratigraphy from the South Pyrenean Basin (Sierras Exteriores, Spain)

An extense systematic description of the Eocene larger foraminiferal faunas recorded in the South Pyrenean Basin (Sierras Exteriores) is presented herein. The large dataset provided in this work includes both Nummulites and Alveolina species, along with a variety of other porcellaneous and hyaline taxa with lesser biostratigraphic relevance, are represented. The larger foraminifera described in this work correspond mainly to the Lutetian (SBZ13 to SBZ16 biozones) interval, but late Ypresian (SBZ11, Cuisian) and Bartonian (SBZ17) shallow benthic zones have also been identified. As one of the most relevant results of this systematic analysis, a new species, Idalina osquetaensis, is described. The systematic revision of middle to late Lutetian alveolines led to a reassessment of A. fusiformis and the finding of two new precursor forms, described as affinis of their corresponding species, A. aff. fragilis and A. aff. elongata. The new forms A. aff. elongata and A. aff. fragilis fill the gap in the middle to late Lutetian alveolinid biostratigraphy. Despite not being exclusive to SBZ16, these new forms provide realiable biostratigraphic information where Nummulites are not present. This realibility lies on the correlation of Nummulites and Alveolina biomarkers in the same sections and their calibration to the global time scale through magnetostratigraphy. In fact, magnetostratigraphic calibration of all described taxa is also provided, along with an update of the SBZ calibration to the current Geologic Time Scale (Gradstein et al., 2012)

Sistema de Información Geográfica de las propiedades magnéticas de los granitos del Pirineo

En el presente trabajo se han georreferenciado las estaciones de medida de anisotropía de sus-ceptibilidad magnética pertenecientes a 21 cuerpos graníticos distribuidos a lo largo del Pirineo. Además se ha realizado una labor de homogeneización de la información que se ha plasmado en la generación de cartografías de síntesis, tanto a escala de cadena como de forma individual (ba-tolito), siguiendo los estándares de la Norma Cartográfica de Aragón. Estos datos provienen de distintas publicaciones sobre anisotropía de la susceptibilidad magnética (ASM) como técnica para caracterizar la estructura y deformación interna de los granitos, su modo de emplazamiento y su relación con la evolución estructural de las rocas encajantes

Three-dimensional Reconstruction of the Caspe Geological Structure (Spain) for Evaluation as a Potential CO2 Storage Site

The Caspe geological structure was formed by the convergence of the Iberian Range and the Catalonian Coastal Range, during the Tertiary compression. Traditionally, the Caspe structure has been interpreted from seismic profiles without considering surface structural data. The aim of this study is to build a 3D geological model taking into account the structural data from the geological map, stress fields and lineaments, and evaluate its possibility as potential CO2 storage site. Four surfaces have been modelled: Buntsandstein Top, Muschelkalk-I Top, Muschelkalk-II Top and Cenozoic Bottom. Considering the geometry and depth for storage the target reservoir was considered to be the Buntsandstein facies. The available seismic data indicate that the Buntsandstein facies top is at approximately 500 m depth and hosts a deep saline aquifer. The target reservoir series include the conglomerate and sandstone of the Hoz del Gallo and Cañizar Fms (Buntsandstein Facies) with an average thickness of 500 m and 21% porosity. The seal comprises the shales and silts of the Röt Fm with an average thickness of 100-150 m. The structure volume was calculated based on the -500 mbsl for the Buntsandstein top deepest closed contour lines. The estimated volume is 5, 800 Mm3 with most of CO2 in gaseous state

The early/middle Eocene transition at the Ésera valley (South Central Pyrenees): Implications in Shallow Benthic Zones (SBZ)

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulitesand Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12

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

La Geología de las sierras de Santo Domingo y Salinas como recurso de desarrollo rural: Propuesta de guía divulgativa; propuesta de gestión y conservación

En este trabajo se valora la potencialidad de la geología de las Sierras de Santo Domingo y Salinas como recurso turístico que fomente el desarrollo rural del sector septentrional de la comarca de las Cinco Villas (Zaragoza). Para ello se propone la elaboración de una guía divulgativa y unas medidas de gestión y conservación del patrimonio geológico, enmarcadas en un futuro Plan de Ordenación de los Recursos Naturales (PORN). A partir de la síntesis geológica se resalta el valor excepcional de las Sierras y se seleccionan unos puntos de interés geológico y unos itinerarios que los enlazan. Síntesis geológica, inventario de puntos de interés e itinerarios son la base para la elaboración de la guía divulgativa. Con las medidas de gestión y conservación se contempla la puesta en valor del patrimonio geológico, sus usos y aprovechamiento (difundir el valor divulgativo, científico y turístico) y sus potenciales amenazas y pautas de protección. El ámbito rural es un buen soporte para dar a conocer y conservar el patrimonio geológico, y a su vez la geología puede representar un recurso adicional con el que contribuir a la reactivación económica del medio rural