Magnetoestratigrafía del Eoceno inferior y medio en el frente Surpirenaico (Sierras Exteriores): implicaciones cronoestratigráficas y cinemáticas

Esta tesis describe un trabajo centrado en la aplicaciones de técnicas paleomagnéticas con el fin de abordar diferentes problemáticas y enfoques estructurales en la parte central y oriental de las Sierras Exteriores de la Cuenca surpirenaica (del Pirineo Alto aragonés). Se presenta la adquisición un conjunto robusto y denso de nuevos datos magnetoestratigráficos a lo largo de casi 2 Km de serie en facies marino someras, principalmente de las Formaciones Boltaña y Guara con la finalidad de aportar una nueva cronología en la cuenca para el Cuisiense y Luteciense. Se presentan un conjunto significativo de datos bioestratigráficos para recalibrar de las biozonas de macroforaminíferos bentónicos involucradas. También se presenta un apartado de estudio de desarrollo metodológico de modelos numéricos y un caso de estudio que aborda en problema de solapamiento de componentes paleomagnéticas. Fuente de error que afecta los valores y estabilidad de los datos paleomagnéticos y que gracias a este estudio puede ser cuantificable y abordable. Finalmente, un estudio de generación de datos robustos y de calidad para el control de cinemática de la estructura del anticlinal de Balzes y alrededores del entorno de Arguis permite develar el origen mixto de la curvatura del pliegue y acotar etapas de plegamiento y rotación para las zonas de estudio. Estos aspectos en conjunto aquí desarrollados, aportan gran cantidad de datos de muy buena calidad y representan una aportación innovadora y significativa para el Eoceno inferior y medio de la Cuenca surpirenaica occidental

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 important 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, Picodel 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

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 important 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, Picodel 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

Flexural unfolding of complex geometries in fold and thrust belts using paleomagnetic vectors

Three-dimensional reconstructions of the subsurface are an important field in Earth Sciences due to their considerable socio-economic implications as exploration of petroleum resources. 3D reconstruction aims at providing a plausible image of the underground which entail the integration of discrete and heterogeneous datasets. They are based on geometric/mechanic laws and are designed to tackle areas with scarce and heterogeneous data. Restoration algorithms are an important tool to validate these 3D geological reconstructions of the subsurface. Restoration is the way back from the deformed to the undeformed states. Undo the deformation and achieve an initial surface with geological meaning is useful to validate the reconstruction of the folded structure and the deformation processes assumed. The main postulate in most restoration methods is the horizontality of the initial layers while restoration algorithms are based in several deformation processes as flexural slip or simple shear. We deepen in restoration techniques in next chapter but we want to emphasize the importance of a continuous feedback between reconstruction and restoration. This become especially important when complex deformation processes are implied and limited data is available. In addition, restoration tools may also be useful to predict deformation patterns for well characterized structures. However, existing restoration methods do not always succeed for complex structures like non-cylindrical, non-coaxial and/or areas undergoing vertical-axis rotations (out-of-plane motions). We suggest using paleomagnetic information, known in the undeformed (horizontal) and deformed states, as an additional and powerful constraint to improve restoration methods and to reduce the uncertainty of the results. The use of paleomagnetism in restoration tools was recommended in the early 1990¿s. So far, however, relatively few researchers have tried using paleomagnetic information to double-check the rotation inferred from restoration methods and hardly ever paleomagnetism is used as primary information of these tools. In this PhD we want to show how paleomagnetism can reduce the uncertainty in restoration tools when it is used as a constraint, particularly for structures with out-of-plane motions. The bedding plane is the basic 2D reference to relate the undeformed and deformed states, but never could be a real 3D indicator. Our proposal is the usage of paleomagnetism together with the bedding plane as references known in both states. The bedding plane determines the horizontal rotation and paleomagnetism the vertical axis rotation. Paleomagnetic vectors are the record of the ancient magnetic field at the time of the rock formation and we assume that it behaves as a passive marker during the deformation process. Its original orientation can be known in the undeformed surface, and it is represented by the paleomagnetic reference vector. If we see the deformation mechanisms, paleomagnetism allow reducing the number of variables, since it is a passive marker that records the internal deformation and provides us with information of vertical axis rotation. Because accurate paleomagnetic data is necessary to improve results we also work on a good data acquisition. Paleomagnetism may be incorporated in many restoration tools, particularly; we centre our study in geometrical surface unfolding algorithms valid for globally developable surfaces. Developable surfaces are those with Gaussian curvature equal to zero everywhere. These surfaces in geology are stratigraphic horizons folded under flexural conditions that have minimum internal deformation. That implies surfaces isometrically folded with preservation of lengths and angles and consequently with preservation of area. By globally we mean that these constraints are valid almost everywhere but there are areas where internal deformation is possible. We can find this kind of structures in the fold and thrust belts of competent layers at crustal levels. In order to test the restoration methods we develop analog models of complex structures. Laboratory-scale models are based on non-coaxial structures of External Sierras (Pyrenees). These analogs are digitalized with photogrametry and X-Ray CT scanner. In this way, models are completely characterized before and after deformation. This allows the calculus of real deformation of the folded surface and the comparison of the restored surface with the initial one

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

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

Density and magnetic susceptibility relationships in non-magnetic granites; a “wildcard” for modeling potential fields geophysical data

EGU2020: Sharing Geoscience Online, 4-8 May 2020Geophysical surveying (both gravity and magnetic) is of great help in 3D modeling of granitic bodies at depth. As in any potential-field geophysics study, petrophysical data (density [r], magnetic susceptibility [k] and remanence) are of key importance to reduce the uncertainty during the modeling of rock volumes. Several works have already demonstrated that ¿18O or [SiO2] display a negative correlation to density and to magnetic susceptibility. These relationships are particularly stable (and linear) in the so-called ¿non-magnetic¿ granites (susceptibilities falling within the paramagnetic range; between 0 and 500 10-6 S.I.) and usually coincident with calc-alcaline (CA) compositions (very common in Variscan domains). In this work we establish robust correlations between density and magnetic susceptibility at different scales in CA granites from the Pyrenees. Other plutons from Iberia were also considered (Veiga, Monesterio). The main goal is to use the available and densely sampled nets of anisotropy of magnetic susceptibility (AMS) data, performed during the 90¿s and early 2000¿s, together with new data acquired in the last few years, as an indirect measurement of density in order to carry out the 3D modelling of the gravimetric signal. We sampled some sections covering the main range of variability of magnetic susceptibility in the Mont Louis-Andorra, Maladeta and Marimanha granite bodies (Pyrenees), all three characterized by even and dense nets of AMS sites (more than 550 sites and 2500 AMS measurements). We performed new density and susceptibility measurements along two main cross-sections (Maladeta and Mont Louis-Andorra). In these outcrops, numerous measurements (usually more than 50) were taken in the field with portable susceptometers (SM20 and KT20 devices). Density data were derived from the Arquimedes principle applied on large hand samples cut in regular cubes weighting between 0.3 and 0.6 kg (whenever possible). These samples were subsampled and measured later on with a KLY-3 susceptibility bridge in the laboratory. Additionally, some density data were derived from the geometry and weighting of AMS samples. After the calibration of portable and laboratory susceptometers, density and magnetic susceptibility were plotted together. Regressions were derived for every granite body and they usually followed a linear function similar to: r = 2600 kg/m3 + (0.5 * k [10-6 S.I.]). As previously stated, this relationship is only valid in CA and paramagnetic granites, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). These relationships allow transforming magnetic susceptibility data into density data helping in the 3D modelling of the gravimetric signal when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signal

Forest Restoration in a Fog Oasis: Evidence Indicates Need for Cultural Awareness in Constructing the Reference

Background: In the Peruvian Coastal Desert, an archipelago of fog oases, locally called lomas, are centers of biodiversity and of past human activity. Fog interception by a tree canopy, dominated by the legume tree tara (Caesalpinia spinosa), enables the occurrence in the Atiquipa lomas (southern Peru) of an environmental island with a diverse flora and high productivity. Although this forest provides essential services to the local population, it has suffered 90% anthropogenic reduction in area. Restoration efforts are now getting under way, including discussion as to the most appropriate reference ecosystem to use. Methodology/Principal Findings: Genetic diversity of tara was studied in the Atiquipa population and over a wide geographical and ecological range. Neither exclusive plastid haplotypes to loma formations nor clear geographical structuring of the genetic diversity was found. Photosynthetic performance and growth of seedlings naturally recruited in remnant patches of loma forest were compared with those of seedlings recruited or planted in the adjacent deforested area. Despite the greater water and nitrogen availability under tree canopy, growth of forest seedlings did not differ from that of those recruited into the deforested area, and was lower than that of planted seedlings. Tara seedlings exhibited tight stomatal control of photosynthesis, and a structural photoprotection by leaflet closure. These drought-avoiding mechanisms did not optimize seedling performance under the conditions produced by forest interception of fog moisture. Conclusions/Significance: Both weak geographic partitioning of genetic variation and lack of physiological specialization of seedlings to the forest water regime strongly suggest that tara was introduced to lomas by humans. Therefore, the most diverse fragment of lomas is the result of landscape management and resource use by pre-Columbian cultures. We argue that an appropriate reference ecosystem for ecological restoration of lomas should include sustainable agroforestry practices that emulate the outcomes of ancient uses

Anisotropy of magnetic susceptibility of the Pyrenean granites

In this paper, we report on a compilation of more than 2200 sites (more than 10,000 individual measurements) where anisotropy of magnetic susceptibility (AMS) was studied in granites from the Variscan Pyrenees. The standardization and homogenization of this information has allowed us to produce three Main Maps that synthesize all the information related with the AMS of the Pyrenean granites. We also describe the problems found during the construction of the database (variable geo-positioning, different published information, etc.). The information derived from 21 granite bodies, the database, and the synthesis maps (magnetic susceptibility, Km, and the orientation of the magnetic foliation, plane perpendicular to k3, and of the magnetic lineation, k1) allow us to see for the first time a complete image of this important kinematic and petrographic indicator

Residual Bouguer anomalies in the Axial Zone (Central Pyrenees); characteristics and origin

Centro Nacional de Información Geográfica (España)[EN] This work integrates geological, geophysical and petrophysical data in order to study residual Bouguer anomalies localized in the Central Pyrenean Axial Zone (between the Noguera-Ribagorzana and Segre rivers to the West and East, respectively). The study area is characterized by thrust sheets of basement Paleozoic rocks forming an antiformal stack and southwards vergence due to the Alpine orogeny, high structural complexity related to the Variscan and Alpine deformation and scarce subsurface data. The Paleozoic rocks present a high variability both in lithology and age. The geological data are based on published geological cartographies and new acquired data, the gravimetric data consist of previous and new data acquired during the 2018 and 2019 (reaching a total of 3590 gravity stations) and the petrophysical data correspond to 526 density measurements. The Bouguer anomaly map of the study area shows a longwave relative minimum (~40 km) with several relative maxima and minima of short- and medium wave (between 2 and 20 km). The residual anomaly map, which allows to investigate the gravimetric anomalies that originated in the upper crust, shows a complex pattern of maxima and minima that does not follow the N110E Pyrenean main direction. Six NNESSO geological cross sections were gravimetrically modeled. The observed gravity response along the cross sections varies according to lithological and rheological changes in the upper crustal rocks, presence of evaporitic rocks both at surface and subsurface, presence of Upper Carboniferous granites, Ordovician gneisses and Neogene rocks belonging to the Cerdanya basin and rocks with different metamorphic grade. Our results also allow to delineate the lateral continuity of structures. This work highlights, in absence of other more resolute geophysical data, the high potential and applicability of gravity data acquired in structurally complex areas when combining with geological and petrophysical data in order to constrain geological models.Este trabajo se ha financiado con el proyecto PID2020-114273GB-C22 financiado por MCIN/AEI/10.13039/501100011033 del Ministerio de Ciencia e Innovación de España.Peer reviewe