Granada Basin Research Articles

Diagenetic evolution of Tortonian temperate carbonates close to evaporites in the Granada Basin (SE Spain)

The Granada Basin (SE Spain) is a small basin located in the central part of the Betic Cordillera, structured as such in the late Tortonian and initially connected to the Atlantic Ocean and to the Mediterranean Sea. During the late Tortonian, normal marine conditions prevailed, leading to the deposition of skeletal carbonate sediments on platforms around structural highs. The marine connections were later interrupted, first to the Atlantic Ocean and then to the Mediterranean Sea, and a thick evaporite sequence, marking the transition from marine to continental conditions, was deposited during the latest Tortonian. In this work, the diagenetic evolution of the Tortonian temperate carbonates (TTC), underlying and close to the evaporite bodies, is revealed and discussed. The diagenetic study includes petrographic analyses (conventional petrography, cathodoluminescence, and fluorescence), geochemical analyses (major, minor and trace elements, and δ13C and δ18O stable isotopes), and microthermometry of fluid inclusions. In the TTC, marine diagenetic processes such as micritization and fibrous calcite-cement precipitation and mechanical compaction took place during or just after deposition (Eogenesis). An initial burial event (Mesogenesis 1) is characterized by: 1) stabilization of the temperate-water carbonates by freshwater, and 2) porosity occlusion via precipitation of low-Mg bladed and syntaxial/mosaic calcite cements. The TTC were then subaerially exposed (or got close to the surface) during evaporite deposition and underwent pedogenesis, Mg-smectite infiltration, and pyrite formation (Telogenesis 1). Subsequent brine-related diagenetic alterations, such as dolomitization and silica, halite, and sylvite replacements of carbonate grains occurred during a second burial episode (Mesogenesis 2) concomitant with the Messinian lacustrine deposition, this being followed by chemical compaction (stylolite formation). Finally, the area was uplifted and the TTC exhumed. Microstalactitic (dripstone) and fibre/whisker calcite cement precipitation and extensive dissolution relate to this Pliocene–Quaternary late event (Telogenesis 2). In the study case diagenetic history is closely linked to basin evolution, as diagenetic pathways of carbonate rocks were related to major geodynamic events, including basin restriction leading to evaporite deposition, and several episodes of subsidence and uplift. Up to now, only very few diagenetic studies have attempted to demonstrate this correlation between diagenetic history and basin evolution.

Active shallow extension in central and eastern Betic Cordillera from CGPS data

The Betic Cordillera is an Alpine belt formed in the western Mediterranean by the westward displacement of the Alboran Domain in between the Eurasian and African convergent plates. New CGPS data from the central and eastern Betic Cordillera and its foreland—obtained mainly from the Topo-Iberia project—allowed us to precisely determine the rate of tectonic deformation. Most of the displacements of the central and eastern Betics are westward, with a variable southwestward component, in relation to the Eurasian stable plate. While in the Iberian foreland the displacements are extremely low, some deformation related to low compressional deformation occurs in the easternmost foreland basin and eastern Betic Cordillera. The displacement increases substantially southwards and westwards in relation to present-day extensional deformation. Major active discontinuities correspond to the NW–SE normal fault zones, which dip westwards; they are located in Almeria–Tabernas; Balanegra, and western Sierra de Gador; whereas the Padul fault zone located west of Sierra Nevada extends northwards to the Granada Basin. NW–SE extensional faults are also observed to the north, in the Baza Basin. Moreover, the activity of dextral faults along the Sorbas–Tabernas–Alpujarras–Guajares band, generally considered as a transfer fault zone, is evidenced by the displacement data. These results come to demonstrate the low activity or inactivity of the large northern E–W oriented folds of the central and eastern Internal Zone, such as the Sierra de Los Filabres antiform. They also point to the possible residual activity of the northern part of the NE–SW Sierra Nevada antiform, where the maximum relief of the Cordillera is found. Altogether, our data support a heterogeneous present-day westward extension that affects the upper crust of the Betic Cordillera and increases towards the thinned continental crust of the Alboran Sea and towards the west, which is compatible with roll-back subduction along the Gibraltar Arc.

Quaternary landscape evolution driven by slab-pull mechanisms in the Granada Basin (Central Betics)

The Granada Basin is one of the largest Neogene-Quaternary intramontane basins of the Betic Cordillera in SE Spain. The landscape evolution in this basin is complex and does not respond to a simple model of headward erosion following river capture of a former endorheic catchment. In the NE border of the basin, the drainage network is highly incised and reveals two different stages of river development since the Pleistocene. The older drainage network presents low incision, being locally controlled by ENE-WSW open folds. The present-day drainage network features deep incised valleys with a well-defined local base-level controlled by NW-SE normal faults. The ENE-WSW open folds were generated by compressional stresses and affect a geomorphic surface that caps the local sedimentary sequence. These folds are thought to reactivate a Pliocene roll-over formed in the hanging wall of ENE-WSW normal faults that bound the Granada Basin to the north and the deepest Pliocene depocenter. On the contrary, Quaternary depocenters are located in the hanging wall of the NW-SE–oriented normal faults that control the present-day drainage network (NW-SE oriented). The activity of these faults also contributes to the erosion of the Pliocene depocenter located to the north, thus suggesting a southwestward migration of the loci of extension to the center of the basin. The broad-scale scenario envisaged to explain the Pliocene–Quaternary evolution of the NE border of the Granada Basin is one dominated by mantle slab-pull coeval with the Africa–Iberia continuous convergence.

A multiproxy approach for the reconstruction of ancient continental environments. The case of the Mio–Pliocene deposits of the Granada Basin (southern Iberian Peninsula)

Palaeoenvironmental reconstructions from fossil mammals are based on the straightforward relationship between the environment and the mammal assemblage living in the area. However, in some cases the environmental variables estimated from mammals are biassed by local influences. The palaeoenvironmental reconstruction of the Granada Basin (southern Spain) based on carbon and oxygen isotopes from enamel rodent teeth is compared with the palaeoenvironmental data from small mammal assemblages. Estimated temperatures from both proxies coincide, in general terms: cold-temperate conditions during the latest Tortonian (~16°C; cold-temperate climate), dry sub-tropical conditions during the Messinian (16.6°C–22°C), and dry sub-tropical conditions during the early Pliocene (16.6°C–17.2°C). Reconstructed humidity trends from both proxies only agree in the first part of the record, showing dry conditions during the Tortonian–Messinian boundary and an increase in humidity at the beginning of the Messinian. During the Messinian and earliest Pliocene, humidity trends in each proxy are frequently opposed: small mammal assemblages suggest a huge increase in humidity at the beginning of the Messinian, and a decreasing trend towards the Pliocene, whereas carbon isotopes from rodent teeth suggest moderate humidity conditions during the Messinian. It can be concluded that physical changes in the landscape would affect taxa with high dependence on humid conditions, and they are more likely to record local environmental humidity changes rather than regional or global humidity ones. However, the past reconstructions of temperatures are not biassed by this effect, as the general temperature trends deduced from the faunal assemblages as well as those deduced from the isotopic approaches coincide. The general climatic trends reconstructed from isotopic analyses in small mammal teeth agree with the general environmental change in the western Mediterranean region as well as with the global evolution of sea temperatures.

Pedogenetic processes and pedostratigraphy of the Quaternary on the Balearic Islands and in the Granada Basin, Spain

Sediment-soil-sequences are suitable geoarchives and may contribute to resolving palaeoclimate conditions and reconstructing the according stratigraphy. We highlight the characteristics of Holocene soils, Pleistocene palaeosols, aeolianites, loess, slope debris and calcretes on the Balearic Islands at 17 new locations on Mallorca, Ibiza, and Menorca. Their stratigraphy is correlated with sedimentary and pedogenetic processes, and compared to sequences in the Granada Basin (Southern Spain).On the Balearic Islands, surface soils are mainly brunified and loamy, while underlying palaeosols have different features due to clay illuviation, iron weathering and intense reddening, as emphasized by higher iron indices [FeIndex = (% Fed − % Feo)/(% Fet/% clay)] and their close correlation to redness. Intermediate sediments appear as aeolianites, silty loess, calcretes and silt–clay dominated slope debris, and may reflect rather dry-cool climates and scarce vegetation. The increase of palaeosol redness with depth underlines a successive development in respect of polygenesis. While the palaeoclimate is humid Mediterranean, the declined pedogenetic intensity refers to gradual transition to less pronounced humidity and lower temperatures.The palaeosols of the Granada Basin are comparatively less developed. Surface soils are brunified and loamy, and underlying palaeosols show features connected to clay-illuviation and reddening, while a distinctly smaller FeIndex is evidence of less intense weathering. Soil properties indicate declined pedogenetic intensity upon time. Soil formation is influenced by distinct sea level oscillations and a seasonal humid climate. Close correlations between FeIndex and RRvisual (R2 = 0.89) highlight hematite formation as particularly intense in the Early Pleistocene. It followed a more arid Late Pliocene with intense erosion and sedimentation, as underlined by distinctly lower values of both FeIndex and RRvisual during this time. Quaternary processes of pedogenesis and sedimentation therefore not only substantiate a distinct climatic cyclicity in the Western Mediterranean, but also reflect advanced development of palaeosols with depth and thus with time.

An insight into the organisation of metal production in the Argaric society

Metallurgy is a common topic when discussing Early Bronze Age societies, as its social impact has been traditionally used to support the appearance of social inequality. Different models have been proposed for the Bronze Age Argaric society of SE Iberia. One includes a highly centralised hierarchical production system, and the other consists of decentralised production at a local scale.Though metallurgical debris has been found in more than 30 sites in the Argaric society, and despite metallurgy being a core subject of discussion, very little research has been conducted on these finds. In this article, we draw from provenance studies using lead isotope analysis to gain a better understanding of the organisation of metal production and distribution.We present new MC-ICP-MS lead isotope and SC-ICP-MS trace element analyses of 23 arsenical copper and bronze objects from two Argaric sites: Cerro de la Encina and Cerro San Cristóbal. Both sites are located in the Granada basin. These results, contextualised with metallurgical evidence already published, allow us to depict a decentralised system of metal production in which different and distantly located copper mines were being exploited.

Large celestine orebodies formed by early-diagenetic replacement of gypsified stromatolites (Upper Miocene, Montevive–Escúzar deposit, Granada Basin, Spain)

The Montevive and the Escúzar stratabound celestine orebodies in the Upper Miocene evaporite succession of the intramontane Granada Basin (Spain) constitute one of the largest strontium deposits in the world. Celestine occurs within a gypsum/anhydrite–halite evaporite sequence where it replaces gypsum and gypsified stromatolites preserving carbonate peloids. 87Sr/86Sr and δ34S values in the Montevive celestine deposit are close to those reported for the saline unit (Chimeneas Halite; marine to nonmarine) but higher than those of the overlying gypsum unit (Agrón Gypsum; nonmarine). 87Sr/86Sr and δ34S isotope values in the Escúzar celestine deposit match the nonmarine values recorded in the upper part of the Agrón Gypsum. The similarity in isotope values between celestine and the corresponding gypsum host in the Escúzar deposit points to early-diagenetic mineralization. According to that, both orebodies are diachronous. Gypsum pseudomorphs and molds, intraformational breccias and karst structures in these celestine deposits point to dissolved gypsum as the main sulfate source. Diagenetic–hydrothermal CaCl2 brines are interpreted to be the main strontium source. The spatial relationship between gypsified stromatolites and the ore deposits suggests the existence of coeval thermal springs related to fractures, bordering the saline lake. The proposed model envisages gypsum dissolution by SO42−-poor and Sr2+-rich, CaCl2 diagenetic–hydrothermal water discharging in coastal ponds at times of dry periods and low meteoric water inflow. The increase in SO42− concentration by gypsum dissolution and the low solubility of SrSO4 would lead to celestine precipitation replacing gypsum and gypsified stromatolites.

Morphotectonics of the Padul-Nigüelas Fault Zone, southern Spain

The Padul-Nigüelas Fault Zone (PNFZ) is situated at the south-western mountain front of the Sierra Nevada (southern Spain) in the Internal Zone of the Betic Cordilleras and belongs to a NW-SE trending system of normal faults dipping SW. The PNFZ constitutes a major tectonic and lithological boundary in the Betics, and separates the metamorphic units of the Alpujárride Complex from Upper Tertiary to Quaternary deposits. Due to recent seismicity and several morphological and geological indicators, such as preserved fault scarps, triangular facets, deeply incised valleys and faults in the colluvial wedges, the PNFZ is suspected to be a tectonically active feature of the south-eastern Granada Basin. We performed morphotectonic GIS analyses based on digital elevation models (DEM, cell size: 10 m) to obtain tectonic activity classes for each outcropping segment of the PNFZ. We have determined the following geomorphic indices: mountain front sinuosity, stream-length gradient index, concavity index and valley floor width to height ratio. The results show a differentiation in the states of activity along the fault zone strike. The western and eastern segments of the PNFZ indicate a higher tectonic activity compared to the center of the fault zone. We discuss and critically examine the comparability and reproducibility of geomorphic analyses, concluding that careful interpretation is necessary, if no ground-truthing can be performed.

Multi-temporal InSAR for Deformation Monitoring of the Granada and Padul Faults and the Surrounding Area (Betic Cordillera, Southern Spain)

The quantification of low rate active tectonic structures is a major target of geodetic and geological studies to improve the knowledge of seismic hazards. The central Betic Cordillera (southern Spain) is affected by moderately active tectonic structures and seismicity. Part of this seismic activity is produced by several NW-SE normal faults located in the E of the Granada Basin.

Finite‐frequency Rayleigh wave tomography of the western Mediterranean: Mapping its lithospheric structure

We present a 3‐D shear wave velocity model for the crust and upper mantle of the western Mediterranean from Rayleigh wave tomography. We analyzed the fundamental mode in the 20–167 s period band (6.0–50.0 mHz) from earthquakes recorded by a number of temporary and permanent seismograph arrays. Using the two‐plane wave method, we obtained phase velocity dispersion curves that were inverted for an isotropic Vs model that extends from the southern Iberian Massif, across the Gibraltar Arc and the Atlas mountains to the Saharan Craton. The area of the western Mediterranean that we have studied has been the site of complex subduction, slab rollback, and simultaneous compression and extension during African‐European convergence since the Oligocene. The shear velocity model shows high velocities beneath the Rif from 65 km depth and beneath the Granada Basin from ∼70 km depth that extend beneath the Alboran Domain to more than 250 km depth, which we interpret as a near‐vertical slab dangling from beneath the western Alboran Sea. The slab appears to be attached to the crust beneath the Rif and possibly beneath the Granada Basin and Sierra Nevada where low shear velocities (3.8 km/s) are mapped to >55 km depth. The attached slab is pulling down the Gibraltar Arc crust, thickening it, and removing the continental margin lithospheric mantle beneath both Iberia and Morocco as it descends into the deeper mantle. Thin lithosphere is indicated by very low upper mantle velocities beneath the Alboran Sea, above and east of the dangling slab and beneath the Cenozoic volcanics.

Geotechnical map of Holocene alluvial soil deposits in the metropolitan area of Granada (Spain): a GIS approach

The results of a geotechnical research on Holocene alluvial deposits in 14 municipalities of the Granada basin are presented, and a procedure to draw a geotechnical map of foundation conditions, using ArcGIS 9.3 (ESRI 2009) is described. Three different alluvial soil units were distinguished: (1) cohesive soils; (2) cohesive and fine granular soil; (3) coarse granular soil, based on their properties concerning grain size, bulk density, cohesion, internal friction angle, and NSPT value. The actual building structures have predominantly shallow foundations. The definition of the minimum depth to actual foundation level was based on the analysis of thickness of disturbed soils, man-made fillings, depth to the water table and bearing capacity. The depth to actual foundation levels varies from 0.5 to 4 m in the study area. Concerning the ground, the geotechnical data compiled on foundation conditions show a high heterogeneity expressed by the spatial distribution of the basic properties in the three distinguished units of cohesive, cohesive and fine-granular, and coarse granular soils, respectively. The fine-grained alluvial soil units (cohesive) have a low bearing capacity varying between 40 and 100 kPa and are associated with a shallow water table appearing near the surface. In contrast, across the wide extension of the coarse-grained alluvial soil unit, a bearing capacity ranging from 60 to 300 kPa is determined; this unit is associated with a deep water table appearing at more than 40 m below the surface. The usefulness of the obtained geotechnical map of foundation conditions extends to the analysis of further alternatives of urban expansion and for the delimitation of future trends for of land-use-development processes in the metropolitan area of Granada, mainly at local and regional scales.

Fault growth as a key control on the sedimentary architecture and depositional environments of extensional basins: the case study of the Tablate area (Granada Basin, Spain)

Evoluzione di sistemi di faglie normali e loro controllo sull'architettura stratigrafica e sugli ambienti deposizionali di bacini estensionali (Tablate, Bacino di Granada, Spagna).L'integrazione di analisi stratigrafiche, sedimentologiche e strutturali ha consentito di dedurre l'evoluzione spazio-temporale, a partire dal Miocene medio, di un piccolo settore del Bacino di Granada, l'area di Tablate. L'architettura stratigrafica e gli ambienti deposizionali vengono descritti ed associati alle varie fasi evolutive del sistema di faglie normali che ha controllato l'evoluzione del bacino. L'architettura stratigrafica ha registrato la completa evoluzione di un bacino estensionale sviluppatosi alla sommita di un orogene (Cordigliera Betica). A partire dal Serravalliano, il progressivo sviluppo di due sets ortogonali di faglie normali orientate ~E-W and ~N-S ha guidato l'evoluzione del bacino da una moltitudine di piccole depressioni lagunari e continentali riempite rispettivamente da marne gessifere e arenarie rossastre, ad un singolo bacino marino presente durante il Tortoniano, dove sedimentarono calcareniti, calciruditi, arenarie e conglomerati. A partire dal Tortoniano superiore una fase di sollevamento regionale condusse ad una regressione deposizionale con la deposizione di sedimenti fluvio-lacustri tardomiocenicisovrastanti i sedimenti marini suddetti. I sovrastanti conglomerati continentali plio-quaternari suturarono le faglie normali oramai inattive. Sulla base della distribuzione latero-verticale delle varie unita sedimentarie mioceniche e stato possibile stimare lunghezza e rigetto verticale delle faglie normali attive tra il Serravalliano ed il Messiniano. Lunghezze fino a 1 km e rigetti verticali fino a 30 m sono stati stimati per le faglie attive nel Serravalliano. Lunghezze fino a 4 km e rigetti verticali fino a 130 m sono invece stati attribuiti alle faglie piu mature attive tra il Tortoniano ed il Messiniano.

Environmental conditions vs. landscape. Assessment of the factors that influence small mammal fauna distribution in Southern Iberia during the latest Messinian by mean of stable isotopes

Tropical conditions during the late Miocene in southwestern Europe influenced the continental environments. Although there are previous qualitative environmental interpretations of these continental landscapes during the late Miocene, quantitative environmental and paleohydrological data are scarce. A very long sequence of small mammals allowed to date the different continental drainage stages of the Granada Basin from latest Tortonian to the Holocene and to reconstruct qualitatively its environmental evolution. The study of the isotopic record of these fossil small mammals and sediments in the stratigraphic sequence of a latest Messinian paleo-lake in the Granada Basin has provided quantitative environmental and paleohydrological data, in order to know if the fluctuations in the faunal distribution were mainly influenced by the paleogeographic configuration, such as changes in the landscape of the basin, or by the climatic conditions. Open habitats with C3 plants predominated. Estimated quantitative data suggest an oxygen isotopic composition of meteoric waters ranging from −4.9 to −3.9‰, past temperatures from ~2.5°C to 4.7°C higher than the current ones, and summer relative paleohumidity from ~60% to ~70%. In this context, changes in the landscape, such as the reduction of the lacustrine system caused by tectonic activity, would affect taxa with high dependence on humid conditions.

Earthquake site effect modeling in the Granada basin using a 3-D indirect boundary element method

In this work, we develop the indirect boundary element method (IBEM) to simulate the seismic site response in a realistic, large-scale 3-D sedimentary basin. Most previous applications of boundary element method have used full-space Green’s functions for wave propagation between element points. We use half-space Green’s functions, which include the seismic wavefield interactions at the free surface and require only the boundary elements of the basin interface. In this way, the size of the matrix equation for solution in the IBEM can be reduced to approximately a quarter of that using full-space Green’s functions. The site response modeling of the Granada basin in southern Spain using the IBEM shows that the basin-induced scattering waves were identified as propagating back and forth inside the basin. The scattered waves also generate surface waves that are weakly propagated outside of the basin. The wave propagation inside and outside of the basin shows different patterns. We observe that the scattered wave is locally amplified, and its propagation direction deviates from that of the incident waves propagation direction. Therefore, the computed seismic response in the basin could provide us with good estimates of the seismic motion.

Salt deposition and brine evolution in the Granada Basin (Late Tortonian, SE Spain)

A group of sedimentary basins in the Betic Chain were formed during the Middle-Late Miocene as a result of the closure of the Tethys during the Alpine orogeny. In the Late Miocene (Tortonian–Messinian) the connections between the Atlantic Ocean and Mediterranean Sea were interrupted and those basins hosted major evaporites. The Granada Basin, an ‘inner basin’ located far from the Mediterranean, contains a thick rock salt deposited during the latest Tortonian in the transition from marine to non-marine conditions. In the centre of the basin, three halite-bearing units overlie a basal anhydrite bed: the Lower Halite Unit, the Intermediate Sandstone Unit and the Upper Halite Unit. Fluid inclusion compositions and bromine concentrations in halite, together with stable isotopes (δ34Ssulfate, δ18Osulfate and 87Sr/86Sr) indicate a mixture of different inflow waters in the Granada Basin, beginning with a marine lagoon that evolved into a salt-pan strongly isolated from the sea. Saline waters evolved from sulfate-rich marine-derived to sulfate-depleted non-marine brines influenced by the addition of CaCl2-rich inputs. These CaCl2-rich waters were probably linked to thermal fluids associated with a major crustal fracture system (Crevillente or Cádiz-Alicante fault system) that cuts through the Granada Basin.

Spacing and distribution of bed-perpendicular joints throughout layered, shallow-marine carbonates (Granada Basin, southern Spain)

This contribution focuses on the controls exerted by sedimentological, petrographic and mechanical rock properties on the distribution of bed-perpendicular joints throughout layered carbonates. The study was conducted on Tortonian, shallow-marine skeletal grainstones and rudstones cropping out in the Granada Basin, southern Spain. The results of combined field and laboratory analyses are consistent with the rock grain size of the studied carbonates exerting a key control on distribution of the bed-perpendicular joints. A positive correlation between joint spacing and mechanical unit thickness is computed for the grainstones, whereas joints are almost absent in rudstones. The rock grain size affected the diagenetic processes, such as cementation and dissolution, and therefore the resulting porosity and uniaxial compressive strength (UCS) values. Quantitative data show that higher UCS values are commonly associated with greater calcite amounts, lower values of porosity and finer grain sizes and, hence, denser bed-perpendicular joint sets. In conclusion, this study documents that it is possible to infer the density of bed-perpendicular joints in layered carbonates based on the sedimentological, petrographic and mechanical parameters. Considering the impact that this type of joints has on subsurface fluid flow, the acquired knowledge can help the management of geofluids as well as the overall prediction of carbonate reservoir quality.

Main active faults in the Granada and Guadix-Baza Basins (Betic Cordillera)

The Granada and Guadix-Baza Basins, the largest Neogene-Quaternary intramontane basins of the Betic Cordillera (southern Spain), undergo active deformation with an associated moderate level of seismic activity. This deformation is controlled by a NNWSSE compressive regime and an approximate orthogonal tensional regime. The compression produced N70oE to E-W folds of several scales, the Sierra Nevada antiform being the largest one. The tension is accommodated mainly by NW-SE active normal faults, the most notable being the Baza Fault, in the Guadix-Baza Basin, and the Granada, Sierra Elvira-Dilar and Padul-Durcal Faults, in the Granada Basin. In addition, other active faults with different orientations also exist, such as the Alfahuara-Botardo and the Galera faults in the Guadix-Baza Basin, and the Huenes, Obeilar-Pinos Puente and N of Sierra Tejeda Faults in the Granada Basin. Moreover, in several sectors, the presence of orthogonal normal fault sets suggests alternating trends or even radial extension. Slip rates of these active faults, based on geologic markers, vary between 0.06 and 0.5 mm/year. Estimates for the maximum expected magnitude of earthquakes caused by these faults vary between MW 6.0 and 7.0. The N of Sierra Tejeda and the Baza Faults, the largest faults in the Granada and Guadix-Baza Basins, respectively, have the greatest seismic potential. They could cause events up to a magnitude of MW 6.5-7.0, although their reference earthquakes, computed for a return period of 475 years, are on the order of MW 5.0-5.5.

Active tectonics in the central and eastern Betic Cordillera through morphotectonic analysis: the case of Sierra Nevada and Sierra Alhamilla

Quaternary activity of folds and faults can be assessed by the analysis of drainage network and the evaluation of geomorphic indexes. These analyses are especially productive in semiarid areas where tectonic rates are low-to-moderate and Quaternary dating is limited. In this work, we have revisited the most relevant GIS-based methodologies used to assess tectonic activity by using morphometric analyses and we discuss the tectonic implications in two key areas of the central and eastern Betic Cordillera (Sierra Nevada and Sierra Alhamilla regions). In the Sierra Nevada area, the use of geomorphic indexes in the mountain range and in the neighboring Granada and Guadix-Baza basins suggests that all are part of the same SW-directed extensional system. The Granada basin (except in its NE border) subsided during the Late Pleistocene as it is located in the hanging wall of the extensional system. On the other hand, the Sierra Nevada mountain range, the NE border of the Granada basin and the Guadix-Baza basin are located in the active uplifted foot wall of the system. Thus, the higher fluvial incision rates in the Guadix-Baza basin can be directly correlated with the most recent uplift history of Sierra Nevada mountain range. In the Sierra Alhamilla region, a geomorphic study shows Late Pleistocene activity along the North Alhamilla Reverse Fault and the dextral transpressive South Gafarillos Fault, two segments of the Polopos Fault Zone, previously considered as an inactive fault.

Updating the marine biostratigraphy of the Granada Basin (central Betic Cordillera). Insight for the Late Miocene palaeogeographic evolution of the Atlantic – Mediterranean seaway

The marine stratigraphic record of the Granada Basin (central Betic Cordillera, Spain) is composed of three Late Miocene genetic units deposited in different sea-level contexts (from base to top): Unit I (sea-level rise), Unit II (high sea-level), and Unit III (low sea-level). The latter mainly consists of evaporites precipitated in a shallow-basin setting. Biostratigraphic analyses based on planktonic foraminifera and calcareous nannoplankton indicate four late Tortonian bioevents (PF1-CN1, PF2, PF3, and PF4), which can be correlated with astronomically-dated events in other sections of the Mediterranean. PF1-CN1 (7.89 Ma) is characterized by the influx of the Globorotalia conomiozea group (including typical forms of Globorotalia mediterranea) and by the first common occurrence of Discoaster surculus; PF2 (7.84 Ma) is marked by the first common occurrence of Globorotalia suterae; PF3 (7.69 Ma) is typified by the influx of dextral Neogloboquadrina acostaensis; and PF4 (7.37 Ma) is defined by the influx of the Globorotalia menardii group II (dextral forms). The PF1 event occurred in the upper part of Unit I, whereas PF2 to PF4 events occurred successively within Unit II. The age of Unit III (evaporites) can only be estimated in its lower part based on the presence of dextral Globorotalia scitula, which, together with the absence of the first common occurrence of the G. conomiozea group (7.24 Ma), points to the latest Tortonian. Comparisons with data from the other Betic basins indicate that the evaporitic phase of the Granada Basin (7.37–7.24 Ma) is not synchronous with those from the Lorca Basin (7.80 Ma) and the Fortuna Basin (7.6 Ma). In the Bajo Segura Basin (easternmost Betic Cordillera), no evaporite deposition occurred during the late Tortonian. The evaporitic unit of the Granada Basin (central Betics) records the late Tortonian restriction of the Betic seaway (the marine connection between the Atlantic and Mediterranean). The diachrony in the restriction of the Betic seaway is related to differing tectonic movements in the central and eastern sectors of the Betic Cordillera.

Inner structure and deformation mechanisms of normal faults in conglomerates and carbonate grainstones (Granada Basin, Betic Cordillera, Spain): Inferences on fault permeability

In the southeastern area of the Neogene-Quaternary Granada Basin, ∼E–W trending normal faults crosscut ∼80 m-thick clay-bearing conglomerates and ∼30–40 m-thick carbonate grainstones containing centimeter-thick microconglomerate and sand interbeds. Three fundamental failure modes took place during fault nucleation: (1) phyllosilicate shear banding in the conglomerates, (2) jointing, mainly in the carbonate grainstones and (3) pressure solution in the carbonate matrix and grains of the microconglomerate and sand interbeds. Within the conglomerates, normal faults developed by pronounced clay smearing and, ultimately, cataclasis. Jointing also occurred within some of the pebbles surrounding the cataclastic rocks. In contrast, in the carbonate grainstones fault growth was characterized by predominant jointing and rock fragmentation, which localized in the extensional quadrants and/or releasing jogs of the evolving slip surfaces. Brecciation and cataclasis occurred only around the well-developed slip surfaces. Based upon their inner structure, we qualitatively assign a combined barrier-conduit fluid behavior to the tens of meters-throw normal faults juxtaposing the conglomerates against the carbonate grainstones. The inner fault cores inhibit fault-orthogonal fluid flow along their entire length. Instead, fault damage zones act as fluid barriers in the conglomerates, and as composite fluid conduits in the carbonate grainstones.