Geogaceta -- Nº 40, (2006)

Permanent URI for this collectionhttps://hdl.handle.net/10272/8543

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Variación estacional de los contenidos en carbono orgánico, inorgánico y azufre en los sedimentos del estuario de los ríos Tinto y Odiel (SO España)
(Sociedad Geológica de España, 2006) López González, Nieves; Borrego Flores, José; Morales González, Juan Antonio; Carro Flores, Berta
The study of 12 sediment traps located in the Tinto and Odiel river estuary show the influence of the acid contributions in the seasonal variation of the contents in organic carbon, inorganic carbon and sulfur. The seasonal relations between organic carbon and sulfur (C/S) have allowed determining environmental conditions of the estuarine system. Of this form, the winter conditions correspond to a normal marine environment, whereas rest of the year varies between euxinic and semi-euxinic conditions due to the high rate of evaporation that takes place in the intertidal zone that favors sulphate precipitation
Variación estacional de las características texturales en los sedimentos intermareales del estuario de los ríos Tinto y Odiel (SO España)
(Sociedad Geológica de España, 2006) López González, Nieves; Morales González, Juan Antonio; Borrego Flores, José; Carro Flores, Berta
The seasonal evolution in the sediment textural characteristics along the Tinto and Odiel river estuaries has been studied by means of 12 sediment traps. The fine-grained material is associated with flocculation and decantation processes that take place in the zones of saline mixing and acid neutralization of both estuaries. The bed load deposits are related with two different processes. In winter they are located in the confluence of the fluvial and tidal currents, while in spring and summer, they are redistributed by the tidal currents that deposit them in the central zones of the estuaries
Variaciones en las faunas de foraminíferos bentónicos del Mar de Alborán durante el evento Heinrich 6
(Sociedad Geológica de España, 2006) Pérez Martín, Rubén; Sierro, Francisco Javier; Flores, José Abel
Heinrich events are cold periods during which icebergs discharge took place in the North Atlantic Ocean. Those cold events modified both the surface water temperature and the North Atlantic deep water formation, thus influencing bottom water ventilation. The present study has been carried out in core ODP 977 from the Alboran Sea in order to analyze the variations in the deep sea water formation in the Western Mediterranean Sea during Heinrich Event 6. During non-Heinrich events benthic foraminifera Cibicidoides pachyderma and Globobulimina spp. dominated the foraminifer association, but during Heinrich Events modification in the amount of the oxygen and organic matter in the environment ocurred, with the consequence of an uprise in the Cassidulina laevigata presence. Those observed changes during Heinrich Event 6 in Western Mediterranean Sea are similar to those previously described by other authors in North Atlantic sediments
Valores de subsidencia reciente (Pioceno-Cuaternario) en el Mar de Alborán mediante análisis de “backstripping”
(Sociedad Geológica de España, 2006) Martínez García, Pedro; Soto, Juan I.
A backstripping analysis is presented for the different scientific ODP wells in the Alboran Sea (Leg 161, Holes 976B, 977A, 978A, and 979A). The study has been performed for the complete Pliocene-to- Quaternary sedimentary sequence, based on the detailed paleontological dataset available in these wells. Logging data together with in-situ determinations of porosity and density have been fitted to obtain robust estimates of the appropriate variables to perform the backstripping study (e.g., porosity, density). The total subsidence pattern shows a remarkable coincidence in all the wells (Y=310-355 m) equivalent to a subsidence rate of 0.06-0.07 mm/y for the last 5.1 Ma. In regions where a significant intra-Pliocene hiatus (2.2-5.0 Ma) occurred, like the Site 976-basement high in the West Alboran Basin or the Alboran Ridge, we infer the existence of a major tectonic pulse with high subsidence rates (2.2-5.0 mm/y) that diminished towards the Quaternary (0.07-0.11 mm/y). According to these results, the estimated stretching factor (b) for this basin is 1.35-1.42
Un protocolo de tratamiento estadístico para muestras polifásicas de lineaciones de disolución
(Sociedad Geológica de España, 2006) Simón Gómez, José Luis
Accurate analysis of orientations of linear elements from polyphase populations involves computing statistics (mean, standard deviation) of each sub-population, which needs previous identification of the polymodal character and separation of sub-samples. The procedure here proposed for a regional study involves: (a) distinguishing polyphase from monophase samples; (b) characterizing mean and deviation of clearly monophase populations; (c) separating poliphase samples into sub-samples using density diagrams in equal-area projection and standard deviation values; (d) applying a correspondence test based upon the 95% confidence cone, as well as an equality F-test for directional samples, by comparison with monophase reference samples. An example of application of this procedure to pressure-solution lineations in carbonate pebbles of the Aliaga Tertiary basin (Teruel, Iberian Chain) is shown
Ultramilonitas de apariencia fluidal, pseudotaquilitas o algo intermedio? (Formación Bacariza, Cabo Ortegal)
(Sociedad Geológica de España, 2006) Puelles, Pablo; Ábalos, Benito; Gil Ibarguchi, José Ignacio
Occurrence of tectonites with features characteristic of both pseudotachylytes and ultramylonites formed under high-pressure granulite-facies conditions is reported in the Cabo Ortegal Complex of NW Spain. We interpret that these rocks were originated due to a seismic event at great depth (1.4 GPa) under high temperatures (740 ºC). Shear heating would have affected the still hot and mechanically rigid granulites and provoked melt formation. Ambient high P and T would have led to subsequent recrystallization of the previously formed melt giving rise to a weak planar fabric
Tensor actual de esfuerzos y fallas potencialmente activas en el Domo del Tormes (NO de Iberia)
(Sociedad Geológica de España, 2006) Antón, Loreto; Vicente, Gerardo de
Located in the NW of the Iberian Peninsula, the Domo del Tormes is an intra-plate granitic domain made up of a Hercynian megastructure and traditionally considered of very low or null seismicity. The geology of the area makes difficult to determine the recent deformations and the characterization of neotectonic activity. The data compilation and further discussion of seismic activity in the area provide information on present day stress tensor orientation and the match of gravimetry, geological and structural data revealed a series of main anomalies related to faulting on a regional scale, defining some potentially active structures in the area
Tasas de erosión en la cuenca de Guadix-Baza durante el Pleistoceno superior - Holoceno
(Sociedad Geológica de España, 2006) Pérez Peña, José Vicente; Azañón, José Miguel; González Lodeiro, Francisco
Erosion rates in the Guadix-Baza basin have been calculated drawing on a volumetric estimation of sediment loss by river erosion since the late Pleistocene. On this purpose we have perform a reconstruction of the geometrical surface dated in 43 Ka and defined by a calcrete layer that capes the basin infilling. By comparing the reconstructed geomorphic surface and the present day topography we have calculated the volume of sediment lost by hidric erosion in the entire basin. The resulting erosion rate is 6.57 m3ha-1yr-1. Individual erosion rates for Guadix and Baza sub-basins (11.80 m3ha-1yr-1and 1.77 m3ha-1yr-1 respectively) suggest different stages of drainage pattern evolution in both sub-basins. We attribute the lower values obtained in the Baza sub-basin as related to the downthrowing of this sub-basin due to very recent activity along the Baza fault
Tafonomía cuantitativa del yacimiento de Cacela (Tortoniense superior; Algarve, Sur de Portugal)
(Sociedad Geológica de España, 2006) Rico García, Alberto; Aguirre, J.; Civis-Llovera, Jorge; González Delgado, José Ángel; Alonso Gavilán, G.
A quantitative taphonomic analysis were performed in the fossil assemblages of the late Tortonian of the lower-mid part of the Cacela Formation (Cacela, Algarve, S Portugal). Taphonomic results, together with sedimentological analysis and the faunal assemblages, allow to inferring palaeoenvironmental changes. The upper Tortonian sedimentation started with fan-delta conglomerates that quickly changed to outerplatform silty marls deposited in a setting with a relatively low sedimentation rate as indicated by the concentration of glauconite. Higher up into the section, a progressive shallowing trend is inferred, and sediments of inner platform settings were formed
Sucesión de secuencias volcánicas félsicas en el Complejo Vulcanosedimentario de la Faja Pirítica Ibérica: discriminación entre modelos volcánicos y subvolcánicos
(Sociedad Geológica de España, 2006) Donaire Romero, Teodosio; Pascual Martínez, Emilio; Valenzuela Aznar, Alfonso; González Roldán, Manuel Jesús; Toscano Macías, Manuel
A field study is presented on two selected areas in the Volcano-Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB), the Odiel River section and the Paymogo Volcanic lineament. Field evidence has allowed to distinguish two major groups of felsic rocks, which successively appear in the stratigraphic column. Probably, this conclusion can be extended to other areas in the IPB. In addition, field, petrographic and geochemical evidence shows that at least the felsic rhyolitic succession in the Odiel River (and probably also in Paymogo) formed in a volcanic, environment, favouring a volcanic-pile model in the VSC
Situación medioambiental de la marisma Joyel (Cantabria): datos aportados por los foraminíferos bentónicos
(Sociedad Geológica de España, 2006) Pascual, Ana; Elorza Remón, M.; Martín Rubio, Maite; Rodríguez Lázaro, Julio
A total of sixty nine species of benthic foraminifers have been identified in the Joyel-Ria of Quejo marsh (Cantabria, N Spain). Fifty six of those species had living individuals in the time of sampling. Main foraminifer assemblages change from the mouth to the head of the estuary. Thus, in the silty channels of the marsh area, the most abundant species is Ammonia tepida, while in the vegetated middle marsh area is Trochammina inflata the dominant species. In the mid area of the Ria of Quejo, dominant assemblage is composed by Ammonia tepida, Cribroelphidium williamsoni, Haynesina germanica and Lobatula lobatula. The last one, besides Rosalina globularis are dominant at the mouth and with Quinqueloculina seminula, in the beaches. The occurrence of abundant living individuals of A. tepida at the flooded area of the head, now occupied by an old sewage point, confirms the recovering of this area thanks to the environmental policy of the last years. Finally, the occurrence of live specimens of Ammonia tepida and Haynesina germanica inside the lagoon of Joyel indicates the influence of brackish water
Sedimentos glaciomarinos del Ordovícico terminal en la Zona Cantábrica (NO de España)
(Sociedad Geológica de España, 2006) Bernárdez Rodríguez, Enrique; Gutiérrez Marco, Juan Carlos; Hacar, M.
Preliminary studies of some stratigraphic sections spanning the Ordovician-Silurian boundary in the southern Cantabrian Zone (Iberian Massif, NW Spain) demonstrate the existence of a record of Hirnantian glaciomarine diamictites and shallow-water quartzites in at least three localities, situated in the Bodón nappe. These rocks, evidenced for the first time in the Cantabrian Zone, are probably related to the infilling of a paleorelief, scoured in the Barrios Formation during the Late Ordovician glaciation. The occurrence of an ubiquitous quartzite unit, generally related to the Ordovician-Silurian boundary in most parts of northern Gondwana, is now extended to the outcrops here analyzed. The Hirnantian quarzite probably occurs in additional areas of the Bodón and Correcilla nappes, where its location and significance might be underestimated, and described as the uppermost part of the Barrios Formation (Middle Cambrian to Arenigian). The same quartzite is probably recognized in the areas with volcanic necks within the Barrios Formation, and also in its stratotype, in which a latest Ordovician/earliest Silurian quartzite overlies unconformably on Middle Ordovician shales
Sedimentología y caracterización paleoambiental de la serie cretácica inferior de Antromero-Luanco (Asturias)
(Sociedad Geológica de España, 2006) Alonso García, Montserrat; Bahamonde, Juan R.
A paleoenvironmental study for a Lower Cretaceuos (Late Barremian-Aptian) succession (Antromero-Luanco section, Asturian coast) is showed in this work based on stratigraphic, sedimentological and paleontological data. The lower part of the succession shows terrigenous deposits (the Peñaferruz Fm) recording fluvial and fan-deltaic sedimentation, while the upper part is characterized by shallow-water carbonates (the Antromero Fm) covering a broad carbonate platform environments from restricted to open marine zones. Fossil associations had been very helpful in order to interpret the main environmental features
Secuencia de emplazamiento, alteración hidrotermal y metamorfismo en el Complejo Intrusivo de Jörn, distrito minero de Skellefte, norte de Suecia
(Sociedad Geológica de España, 2006) González Roldán, Manuel Jesús; Allen, Rodney L.; Donaire Romero, Teodosio; Pascual Martínez, Emilio
The Skellefte district is one of the most important mining districts in Sweden, located in an early Proterozoic (1.90-1.87Ga) volcanic arc province in the Baltic Shield, northern Sweden. The district consists of a complex volcanosedimentary succession formed by submarine, mainly felsic, volcanic rocks named Skellefte Group, overlain by a subaerial, felsic volcanic succession named Arvidsjaur Group and shallow- to deep-marine sedimentary rocks known as Vargfors Group (Allen et al., 1996). The Jörn Granitoid Complex (JGC) crops out at the northern boundary of the Skellefte district, and is constituted by several intrusions ranging in composition from gabbro to granite. Some features of the JGC suggest that it is comagmatic with the volcanic rocks of the Skellefte and Arvidsjaur Group. Our recent study has revealed that earlier intrusives in the complex (GI) have significant geochemical differences with the rest of plutonic rocks in the complex (GII to GIV). Crystallization of GI was followed by intense hydrothermal alteration and late, regional contact metamorphism that do not affect the later GII to GIV facies. This sequence in time, together with the chemical contrasts between the successive Jörn facies, suggests that a significant time gap lasted between the emplacement of GI and the later plutonic rocks in the Jörn complex. This is probably relevant to the geological history and ore research in the district, in that a major change occurred between GI and the rest of the JGC facies, involving changes in the geochemical character of magmatism and coeval thermal activity
Secuencia de cabalgamientos en la Zona Sub-Atlásica y cuenca de Ouarzazate; borde sur del Alto Atlas (Marruecos)
(Sociedad Geológica de España, 2006) Tesón, E.; Teixell, Antonio
The Sub-Atlas thrust belt and Ouarzazate basin constitutes the best and almost the unique synorogenic record of the Atlas mountain building. During the Eocene and Oligocene the deformation was concentred in the distant High Atlas whereas the marginal thrust belt was scarcely deformed. In Late Oligocene to early Miocene, deformation migrated forelandwards when complex thrust sequences created the Sub- Atlas foreland fold and thrust belt. Thrusting took place up to Pliocene times entraining the synorogenic sedimentary rocks, locally-sourced terrigenous and lacustrine deposits
Resultados y experiencias de aplicación del método de Refracción por Microtremor (Sísmica Pasiva) para la investigación geofísica de las nuevas líneas de metro en Madrid (España)
(Sociedad Geológica de España, 2006) Muñoz Martín, Alfonso; Carbó Gorosabel, A.
Geophysical exploration with seismic methods in urban zones presents several disadvantages: the presence of numerous sources of seismic noise, the scanty penetration when the seismic source is a hammer and the disability to detect buried low-velocity beds. Recently (Louie, 2001) a new method of seismic investigation has been developed, which allows vertical modeling of Raleygh waves from spectral analysis (Vphase/frequency) using the seismic signal registered with conventional seismographs and geophones. This method allows to detect low-velocity buried beds of great interest in tunneling, and to reach depths below 50 meters. In this work we discuss the conditions of application and experiences obtained during the 2005 geophysical surveys carried out in Madrid before the excavation of the new subway tunnels
Resistencia a la alteración diagenética de conchas de Chondrodonta sp en las calizas rojas del Aptiense – Albiense inferior de Ereño (Bizkaia)
(Sociedad Geológica de España, 2006) Damas Mollá, Laura; Aranburu Artano, Arantza; García Garmilla, Francisco
Chondrodonta sp. shells from Aptian – Lower Albian red limestones of Ereño (Bizkaia, northern Spain) have proved to be excellent indicators of a high resistance to the entrance of diagenetic fluids and further diagenetic alteration. Chondrodonta sp. shells, when compared to their coeval rudist shells, show higher Sr+2 and Na+ contents, together with very dull or even null luminescence. For this reason they could be very appropriate for further C, O an Sr isotopic studies as a tool for reconstruction of palaeotemperatures and palaeoenvironmental conditions
Registro del evento anóxico oceánico OAE1a (Aptiense inferior) en un contexto de plataforma. Prebético (provincia de Alicante)
(Sociedad Geológica de España, 2006) Castro Jiménez, José Manuel; Gea, Ginés A. de; Quijano, María Luisa
The Early Aptian was a time of major global events, being probably the most notable the Oceanic Anoxic Event 1a. In this paper, we present the study of the record of the OAE1a in a platform setting, the Prebetic Zone of the Betic Cordillera, which represents the shallow platform environments of the Southern Iberian Palaeomargin during the Mesozoic. In this context, several events of global and regional character are recorded, whose timing and relationships are extremely interesting to be clarified. The correlation between the studied sections has permitted the establishment of the timing of the main sedimentary events. The transgressive general context recorded in the studied units, linked to the tectonic subsidence, resulted in several retrogradational pulses, leading finally to the drowning of the shallow platform, which was postdated by the OAE1a event. The record of the OAE1a in a platform setting is explained as related to a local combination of factors, as a transgressive general context, strong local subsidence rate, and important input of terrestrial organic matter in the platform, as has been supported by the data provided from the analysis of the organic matter contained in the sediments
Propuesta de clasificación geotécnica del “Efecto Sitio” (Amplificación Sísmica) de las formaciones geológicas de la Región de Murcia
(Sociedad Geológica de España, 2006) Tsige, Meaza; García Flórez, I.
In this paper a geotechnical-siesmic amplification classification based on geological data is proposed for the Murcia region, (SE Spain). The structural damages caused during earthquake are controlled by local geological condition especially surface geology conditions and topography. The presence of some kind of soil type could produce increase in the intensity as a consequence of seismic wave amplification. The factor of amplification which can duplicate or triplicate the seismic waves is directly related to the geotechnical (dynamic) properties of geological materials. Regarding this fact, we have carried out geotechnical classification of the geological materials, in order to see their possible contribution to this local ground amplification. According to this classification the amplification effect in the earthquake area varies from nil, where bedrock is exposed to high where Plio-Quaternary fluvial and alluvial sediments are present
Procesos neotectónicos en los depósitos de rasa de la zona de Canero (Occidente de Asturias)
(Sociedad Geológica de España, 2006) Gutiérrez Claverol, M.; López Fernández, Carlos; Alonso, J. L.
The Pleistocene sediments deposited on the emerged marine abrasion platform near Canero village (Valdés, Asturias) are truncated by reverse faults which are parallel to basement bedding. These structures imply a neotectonic activity with a NW-SE maximum compressive stress, consistent with recent fault population analysis and current seismicity studies. The described deformation corresponds to a reactivation of folds in the Palaeozoic basement through a flexural slip mechanism, with the subsequent accommodation of the unconformable Pleistocene cover

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