Geogaceta -- Nº 37, (2004)

Permanent URI for this collectionhttps://hdl.handle.net/10272/8621

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Vulcanismo lávico y explosivo en la cuenca carbonífera de Los Santos de Maimona (Zona de Ossa-Morena, Badajoz)
(Sociedad Geológica de España, 2004) Larrondo, Egoitz; Carracedo Sánchez, Manuel; Eguiluz, Luis; Gil Ibarguchi, José Ignacio
We report the results of a petrological and structural study on the volcanic rocks from the Los Santos de Maimona Carboniferous basin (Ossa-Morena Zone, SW Spain). This basin is ca. 25 km in length and up to 3 km wide being limited by strike slip faults oriented NW-SE. The volcanic deposits occur interbedded with shallow platform sediments of Visean age which reflect a regression regime. The volcanic rocks are the result of both effusive and explosive volcanic activity. Effusive periods account for the formation of moderately alkaline lava flows, whereas the explosive events resulted in fall deposits and pyroclastic flows. The volcanic center could be situated close to the Los Santos de Maimona site, where it might give rise to a strato-volcan structure. While surface deposits are not excluded, it appears that most volcanic rocks in this area were deposited in a shallow marine environment
Variación estacional en la especiación y movilidad de Fe y As en aguas afectadas por drenajes ácidos de mina en la cuenca del río Odiel (Huelva)
(Sociedad Geológica de España, 2004) Miguel Sarmiento, Aguasanta; Casiot, C.; Nieto Liñán, José Miguel; Elbaz Poulichet, F.; Olías Álvarez, Manuel
The Odiel river drains the central part of the Iberian Pyrite Belt, one of the oldest and most important massive sulphide districts in the world. In these massive sulphide deposits, arsenic can be found in arsenical pyrite (with up to 0.4 % of As), and in some accessory minerals such as arsenopyrite. The oxidative dissolution of these sulphides releases to the Odiel river acidic waters rich in sulphates, metals and metalloids, including considerable amounts of As. Speciation and mobility of Fe and As in these waters show important seasonal variations, especially in samples not very close to the pollution sources. Although in the wet season the concentration of total As tends to be lower because of dilution with rain water, the toxicity of the waters is higher due to an increase in the concentration of As3+
Uso de técnicas geofísicas para caracterizar la extrusión de agua salina en un acuífero costero mediterráneo bicapa (Río Vélez, provincia de Málaga)
(Sociedad Geológica de España, 2004) Benavente Herrera, José; El Mabrouki, K.; Himi, Mahjoub; García Aróstegui, José Luis; Calabrés, C.; Casas Sainz, Antonio
The river Vélez delta (Malaga province) is a two-layer aquifer. The groundwater overexploitation during the 1993-1995 drought period led to a quite general seawater intrusion in both layers, particularly severe in the deepest one (confined). The important aquifer recharge associated to the 1996-1997 abnormally rainy period has induced the flushing of most of the brackish and saline water. This study shows the status of the aquifer in September 2003 by means of geophysical techniques (FDEM soundings and Electrical Resistivity Imaging) and logs of electrical conductivity of the water in boreholes. The confined aquifer seems completely recovered, as flushing by freshwater continues. The phreatic aquifer had a rapid recovery after the recharge event, although during this study the presence of brackish waters –similar to those which existed before the recharge- has been identified. The geophysical methods have identified the vertical and lateral distribution of these waters, which now show different patterns with respect to the situation immediately after the drought
Tonalites from the Hospitais massif (Ossa-Morena Zone, SW Iberian Massif, Portugal) II: Geochemistry and petrogenesis
(Sociedad Geológica de España, 2004) Moita, Patricia; Santos, J. F.; Pereira, Manuel Francisco
As described in the first part of this work (Moita et al., this volume), the Hospitais Massif belongs to a synorogenic Variscan magmatic association, intrusive in a gneissic-migmatitic complex of the Évora High- Grade Metamorphic Terrains. In this paper, geochemical data obtained on tonalites and dioritic enclaves, from the Hospitais Massif, and on gabbros, from smaller plutonic bodies in the neighbourhood of that massif, are used to constrain hypotheses on the petrogenetic processes responsible for the mentioned lithologies. Major and trace element geochemistry reveal calc-alkaline affinities and suggest that gabbros, diorites and tonalites belong to a magma suite derived dominantly by fractional crystallization. The presence of microgranular mafic enclaves, within the tonalites, could be interpreted as representing an additional process of mingling/mixing for the evolution of these rocks. According to their geochemical features, the enclaves may have resulted from an intermediate differentiation product internally mixed with the tonalite melt. A filter-pressing process can explain the amphibole-dominated cumulate REE pattern displayed by the enclaves
Tonalites from the Hospitais Massif (Ossa-Morena Zone, SW Iberian Massif, Portugal) I: Geological setting and petrography
(Sociedad Geológica de España, 2004) Moita, Patricia; Pereira, Manuel Francisco; Santos, J. F.
The Hospitais Massif is an elliptical-shaped plutonic body, with a WNW-ESE long axis, located in the western Ossa-Morena Zone domains in Portugal. This massif, composed essentially of tonalites, is part of an igneous association, ranging from gabbros to granites, intrusive in a gneissic-migmatitic complex, as part of the Évora High-grade Metamorphic Terrains. The tonalites present magmatic fabrics associated with a moderately developed foliation, recording syntectonic crystallization and cooling, co-planar to steep foliations observed within the surrounding sheared gneisses and migmatites. From field and petrographic studies, it is possible to suggest that the deformation of the tonalites and associated basic rocks was synchronous with Variscan progressive shearing of the gneisses and migmatites envelope
Sobre la utilización de la clasificación de las aguas de riego del U.S. Laboratory Salinity (USLS)
(Sociedad Geológica de España, 2004) Olías Álvarez, Manuel; Cerón García, Juan Carlos; Fernández, I.
One of most used methods in our country to determinate the soil salinisation and sodification risk from the irrigation water composition is the U.S. Salinity Laboratory (USLS) classification, which used the electrical conductivity and the SAR (Sodium Adsorption Rate) of the irrigation water. However, it is well known that this method presents serious defects, because of it should be substitute by other more adecuated classifications, as the developped by the FAO
Secuencias acumulativas en el Complejo Plutónico de Valencia del Ventoso
(Sociedad Geológica de España, 2004) Sarrionandia Eguidazu, Fernando; Carracedo Sánchez, Manuel; Eguiluz, Luis; Apalategui, Octavio
In the Valencia del Ventoso plutonic complex it has been detected the basal part of a previous stock formed by cumulates. This accumulative sequence is subdivided in base of textural criteria in five zones, called from the bottom to the upper part Zone I, II, III, IV and V respectively. Textural, modal and mineralogical criteria indicate the existence of at least two chamber recharges. The principal fractionation mechanism that takes place during the early stages is related with continuous convection, but the progressively thermal equilibrium with the host rocks led to crystal settling mechanism. With these two continuous processes, take place eventual processes related with compaction and chamber recharge
Rasgos morfológicos e icnológicos de la superficie erosiva del límite Messiniense-Plioceno (Sierra del Colmenar, Alicante). Relación con la crisis de salinidad del Mediterráneo
(Sociedad Geológica de España, 2004) Soria, Jesús M.; Caracuel, Jesús Esteban; Corbí, Hugo; Yébenes, Alfonso
The Messinian/Pliocene boundary in the Sierra del Colmenar (Alicante) is represented by an erosional surface called the end-Messinian unconformity. This erosional surface cuts the coastal and lagoonal deposits of the late Messinian (Terminal Complex) as a result of the sea-level fall related to the salinity crisis in the centre of the Mediterranean. The beginning of the subsequent transgresion during the lower Pliocene is registered by an erosive surface that carved the underlying Messinian deposits. This surface morphology and trace fossil colonization is controlled by the substrate characteristics. Thus, onto consistent calcareous substrates it is developed coastal palaeocliffs colonized by Trypanites icnofacies, meanwhile on the marly substrates there is no abrupt palaeocliffs with icnofacies of Skolithos colonization. The enhancing Pliocene reflooding was recorded by the sedimentation of coastal and shallow marine deposits over the erosive surface
Profundidad de la transición dúctil-frágil en la corteza de Béticas-Rif y Mar de Alborán
(Sociedad Geológica de España, 2004) Fernández Ibáñez, F.; Soto, Juan I.; Morales, J.
A three dimensional rheological model has been developed in the Betic-Rif and Alboran Sea region to characterize the brittle-ductile transition (BDT) in the upper crust; calculating a multiple set of regularlyspaced strength profiles based on a synthetic 3D lithospheric structure that gathers most of the available geological and geophysical data in the region. This is the first numerical modelling calculated in the region, for either compressional or tensional tectonic regimes, to characterize the rheological layering of the crust in the Betic-Rifean belt. The model results in a BDT topology highly constrained by the lithospheric thickness. The upper-crust brittle domain gets thinnest in the East Alboran Basin and the transition to the South Balearic Basin (7 and 6 km for tensional and compressional tectonic regimes), and becomes thicker westwards, getting the major values in the West Alboran Basin, near the Gibraltar Arc (18-16 km). In the onshore Betics, the BDT deeps towards the NW, with a general trend that results to be oblique to the shore line and to the main orientation of the mountain ranges, with a maximum value in the Southiberian Domain (~15-12 km) continued by a gently thinning of the brittle domain towards the Iberian foreland
Primeros restos de vertebrados del Cretácico superior de Quecedo de Valdivielso (Burgos)
(Sociedad Geológica de España, 2004) Murelaga, Xabier; García Garmilla, Francisco; Pereda Suberbiola, Xabier
Chelonian plates, fish scales and crocodilian remains from the uppermost Cretaceous of the Burgos Province are described for the first time. All the remains have been found in the argilites of the Sobrepeña Formation (Middle-to-Upper Maastrichtian). The fossil bones have been found dispersed all around the outcrop. The bothremydid turtle plates are well preserved and represent the most abundant elements. The solemyid turtle plates are eroded and only a few fragments have been discovered. The bony fishes are represented by one scale that could be referred to the family Lepisosteidae. The crocodilian remains consist of an isolated tooth and an osteoderm. The fossil assemblage is in agreement with the sedimentological interpretation of a lower energy lacustrine system. The bothremydid and solemyidid turtles, bony fishes and crocodrilians are common components of the continental vertebrate faunas of the Ibero-Armorican realm at the end of the Cretaceous
Primera descripción de capas de esquistos cloríticos con circón en las peridotitas de Ronda (Cordilleras Béticas)
(Sociedad Geológica de España, 2004) Tubía, José María; Cuevas, Julia; Esteban, José Julián
This work reports the finding of layers of zircon-bearing chlorite schists in the southwestern part of the Sierra Bermeja peridotites, the biggest massif of the Ronda peridotites (Alpujarride Complex, Betic Cordillera, southern Spain). Structural, petrographic and geochemical data support a metasomatic origin for these rocks, at temperature conditions of 280-350 ºC, related to the serpentinization of the peridotites and the rodingitization of the granite dykes of the Ronda peridotites
¿Por qué son tan diferentes las sierras de Crevillente y Abanilla?
(Sociedad Geológica de España, 2004) Tent Manclús, José Enrique; Yébenes, Alfonso; Estévez, Antonio
The Crevillente and Abanilla mountain ranges form the same structural lineation but show a quite different morphology. The first one is made by calcareous rocks mainly jurassic and cretaceous likewise the Abanilla is made by keuper facies which includes blocks. This keuper facies are not Triassic but Miocene which are interpreted as an ancient salt glacier. Their different litologies of both sierras is due to the activity of the Puerto de Barinas Fault, a transverse fault to the Crevillente-Abanilla lineament. This litological difference in the same structural lineament could be explained as produced before (pre-late Tortonian) the elevation of both sierras (latest Messinian)
Petrografía y condiciones de formación de las rocas ultramáficas con granate asociadas a las eclogitas de Cabo Ortegal
(Sociedad Geológica de España, 2004) Mendia, M.; Gil Ibarguchi, José Ignacio
Garnet-bearing ultramafic rocks forming a decametric outcrop occur associated to the eclogites of the upper catazonal unit of the Cabo Ortegal Complex. These ultramafites are included within variably mylonitized amphibole-pyroxene gneisses located between the eclogite band on top and the so-called ‘banded gneisses’ formation below. They are harzburgites with orthopyroxene, olivine and amphibole as main phases and spinel, garnet and ilmenite as minor phases. Serpentine and chlorite are the main secondary minerals. The absence of pervasive deformational features, lack of anisotropy and poikilitic texture of pyroxene and amphibole are noteworthy and point to a possible magmatic/mantle origin of these rocks. However, a detailed petrographic study has shown the existence of discrete domains made of aggregates of minute pyrope-rich garnet, orthopyroxene and olivine with subgrain recrystallization. The mineralogical and textural features thus reveal a metamorphic origin for, at least part, of the present mineral association. Calculated P-T conditions for the orthopyroxene-garnet assemblages are ca. 760 °C and 19 kbar. The rocks studied bear important textural and, to some extent, mineralogical similarities to ultramafic rocks elsewhere within the complex along major tectonic contacts (e.g. Carreiro Zone of Tectonic Movement), although, in view of the relatively Mg-poor olivine and orthopyroxene compositions, an origin through recrystallization of serpentinite protoliths appears unlikely. Instead, an origin through partial recrystallization of mantle fragments related to the subduction and tectonic stacking processes that gave rise to the Complex is proposed
Origen de circones detríticos ricos en Hf de São João del Rei, Minas Gerais (Brasil)
(Sociedad Geológica de España, 2004) Sáez Ramos, Reinaldo; Pereira, R. M.; Carrasco, R.; Nieto Liñán, José Miguel
Heavy concentrates obtained by pane sampling on several creeks near São João del Rei, Minas Gerais (Brasil) provide unusual Hf-rich zircons. Image and chemical analyses performed on these zircons by SEM and LA-ICP-MS show uncommon textural and compositional features. The core of zircons exhibits a complex texture including evidences of hydrothermal recrystallization. Here it is also conspicuous the abundance of rare metal minerals as inclusions. The average content of HfO2 in the core is of about 12 weigh %. The rim of zircons shows different zoning features with HfO2 content up to 35 weigt %. An origin related with rare element pegmatites and further reworking by hydrothermal fluids is suggested as the more suitable scenario for these unusual zircons
Nuevos mamíferos vallesienses en Masía de La Roma (Cuenca de Teruel)
(Sociedad Geológica de España, 2004) Alcalá, Luis; Van Dam, J.; Luque, L.; Montoya, P.; Abella, J.
The number of upper Vallesian (continental Upper Miocene) localities in the Teruel-Alfambra area has been increased by the sampling of a new road cut at Masia de La Roma. Two new levels have been sampled (MR-604-A and MR-604-B), which both belong to local Zone J3 (9.4-9.0 Ma) and correspond to Neogene mammal unit MN10. The levels have yielded the youngest representative of the viverrid Semigenetta and the oldest ursid Indarctos atticus known thus far, although it should be noted these forms are rare in general. The small mammal fauna contains characteristic J3 forms such as Huerzelerimys minor and Crusafontina fastigata. The two levels show a difference in small-mammal relative abundances, which could be due to factors related to formation of the sites (characteristics of the predators responsible for the concentration of the skeletal elements)
Nuevos datos sobre estratigrafía del Ordovícico y estructura varisca en el Macizo de Santa María la Real de Nieva
(Sociedad Geológica de España, 2004) Alonso, F.; Rubio, F. J.; Martín Parra, L. M.; Rodríguez Fernández, L. R.
We present a new geological map of the lower Ordovician materials cropping out in the Santa Maria la Real de Nieva Massif. The Ordovician sequence, Fm. Capas de Domingo García, comprises two separate stratigraphic units. The lower unit contains conglomerate with clasts of felsic volcanic rocks at its base, slates, and quartzite with cruziana. The upper unit is composed by the quartzite and slate, which is considered a regional equivalent of the sequence at the base of the Armorican Quartzite. The structure of the area is the result of the interference of the Variscan D3 folding with the D1 and D2 structures. Despite the interference, evidence is preserved that indicates an anomalous westward vergence of the Variscan D1 structure, analogous to local D1 structures in parts of the Portuguese sector of the Central Iberian Zone
Nuevos datos sobre la escoria de Getafe caida en un vehiculo en 1994
(Sociedad Geológica de España, 2004) García Guinea, Javier; Sánchez Chillón, B.; Mazo, A.; Tormo, Laura; González Martín, R.; Correcher, V.; Pardillo Mayora, J. M.
This work studies the characteristics of the steel slag heaps that have accumulated in the vicinity of the Andalusia motorway from km-11 to km-22, and throws new light on two traffic accidents attributed to meteorite impacts. Samples were collected from 13 sites at the side of this section of the Andalusia motorway, from the Aristrain and Varosa (Madrid) smelting factories and from the two cars inside BMW- 1994 and LADA-1999. The magnetic susceptibility, specific gravity, X-ray diffraction and ESEM analyses of samples were determined and the photographs of the ‘meteorite-impacted’ cars studied. The composition, textures and structures of these samples and the trajectories of the projectiles that hit the cars (circa 25º from the horizontal) together suggest that these accidents were caused not by falling meteorites, but by slag thrown either from the roadside or from overpasses
Niveles escalonados de cuevas marinas cuaternarias en la costa oriental de Gibraltar
(Sociedad Geológica de España, 2004) Rodríguez Vidal, Joaquín; Cáceres Puro, Luis Miguel
Several sets of staircased Quaternary marine deposits can be observed along the Gibraltar coast ranging from 1 to 210 m above the present mean sea level. Geomorphological mapping establishes, from the relationship between shore, scree and dune sedimentary formations, five main morphotectonic steps on the Rock: marine terraces between 1 and 25 m, 30-60 m, 80-130 m, 160-210 m, and above. Each terrace level and its shore linked morphologies is backed by a steep relict sea cliff with sea caves and notches along its landward margin. Staircased sea cave levels are representative of Quaternary hightstand position. Inside the caves remains of both notch and boring levels are found. We have distinguished three main sea cave levels at the Eastern flank of the Rock: A, at present sea level; B, +55 m; C, +180 m.
Modificación diagenética temprana de las conchas de inocerámido (Bivalvia). Maastrichtiense inferior. Cuenca Vasco-Cantábrica
(Sociedad Geológica de España, 2004) Gómez Alday, Juan José; Elorza, Javier
The petrographic analysis of the inoceramid shells allows to identify some microstructures, which suggest their early modification, previously and during the first burial stages. In this sense, it is important to emphasize the borings produced by epibionts and the formation of an early ferrous-manganese coating in the outer surface of the shell. The desegregation of the prismatic framework and its dispersion in the sediment are other processes that took place during the early stages of burial. The study of the post-mortem modification of the shells brings forward some evidences about the marine bottom oxygenation in the Basque-Cantabrian Basin, just before the inoceramid extinction near the lower-upper Maastrichtian boundary (~69,3 m.a.)
Microestructura e interrupciones en el crecimiento de las conchas de inocerámido (Bivalvia) del Maastrichtiense inferior. Cuenca Vasco-Cantábrica
(Sociedad Geológica de España, 2004) Gómez Alday, Juan José; Elorza, Javier
Lower Maastrichtian inoceramid shells from the Basque-Cantabrian Basin were deposited in a carbonate deep-sea environment. The referred shells show a well-developed first order prismatic microstructure formed by crystals of low magnesium calcite (LMC). Each prism, composed by several crystals, is formed by stacked crystalline tablets. Although shells have undergone burial diagenesis, it is possible to determine an important number of pairs of clear and dark growth lines (>250), more vigorous in the initial stages of growth. Occasionally, these lines can exhibit ruptures in their development of difficult interpretation, since they do not seem to be product of dramatic temperature-salinity or energy (i.e. storms) changes in the environment. The origin of the growth ruptures may be related to physiological factors without being directly associated to the stress produced by periodical spawning

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