Geogaceta -- Nº 44, (2008)

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Variaciones en el registro isotópico del carbono en dos secciones de edad Aptiense inferior en la zona de transición entre el Subbético Externo y el Subbético Medio (Cordilleras Béticas, Provincia de Jaén)
(2008) Gea, Ginés A. de; Aguado, Roque; Castro Jiménez, José Manuel
The lower Aptian pelagic and hemipelagic sediments of the Carbonero Fm were deposited in the Southern Iberian Palaeomargin, within the transition between the External to Middle Subbetic palaeogeographic domains. The concrete area of deposition was a subsiding sector bounded by faults. A stratigraphic and sedimentological study of two nearby sections from this area (Solana de Morales and La Frontera) has revealed the existence of notable differences in their stratigraphic record, which are interpreted in terms of a different sedimentary context. Both sections include a lower Aptian episode of black shales, which is interpreted to represent the local record of the Oceanic Anoxic Event 1a (OAE1a). The d13Ccarb curves from both sections can be easily correlated, and also a good correlation is observed with respect to curves from other areas, which record the global carbon cycle perturbation related with the OAE1a. The discrepancies in the isotopic d13Ccarb record between the two sections are interpreted in terms of local differences in the sedimentary environment
Transformación de andalucita a sillimanita en granitos peralumínicos del batolito de los Montes de Toledo: implicaciones petrogenéticas
(2008) Merino, E.; Villaseca, Carlos; Pérez Soba, C.; López García, José Ángel
The Montes de Toledo Batholith comprises several felsic peraluminous granitic plutons characterized by the presence of two Al2SiO5 polymorphous: andalusite and sillimanite (as fibrolitic variety). Textural features indicate an igneous origin for andalusite, variably replaced by muscovite and fibrolite around it. We propose a combination of factors to explain this probable magmatic reaction: the decrease in minor element contents of andalusite (Fe, Mg, Mn, Ti) and the increase of volatiles in the melt (B, P, F, H2O) along its cooling. This chemical variation influences the stability of both polymorphs, crystallizing initially igneous andalusite and, when the Fe content decreases, the sillimanite, in relation with muscovite, in a restricted P-T space close to the granite solidus conditions
Tectónica reciente en el frente de Cabalgamiento Bético. Las deformaciones de Jimena y Bedmar (Jaén)
(2008) García Tortosa, F.J.; Sanz de Galdeano, Carlos; Sánchez Gómez, Mario; Alfaro García, Pedro
In the area of Jimena-Bedmar, in the Guadalquivir basin, the northwards displacement of the External Betic units deformed the sedimentary Miocene infilling of the basin. Especially remarkable is an E-W anticline affecting middle-late Miocene limestones and marls. This structure is dissected by two fault sets, striking N20º and N140º and some reverse faults. Striation and sense of shearing of minor faults in the Cerro Atalaya indicate the existence of two main deformation phases. The first one is characterized by N-S compression congruent with the orientation of regional folds and thrust kinematics. The last one is characterized by a roughly E-W extension that produces faults with topographic expression, as the Golondrinas and Bedmar faults. The time of the deformation ranges between the uppermost Miocene (compression) and the present (extension)
Sistema de canales submarinos en una rampa de carbonatos templados, Cuenca de Sorbas, sureste de España
(2008) Puga Bernabéu, Ángel; Martín, J. M.; Braga, Juan C.
Temperate carbonates with abundant remains of braquiopods and bivalves deposited in a carbonate ramp developed at the northern margin of the Sorbas Basin during the latest Tortonian-earliest Messinian. Small submarine channels linked to ephemeral rivers curses (ramblas) excavated into the ramp, eroding and transporting sediment seawards from the factory. Lateral bars developed at the margin of the channels indicate an active sediment transport though the submarine channels. Small submarine fans formed on the ramp at the end of the channels
Secuencia paragenética del skarn de scheelita de Los Santos (Salamanca, NO España)
(2008) Timón, S. M.; Moro, M. C.
The Los Santos skarn shows several chemical and mineralogical features common to many other W-bearing calcic mesozonal reduced skarn deposits. Early exoskarn consists of hedenbergite (Hd82-87), grossular (Grs53- 73) and Mo-rich scheelite. The mineral assemblage which formed during the cooling of the system is very complex and is constituted mainly by subcalcic garnet, other hydrated silicates (amphibole, phlogopite, prehnite, epidote-clinozoisite, chlorite, white mica and zeolite) and metallic mineralization with Mo-poor scheelite. The aplitic granite is replaced by a calcic plagioclase and clinopyroxene endoskarn. Stockscheider, breccias and fractures indicate a forceful emplacement and over pressure associated with volatile exsolution from granite magma. The occurrence of zeolites indicates that the hydrothermal fluid circulation probably communicated with the surface as in present-day geothermal systems
Rutilos ricos en Zr incluidos en granates de xenolitos granulíticos de la corteza inferior del Sistema Central Español: implicaciones geodinámicas
(2008) Villaseca, Carlos; Orejana, David
Two petrographic types of rutile are observed in the peraluminous felsic meta-igneous granulites, the most common type of the lower crustal xenolith suite of the Spanish Central System (SCS). Rutile-1 (Rt-1) corresponds to small crystals (mainly < 80 mm) only preserved as micro-inclusions within garnet, whereas rutile-2 (Rt-2) is commonly found as big idiomorfic crystals forming the granulite granoblastic matrix. Chemical analyses by EMP show a higher Zr content in Rt-1 (up to 7800 ppm) than in Rt-2 (up to 5200 ppm) of the same granulite. Applying Zr-in-rutile thermometry, Rt-1 gives 50-60 ºC higher for rutile crystallization (950-1015 ºC) when compared to Rt-2 thermometry (940-955 ºC). These ultra-high temperatures (UHT) are likely attained at Moho depths without external heat sources (e.g. mantle input) as supported by the high heat production estimated for the crustal section of the SCS. The granulitegranite petrogenetic link suggests that these HT-UHT granulites were generated by intra-crustal reworking during Hercynian continental thickening
Relaciones de campo y geoquímica de las carbonatitas de Esquinzo-Agua Salada, NW de Fuerteventura, Islas Canarias
(2008) Ignacio, Cristina de; Muñoz, Mercedes; Sagredo, J.
Carbonatites are rather uncommon rocks, the origin of which still stands a subject of debate, especially regarding if they crystallize from primary carbonatitic melts from the mantle, or if they are generated, by some magmatic differentiation process, from an alkaline-silicate parent magma. The Esquinzo-Agua Salada carbonatites are associated, both in space and time, to an ensemble of alkaline silicate lithologies comprising, from ultramafic-mafic (perovskite-clinopyroxenites-ijolitic rocks) to felsic (nepheline-syenites) types. In this work, field relationships between both groups of lithologies as well as the main geochemical characteristics of the carbonatites, which are compared to those of the alkaline silicate rocks, are presented. Both aspects seem to indicate an origin for the carbonatites by liquid immiscibility, from a CO2-rich, alkaline silicate parental magma
Reconstrucción paleoclimática de la plataforma continental gallega basada en datos geoquímicos y magnéticos
(2008) Ares, A.; Rey, Daniel; Rubio, Belén; Mohamed, K.; Bernabeu, Ana M.; Vilas, Federico
The study of the composition and provenance of the sediments from two cores from the Galician continental shelf (NW of the Iberian Peninsula) based on their textural, geochemical and magnetic properties has allowed us to reconstruct the paleoclimatic evolution of this region. Based on the temporal framework of the identified facies, it was observed that during the Holocene Optimum the continental shelf was under a high-energy regime. The most notable record of this period was a bioclastic lag founded in both cores, which could also be correlated to nearby cores. After the Holocene Optimum, the ongoing marine transgression favoured deposition of sandy sediments. The following stabilization of the sea-level favoured an increase of continental muddy sediments from the Miño and Duero rivers since the Roman Warm Period. On the contrary, this process was negligible in the outer shelf, generating conditions which allowed the neoformation of glauconitic minerals
Reconstrucción de paleotemperaturas en el golfo de León durante los estadios isotópicos 6 y 7 utilizando la técnica de los análogos modernos
(2008) González Mora, Beatriz; Sierro, Francisco Javier; Berné, S.
Planktonic foraminifer assemblages from core PRGL1-4 have been studied to reconstruct sea surface temperatures (SST) in the Gulf of Lions during Marine Isotope Stages 6 and 7 based on the modern analog technique. This method consists of a comparison between core and modern sample assemblages assuming that similar planktonic foraminifer assemblages develop under the same ecological conditions and that foraminifer ecological preferences have not changed in time. During stage 6 (glacial) a strong millennial variability is observed in SST, whereas in stage 7 (interglacial) the astronomical forcing controls SST. These features have been already reported in temperature records from other areas out of the Mediterranean Sea, which means that SST in the Gulf of Lions during stages 6 and 7 was influenced by global climate changes. Moreover, some differences exist between paleotemperature records from different areas in the Mediterranean region. In the Gulf of Lions temperature records are more extreme since this area is directly influenced by Mistral and Tramontane winds, which cause important water cooling during cold periods. Furthermore, this study suggests that seasonality in the Gulf of Lions is not influenced by Northern Hemisphere summer insolation
Phase equilibrium modelling in the KFMASH system to show the Metamorphic Evolution of the Ceán Schists (Malpica-Tui Unit, NW Iberian Massif)
(2008) López Carmona, A.; Abati, Jacobo; Reche, J.
Para complementar los resultados obtenidos mediante termobarometría convencional (termómetro granatemoscovita y barómetros GRIPS y GASP) en los Esquistos de Ceán (López-Carmona et al., 2008) se ha construido una pseudosección P-T en el sistema químico KFMASH para una composición media de estas metapelitas [SiO2:71.42; Al2O3:13.42; MgO:4.78; FeO:7.04; K2O:3.34]. Adicionalmente, la proyección de isopletas que reflejan el contenido en sílice de las fengitas en los diferentes campos de estabilidad de la pseudoseción, proporciona otro barómetro muy fiable. En base a los resultados obtenidos, y de acuerdo principalmente con las paragénesis naturales preservadas en los esquistos, las condiciones P-T obtenidas para el pico metamórfico son P=23-24 Kb y T=530-540 ºC, mientras que para un segundo evento metamórfico se obtuvieron valores de P=20-23 Kb y T=550-560 ºC. Los resultados proporcionados por la termobarometría convencional indican P=19-21 Kb y T=430-500 ºC para el pico y P=16-19 Kb y T=440-515 ºC cuando se emplean las composiciones de los minerales del segundo evento metamórfico
Parasecuencias Transgresivo-Regresivas en un Cortejo Transgresivo: parte superior de la Fm Utrillas en Olleros de Pisuerga, Palencia
(2008) Pujalte, Victoriano; Robles, Sergio
Field and borehole data demostrate that the well-known fluviatile Utrillas Fm of N Spain is part of the transgressive system tract of a major second-order sequence. However, the analysis of its upper part in the Olleros de Pisuerga area (Palencia) and in the Trashaedo-1 borehole reveals the existence of three parasequences indicative of smaller scale transgressive-regressive episodes superimposed on the overall transgressive trend. These transgressive-regressive episodes have resulted in the vertical alternation of two different facies associations, a coarse-grained fluviatile association and a finer-grained littoral association, a favourable situation for the development of stratigraphic or mixed hydrocarbon traps that may prove of interest in future subsurface explorations
Palaeoceanographer, una herramienta informática para estimar características paleoceanográficas de las aguas marinas superficiales del Cuaternario y Neógeno superior
(2008) Serrano Rebollo, Francisco; Serrano Lozano, Francisco
This work presents Palaeoceanographer as a new computer tool that we designed for palaeoceanographic studies. However, the software utility can be also extended to other scientific areas in which the aim is to carry out a similarity multivariant analysis between cases, or the assignment of characteristics to samples on the basis of a calibration set. The computer application analyzes the proximity between samples by means of distance algorithms. Different options allow to select among the utilities offering the program, the mathematical operators of similarity and the number of cases to consider
Nueva evidencia sobre la edad del tránsito endorreico-exorreico de la cuenca de Guadix-Baza
(2008) García Tortosa, F.J.; Sanz de Galdeano, Carlos; Alfaro García, Pedro; Jiménez Espinosa, Rosario; Jiménez Millán, Juan; Lorite Herrera, M.
The Guadix-Baza basin was an endorheic continental basin during the Pliocene and part of the Pleistocene, later being captured by a tributary of the Guadaquivir River which would turn into the Guadiana Menor River. This event had significant implications in the evolution of the basin, leading to a stage in which erosion dominated over sedimentation. However, there is no consensus about the time in which the fluvial capture took place and various authors have proposed different ages using diverse chronological criteria. This work describes a different hypothesis about the age of the fluvial capture and also provides new insights on the evolution of the basin. The presence of metamorphic clasts in the fluvial sediments that comprise the upper terrace of the middle and upper course of the Guadalquivir River allowed us to establish new criteria about the age of the mentioned fluvial capture process
Novedades paleontológicas del Ordovícico en el Parque Nacional de Cabañeros (Castilla-La Mancha)
(2008) Gutiérrez Marco, Juan Carlos; Pieren Pidal, A.; Rábano, Isabel; Reyes Abril, J.
Lower and Middle Ordovician rocks outcropping in the Cabañeros National Park (Central Iberian Zone) are being explored within a mapping project aimed at identifying geosites representative of the geological and paleontological heritage on this natural area. Ongoing field-work has led to the discovery of three fossil localities that bring out significant paleontological data relevant to the whole Iberian Massif. The oldest comes from the upper part of the Armorican Quartzite Fm. (Floian/middle Arenigian) and is a large ichnofossil identified as Tumblagoodichnus? isp., which probably represents a shallow burrow filled by collapse of sand from above, and dug as a temporary refuge by a large arthropod. The trace is 45 cm wide, much bigger than the large arthropod traces previously reported from the Iberian Ordovician (rare Cruziana reach up to 26 cm in width). The second fossil locality lies towards the middle part of the overlying Marjaliza Beds (Dapingian to lower Darriwilian/middle-upper Arenigian) and is represented by a thick coquina of paleotaxodont and paleoheterodont bivalves, apparently formed due to a catastrophic event (an exceptional storm?) that transported and entombed en masse millions of individuals now preserved as complete specimens with closed valves. This local abundance strongly contrasts with the scarcity of Arenigian bivalves preserved in the Cruziana sandstone facies of SW Europe. Finally, the youngest locality is a rich fossiliferous bed of lower Oretanian (Darriwilian) age recorded in the Navas de Estena Shales, where the brachiopod genus Eodalmanella (Ranorthidae) makes its second European occurrence and reinforces the Ibero-Bohemian paleobiogeographic affinities
Morfología de perfiles de ríos en roca. Control tectónico y significado evolutivo en el Bajo Guadiana
(2008) Garzón Heydt, Guillermina; Ortega, J.A.; Garrote, J.
Bedrock rivers are increasingly becoming of interest due to their significance in controlling upstream entrenchment by fixing the base level. Longitudinal profiles are dependant not only of discharge but also on incision capability due to bedload transport thresholds determined by gradient availability. The lower Guadiana River incises into the large Extremadura-Alentexo planation surface, developing large canyon carved on extended flat rocky benches with internal channels. Their development cannot be understood as that of simple hydrodynamic features produced and backwards erosion by lithologic control. In order to determine drainage network evolution in relation to regional surfaces and tectonics, longitudinal profiles river profiles from the Guadiana River and its tributaries have been reconstructed and their concavity index and mathematical fitting curves analysed. Different reaches might be interpreted on a morphostructural framework, with convex river profiles adjusting to active base level lowering as compared to the more stable and better evolved upstream rivers. To explain the convexity towards the south, one must consider the subsidence of the Guadalquivir flexure, which coincides roughly with the Guadiana mouth
Microestructuras en conchas de rudistas y Chondrodonta sp. del Complejo Urgoniano de Ereño (Bizkaia)
(2008) Damas Mollá, Laura; Aranburu Artano, Arantza; García Garmilla, Francisco
Rudist and Chondrodonta sp. shells present in Ereño limestones show different responses to the influencece of diagenetic fluids. The different microstructures of shells could be responsible for different ways followed by penetrating fluids. It seems to be a clear correlation between chemical analyses and shell microstructure types. In this way, whereas Chondrodonta sp. and requienid shells show the more resistant behaviour for influence of diagenetic fluids, the monopleurid and caprotinid ones are more intensity affected by diagenesis. The SEM studies reflect that less mechanical altered and more structurally hermetic shells, the less diagenetically affected
Microcodium en calizas del Eoceno Medio (Luteciense) de la Sierra de la Pila (Prebético Interno, Murcia)
(2008) Molina, José Miguel; Nieto, Luis M.
Microcodium is a calcitic microfeature, mainly interpreted as root calcification products of terrestrial plants on carbonate-rich substrates, that is abundant in Paleogene successions of the peri-Tethyan realm. In the Betic Cordillera most of Microcodium appears as reworked in calcarenites interbedded in pelagic sedimentary rocks. In this study we analyse outcrops with in situ Microcodium aggregates located in Sierra de la Pila (Internal Prebetic, Murcia province). Microcodium appears on top of Lutetian (Middle Eocene) platform limestones and shows: 1) cylindrical morphologies showing «corncob» colonies longitudinally, and «rosette» structures in transverse section, and 2) individual or plural globular morphologies, similar to «rosettes» in section. Microcodium is interpreted as developed in calcic paleosols, related with a seasonal semiarid climate, before the boundary Middle-Upper Eocene and the important climatic change marked with the beginning of the transition from the extreme global warmth of the early Eocene «greenhouse « climate to the present glaciated state
Los sulfuros masivos volcanogénicos de la Cuenca Lancones (Perú)
(2008) Ríos Carranza, A. M.; Castroviejo Bolibar, R.; García Jiménez, J. M.
The Lancones basin is located on the north west coastal belt area of Peru, in the Department of Piura. It is bordered to the west by the Palaeozoic Amotapes coastal massif and to the east by the Western Andes pre-mountain range region. This basin extends to Ecuador, where it is called Celica basin. The Lancones basin contains arc-related felsic and mafic volcanic rocks, which make it an excellent target for exploration for volcanogenic massive sulphide (VMS) deposits in Peru. Actually the Lancones basin hosts the Tambogrande VMS group of deposits, which constitute the most advanced VMS project in Peru. This group consists of three world-class massive sulphide deposits TG1, TG3 and B5. The Lancones basin is part of a first-order extensive rift, in which tholeiitic oceanic-arc crust was generated. This extensional basin developed between the late Jurassic and the early Cretaceous period. The breakup of Laurasia and Gondwana, which began in the middle Jurassic, resulted in the north-west movement of what is presently the South American continent. The rift formed along a subduction zone on the western side of this continent. The stratigraphy of the submarine volcanic sequences is composed of a basal formation, the Basal Volcanic Group or GBV, which is disconformably overlain by a volcano-sedimentary formation, the Volcanic Sedimentary Group or GVS. These two formations contain two distinct metallogenic suites within the Lancones basin. Each is distinguished by specific lithogeochemical, petrographic and mineral attributes, age determinations and VMS deposit types. The pre-Albian mafic bimodal GBV contains high grade, large tonnage Cu-Zn type VMS deposits (Tambogrande type) associated to dacitic domes formed in second – or third-order extensional basins. The middle to upper Albian GVS contains low tonnage Zn-Pb-Cu type VMS mineralizations (Kuroko type). These are associated with felsic sequences of rhyolitic to dacitic composition, associated with a felsicdominated arc setting. The rocks of the GBV, which contain the polymetallic Tambogrande deposits, are tholeiitic. The rocks of GVS are mainly transitional between calc-alkaline and tholeiitic
Las «minas de agua» de Ciempozuelos (Madrid)
(2008) Villarroya Gil, Fermín; Senderos, A. J.; Alcázar, María
Ciempozuelos is located to the south of Madrid on the Miocene gypsum formations. From old times (XIV century or former) the water supply was made mainly by means of dug galleries (denominated «mines» of water). Given the easiness of excavation of the galleries in gypsum materials and the robustness of they without lining necessity, made proliferate the «mines» and also the excavation of caves in the basements of the housings. Finally it was a crossroad of galleries, holes, mines… that extend for the underground of Ciempozuelos. The historians speculates, that Spanish name of the city mentions this proliferation of wells and mines. Actually this rich hydraulic patrimony is abandoned and in phase of deterioration due to its partial destruction. The Town Hall has undertaken archaeological and hydrogeological studies in order to improve the knowledgement of the nature and singularities of these infrastructures and later to management them properly. The hydrogeological study made, has distinguished clearly among those denominated «mines» and other types of built hollows under the urban underground. Forty six wells have been inventoried. The equipotential lines map show that the direction of the groundwater flow is mainly from the southwest toward the northeast. Thirty five chemical analysis and fifteen bacteriological samples have been made and they confirm the sulphate calcium facies with high conductivity (1,700 mS/cm) and the inadequate bacteriological quality in order to possible use in urban water supply. We recommend their use for ornamental uses, and cultural memory of the singular water supply that has persisted in the city during centuries
High-pressure relics and structure of the Bou Azzer Neoproterozoic ophiolite (Anti-Atlas, Morocco)
(2008) El Hadi, H.; Simancas Cabrera, J. F.; Martínez Poyatos, David; Tahiri, A.; González Lodeiro, Francisco; Azor, A.
La ofiolita de Bou Azzer marca la sutura del orógeno Pan-africano en el Anti-Atlas (Marruecos). En esta ofiolita se ha observado una paragénesis relicta de granate y rutilo, que sugiere un episodio inicial de alta presión. Tras este episodio, la ofiolita sufrió, durante su exhumación, una retrogradación a facies esquistos verdes, al tiempo que se desarrollaba la fábrica plano-linear (S2, L2) que domina en estas rocas. La macroestructura asociada a esta fábrica principal consiste en pliegues volcados vergentes al SW y cabalgamientos con movimiento de bloque de techo al W/SW. Estas estructuras emplazaron la ofiolita sobre rocas de la plataforma continental del Cratón Oeste Africano. Una sucesión clástica (Formación Tiddiline) aparece discordante sobre la ofiolita, las rocas de arco y los sedimentos de plataforma, estando a su vez deformada por pliegues erguidos de dirección ESE-WNW y fallas inversas. La convergencia Neoproterozoica concluyó con el desarrollo de fallas de salto en dirección izquierdo

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