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The Zafra de Záncara anticline (also known as the El Hito anticline), located in the Loranca Cenozoic Basin (part of the Tagus Basin, Central Spain), had been studied by several oil companies during the late 1960s and early 1970s. In 2009, within the ‘Plan for selection and characterization of suitable structures of CO 2 geological storage’, this anticline was selected as a potential CO 2 storage site. A preliminary three-dimensional geological model, based on five geological cross sections that were constrained with the interpretation of the available seismic profiles (that are rather old and do not have very good quality), was created. With the aim of improving the geological knowledge of the Zafra de Záncara anticline and helping to investigate the suitability of a nearby anticline, namely La Rambla, as another structural closure that might make it a possible CO 2 storage site, a local gravity survey (1 station every km 2 ) was carried out in the area, seven new geological cross sections, based on these existing seismic profiles and field geology, were build, and a new three-dimensional geological model that included both anticlines, improved through three-dimensional stochastic gravity inversion, was constructed. The densities needed for the geological formations of the model come from the analysis of rock samples, logging data from El Hito-1 drillhole and petrophysical information from Instituto Geológico y Minero de España database. The inversion has improved the knowledge about the geometry of the anticlines’ traps and seals as well as the geometry of the basement relief and the structural relationship between basement and cover. © 2019 European Association of Geoscientists & Engineers, This study has been supported by the Instituto para la Reestructuración de la Minería del Carbón y el Desarrollo Alternativo de las Comarcas Mineras, Ministry of Energy and Industry, Spain

The southwest Taiwan fold-and-thrust belt is forming on the outer shelf and slope of the Eurasian continental margin. It comprises a roughly N-S striking, west verging imbricate thrust system that has been developing since the Late Miocene. Here we present the results of new surface geological mapping from which we construct balanced and restored cross sections and along-strike sections. From these we compile maps of the basal thrust, thrust branch lines and, where possible, stratigraphic cutoffs. To interpret the structure in the subsurface and beneath the basal thrust, we use a P wave velocity of 5.2km/s as a proxy for the top of the Mesozoic basement. We divide the southwest Taiwan fold-and-thrust belt into a number of thrust sheets that form the basis of our description and interpretations. From these data we interpret the 3-D structure of the fold-and-thrust belt and the influence that the structure and morphology of the continental margin is having on its development. We show that there is a significant along-strike change in the structure. This change takes place across a transverse zone that is composed of a suite of structures at the surface. We suggest that this transverse zone has a causal relationship with variations in the geometry of the basal thrust which in turn is related to (possibly fault bounded) basement highs and lows that are inherited from the continental margin. Plain Language Summary The southwest Taiwan fold-and-thrust belt comprises a roughly N-S striking, west verging imbricate thrust system that has been developing since the Late Miocene. We present the results of new surface geological mapping from which we construct balanced and restored cross sections and along-strike sections. We compile maps of the basal thrust, thrust branch lines, and stratigraphic cutoffs. We divide the southwest Taiwan fold-and-thrust belt into a number of thrust sheets that form the basis of our description and interpretations. From these data we interpret the 3-D structure of the fold-and-thrust belt and the influence that the structure and morphology of the continental margin is having on its development. We show that there is a significant along-strike change in the structure. This change takes place across a transverse zone that is composed of a suite of structures at the surface. We suggest that this transverse zone has a causal relationship with variations in the geometry of the basal thrust which in turn is related to (possibly fault bounded) basement highs and lows inherited from the continental margin., D. B., J. A-M., and C. B. acknowledge funding provided by the Spanish Ministerio de Economia y Competividad grant CGL2013-43877-P. H. K-C. acknowledges funding by MOST 104-2628-M-008-005-MY3.

Studies of mountain belts worldwide show that along-strike changes are common in their foreland fold-and-thrust belts. These are typically caused by processes related to fault reactivation and/or fault focusing along changes in sedimentary sequences. The study of active orogens, like Taiwan, can also provide insights into how these processes influence transient features such as seismicity and topography. In this paper, we trace regional-scale features from the Eurasian continental margin in the Taiwan Strait into the south-central Taiwan fold-and-thrust belt. We then present newly mapped surface geology, P-wave velocity maps and sections, seismicity, and topography data to test the hypothesis of whether or not these regional-scale features of the margin are contributing to along-strike changes in structural style, and the distribution of seismicity and topography in this part of the Taiwan fold-and-thrust belt. These data show that the most important along-strike change takes place at the eastward prolongation of the upper part of the margins necking zone, where there is a causal link between fault reactivation, involvement of basement in the thrusting, concentration of seismicity, and the formation of high topography. On the area correlated with the necking zone, the strike-slip reactivation of east-northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones. Here, basement is not involved in the thrusting, there is weak focusing of seismicity, and localized development of topography. We also show that there are important differences in structure, seismicity, and topography between the margins shelf and its necking zone.

EGU General Assembly 2020, Online, 4–8 May 2020, Studies of mountain belts worldwide have shown that the structural, mechanical, and kinematic evolution of their foreland fold-and-thrust belts are strongly influenced by the structure of the continental margins that are involved in the deformation. The area on and around the island of Taiwan provides an unparalleled opportunity to investigate this because the entire profile of the SE margin of the Eurasian plate, from the shelf in the north to the slope and continent-ocean transition in the south and the offshore, is currently involved in a collision with the Luzon arc on the Philippine Sea plate. Taiwan can, then, provide key insights into how such features as rift basins on the shelf, the extensional faults that form the shelf-slope break in the basement, or the structure of the extended crust and morphology of the sedimentary carapace of the slope can be directly reflected in the structural architecture, the location and pattern of seismicity, topography, and the contemporaneous stress and strain fields of a fold-and-thrust belt. For example, east-northeast striking faults that have been mapped on the necking zone of the Eurasian margin can be traced into the island of Taiwan where they are causing important along-strike changes in various aspects of the structural, mechanical, kinematic, and morphological behavior of the fold-and-thrust belt. In particular, across the upper part of the necking zone there is an abrupt north-south change in structure, an increase in the amount of seismicity, an increase in topography, a rotation of the direction of maximum compressive horizontal stress, of the GPS displacement vectors, the compressional strain rate, and the maximum shear strain rate. These changes are interpreted to be caused by east-northeast striking, dextral strike-slip faulting in the basement that is taking place as a result of the reactivation of pre-existing faults along the upper part of the necking zone. The abrupt southeastward increase in topography across the upper part of the necking zone is the surface expression of the basal thrust of the fold-and-thrust belt ramping down into the basement, with maximum elevations reached in the basement-involved thrust sheets, suggesting a causal link between basement involvement in the thrusting and high topography. On the shelf, the roughly northeast-oriented Hsuehshan Trough is inverting along almost north-south striking basin bounding faults that penetrate into the middle crust and have well-clustered, deep seismicity. There are no substantial differences in the contemporaneous stress and strain field. There is, however, a clear relationship between basement involvement in the thrusting and the development of high topography in the Hsuehshan Range. Only the upper part of the slope is involved in the fold-and-thrust belt in southernmost Taiwan. In this area, there is a reduction of the amount of seismicity and lower topography. The largest part of the corresponding thrust wedge developed in the lower slope is offshore., This work is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades grant PGC2018-094227-B-I00.

In this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (sigma(1), sigma(2) and sigma(3)) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (S-H) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of SH from north to south across the study area, with the direction of SH remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45 degrees counter-clockwise. The direction of the horizontal maximum compression strain rate (epsilon(H)) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. We interpret the southward change in the SH, eH and the dextral maximum shear plane directions, together with that of the horizontal displacement field to be related to the reactivation of east-northeast striking faults inherited from the rifted Eurasian margin and to the shelf/slope break. Inherited faults in the basement are typically reactivated as strike-slip faults, whereas newly formed faults in the fold-and-thrust belt are commonly thrusts or oblique thrusts. Eastwards, the stress inversions and strain data show that the western flank of the Central Range is undergoing extension in the upper crust. SH in the Central Range is roughly parallel to the relative plate convergence vector, but in southwestern Taiwan it undergoes a marked counter-clockwise rotation westwards across the Chaochou fault. Farther north, however, there is no significant change across the Lishan fault. This north to south difference is likely due to different margin structures, although local topographic effects may also play a role., DB, JA-M and CB acknowledge funding provided by the Spanish Ministerio de Ciencia, Innovacion y Universidades (former Ministerio de Economia y Competitividad) grants CGL2013-43877-P. H. and PGC2018-094227-B-I00, with additional support from the Generalitat de Catalunya grant 2017SGR1022.

This article presents the second study of ochres associated with the Lower Magdalenian (18.7 cal kya) “Red Lady” human burial in El Mirón Cave (Cantabria, Spain). In the first study (Seva Román et al., 2015), we determined that the burial deposit contained iron oxides and idiomorphic hematite that were not from sources near the site, but possibly from Monte Buciero, some 27 km to the north on the present Atlantic shore in Santoña. We have now analyzed sediments both from the burial and from samples taken during prospection on Monte Buciero, along with ochres from deposits above the burial layer, from the face of a large limestone block immediately adjacent to the burial, and from an area of the cave wall close to it in the NE corner of the cave vestibule that bears the engraving of a horse. As before, the analyses used were binocular microscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM-EDX) and inductively coupled plasma mass spectrometry (ICP-MS). We were thus able to determine that the sources of the ochres in the burial deposit and on the block are the same—Monte Buciero. However we found substantial differences between the ochre on the block and the ochre underlying the horse panel image on the cave wall, which very likely also dates to sometime in the Magdalenian. This ochre analysis project was financed by Ministerio de Ciencia y Tecnología of Spain (HAR2010-22115-C02-02).

The main objective of this work is to characterize the structures belonging to the Altomira Range and Loranca Basin (SW Iberian Chain, Central Spain) in terms of understanding their present-day orientation, highly oblique with respect to the NW-SE orientation of adjacent structures of the Iberian Chain. The Altomira and Loranca fold and thrust belts present a slightly curved geometry with a general north-south orientation at their central sector, and structures oriented NNE-SSW and north-south to NNW-SSE at their northern and southern sectors, respectively. Palaeomagnetic data from Middle Eocene-Lower Miocene rocks (including clays, fine sandstones and limestones) reveal the absence of vertical-axis rotations in the central sector of the studied area, where structures are oriented north-south, and up to 17° of clockwise and 21° of anticlockwise vertical-axis rotations in the northern and southern sectors, respectively. These data are supported by calculations of the theoretical vertical-axis rotations from shortening estimates and basement-cover structural relationships. This approach highlights the importance of integrating different datasets to characterize the obliquity of fold and thrust belts. © 2016 The Author(s)., This work was funded by the project KINESAL (CGL2010-21968-C02-02) of the Spanish Ministry of Economy and Competitiveness and a PhD-IGME grant for the first author. It is a contribution of the Geomodels Research Institute and the Grup de Recerca de Geodinámica i Análisi de Conques (2014SGR467, supported by the Agència de Gestió d’Ajuts Universitaris i de Recerca and the Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya).

Magnetotelluric surveys were conducted to investigate the structure in the El Hito Anticline in the southern Loranca Basin, Spain. The structure of this anticline is partly known from nearby data (geological cross sections, geological maps, well-logs) from vintage geophysical and geological basin-scale surveys. Unfortunately, these surveys do not have the appropriate resolution to determine certain characteristics of the anticline accurately, such as the thickness or geometry of geological units. To address this deficiency, magnetotelluric data were acquired at 51 sites along three profiles to image the electrical resistivity of the anticline. To identify a geologically reasonable resistivity model, a conceptual model based on previous geological and geophysical information (cross sections and well-log data) was generated. Several inversions were performed using the conceptual model, which played a key role in the interpretation of the magnetotelluric data, and the construction of a suitable initial model was essential in producing geologically meaningful models. Using these results, we obtained 2-D resistivity models that provide information on the main geological units and structures. We also performed sensitivity tests to understand the morphology and structure of the resistive basement better. The results indicate the presence of basement highs that show different structural styles for the basement and its cover, and an increase in the basement depth towards the south. The final 2-D resistivity models provide new information regarding the structure of the anticline and demonstrate a clear correlation between the main geological units and resistivity, as well as correlations with mapped surface faults.

Los resultados de este trabajo se insertan dentro de los proyectos “El horizonte campaniforme y los inicios de la jerarquizacion social en la cuenca del Vinalopo (gre09/15), financiado por el Programa de Proyectos Emergentes de la Universidad de Alicante, y “VIII-IV milenios cal BC: Arte rupestre, poblamiento y cambio cultural entre las cuencas de los rios Jucar y Segura” (HAR2009-13723), financiado por el Plan Nacional de I+D+i 2008-2011 del Ministerio de Ciencia y Tecnologia del Gobierno de Espana.