Geogaceta -- Nº 32, (2002)

Permanent URI for this collectionhttps://hdl.handle.net/10272/9112

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Diagénesis en las conchas de inocerámidos de la Isla de Castro (Coniaciense final-Santoniense inferior, Cuenca Vasco-Cantábrica): evidencias petrológicas e isotópicas
(Sociedad Geológica de España, 2002) Jiménez Berrocoso, A.; Elorza, Javier
Pétrographie and isotopic (á!80 and a13C) analyses have been carried out on inoceramid shells from shallow-marine limestone-marl couplets at the Castro Island section (latest Coniacian-lower Santonian, Basque-Cantabrian Basin), in order to determine their diagenetic alteration. Results show that the prismatic microstructure of the shells was mainly affected by silica replacement during diagenesis, but very little compaction, cementation and recrystallization occurred. However, these changes do not seem to have modified largely the isotopic composition of the inoceramids, as supported by the low luminescence intensity that show all the shells. In addition, à780 and al3C mean values from inoceramids included in limestones are heavier than those from inocermids in marls, which confirms that the isotopic values were influenced by a paleoceanographic circulation model with estuarine and anti-estuarine regimens
Variaciones en la composición isotópica del Pb en galenas del área de Los Pedroches: diferencias entre los yacimientos de El Zumajo y Linares-La Carolina
(Sociedad Geológica de España, 2002) García de Madinabeitia, S.; Santos Zalduegui, José Francisco; Carracedo Sánchez, Manuel; Larrea Bilbao, F. J.
We report the results of Pb isotope analyses on representative galena samples from the El Zumajo quartz-rich dyke. This is a late intrusion within the Cardeha-Virgen de La Cabeza granite of the Los Pedroches Hercynian batholith. The batholith granodiorite-granite alignment accounts for the largest composite granitic intrusive in southern sectors of the Central Iberian Zone of southwestern Spain. Located in the south of this magmatic lineation there occurs the Cardena-Virgen de La Cabeza granite, the largest pluton of the granitic unit of the batholith. An important dyke complex, mainly composed of trachyandesite, dacite, rhyolite, aplite, pegmatite and quartz dykes (Carracedo et al., 1993, 1994), outcrops in central sectors, mostly within the granodioritic unit, of the batholith. The El Zumajo dyke is distinctive because of its composition (almost only quartz with an important amount of galena), direction (N 120°E, that is, similar to the dacite-rhyolite dykes and different from that of the other quartz dykes) and because it is found in the granite unit which bears scarce evidence of dyke intrusions. Isotopic compositions of analysed galena are: 206Pb/204Pb = 18.457, 207Pb/204Pb = 15.636 and 20SPb/204Pb = 38.611. These data were compared with published data from the same mineral of the Linares-La Carolina sector, a mining district also related to granites of the Los Pedroches batholith. The new results are markedly different from those published by Lillo (1992) and Arribas (1993) for Linares-La Carolina. The observed difference in Pb isotopic compositions with respect to the known data might be related to: a different age of the intrusion, a difference source for the metal enrichments, or to a combination of both factors. On the basis of field relationships, it appears evident that the dyke is younger than nearby intrusives, including other dyke types. Nevertheless, the possibility of a different source cannot be discarded. A more solid conclusion would require new Pb and other isotope data on the Linares-La Carolina sector and related granites, and further more precise structural constrains on the relationships between the granites and the mineralizations
The Argentine Frontal Cordillera between 30° OO'and 31° 30'S latitude: polycyclic structure and tectonic evolution
(Sociedad Geológica de España, 2002) Rodríguez Fernández, L. R.; Heredia, N.; Gallastegui, G.; Busquets, Pere (Busquets i Buezo)
En el sector de la Cordillera Frontal Argentina comprendido entre los 30° y 31° 30' de latitud S, se diferencian dos conjuntos de rocas con naturaleza y estructuración diferentes: un substrato paleozoico y una cobertera mesozoico-terciaria. El substrato paleozoico está constituido por rocas sedimentarias depositadas en ambientes marinos o de transición, entre el Devónico superior y el Pérmico inferior, deformadas durante los Ciclos Orogénicos Famatiniano y Condwánico, e intruidas por rocas graníticas permotriásicas. En la serie carbonífero-pérmica se diferencian una sucesión preorogénica, y otra sinorogénica separadas por una discordancia. Las principales estructuras gondwánicas son sistemas de cabalgamientos y pliegues relacionados, con un acortamiento del 60-70%. La cobertera mesozoico-cenozoica se caracteriza por un predominio de rocas volcánicas, depositadas en ambientes continentales, intruidas por granitoides mesozoicos y cenozoicos. Se pueden diferenciar dos conjuntos de rocas originadas en contextos tectónicos distintos y separadas por discordancias de diversa magnitud: uno inferior (Grupo Choiyoi), ligado a un proceso extensional, que desarrolla fallas de dirección N-S, con geometría lístrica, y otro superior, ligado a un evento compresional posterior que produce la inversión de las estructuras extensionales previas. El acortamiento cortical calculado en la Cordillera Frontal es del orden del 10%
Tectónica y magmatismo Ordovícicos en el área de Sanabria, Macizo Ibérico
(Sociedad Geológica de España, 2002) Díaz García, F.
Structural and metamorphic criteria allow us to distinguish two units (Cneissic and Porphyroid) belonging to the Olio de Sapo formation in the Sanabria región. The high-grade gneissic unit and the lower Ordovician metasediments were brought together by a top-to-east extensional detachment with related flat-lying foliation. The low grade porphyroid unit, only affected by vertical foliation, intruded along subvertical faults that cross-cut the detachment. These Upper Ordovician tectonic and magmatic processes in the Sanabria area seem to be related to the extension in the continental margin of Condwana that permitted the formation of deep basins and the addition of huge volumes of granitic magma to the crust
Tectonic setting of the Monte Castelo Gabbro (Ordenes Complex, NW Iberian Massif)
(Sociedad Geológica de España, 2002) Andonaegui, P.; González del Tártago, J.; Arenas, R.; Abati, Jacobo; Martínez Catalán, José R.; Peinado, M.; Díaz García, F.
En el Complejo de Ordenes (NW del Macizo Ibérico) la unidad tectonoestratigráfica superior está constituida por una potente secuencia metasedimentaria (Serie de Ordenes), intruida por ortogneises y gabros. El Cabro de Monte Castelo se localiza en la parte inferior de la Serie de Ordenes, en él se han distinguido tres tipos composicionales: Vgabronoritas olivínicas (Pl+Cpx+Opx+OI +Hbl), 2)gabronoritas anfibólicas (PI+Cpx+Opx+Hbl±Bt), y 3) gabronoritas biotíticas (Pl+Cpx+Opx+Bt). Las características geoquímicas, tanto de elementos mayores como trazas, indican que el Cabro de Monte Castelo es de carácter toleítico, con rasgos químicos que presentan afinidad con tipos toleíticos generados en arcos-islas. Por otro lado, los datos de geocronologia de U-Pb indican que una parte de la evolución tectonotermal de la Serie de Ordenes tuvo lugar en el Cámbrico superior - Ordovicico inferior, y demuestran también que la intrusión delgabro de Monte Castelo (499±2 Ma, U-Pb en circones) fue seguida de un episodio metamòrfico que alcanzó las facies de las granulitas (493 - 498 Ma, U-Pb en monacitas). Estos datos afianzan la hipótesis de la generación del gabro en una zona de subducción insular, ya que un contexto acrecionario es el más propicio para integrar de forma contemporánea magmatismo, metamorfismo y fuerte deformación
Superposición de estructuras en el Anticlinal de Santa María de las Hoyas. Borde meridional de la Cadena Ibérica (provincias de Burgos y Soria)
(Sociedad Geológica de España, 2002) Espina, R. G.; Heredia, N.; Rodríguez Fernández, L. R.; Suárez Rodríguez, Ángela
The Santa María de las Hoyas anticline is located in the southern front of the Iberian Chain in the limit of Burgos and Soria provinces. The the geological map and the cross-sections show a carbonated formations of the upper Cretaceous deformed by thrust sheets, faults and related folds with SW vergency, overthrusting onto Duero Basin. The oldest structures recognised are thrust sheets with SW tectonic transport direction. Other set of the out of sequence thrusts and related folds deform the oldest thrust. The best represented tear fault is Espeja fault with dextral component. Lateral an oblique ramps are also recognised. The calculated shortening along the cross section A-A' is about 7 km, but very important variations in the shortening can be observed in other cross sections
Sobre la contaminación microbiológica del acuífero de la Vega de Granada
(Sociedad Geológica de España, 2002) Castillo, A.; Ramos Cormenzana, A.
The microbiologic quality of the groundwater in the alluvial aquifer of the Vega de Granada is acceptable. Nevertheless, almost 20% of the points sampled present low to moderate degrees of faecal contamination. These cases are closely related with leaks and the discharge of urban wastewater. A further contributory factor is the existence of high-risk irrigation practices, such as inundation with untreated (or ineffectively treated) urban wastewater where the piezometric levels are less than 20 m below ground level. Consequently, the incidence of contamination detected corresponds to specific situations or practices, in particular geographic areas and is generally of very limited duration
Sedimentación y volcanismo al este de las islas de Fuerteventura y Lanzarote ( Surco de Fúster Casas)
(Sociedad Geológica de España, 2002) Martínez del Olmo, W.; Buitrago Borrás, J.
Fuerteventura and Lanzarote islands were created by volcanic processes that took place on the western margin of the triassic rift basin developed during the initial opening of the Central Atlantic. Thick syn-rift deposits consisting mainly of salt-anhidrite, were soon substituted by a deep water paleogeography developed west of the distant shelf, of passive type, built on the african continental margin. Seismic lines and wells inthe area, allow us differentiating the extent, the approximated age and morphological characteristics of the volcanic products that, originated in Fuerteventura and Lanzarote, were intercalated within the sedimentary record of the basin as well as interpreting some of the peculiarities of the Jurassic and Cretaceous outcropping onshore Fuerteventura
Secuencia de facies volcánicas en el área del río Odiel (Faja Pirítica Ibérica, España)
(Sociedad Geológica de España, 2002) Valenzuela Aznar, Alfonso; Donaire Romero, Teodosio; Pascual Martínez, Emilio
We present a detailed study of a 10 km2 area located in the Odiel River, to the northwest of Zalamea la Real (northern flank of Riotinto antiform, Huelva), where we describe the main facies characteristics of a section of the Volcano-Sedimentary Complex (VSC) which is relevant to the stratigraphy of the central part of the Iberian Pyrite Belt (IPB). The following rock types have been distinguished: felsic and mafic sills, felsic volcaniclastics and siliciclastic rocks. Sills intrude at different parts of the stratigraphic column and show peperitic borders. Perlitic textures are very often found at the borders of large felsic sills. Volcaniclastic deposits consist of poorly organized individual packages, up to 20 m thick. All of the volcaniclastics exhibit a narrow range of exclusively juvenile volcanic clasts. We suggest that the studied volcaniclastic packages must have formed by mass-flow processes, directly related to volcanism, most probably related to the collapse of a zoned dome or, in some instances, to a pyroclastic mass flow entering seawater
Secuencia magnetoestratigráfica y edad de los materiales volcánicos y sedimentarios de Poblete (Ciudad Real)
(Sociedad Geológica de España, 2002) Gallardo Millán, José Luis; Ancochea, Eumenio; Pérez González, Alfredo
The magnetostratigraphic sequence of the volcanosedimentary materials near to Poblete (Ciudad Real) has allowed dating the most recent eruption of the volcanism of the Campo de Calatrava. The chronology of the magnetostratigraphic sequence has based on the radiometric dating of one lava flow that was previous to the explosive episodes. A great variety of volcanic materials and several sedimentary levels and soils compose the sequence
Reconstrucción morfoestructural mediante modelos de elevación digital en un SIG del fondo de la cuenca sedimentaria de la Cubeta del Saltador (Cordilleras Béticas Orientales)
(Sociedad Geológica de España, 2002) García Meléndez, Eduardo; Ferrer Julia, Montserrat; Goy, José L.; Zazo, C.
GIS analysis operations are applied to both a set of available vertical electric sounding data (VES), and topographical data using digital elevation models (DEM) allowing the reconstruction of the approximate three-dimensional shape of the Cubeta del Saltador basin-floor and its limiting faults, as well as affording the thickness of the Plio-Quaternary sedimentary filling. From the morphological configuration of the basin floor, several furrows related to Plio-Quaternary fluvial systems are identified.
Reconstrucción de una plataforma carbonatada Viseense no preservada en el Área del Guadiato (Córdoba, SO de España)
(Sociedad Geológica de España, 2002) Rodríguez, Sergio; Rodríguez Curt, L.
Calcareous breccias from Antolin (Guadiato Área, Córdoba Province) have been analysed. Paleontological and sedimentological studies of those breccias, allowed a reconstruction of a not-preserved calcareous platform or ramp. Breccias from Antolin show six types of clasts and blocks: oolithic grainstones originated in calcareous shoals, coral-algal boundstones originated in patch-reefs, packstones that are mainly composed of solitary corals and brachiopods produced in shallow quiet waters, crinoidal packstones originated in crinoida! prairies, mudstones-wackestones with micropeloidal and cryptalgal textures that were originated in mud mounds and calcareous sandstones originated in a mixed ramp. The debris flow was located in the photic zone of a middle, mixed ramp, because clasts show algal and bryozoan crusts; moreover, clasts and blocks show signs of short transportation
Reconstrucción paleogeográfica de depósitos volcanosedimentarios Pliocenos en el litoral NE de Gran Canaria (Islas Canarias) mediante métodos topográficos
(Sociedad Geológica de España, 2002) Pérez Torrado, Francisco J.; Santana, F.; Rodríguez Santana, A.; Melián, A. M.; Lomoschitz Mora-Figueroa, A.; Gimeno, Domingo; Cabrera, María Carmen; Báez, M. C.
Palaegeographical reconstructions of marine deposits in volcanic islands represent powerful geological tool to identify eustatic vs. isostatic relative movements. NE coastal areas of Gran Canaria offer excellent outcrops of Pliocene marine deposits. They have allowed not only the reconstruction of marine ground surfaces at that time, but also the marine level registration that is shown in lava flows at the transition of submarine to subaerial structures. Based on both geological and topographic methods, this work presents the palaeogeographical reconstruction of the two aforementioned levels, with centrimetre accuracy for three-dimensional coordinates
Rango de magnitudes de los esfuerzos tectónicos en una zona intraplaca: el macizo de El Berrocal, borde sur del Sistema Central Español
(Sociedad Geológica de España, 2002) Martín Velázquez, Silvia; Vicente, Gerardo de; Muñoz Martín, Alfonso; Elorza, F. J.; Vela, A.
Stress magnitudes throughout a NW-SE cross-section in El Berrocal granitic massif (Spanish Central System) have been analysed by means of finite element modelling. Topographic surface, lithological differences and recent compressive tectonic stresses have been included. Two kinds of models have been performed to study the influence of rheologic properties, one with average cortical mechanical properties and the other with the main lithologies. Horizontal tectonic stress magnitudes obtained in the last model have been checked with the recent stress ratio got by stress inversion of fault slip data. Horizontal tectonic load that better fits recent tectonic stress distribution is in the range of 10-15 MPa.
Propuesta de correlación entre los sedimentos Pérmicos y Triásicos de la Cordillera Ibérica Este y de las Islas Baleares
(Sociedad Geológica de España, 2002) Arche, A.; López Gómez, José; Vargas, H.
The sedimentary record of Permian and Triassic age exposed in the Balearic Island is reasonably well dated, and several unconformities and breaks of sedimentation have been identified inside it. A combination of lithostratigraphic and biostratigraphic criteria allow for a formation-scale correlation between both geographic areas that also show a very similar extensional tectonic evolution during these periods. Lateral changes of facies in the Muschelkalk and Keuper facies are also shown, indicating, as expected, the presence of more open, shallow marine facies in the Balearic Island during the Middle and Late Triassic
Propiedades hidrogeológicas de la matriz de rocas carbonatadas de la Cordillera Bética (sur de España)
(Sociedad Geológica de España, 2002) Motyka, J.; Pulido Bosch, Antonio; Pulido Leboeuf, P.; Borczak, S.
The study of 181 rock samples from boreholes drilled in different locations of the Betic Cordillera throw hydraulic conductivity values that range from 5,25x10's to 2.71x10',2 cm/s and interconnected porosity values between 0.2091 and 0.004458. Higher values generally correspond to miocene calcareous sandstones, although hydraulic conductivity can reach more elevated values in some limestone and dolostone samples. Lower values were found in marly limestones and marbles
Preliminary thermobarometric data from the Ouguela and Contenda-Barragem do Caia Units: Coimbra-Cordoba shear zone (Northeast Alentejo, Portugal)
(Sociedad Geológica de España, 2002) Francisco Pereira, M.; Apraiz, A.
The Coimbra-Cordoba shear zone comprises different tectonic units with a complex metamorphic evolution. In the Northeast Alentejo (Portugal) some of these units contain mineral parageneses of high-temperature/ intermediate-pressure metamorphism, which were subsequently retrogressed, to low-temperature/low-pressure conditions. Detailed microstructural studies show that the relationships between metamorphic assemblages and deformation stages in these rocks relate to strong shearing. In this preliminary study conventionalgeothermobarometrical techniques performed on rocks with appropriate mineral assemblages allows us to determine the P-T conditions near the metamorphic peak of two major rock units: (1) garnet-bearing leucocratic gneisses from the Ouguela Unit (600-700°C and 7-9 kbar), and (2) garnet-rich amphibolites (~550-600°C and 8-10 kbar) and garnet-rich amphibolitic boudins (650-700°C and 8.5-9.5 kbar) associated with calc-silicate rocks from the Contenda-Barragem do Caia Unit. These P-T determinations suggest that the rocks from Northeast Alentejo were buried to lower crustal depths of —25-35 km consistent with the high-grade metamorphism (upper amphibolite facies) deduced from the relict mineral assemblages. Later, during the uplift and exhumation the rocks experienced strong retrogression in the greenschist-facies.
Petrología del macizo granítico de Manzalvos-Castromil (NO de la Zona Centro-Ibérica)
(Sociedad Geológica de España, 2002) Bellido Mulas, F.; Gallastegui, G.; Díez Montes, Alejandro
The Manzalvos-Castromil massif (NW Iberian Hercynian Belt) is mainly composed of granitoids that define an alumino-potassic association. Magmatic microgranular enclaves and scattered amphibole-biotite intermediate rocks are present in the massif. These rocks are later intruded by some two micas granites and leucogranites that result in hybrid contact zones. Field relationships point out to a quasi-simultaneous intrusion of both basic magmas and granitoids. The hybrid nature of the calcoalkaline basic magma is deduced from its petrological, mineralogical and geochemical characteristics. They are derived from a basic magma evolving by assimilation and contamination with crustal components in the middle continental crust
Período vital y velocidad de crecimiento de rudistas radiolítidos (Bivalvia) del Cretácico Superior de Gredilla de Sedaño (Norte de Burgos, España)
(Sociedad Geológica de España, 2002) Regidor Higuera, I.; García Garmilla, Francisco; Elorza, Javier
Eight radiolitid shells (Hippuritacea, Bivalvia) collected from the Upper Campanian-Lower Maastrichtian sediments of the Quintanaloma Formation at Gredilla de Sedaño section (Northern Burgos, Spain) have been studied with regard to their arrangement of growth lines for a first approximation to their life span. The walls that separate internal skeletal cells («honeycomb») as well as the compact layers showing the alternance of obscure and clear lines (microrhythms) have allowed to us to make a first account of laminae sets. The very thin microrhythms are grouped in sets separated by growth lines. The more vigorous growth of the rudist, the thicker development of laminae within the walls, even overlying the growth line. The calculations suggest that Biradiolites could have had a more continuous growth in comparison to Radiolites, and could live in normal environmental conditions as much as 18-19 years in age. On the other hand, the individuals of Radiolites could live between 15 and 24 years in age. Some specimens of Biradiolites could grow up to 1.5 cm. in length during the better youth year, in contrast with Radiolites, which could not reach up to 1 cm each year lacking growth lines in practically all the annual cycles. Nevertheless, some slight Interruptions into the laminae series of Biradiolites suggest reproductive periods, or perhaps a response to variations In sedimentation rate. Radiolites shows non-erosive annual truncations in their sclerochronological profiles suggesting "biological" rather than physical gaps. The absence of evaporitic manifestations in the sediments leads us to think in possible annual changes in water salinity owed to seasonal factors (rain periods)
Nuevos datos geocronológicos y geoquímicos de las manifestaciones volcánicas de Picasent y Cofrentes (Valencia)
(Sociedad Geológica de España, 2002) Ancochea, Eumenio; Huertas, María José
The volcanic region of eastern Spain is badly known, mainly because of lack of subaerial exposures, which are restricted to the Cofrentes and Picasent outcrops. Moreover, these volcanic occurrences show somewhat compositional differences and their ages are clearly distinctive. The Picasent occurrence consists of alkaline rocks which have been dated at 8 Ma. These rocks constitute an on land representation of the volcanic activity developed in the Valencia Gulf during the Miocene. The Cofrentes occurrence is made up of ultra-alkaline volcanic rocks, ranging 1 -2 Ma in age, thus evidencing a second phase of volcanic activity in eastern Spain that can be related to the Campos de Calatrava volcanic area

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