Suchergebnisse

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.

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.

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).