In this paper we present and discuss Cretaceous extensional folds of the eastern Basque-Cantabrian Basin (Northern Spain). Geometry and kinematics of folds is constrained by means of structural and sedimentological fieldwork integrated with geological mapping, revealing an intimate link between coeval folding, extensional faulting, and salt mobilization. In detail, the Mesozoic succession of the northwestern and southern borders of the Palaeozoic Bortziriak-Cinco Villas massif (eastern margin of the BCB) host late Albian–early Cenomanian syn-rift forced folds. The studied forced fold axes trend parallel and are located above main and inferred Cretaceous syn-sedimentary basement faults. Structural data indicate that these folds formed during the late Albian − early Cenomanian interval. The presence of Upper Triassic clay and evaporite outcrops along and/or close to the axes of folds and their stratigraphic relationship with Upper Cretaceous strata indicate their halokinetic origin and extrusion during folding. The trigger of salt tectonics is attributed to a basement extensional pulse during the Bay of Biscay – Pyrenean rifting. Related high subsidence-rates allowed salt to flow towards faults, forming salt walls and causing the inflation and folding of the overburden. ; grant BFI05.398 from the Basque Government to A. Bodego and grant AP98-44159606 from the Spanish Science Ministry to E. Iriarte. Funds were also supplied by Ministerio de Educación y Ciencia (MEC) – Ministerio de Ciencia e Innovación (MICINN) (projects CGL2006-05491/BTE and CGL2009-08545) and Euskal Herriko Unibertsitatea (UPV/EHU) (projects EHU06/62, UNESCO06/03 and EHUA15/18)
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.
18 pages, 9 figures.-- Access to the field data: Bathymetric data from German research cruises (e.g., R/V SONNE SO104, SO244) can be requested through the German Bundesamt für Seeschifffahrt und Hydrographie (BSH; http://www.bsh.de). The bathymetric data collected during R/V Marcus G. Langseth cruise MGL1610 are available from the Rolling Deck to Repository (R2R) Web site (http://www.rvdata.us/). Seismic reflection data from R/V SONNE cruise SO104 are stored at the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) and can be requested through the Geo‐Seas data portal (http://www.geo‐seas.eu/). Access to processed data: The following data used in this manuscript are available from the PANGAEA data archive (https://doi.pangaea.de/10.1594/PANGAEA.893034): (I) A gridded DEM (100 m) that combines the bathymetric data from R/V SONNE cruises SO104, SO244, and R/V Marcus Langseth cruise MGL1610. (II) A GeoTIFF that contains the backscatter information from the multibeam data collected during R/V SONNE cruise SO244 ; New multibeam bathymetry allows an unprecedented view of the tectonic regime and its along-strike heterogeneity of the North Chilean marine forearc and the oceanic Nazca Plate between 19 and 22.75°S. Combining bathymetric and backscatter information from the multibeam data with subbottom profiler and published and previously unpublished legacy seismic reflection lines, we derive a tectonic map. The new map reveals a middle and upper slope configuration dominated by pervasive extensional faulting, with some faults outlining a >500-km-long ridge that may represent the remnants of a Jurassic or pre-Jurassic magmatic arc. Lower slope deformation is more variable and includes slope-failures, normal faulting, re-entrant embayments, and NW-SE trending anticlines and synclines. This complex pattern likely results from the combination of subducting lower-plate topography, gravitational forearc collapse, and the accumulation of permanent deformation over multiple earthquake cycles. We find little evidence for widespread fluid seepage despite a highly faulted upper-plate. An explanation could be a lack of fluid sources due to the sediment starved nature of the trench and most of the upper-plate in vicinity of the hyperarid Atacama Desert. Changes in forearc architecture partly correlate to structural variations of the oceanic Nazca Plate, which is dominated by the spreading-related abyssal hill fabric and is regionally overprinted by the Iquique Ridge. The ridge collides with the forearc around 20–21°S. South of the ridge-forearc intersection, bending-related horst-and-grabens result in vertical seafloor offsets of hundreds of meters. To the north, plate-bending is accommodated by reactivation of the paleo-spreading fabric and new horst-and-grabens do not develop ; R/V SONNE Cruises SO104 (grant 03G104A) and SO244 (grant 03G0244A) were supported by the German Bundesministerium für Bildung und Forschung (BMBF). A. M. T. thanks the U.S. National Science Foundation (NSF) for support through grant OCE1459368. We also thank the crew and technical staff of the R/V Marcus Langseth, which is funded by the NSF and operated by the Lamont‐Doherty Earth Observatory. […] Jacob Geersen was partly funded by a grant (CP1404) of the Cluster of Excellence 80 "The Future Ocean," funded within the framework of the Excellence Initiative by Deutsche Forschungsgemeinschaft (DFG) on behalf of the German federal and state governments. C. R. R. was supported by the Grup de Recerca 2014SGR940 de la Generalitat de Catalunya and Spanish Ministry of Science grant PCIN‐2015‐053. E. C.‐R. gratefully acknowledges the support of the Chilean National Science Foundation (FONDECYT) grant 1170009 and the Programa de Investigación Asociativa: ANILLOS DE INVESTIGACIÓN EN CIENCIA Y TECNOLOGÍA, CONICYT, grant ACT172002, project "The interplay between subduction processes and natural disasters in Chile." ; Peer Reviewed
Abstract. South-eastern Sicily has been affected by large historical earthquakes, including the 11 January 1693 earthquake, considered the largest magnitude earthquake in the history of Italy (Mw = 7.4). This earthquake was accompanied by a large tsunami (tsunami magnitude 2.3 in the Murty-Loomis scale adopted in the Italian tsunami catalogue by Tinti et al., 2004), suggesting a source in the near offshore. The fault system of the eastern Sicily slope is characterised by NNW–SSE-trending east-dipping extensional faults active in the Quaternary. The geometry of a fault that appears currently active has been derived from the interpretation of seismic data, and has been used for modelling the tsunamigenic source. Synthetic tide-gauge records from modelling this fault source indicate that the first tsunami wave polarity is negative (sea retreat) in almost all the coastal nodes of eastern Sicily, in agreement with historical observations. The outcomes of the numerical simulations also indicate that the coastal stretch running from Catania to Siracusa suffered the strongest tsunami impact, and that the highest tsunami waves occurred in Augusta, aslo in agreement with the historical accounts. A large-size submarine slide (almost 5 km3) has also been identified along the slope, affecting the footwall of the active fault. Modelling indicates that this slide gives non-negligible tsunami signals along the coast; though not enough to match the historical observations for the 1693 tsunami event. The earthquake alone or a combination of earthquake faulting and slide can possibly account for the large run up waves reported for the 11 January 1693 event.
The Basque–Cantabrian Basin of the northern Iberia Peninsula constitutes a unique example of a major deformation system, featuring a dome structure developed by extensional tectonics followed by compressional reactivation. The occurrence of natural resources in the area and the possibility of establishing a geological storage site for carbon dioxide motivated the acquisition of a 3-D seismic reflection survey in 2010, centered on the Jurassic Hontomín dome. The objectives of this survey were to obtain a geological model of the overall structure and to establish a baseline model for a possible geological CO2 storage site. The 36 km 2 survey included approximately 5000 mixed (Vibroseis and explosives) source points recorded with a 25 m inline source and receiver spacing. The target reservoir is a saline aquifer, at approximately 1450 m depth, encased and sealed by carbonate formations. Acquisition and processing parameters were influenced by the rough topography and relatively complex geology. A strong near-surface velocity inversion is evident in the data, affecting the quality of the data. The resulting 3-D image provides constraints on the key features of the geologic model. The Hontomín structure is interpreted to consist of an approximately 107 m2 large elongated dome with two major (W–E and NW–SE) striking faults bounding it. Preliminary capacity estimates indicate that about 1.2 Gt of CO2 can be stored in the target reservoir ; Funding for this Project has been partially provided by the Spanish Ministry of Industry, Tourism and Trade, through the CIUDEN-CSIC-Inst. Jaume Almera agreement (Characterization, Development and Validation of Seismic Techniques applied to CO2 Geological Storage Sites) and by the European Union through the Technology Demonstration Plant of Compostilla OXYCFB300 project (European Energy Programme for 534 Recovery). Additional support has been provided by Spanish Ministry of Education Science (CSD2006-00041), Generalitat de Catalunya (2009SGR006) and CSIC JAE-Doc postdoctoral research contract (E.S.). ; Peer Reviewed
The Coles Hill uranium deposit, with an indicated resource of about 130 Mlb of U3O8, is the largest unmined uranium deposit in the United States. The deposit is hosted in the Taconian (approx. 480-450 Ma) Martinsville igneous complex, which consists of the Ordovician Leatherwood Granite (granodiorite) and the Silurian Rich Acres Formation (diorite). The host rock was metamorphosed to orthogneiss during the Alleghanian orogeny (approx. 325-260 Ma), when it also underwent dextral strike-slip movement along the Brookneal shear zone. During the Triassic, extensional tectonics led to the development of the Dan River Basin that lies east of Coles Hill. The mineralized zone is hosted in brittle structures in the footwall of the Triassic Chatham fault that forms the western edge of the basin. Within brittle fracture zones, uranium silicate and uranium-bearing fluorapatite with traces of brannerite form veins and breccia-fill with chlorite, quartz, titanium oxide, pyrite, and calcite. Uranium silicates also coat and replace primary titanite, zircon, ilmenite, and sulfides. Sodium metasomatism preceded and accompanied uranium mineralization, pervasively altering host rock and forming albite from primary feldspar, depositing limpid albite rims on igneous feldspar, altering titanite to titanium oxide and calcite, and forming riebeckite. Various geothermometers indicate temperatures of less than similar to 200 degrees C during mineralization. In situ U-Pb analyses of titanite, Ti-oxide, and apatite, along with Rb/Sr and U/Pb isotope systematics of whole-rock samples, resolve the timing of geologic processes affecting Coles Hill. The host Leatherwood Granite containing primary euhedral titanite is dated at 450 to 445 Ma, in agreement with previously obtained ages from zircon in the Martinsville igneous complex. A regional metamorphic event at 330 to 310 Ma formed anhedral titanite and some apatite, reequilibrated whole-rock Rb/Sr and U-Pb isotopes, and is interpreted to have coincided with movement along the Brookneal shear zone. During shearing and metamorphism, primary refractory uranium-bearing minerals including titanite, zircon, and uranothorite were recrystallized, and uranium was liberated and mixed locally with hematite, clay, and other fine-grained minerals. Uranium mineralization was accompanied by a metasomatic episode between 250 and 200 Ma that reset the Rb-Sr and U-Pb isotope systems and formed titanium oxide and apatite that are associated and, in places, intimately intergrown with uranium silicate dating mineralization. This event coincides with rifting that formed the Dan River Basin and was a precursor to the breakup of Pangea. The orientation of late-stage tectonic stylolites is compatible with their formation during Late Triassic to Early Jurassic basin inversion, postdating the main stage of uranium mineralization and effectively dating mineralization as Mesozoic. Based on the close spatial and temporal association of uranium with apatite, we propose that uranium was carried as a uranyl-phosphate complex. Uranium was locally reduced by coupled redox reactions with ferrous iron and sulfide minerals in the host rock, forming uranium silicates. The release of calcium during sodium metasomatic alteration of primary calcic feldspar and titanite in the host rock initiated successive reactions in which uranium and phosphate in mineralizing fluids combined with calcium to form U-enriched fluorapatite. Based on the deposit mineralogy, oxygen isotope geochemistry, and trace element characteristics of uranium silicate and gangue minerals, the primary mineralizing fluids likely included connate and/or meteoric water sourced from the adjacent Dan River Basin. High heat flow related to Mesozoic rifting may have driven these (P-Na-F- rich) fluids through local aquifers and into basin margin faults, transporting uranium from the basin or mobilizing uranium from previously formed U minerals in the Brookneal shear zone, or from U-enriched older basement rock. ; Published version ; Public domain authored by a U.S. government employee
The Neoproterozoic Schisto-Calcaire Group (630 to ca. 580 Ma) was deposited on an extensive carbonate shelf in the margin of the Congo Craton in the Niari-Nyanga and Comba subbasins (Gabon and Republic of the Congo). It consists of three carbonate-dominated subgroups (SCI to SCIII, up to 1300m-thick) recording relative sea-level changes. The SCI c Formation, at the upper part of the SCI Subgroup, is a carbonate succession of meter-scale shallowing-upward cycles, composed of a standard sequence of 7 facies grouped in 5 facies associations recording the evolution of a marine ramp from distal carbonate muds and giant stromatolitic bioherms (F1–F2) and extensive ooid shoals (F3), to proximal settings submitted to evaporation near a sabkha (F7). Fifth-order 'meter-scale' (or elementary parasequences) packages are grouped into fourth-order sequences (parasequence sets), which are not correlative in the whole basin. Two categories of fifth-order elementary parasequences are recognized, on the basis of physical bounding surfaces: (i) subtidal cycles bounded by marine flooding surfaces across which subfacies deepen; and (ii) peritidal cycles bounded by subaerial exposure surfaces. These cycles are the result of the interplay of relative sea-level changes due to eustatic variations related to periodic extensional tectonic events affecting the whole basin. The Niari-Nyanga and Comba subbasins experienced basin tectonics in the general context of the rifting of Rodinia creating changes of relative sea-level in the different parts of the shelf. The SCI c cycles are enclosed into a third-order sequence with two major transgressive-regressive phases, related to the deposition of the SCI Subgroup. The most typical sedimentologic feature of the SCI c Formation is the deposition of giant stromatolitic bioherms (stacked up to 20m) topped by ooid shoals (up to 75m thick) deposited during high systems tract prograding and forced regressive systems tract phases that ended with a lowstand systems tract phase with evaporitic and karstic conditions at the top of the SCI c Formation. The elementary parasequences and parasequence sets are probably the result of the migration of lateral environments related to the variation of the energy in relation to tectonic setting. As a result, a regional sea-level increase is for the first time highlighted in transgressive systems tract phase (composed of microbial induced sedimentary structures Facies) in the lower part of the SCI c Formation. The third-order succession can be followed more than 100km in the Republic of the Congo and several hundred meters from South of Gabon to the Lower Congo in the Democratic Republic of the Congo. Tentative detailed sequence stratigraphy correlations between both Congo's highlight the role of tectonics affecting both areas.
