Geogaceta -- Nº 27, (1999)

Permanent URI for this collectionhttps://hdl.handle.net/10272/9894

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Wave-induced cross-shore sediment transport in the Ebro delta inner shelf
(Sociedad Geológica de España, 1999) Jiménez, J. A.
The near-bottom wave-induced cross-shelf sediment transport is one of the main mechanisms to maintain morphologically inner shelves. In opposition to suspended sediment transport by currents that controls fine sediment dispersal (and in consequence sediment deposits) in the shelf according to the ambient current direction, when waves actively resuspend and transport sediment in the inner shelf, their contribution is generally shoreward. In this paper, the wave-induced cross-shore sediment transport in the Ebro delta inner shelf is analysed and a method to predict their importance is presented. The obtained results show that the efficiency of the waves can be predicted in terms of the Ursell number that indicates how nonlinear the waves are. Thus, it was estimated that the annual frequency of occurrence of efficient waves to promote cross-shelf sediment transport in the Ebro delta is about 4.8% and that the integrated cross-shelf sediment transport is about 4.7 m3/m/yr
Variaciones de turbidez de las aguas de la bahía de Cádiz determinadas a partir del análisis de imágenes Landsat TM
(Sociedad Geológica de España, 1999) Gutiérrez Mas, José Manuel; Luna del Barco, A.; Parrado Román, J. M.; Sánchez, E.; Fernández Palacios, A.; Ojeda, J.
Landsat TM images has been analysed to obtain extent and direction data about turbidity flumes in several hydrodinamic sinoptic situations in Cadiz bay waters. Results are beside data from water samples. Five turbidity levels has been differentiated: very high turbidity, high, middle, low and very low, and three geographic sectors: a) Inner zone, closed to coast and with shoal waters of high and very high turbidity. This sector is very affected by littoral processes (tidals, surge and continental contribution); b) Middle zone, with middle and low turbidity waters, unafected by continent contributions and surge, although if by tidal ebb; c) Outer zone, with low and very low turbidity waters, little or nothing affected by coastal dynamic, except at moments of spring tides and great fluvial growings. Study of analysed Landsat images demonstrates that for a point given, turbidity range variation is very big and depends of each hydrodynamic concrete situation, and is controled by same factor as: hydrodynamic system (tides, surge and currents), climate and meteorology, coast and sea bottom phisiography and continental contributions rates
Transición dúctil-frágil en la corteza de la zona central de la Península Ibérica
(Sociedad Geológica de España, 1999) Tejero López, Rosa; Ruiz, J.
Brittle-ductile transition is estimated on the basis of pore-pressure dependent frictional failure in the brittle regime, and power-law steady-state creep in the ductile regime. Structure and lithological composition of the Central Iberian Peninsula Crust combined with geotherm are used to generate rheological profiles. Two brittle-ductile transitions are shown in the crust. The shallower one is located at ~ 7 km under compressional stresses, and at » 9 km under tensional stresses. The deepest is located at the top of the middle crust, at -14 km in compression and =>17 km in tension regime. Below it, the material is ductile throughout, with a jump in strength at the Moho, which is a main rheological discontinuity. Upper part of lithospheric mantle behaviour is dominated by brittle mechanisms when the crust thickness is 30 km, but ductile mechanisms prevail in 34 km crust thickness
The intrusion of the Plasencia (Messejana) dike as part of the Circum-Atlantic Early Jurassic magmatism: Tectonic implications in the southwestern Iberian peninsula
(Sociedad Geológica de España, 1999) Vegas, Ramón
The Plasencia dike belongs to a vast Early Jurassic magmatic province that extends around the Central Atlantic. The origin of this magmatic event is related to a thermal anomaly at the base of the lithosphere, and its age has been fixed within a short time span around 200 Ma. In close relationship with this thermal anomaly a process of underplating of the lower crust has been proposed. Assuming the existence of this underplated lower crust, some tectonic features can be explained in the SW Iberian Peninsula such as the nature of the crust, the pattern of Bouguer anomalies and the extension of the area of low relief
Superposición de estructuras corticales en la región de Archidona a partir de datos geofísicos (Zonas Externas de las Cordilleras Béticas)
(Sociedad Geológica de España, 1999) Bohoyo, Fernando; Galindo Zaldívar, Jesús; Serrano, I.
The region located at the NE of Archidona shows a maximum of aeromagnetic anomaly up to + 70 nT. This region, however, has minimum values of Bouguer anomaly (-120 mCal). New magnetic and gravimetric data and a P-wave seismic tomography allow to study the main features of the bodies located at different depths. One of the most significant and large detected bodies, that do not crop-out, is probably composed by basic rocks and may reach up to 18 km in depth. In the shallowest part of the crust, we detect variations in thickness of the subbetic units and the presence of small basic rock bodies of ofites
Sobre la contaminación de las aguas del estuario de los ríos Tinto y Odiel (Huelva)
(Sociedad Geológica de España, 1999) Cerón García, Juan Carlos; Borrego Flores, José; Morales González, Juan Antonio
The waters of the Huelva Estuary are polluted because of indiscriminate dumping of urban effluents. The nutrient contents of samples taken at the surface and from the bottom of the estuary were analysed to characterise the pollution of the waters. The pH values found range between 5.88 and 7.65. Salinity levels range between 34 and 42 g/L and show that the waters are very homogeneous. The 02 water content ranges between 7 and 13.8 mg/L, indicating a good level of oxygenation derived form the large amount of photosynthetic activity. Nitrate, nitrite and ammonia concentrations range between 0.1 and 0.4 mg/L, 2 and 12 fJg/L, and 0.1 and 0.6 mg/L respectively. The orthophosphate and total phosphate contents are high and usually similar, which indicate that a large part of the total phosphorus is present in form of orthophosphate that can be easily assimilated by the organisms. The high nutrient content of the water favours photosynthesis, which can lead to eutrophication
Sedimentologia y paleogeografía de la secuencia de deposito Aptiense inferior (Facies Urgón) en la subcuenca de Las Parras. (Teruel)
(Sociedad Geológica de España, 1999) Clariana, M. P.; Meléndez Hevia, Alfonso; Soria, Ana Rosa
The Lower Aptian D.S. is made up of materials which settled in shallow carbonate ramp enviroments. This sequence shows a retrogradational evolution, that is, from internal to mid ramp enviroments. The vertical evolution of this sequence and its sedimentological features allowed us to differenciate three system tracts (L.S.T, T.S.T and H.S.T). The Low System Tract appears only in the western area of the basin and it consits of facies of typical shallow marine enviroments. Transgressive System Tract and Highstand System Tract are identified in the central and eastern areas of the basin and characteristic facies associations stand for opener sea enviroments. Finally, the paleogeography of the basin in the Lower Aptian period shows that Las Parras subbasin was opened up eastwards. This fact is due to the thickness that raise south and eastwards and to the opener sea enviroments that are spreaded out in the easternmost area of the basin
Revisión taxonómica de "Echinosphaerites" murchisoni Verneuil y Barrande, 1855 (Echinodermata, Diploporita) del Ordovícico Medio centroibérico (España)
(Sociedad Geológica de España, 1999) Gutiérrez Marco, Juan Carlos
The holotype of''Echinosphaerites'' murchisoni Verneuil and Barrande 1855 is reviewed, and proposed as the type species of Oretanocalix gen. nov. The new genus is characterised by an elongate theca of medium size, that aborally shows a pair of long and prominent parietal septa interpreted as mesenterical; mouth narrow and elongate, with five very short ambulacra, the anterior comparatively reduced, ending in a set of few brachiole facets. The presence of a 2-1-2 ambulacraI system with an atrophied A-ambulacrum could denote a simplification leading to the 2-2 pattern of Calix or Phlyctocystis. The new genus ranges from Oretanian to Dobrotivian in age, and is distributed in Central Spain, the Moroccan Anti-Atlas and the French Armorican Massif
Resuspensión de sedimento en la plataforma interna del delta del Ebro
(Sociedad Geológica de España, 1999) Guillén, J.; Jiménez, J. A.; Palanques, Albert; Gracia, V.; Sánchez Arcilla, A.
This study deals with the resuspension processes in the inner shelf of the Ebro delta using field measurements of hydrodynamics and suspended sediment distribution in the water column. Two instrumented tripods were simultaneously deployed at 8.5 and 12.5 m of water depth across a profile perpendicular to the shoreline. The record analysed corresponds to a period of increasing wave activity, from fair-weather conditions (no sediment movement) to storm conditions. Critical wave conditions for sediment entrainment in both field sites were determined. The comparison of measurements indicates that the temporal variability of the measured parameters displays a similar behaviour between both field sites, although the intensity of processes is higher in the shallower site. Resuspension processes in tideless shelves affected by short-period waves are restricted to wave-storm conditions and, in addition, only the shallow area of the shelf can be affected
Propagación de la onda de marea en el Estuario del Río Tinto (Huelva, España)
(Sociedad Geológica de España, 1999) Morales González, Juan Antonio; Borrego Flores, José
The Tinto River Estuary, located at the central sector of the Huelva Coast is a mesotidal estuary, where the mean tidal range is two meters. Tinto river has small mean discharges (100.48 Hm3) but it is strongly seasonal. Tidal wave propagates Into the estuary according a hyposynchronic model, that increases during neap tides. The study of the tidal behavior at 6 stations along the estuary, allows the construction of curves of the instantaneous water position. These curves show different hydraulic gradients interpretable as sense of tidal currents. Points without hydraulic gradient mean slacks with nule velocity of currents. These slacks can be convergent or divergent. Both types experiment a displacement to the inner part of the estuary, the former during the flood, the second during the ebb. The convergent slack remain in the tidal limit until the arrival of the divergent slack. Then both become link and dissappear generating a general ebb situation. Southwest winds can accelerate this proccess
Plataformas carbonatadas aisladas (guyots) en el Jurásico del Subbético
(Sociedad Geológica de España, 1999) Molina, José Miguel; Vera, J. A.
In a sector of the Southern Iberian Continental Margin (in the Median Subbetic) isolated carbonate platforms developed over volcanic edifices, forming guyots, during the middle Jurassic. In these platforms, the sedimentation started with pelagic carbonates, then calcislltites with hummocky cross-stratification were deposited and ended with oolitic bahamian limestones. These shallowing-upward sequences frequently show palaeokarstic features at the top
Patrón de presentación de morfologías intermareales en dos playas expuestas de la Bahía de Cádiz
(Sociedad Geológica de España, 1999) Benavente, Javier; Reyes, J. L.; Anfuso, Giorgio
The paper compares the ocurrence patterns of intertidal morphologies across two exposed beaches in the Bay ofCâdiz: Vistahermosa beach, in the south, and La Barrosa beach, in the north. Topographic profiles over a complete year in a monthly and a weekly secuence are shown. A roughly stable intertidal stage, named type I in Davidson-Arnott description, is obtained for La Barrosa beach. The intertidal morphologies detected in Vistahermosa beach are less stable and related to type II in Davidson-Arnott description
Palaeoenvironmental reconstruction based on a detailed stable isotope analysis and dating of a Holocene speleothem from Valporquero Cave, Northern Spain
(Sociedad Geológica de España, 1999) Durán Valsero, Juan José; López Martínez, Jerónimo; Dallai, L.; Bruschi, G.; Caballero, E.; Jiménez de Cisneros, C.; Julià, Ramón
Ages of ca. 8170 and 7180 BP have been established through a Th/U dating for the base and the top, respectively, of a speleothem collected inside Valporquero Cave (Cantabrian Zone, northern Iberian Peninsula). Three series of carbon (8'3C) and oxygen (8iaO) stable isotope analyses have been carried out parallelly to the stalagmite axis, sampling being done in each growth layer, for a total amount of 66 analyses. The high degree of correspondence between the results of the analyses in the three series is highly significant, showing each similar general tendencies. The isotopic sequence can thus be considered as representative for the regional environmental conditions along the mid-Holocene period which is being studied. In the oxygen and carbon isotopical variation graphics, five sections with different characteristics can be distinguished, which correspond to four isotopically different periods: The first and third ones show more negative values than the mean general value; the second one offers less negative values, and the fourth one includes variations close to the mean. Differences bigger than 1%0 between maximum and minimum values are appreciated in the oxygen isotopic curve, which could probably correspond to environmental temperature oscillations wider than 4°C during the studied period
Paleobiocenosis de Heterostegina en sedimentos de origen litoral de la Fm. Calcarenita de Niebla (Mioceno superior, Cuenca del Guadalquivir, SO España)
(Sociedad Geológica de España, 1999) Tosquella Angrill, Josep; Baceta, Juan Ignacio; González-Regalado Montero, María Luz; Ruiz Muñoz, Francisco
A taphonomic analysis of some lumaquellic levels of Heterostegina interbedded in the basal sandy unit of the Calcarenita de Niebla Fm. (Huelva, Spain) is presented. However, it is made a revision of the main factors that determine nummulitid distribution in recent marine environment and the interest of their study for the paleobatimetric and trophic conditions inference. The integration of all these data with paleobiologie analysis deduced from fossiliferaI assemblage and with the sedimentological data of these levels, allow us to interprete their lumaquellic origin as true paleobiocoenosis in a transgressive coastal context with deltaic influences. We also discuss some morphofunctional aspects on Heterostegina test, that apparently present some contradictions in relation to the environmental conditions considered
Los ostrácodos infralitorales y circalitorales actuales del norte del Golfo de Cádiz
(Sociedad Geológica de España, 1999) Ruiz Muñoz, Francisco; González-Regalado Montero, María Luz; Baceta, Juan Ignacio; Pendón Martín, José Gabriel; Hernández Molina, F. Javier; Somoza, L.; Díaz del Río, Víctor
The study of the ostracod distribution in the inner part of the Spanish continental she/fallows to recognize the presence of a zonation which reflects changes in both depth and substrate. Four assemblages may be distinguished: two inner infralittoral (medium sands and silty fine.to very fine sands), outer infralittoral and interne circalittoral
Los ostrácodos de la cuenca del Lido (Laguna de Venecia, NF Italia)
(Sociedad Geológica de España, 1999) Ruiz Muñoz, Francisco; González-Regalado Montero, María Luz; Menegazzo, L.; Rampazzo, G.; Pistolato, M.; Molinaroli, E.
The ostracofaune of the Lido basin (Venice lagoon) is dominated by Cyprideis torosa, with the presence of Loxoconcha elliptica in zones drained by industrial and agricultural waters and Xestoleberis if the energy is very low. No ostracods were found in stress conditions due to environmental polution
Los depósitos transgresivos flandrienses de la plataforma continental del Golfo de Cádiz
(Sociedad Geológica de España, 1999) Lobo, Francisco J.; Hernández Molina, F. Javier; Somoza, L.; Díaz del Río, Víctor
The analysis and interpretation of high-resolution seismic profiles collected in a sector of the Gulf of Cadiz continental shelf hve been used as a basis to characterise the Flandrian transgressive deposits developed after the last eustatic maximum. Four seismic units (TA to TJ have been attributed to the Transgressive System Tract (TST), and they represent coastal deposits developed during periods of sea-level stillstand during the last global rising trend. The stacking pattern, regional distribution and seismic facies of those seismic units are highly variable in a longitudinal direction, and two main kind of sedimentary environments have been identified: 1) Sector A, located offshore of the Guadiana river mouth, where the seismic units are disposed in a classical backstepping pattern. This continental shelf is a high-energy environment, dominated by the influence of storm events coming from the SW, resulting in the deposition of small infralittoral lithosomes. 2) Sector B, located offshore of the Donana National Park, where a low-gradient shelf developed during each transgressive stillstand, and large coastal depositional systems composed of marshes, lagoon, beaches and spit bars were formed as a consequence of southeastward redistribution of the sedimentary terrigenous supply introduced in this continental shelf by the main rivers
Los depósitos terrigenos de la base de la secuencia de depósito Aptiense superior. Subcuenca de las Las Parras (provincia de Teruel)
(Sociedad Geológica de España, 1999) Clariana, M. P.; Meléndez Hevia, Alfonso; Soria, Ana Rosa
The bottom ofVillarroya de los Pinares formation, that is, the bottom of Upper Aptian D.S., is made up of terrigenous sediments. These materials show a retrogradational vertical evolution. This evolution started with fluvial channel facies, continuing later with tidal channel facies and finally this evolution finished with shoals facies. These sediments form the low system track of the Upper Aptian D.5. and they are represented in all basin. The continental enviroment sediments are distributed mainly at the western part of the basin and the sea dynamic action is represented at the central and eastern areas of the basin
La cuña progradante infralitoral del Holoceno Superior de Faro-Tavira
(Sociedad Geológica de España, 1999) Hernández Molina, F. Javier; Roque, C.; Lobo, Francisco J.; Somoza, L.; Díaz del Río, Víctor
A very good example of a progradational sedimentary body, the Infralittoral Prograding Wedge (IPW) has been characterized in the Algarve continental shelf developing below the storm wave base between the onshore (beach) and the offshore (inner continental shelf) depositional zones during the Late Holocene. The main lithosome is composed of large-scale cross-beds, prograding seaward and paralleling the shoreline, which are formed by avalanches of sediments swept by waves from shallower littoral environments. Sediment transport to produce the IPW is generated by downwelling storm currents and their associated seaward bottom flow
Interpretación combinada de los datos geológicos y gravimétricos del sector central de Extremadura: aplicación a la exploración de yacimientos minerales
(Sociedad Geológica de España, 1999) Campos Egea, R.; Gumiel Martínez, Pablo; Tejero López, Rosa; Plata Torres, J. L.
As a result of the combined interpretation of a gravity study, geological mapping and the lineament analysis of TM Landsat Imagery from the central sector of Extremadura region (Western of Spain), a series of units delimited by gravity alignments have been established confirming that there is an structural setting of the area in blocks. The limits, although irregular, are limited by high density fracture zones, whose intersections may have a major structural and metallogenic interest

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