Resumen: This paper describes a new procedure for assessing the ratio between in situ stresses in rock masses by
means of K (K=σH/σv, being σH and σv principal stress) and tectonics for purposes of engineering geology
and rock mechanics. The method combines the use of the logic decision tree and the empirical relationship
between the Tectonic Stress Index, TSI, and a series of K
in situ values obtained from an extensive database.
The decision tree considers geological and geophysical factors affecting stress magnitudes both on the
regional and local scale. The TSI index is defined by geological and geomechanical parameters. The method
proposed provides an assessment of the magnitude of horizontal stresses of tectonic origin. Results for
several regions of Europe are presented and the possible applications of the procedure are discussed.
Resumen: This paper presents a computational model for mapping the regional 3D distribution in which seafloor
gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment.
The construction of the model is comprised
of three primary steps, namely: (1) the construction of
surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient
and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various
hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the
thickness of the hydrate stability zone. The solution is based on a transcendental function, which is
solved iteratively in a GIS environment.
The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an
abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures,
is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the
model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic
gas compositions, and explains the geometry and distribution of geological structures derived
from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper
continental slope.
Palabras clave: Gas hydrates, GIS, Heat flow, Fluid flow, Mud volcanoes, Gulf of Cadiz
ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the
Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins,
whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic
evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic
evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and
the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and
collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots.
[RÉSUMÉ]
Une suture sans racines et la perte des racines d’une chaîne montagneuse : la chaîne varisque du Nord-Ouest de
l’Ibérie. Des ophiolites d’âges différents affleurent dans le Nord-Ouest de l’Ibérie dans une suture sans racines, témoin de l’océan Rhéïque. Les terrains allochtones sur et sous la suture dérivent de ses deux marges, tandis que l’autochtone relatif appartient à la
marge passive du Nord de Gondwana. On peut déduire l’évolution des plaques dans cette partie de la région circum-Atlantique Ã
partir des données stratigraphiques, pétrologiques, structurales, métamorphiques et géochronologiques. Cette évolution inclut le
développement d’un rift continental et l’ouverture de l’océan Rhéïque pendant le Cambro-Ordovicien ainsi que sa fermeture
au Dévonien moyen à supérieur. On décrit aussi l’évolution de la convergence et collision varisque entre Laurussia et
Gondwana, du début jusqu’aux derniers stades d’un effondrement associé à la perte des racines orogéniques.
Resumen: In the northwest Iberian Range the Aalenian to Bajocian interval is represented by condensed, as well as
more expanded marine carbonate strata deposited in a shallow epicontinental-sea setting. Precise
biochronological data (successive ammonites assemblages) from 29 measured sections, along with a bedby-
bed facies analysis, allowed a detailed correlation between sections,
the definition of a number of
successive transgressive–regressive cycles and of two distinct sedimentation areas, as well as the compilation
of isopach maps for short time intervals (duration of ammonites Zone/Subzone) and the assessment of
sediment accumulation rates.
Differences in facies and thickness in the studied interval, and the sequential organization, reveal significant
changes in the depositional environment. A tectonically-controlled compartmentalization of the sedimentation
area is suggested by a detailed reconstruction of the accumulation history. An active extensional tectonic
regime is supported by contemporaneous volcanic activity in the southeastern Iberian Basin.
A precise timing of the main tectonic pulses recorded in NW Iberian Basin for the Upper Toarcian–Lower
Bajocian interval is presented, which may help to better resolve the stratigraphy in otherW European during
this time interval.
Resumen: Episodic hydrothermal alterations in the Sierra de Guadarrama took place between ca. 300 Ma and
10 Ma. New K-Ar ages for hydrothermal minerals have been obtained that along with previous data allow
to better constrain the late- to post-Variscan history of tectono-hydrothermal activity. This activity can
further be correlated with Alpine tectonic events in central
Iberia recorded in Permian to Cainozoic
sedimentary basins. Dating of hydrothermal events in the basement is thus a useful tool to better constrain
the chronology of tectono-sedimentary events in the cover.
Palabras clave: K-Ar dating, Hydrothermal alterations, Sierra de Guadarrama, Variscan basement, Alpinecycle
Resumen: La Comarca de El Bierzo tiene una cuenca carbonífera que se extiende a través de 31.000 ha y ha sido explotada desde mediados del siglo XIX. Esta intensa actividad ha generado alrededor de 571 escombreras que ocupan antiguos suelos abarcando una superficie de 5.251 ha y están expuestas a la alteración natural que incluye procesos físicos, químicos y biológicos. Esta alteración genera numerosos
impactos ambientales en el aire, el agua y en los suelos, tales como los drenajes ácidos de mina, la autocombustión del carbón o la contaminación por metales pesados, además de impacto visual, que afecta de forma notoria el paisaje de la comarca. Esta tesis presenta la metodología desarrollada y los resultados obtenidos para conocer y caracterizar los impactos que ha ocasionado la actividad minera en los parámetros físicos y químicos de los suelos en la cuenca carbonífera de El Bierzo, con la pretensión de tener un conocimiento más preciso de la situación y establecer los fundamentos para afrontar una futura recuperación de los suelos y los paisajes afectados. Para este trabajo se eligieron ocho zonas representativas de la variabilidad espacial que se puede encontrar en la cuenca superior del río Rodrigatos, teniendo en cuenta áreas testigo, sin alteraciones asociadas a la minería, y zonas alteradas por la actividad minera. Además se incluyeron tres escenarios fuera del área de estudio con objeto de incluir gran parte de la variabilidad de los procesos de restauración no contemplados en la zona de estudio. [ABSTRACT]
El Bierzo District has a carboniferous basin across 31.000 ha that has been exploited since middle of XIX century. This intense activity has generated about 571 mine tailings, which are deposited in old soils, and occupy an area of 5.251 ha. The dumped materials are exposed to natural alterations that include physical, chemical and
biological processes.This alteration generates many environmental impacts on air, water and soils like acid mine drainage, spontaneous combustion of coal, or pollution
with heavy metals. The mine tailings also cause a serious visual impact on the landscape. This thesis presents the methodological contributions and the obtained results to
identify and characterize the impacts of mining activity on the physic and chemical soils parameters in the coal basin of El Bierzo with the aim of obtain a more precise understanding of the situation to be able to approach the recovery of soils and landscapes affected.
Palabras clave: Degradación de Suelos, Minería del carbón, Escombreras
Resumen: We infer that the Alboran Basin, the first western Mediterranean Basin found after crossing Gibraltar, is an orogenic float underlained by a de´ collement system, a multi-layered ductile shear extending from 10km to between 30 and 40km below sea level. This float was formed as consequence of the
collision of the African–Eurasian plates in the Oligocene–late Miocene. Synchronous with this compression the float experienced basin wide crustal thinning and subsidence about 25 m/year ago by subcrustal processes. Since latest Miocene the float has undergone compression due to the continuous convergence of Eurasia and Africa. The faults created as a result of this compression are dominated by a conjugate system of northeast trending left-lateral and northwest right-lateral strike–slip faults. This deformation is taking place under a simple shear mechanism. Associated with the northwest and northeast lateral faults are zones of compression trending west and east of north extending from the base of the basin’s north upper slope to the Alboran Ridge. The initial morphology of the Alboran Ridge on the southern side of the Alboran Basin was due to the construction of a volcanic edifice at the northeast end of the ridge and igneous activity along northeast trending fractures southwest of the edifice. At the northeast end of the Alboran Ridge motion along a right-lateral fault cutting across the ridge led to sediment collapse and the creation of a prominent embayment on the ridge’s northwest flank. Deformation is more subdued in the western than in the eastern part of the Alboran Basin, a tectonic style due either to differences in sediment rheology or that the accommodation of the convergence of Africa and Iberia is more diffused and attenuated in the west than in the east.
Resumen: The study of intraplate tectonics is crucial for understanding the deformation within plates, far from active plate
boundaries and associated stress transmission to the plate interiors. This paper examines the tectonic evolution
of the Variscan basement at the western margin of the Cenozoic Duero basin. Located east of the Vilariça
Fault
System in NW Iberia, this intraplate zone is a relatively flat but elevated area with an intense NNE-SSW
trending fault system and associated moderate seismicity. Although the area has played an important role in
the Duero basin configuration, its Alpine to present-day tectonic evolution has not been well constrained.
In order to characterize the successive paleostress fields, 1428 pairs of fault-striae were measured at 56 sites
and two focal mechanisms were used. Stress inversion methods have been applied to analyze paleostress
regimes. Results show the existence of three dominant maximum horizontal stress (Shmax) trends: N-S,
NE-SW and E-W. Relative and absolute dating of the activated faults for each Shmax shows that the clearly
predominant N-S paleostress field in the zone has been active since the Oligocene up to the present day; while
a NE-SW stress field is found to have been active during the Cretaceous and an older E-W paleostress field
was active in the earlier Alpine cycle (Late Triassic).
Resumen: Las Areniscas de Villamayor presentan un carácter cíclico, manifestado por la
sucesión de secuencias granodecrecientes organizadas en una megasecuencia granocreciente al ir
aumentando el tamaño del clasto en la base de la secuencia. Las características sedimentológicas, indican un dispositivo
sedimentario fluvial trenzado de arenas con caidas cíclicas de energía, avulsiones frecuentes y relleno de los canales abandonados, en varios episodios, desarrollándose paleuelos sobre las fracciones más finas de la secuencia. Las direcciones de paleocorrientes
abogan por aportes procedentcs del SE y drenando un área madre de bajo rango metamórfico y
granitoide, lo que confiere al sedimento un carácter fuertementes arcósico. En cada una de las
secuencias litológicas se desarrolla un perfil de alteración confirmado por a) un proceso de
encostramiento en el techo (nódulos aislados, agrupados y encostramientos difuso); b) aparecer
reorientaciones del plasma arcilloso acompañadas de neoformaciones argílicas, y c) tener una intensa
actividad orgánica (bioturbaciones). Este perfil de alteración se caracteriza, de muro a techo, por
presentar: lú .- disminución del porcentaje de feldespatos: 2ú.- acumulación progresiva de dolomita en forma de encostrameento carbonatado que reemplaza al material arcósico y 3ú.- aumento de palygorskita. coincidiendo su máximo con el de la dolomita. Todo ello indica que la génesis de la secuencia de alteración está relacionada: a) con movomientos de los niveles freáticos próximos a arterias de agua (base de la secuencia) y b) con los procesos de generación de suelo ligados a la
estacionalidad del clima.
[ABSTRACT]
The Villamayor Sandstones consits of fining upwards sequences which, in turn, form a coarsening upwards megasequence. Scdimentological arguments point out to a genesis related to a sandy braided fluvial system with cyclic variations of flow velocity, avulssions and infilling of abandonedchannels with development of paleosoils between different stages (grained terms). The pattern of paleocurrents and heavy minerals indicate drainage of low range metamorphic and granitic source area placed toards the SE which produced arkosic sediments. Each lithologic sequence shows an alteration profile confined by: (a) crusting processes at the top of the sequence (with grouped and scattered nodules and diffuse cruting); (b) reorientaton of clay plasma accompanied by clay neoformations and (c) biological activity (burroging). The profile is characterized, from bottom to top, by: 1ú. decrease of the percentage of feldspar; 2ú.- accumulation of dolomite as crust replacing arkosic sediment and 3ú. increase of palygorskite, with a maximum matching the one of dolomite. All these feature indicate that the genesis of the weathering profile probably related to oscillations of phreatic water table through the coarse sediments filling the narrowlyspaced active channels which produced transformations due to water circulation and, independently, pedogenic plocesses related to a climatic seasonality.
Resumen: Analyses of the effective elastic thickness of the Martian lithosphere have been
previously used to calculate surface heat flow on Mars at different places and times. In this
work, I use elevation differences in a putative Late Hesperian shoreline, named
Deuteronilus shoreline, and the relation between thermal state and buoyancy of the
lithosphere, in order to estimate the amplitude of the variations
of surface heat flow on
Mars, probably related to the time in which this feature was formed. The results suggest
that, if the Deuteronilus shoreline is a true paleo-equipotential surface, the relative
amplitude of surface heat flow variations on the shoreline regions in the Late Hesperian
were less than present-day ones in terrestrial continental areas. The results are also roughly
valid for the outer contact of the Late Hesperian Vastitas Borealis Formation, if this
contact is related to the limits of an ancient ocean. These results could imply that large
areas of the Martian lithosphere have been tectonothermally stable since at least that
time.
