Structure of Alluvial Valleys from 3-D Gravity Inversion: The Low Andarax Valley (Almería, Spain) Test Case

This paper presents a gravimetric study (based on 382 gravimetric stations in an area about 32 km2) of a nearly flat basin: the Low Andarax valley. This alluvial basin, close to its river mouth, is located in the extreme south of the province of Almería and coincides with one of the existing depressions in the Betic Cordillera. The paper presents new methodological work to adapt a published inversion approach (GROWTH method) to the case of an alluvial valley (sedimentary stratification, with density increase downward). The adjusted 3D density model reveals several features in the topography of the discontinuity layers between the calcareous basement (2,700 kg/m3) and two sedimentary layers (2,400 and 2,250 kg/m3). We interpret several low density alignments as corresponding to SE faults striking about N140?145°E. Some detected basement elevations (such as the one, previously known by boreholes, in Viator village) are apparently connected with the fault pattern. The outcomes of this work are: (1) new gravimetric data, (2) new methodological options, and (3) the resulting structural conclusions.

Compositional and Geochemical Signatures for the Sedimentary Evolution of the Middle Triassic–Lower Jurassic Continental Redbeds from Western-Central Mediterranean Alpine Chains

Compositional and chemical analyses suggest that Middle Triassic–Lower Liassic continental redbeds (in the internal domains of the Betic, Maghrebian, and Apenninic chains) can be considered a regional lithosome marking the Triassic-Jurassic rift-valley stage of Tethyan rifting, which led to the Pangaea breakup and subsequent development of a mosaic of plates and microplates. Sandstones are quartzose to quartzolithic and represent a provenance of continental block and recycled orogen, made up mainly of Paleozoic metasedimentary rocks similar to those underlying the redbeds. Mudrocks display K enrichments; intense paleoweathering under a hot, episodically humid climate with a prolonged dry season; and sediment recycling. Redbeds experienced temperatures in the range of 100°–160°C and lithostatic/tectonic loading of more than 4 km. These redbeds represent an important stratigraphic signature to reconstruct a continental block (Mesomediterranean Microplate) that separated different realms of the western Tethys from Middle-Late Jurassic to Miocene, when it was completely involved in Alpine orogenesis.

Brachiopod assemblages from the Early-Middle Jurassic transition in the Eastern Subbetic (SE Spain): Systematic and palaeobiogeographic implications and palaeoenvironmental significance

New data on brachiopod assemblages recorded in the Eastern Subbetic area (Alicante, SE Spain) and attributed to the Early Bajocian (Humphriesianum Zone and/or immediately older) are provided. Eleven species have been distinguished and reported for the first time in the Subbetic domain of the Betic Cordillera. The description of the morphological evidences on each analysed taxa, especially in relation to their internal morphology, brings new implications in the systematics of the Middle Jurassic brachiopods. The analysis of faunistic affinity between the recorded assemblages and those from other palaeogeographic domains, shows that the Subbetic brachiopod fauna has a clear Mediterranean affinity, as proved by the different species belonging to the genera Striirhynchia, Septocrurella, Mondegia?, Karadagithyris, Linguithyris, Papodina?, Viallithyris?, and Zugmayeria?. It is also evidenced that the Early-Middle Jurassic transition in the Eastern Subbetic accounted, in qualitative terms, a remarkable interval of faunistic renewal in the brachiopod assemblages, strongly influenced by a complex tectonic and stratigraphic framework controlled by a period of intense extensional tectonics, globally framed in the evolution of the Atlantic Ocean.

Nannoplankton and planktonic foraminifera biostratigraphy of the eastern Betics during the Tortonian (SE Spain)

El final del Serravalliense y principio del Tortoniense es un periodo de fuerte actividad tectónica en la Cordillera Bética. Además, existe un debate sobre la existencia de sedimentos de edad Tortoniense inferior al no existir claras atribuciones fósiles en esa edad. Estos sedimentos se asignan a dicha edad por criterios indirectos, tanto estratigráficos como por la ausencia de contenido fósil más antiguo o más reciente. En este trabajo se describe la sección compuesta de Les Moreres-Albatera, que es probablemente una de las secciones más completas de edad Tortoniense en la bibliografía de la Cordillera Bética, pese a tener un importante hiato de cerca de 1 Millón de años ligado a un evento tectónico intra-Tortoniense. La sección presenta dos unidades litológicas calizas a la base (El Castellà) y al techo (Las Ventanas) y dos unidades intermedias margosas, la inferior, llamada Les Moreres, y la superior, Galería de los Suizos se encuentran separadas por el conglomerado de la Raya del Búho. Se han identificado las biozonas de nanofósiles calcáreos CN5b/NN7 a CN9a/NN11a (Okada & Bukry, 1980; Martini, 1971) y de foraminíferos planctónicos de MMi9 a MMi12a (Lourens et al., 2004). La biostratigrafía de los primeros ha permitido identificar un hiato que incluye la parte alta de las biozonas CN7/NN9 hasta la parte baja de CN9a/NN11a (Okada & Bukry, 1980; Martini, 1971). La integración de los datos biostratigráficos con los paleomagnéticos en la sección Albatera permite la calibración del límite de los magnetocrones C4r.1r/C4n.2n.

Caracterización de los depósitos miocenos de la isla de Nueva Tabarca (Alicante) y su empleo como material de construcción en el patrimonio local

El presente trabajo muestra la caracterización en detalle de la secuencia estratigráfica de los depósitos miocenos de la isla de Nueva Tabarca, el empleo de estos materiales en el patrimonio arquitectónico de la isla y su comportamiento frente la degradación. En la serie miocena, a grandes rasgos, se definen tres tramos. El tramo inferior, rico en clastos dolomíticos, muestra una alternancia de arenitas y calcarenitas. El tramo intermedio corresponde a una sucesión de niveles de calcirruditas con laminación cruzada cuya parte superior está representada por un nivel de grandes bioclastos, rodolitos y arenitas de grano fino. El comienzo del último tramo está marcado por la presencia de varias superficies arenosas más litificadas sobre las que se sitúa un banco de arenitas de grano fino y laminación paralela. Si bien las canteras extraían sillares de todas estas litofacies, existe una mayor extracción de los últimos niveles de la serie. Estas rocas presentan una durabilidad moderada-baja, degradándose fácilmente mediante arenización, escamación y/o alveolización.

Evolución tectónica del borde norte de la cuenca del Bajo Segura. Implicaciones en la evolución de la falla de Crevillente (sector Abanilla-Alicante)

En este estudio presentamos los resultados del análisis estructural del borde norte de la cuenca del Bajo Segura, en la cordillera Bética oriental. En este borde se desarrolla el sinclinal de Crevillente; se trata de un pliegue de propagación de falla con geometría de crecimiento y vergente al sur asociado a la falla de Crevillente (sector Abanilla-Alicante). El estudio cuantitativo de la discordancia progresiva asociada a dicho pliegue ha puesto de manifiesto que la actividad de esta falla se inició en el Tortoniense, aumentó durante el Messiniense y, a partir de ese momento se ha mantenido constante o ha disminuido durante el Plioceno y el Cuaternario. La escasez de depósitos cuaternarios deformados no implica que no exista actividad cuaternaria de la falla de Crevillente (sector Abanilla-Alicante), ya que la mayoría de los depósitos más recientes son discontinuos o se localizan al sur, alejados de la zona de máxima deformación. Por otro lado, el hecho de que la actividad de la falla del Bajo Segura, situada en el borde meridional de la cuenca, se iniciara durante el Plioceno, parece indicar una migración de la deformación hacia el sur.

Seismically-induced landslides by a low-magnitude earthquake: The Mw 4.7 Ossa De Montiel event (central Spain)

The Ossa de Montiel (2015/02/23, Mw 4.7) earthquake struck the central part of Spain and was felt far from the epicenter (> 300 km). Even though ground shaking was slight (Imax = V, EMS-98 scale), the earthquake triggered many small rock falls, most at distances of 20–30 km from the epicenter, greater than previously recorded in S Spain (16 km) for earthquakes of similar magnitudes. The comparative analysis of available data for this event with records from other quakes of the Betic cordillera (S and SE Spain) seems to indicate a slower pattern of ground-motion attenuation in central Spain. This could explain why slope instabilities occurred at larger distances. Instability was more frequent, and occurred at larger distances, in road cuts than in natural slopes, implying that such slope types are highly susceptible to seismically induced landslides.

The Pliocene Mediterranean infilling of the Messinian Erosional Surface: New biostratigraphic data based on calcareous nannofossils (Bajo Segura Basin, SE Spain)

The Bajo Segura Basin (eastern Betic Cordillera) is a Mediterranean marginal basin where the Messinian Erosional Surface (MES), formed during the Messinian Salinity Crisis sea-level fall, is well developed. Overlying this major discontinuity the lower Pliocene transgressive sediments record the reflooding of the Mediterranean and the return to an open marine environment, the continental shelf being rebuilt after the Messinian erosion. The stratigraphic and biostratigraphic study of six sections allows two transgressive-regressive sequences filling the MES to be distinguished, correlated with the previously distinguished Mediterranean offshore seismic units. Ten calcareous nannofossil bioevents have been identified. The lower sequence can be dated according to nannofossil biozones NN12 to NN14 and the upper sequence by NN15 to NN16. The boundary between both lower Pliocene sedimentary sequences occur after the first common occurrence (FCO) of Discoaster asymmetricus found in the uppermost sediments of the lower sequence and before the first occurrence (FO) of Discoaster tamalis in the lowermost part of the upper sequence. Thus this sequence boundary can be estimated at between 4.1 and 4.0Ma ago.

(Table 2) Grain composition of sediments from ODP Hole 161-974B and from beach samples

Miocene to Pleistocene sand and sandstone were recovered at Ocean Drilling Program Site 974 in the Tyrrhenian Basin and Sites 976 and 977 in the Alboran Basin. Sand detrital modes were determined for 45 samples from these sites, as well as 10 samples of Spanish beach sand. At Site 974, the Pleistocene section includes a number of volcaniclastic (vitric ash) and terrigenous sand layers; the latter are heterogeneous and contain sedimentary and metamorphic lithic fragments. Submarine canyon and onshore drainage patterns suggest that the most likely source of this sediment is the Tiber River drainage basin in central Italy, where a Pleistocene volcanic field is superimposed on Apennine orogenic rocks. In contrast, the Miocene sand in Unit III at Site 974 may have been derived from local basement highs. The quartzolithic composition and preponderance of metamorphic and sedimentary lithic debris in sand samples from Unit II at Site 976, Unit I at Sites 977 and 978, and Unit I at Site 979 are consistent with derivation from metamorphic rocks and sedimentary cover sequences that crop out in the Betic Cordillera of southern Spain (976-978) and in the Rif of Northern Africa (979). The sedimentary to metamorphic lithic fragment ratios in these samples reflect the relative proportion of metamorphic and sedimentary rocks exposed in onshore source terranes. In contrast, the source of the few quartzose Pleistocene sands at Site 976 was likely the Flysch Trough Units that crop out near Gibraltar. The significant volcanic component in certain intervals at Sites 976 (upper Miocene) and 977 (lower Pliocene to Miocene) is consistent with widespread volcanic activity during basin inception and development. Mean sand detrital modes for sand subgroups from both the Alboran and Tyrrhenian Basin sites plot in the Recycled Orogenic and Magmatic Arc compositional fields of Dickinson et al. (1983, doi:10.1130/0016-7606(1983)94<222:PONAPS>2.0.CO;2), reflecting the hybrid tectonic histories of these basins.

Table 1. pH, Temperature, conductivity and hydrochemistry of samples

Carbon dioxide deep geological storage, especially in deep saline aquifers, is one of the preferred technological options to mitigate the effects of greenhouse gases emissions. Thus, in the last decade, studies characterising the behaviour of potential CO2 deep geological storage sites along with thorough safety assessments have been considered essential in order to minimise the risks associated with these sites. The study of natural analogues represents the best source of reliable information about the expected hydrogeochemical processes involved in the CO2 storage in such deep saline aquifers. In this work, a comprehensive study of the hydrogeochemical features and processes taking place at the natural analogue of the Alicún de las Torres thermal system (Betic Cordillera) has been conducted. Thus, the main water/CO2/rock interaction processes occurring at the thermal system have been identified, quantified and modelled, and a principle conclusion is that the hydrogeochemical evolution of the thermal system is controlled by a global dedolomitization process triggered by gypsum dissolution. This geochemical process generates a different geochemical environment to that which would result from the exclusive dissolution of carbonates from the deep aquifer, which is generally considered as the direct result of CO2 injection in a deep carbonate aquifer. Therefore, discounting of the dedolomitization process in any CO2 deep geological storage may lead to erroneous conclusions. This process will also influence the porosity evolution of the CO2 storage formation, which is a very relevant parameter when evaluating a reservoir for CO2 storage. The geothermometric calculation performed in this work leads to estimate that the thermal water reservoir is located between 650 and 800 m depth, which is very close to the minimum required to inject CO2 in a deep geological storage. It is clear that the proper characterisation of the features and hydrogeochemical processes taking place at a natural system analogous to a man-made deep geological storage will provide useful conceptual, semi-quantitative and even quantitative information about the processes and consequences that may occur at the artificial storage system.

Sedimentology of a Middle Jurassic Base-of-Slope environment, Cutri Formation, Mallorca

The Cutri Formation’s, type location, exposed in the NW of Mallorca, Spain has previously been described by Álvaro et al., (1989) and further interpreted by Abbots (1989) unpublished PhD thesis as a base-of-slope carbonate apron. Incorporating new field and laboratory analysis this paper enhances this interpretation. From this analysis, it can be shown without reasonable doubt that the Cutri Formation was deposited in a carbonate base-of-slope environment on the palaeowindward side of a Mid-Jurassic Tethyan platform. Key evidence such as laterally extensive exposures, abundant deposits of calciturbidtes and debris flows amongst hemipelagic deposits strongly support this interpretation.

Strontium isotopes and sedimentology of a marine Triassic succession (upper Ladinian) of the westernmost Tethys, Spain

Chemical Stratigraphy, or the study of the variation of chemical elements within sedimentary sequences, has gradually become an experienced tool in the research and correlation of global geologic events. In this paper 87Sr/ 86Sr ratios of the Triassic marine carbonates (Muschelkalk facies) of southeast Iberian Ranges, Iberian Peninsula, are presented and the representative Sr-isotopic curve constructed for the upper Ladinian interval. The studied stratigraphic succession is 102 meters thick, continuous, and well preserved. Previous paleontological data from macro and micro, ammonites, bivalves, foraminifera, conodonts and palynological assemblages, suggest a Fassanian-Longobardian age (Late Ladinian). Although diagenetic minerals are present in small amounts, the elemental data content of bulk carbonate samples, especially Sr contents, show a major variation that probably reflects palaeoenvironmental changes. The 87Sr/86Sr ratios curve shows a rise from 0.707649 near the base of the section to 0.707741 and then declines rapidly to 0.707624, with a final values rise up to 0.70787 in the upper part. The data up to meter 80 in the studied succession is broadly concurrent with 87Sr/86Sr ratios of sequences of similar age and complements these data. Moreover, the sequence stratigraphic framework and its key surfaces, which are difficult to be recognised just based in the facies analysis, are characterised by combining variations of the Ca, Mg, Mn, Sr and CaCO3 contents

On the microstructure, growth pattern and original porosity of belemnite rostra: insights from calcitic Jurassic belemnites

Calcitic belemnite rostra are usually employed to perform paleoenvironmental studies based on geochemical data. However, several questions, such as their original porosity and microstructure, remain open, despite they are essential to make accurate interpretations based on geochemical analyses.This paper revisits and enlightens some of these questions. Petrographic data demonstrate that calcite crystals of the rostrum solidum of belemnites grow from spherulites that successively develop along the apical line, resulting in a “regular spherulithic prismatic” microstructure. Radially arranged calcite crystals emerge and diverge from the spherulites: towards the apex, crystals grow until a new spherulite is formed; towards the external walls of the rostrum, the crystals become progressively bigger and prismatic. Adjacent crystals slightly vary in their c-axis orientation, resulting in undulose extinction. Concentric growth layering develops at different scales and is superimposed and traversed by a radial pattern, which results in the micro-fibrous texture that is observed in the calcite crystals in the rostra.Petrographic data demonstrate that single calcite crystals in the rostra have a composite nature, which strongly suggests that the belemnite rostra were originally porous. Single crystals consistently comprise two distinct zones or sectors in optical continuity: 1) the inner zone is fluorescent, has relatively low optical relief under transmitted light (TL) microscopy, a dark-grey color under backscatter electron microscopy (BSEM), a commonly triangular shape, a “patchy” appearance and relatively high Mg and Na contents; 2) the outer sector is non-fluorescent, has relatively high optical relief under TL, a light-grey color under BSEM and low Mg and Na contents. The inner and fluorescent sectors are interpreted to have formed first as a product of biologically controlled mineralization during belemnite skeletal growth and the non-fluorescent outer sectors as overgrowths of the former, filling the intra- and inter-crystalline porosity. This question has important implications for making paleoenvironmental and/or paleoclimatic interpretations based on geochemical analyses of belemnite rostra.Finally, the petrographic features of composite calcite crystals in the rostra also suggest the non-classical crystallization of belemnite rostra, as previously suggested by other authors.

Incisión fluvial del río Darro durante el periodo 1890-2010 en el sector urbano de Granada (Alambra-Valparaíso, España) determinada a partir de fotografías históricas

En este trabajo se calcula la tasa media de incisión fluvial del río Darro (Granada, España) durante el periodo 1890-2010 en su tramo urbano (sector Alhambra-Valparaíso). Para ello se han utilizado fotografías históricas en las que aparece dicho río, a partir de las cuales se ha podido determinar la posición del cauce en el momento en el que se realizaron las fotografías. La comparación con los escenarios actuales de tales imágenes ha permitido determinar la diferencia de altura del cauce a través de medidas de cotas absolutas realizadas mediante teodolito. Esta metodología ha permitido estimar de modo cuantitativo un índice de encajamiento vertical medio del río de 1,05 cm/año para el periodo histórico considerado.

Paleogene evolution of the External Betic Zone and geodynamic implications

Interdisciplinary studies combining field data (geological and tectonic mapping, lithostratigraphic reconstructions, lithofacies characterization, correlations and sampling) and laboratory analyses (biostratigraphy, chronostratigraphy, clay mineralogy and sandstone petrography) of eight Senonian-Paleogene successions from the Sierra de La Pila and Sierra de El Carche areas (Murcia province, SE Spain) belonging to the External Betic Zone are presented. Field evidence of tectonic activity (slumps, olistostromes, syn-genetic folds, lateral variability, changes in thicknesses, para- and unconformity boundaries, stratigraphic gaps, shallowing upward trends to emersion, etc.) was found in several Paleogene intervals. The results enable a better reconstruction of the stratigraphic architecture and chronostratigraphy of the Paleogene record, highlighting in particular: facies evolution, discontinuities, depositional sequences (Middle-Upper Maastrichtian, Upper Paleocene-Middle Eocene, Oligocene-Lower Aquitanian), environmental evolution (homogeneous conditions during the Late Cretaceous and successive realm diversification from platform to slope to basin) and correlations, along the Prebetic to Subbetic transition, which is a key sector to understand the northeastward variations of the South Iberian margin. A conclusive paleogeographic and geodynamic evolutionary model for the study area is proposed, hypothesizing that Paleogene compressive tectonics affected the eastern External Betic Zone. In addition, correlations with successions from the western External Betic Zone evidenced asynchronous deformation from east to west along the internalmost External Betic Zone. Moreover, a comparison with the external Tunisian Tell enables the recognition of similar sedimentarytectonic events, imposing new constraints in the Paleogene geodynamic reconstruction throughout the western Tethys.