Stolz, J.F., Margulis, l. & Guardans, R. (1987): La comunidad microbiana estratificada de la Laguna Figueroa, Baja California, Mexico: Un posible modelo de comunidades laminadas y microfósiles prefanerozoicos preservados en pedernales. Stvdia Geologica Salmanticensia, 24: 7-23.
ABSTRACT: The microbial mat community of an evaporite flat at North Pond, Laguna Figueroa (Baja California, Mexico) was actively involved in the production of laminated sediments prior to 1978. Heavy rains in 1979 and 1980 flooded the mat with 1 and 3 m. of meteoric water. The flooding deposited up to 10 cm of silicoclastic sediment over the Microcoleus dominated mat and resulted in a thich mud layer associated with laminated sediment deposition. In 1982, the surface had been recolonized by species of cyanobacteria (Sirulina, Oscillatoria) and purple phototrophic bacteria (Chromatium, Thiocapsa). The composite structure of the sediments resulting from the mat activity and the abiotic factors are proposed as a model to explain the fact that prePhanerozoic microfossils are found in smooth black cherts and not in the associated banded sediments.
Flores Villarejo, J.A. (1987): Estudio sistemático de los asterolitos de algunas series del sector NO de la Cuenca del Guadalquivir (SO de España) y sondeos oceánicos D.S.D.P. próximos. II. Stvdia Geologica Salmanticensia, 24: 25-66.
ABSTRACT: The present work completes the communications presented by the author in issue XXIII of this publications.
The communication enumerates and describe 14 species of asteroliths included in the groups of Eu discoaster variabilis and Eu discoaster calcaris recorded in section of the NW border of the Guadalquivir Basin and adjacent Atlantic D.S.D.P. sites.
The interval of distribution of the sections and cores lies within the Lower Tortonian Pliocene.
Pineda Velasco, A. (1987): Sobre la geología de la región de Archidona y la pertenencia de la Alta Cadena al Subbético. Stvdia Geologica Salmanticensia, 24: 67- 81.
ABSTRACT: A new overall structure for the Archidona region (Betic Cordillera, southern Spain) is proposed on the basis of new paleogeographic and tectonic interpretations of the Alta Cadena Complex and the Triassic of Antequera units. As a result, simpler interpretations may be invoked.
It is proposed that the "Alta Cadena Complex" was originally placed between the (central) middle and internal Subbetic units, the Triassic of Antequera being its "basal formation". The socle of the whole unit is asumed to consist of paleozoic rocks of Malaguide affinities. The Mesozoic rocks are unconformably overlain by sediments of flysch facies similar to the "Flysch of Campo de Gibraltar".
Andrés, I. (1987): Los Heterodonta (Bivalvia) en el Plioceno marino de Bonares (Huelva). Stvdia Geologica Salmanticensia, 24: 83- 150.
ABSTRACT: In this work 28 species of subclase Heterodonta from a marine Pliocenic outcrop in Huelva (Spain) are studied.
Paleoecoloic and chronostratigraphic data, relating to the said forms, are included too.
Vacas, J.M. & Martínez Catalán, J.R. (1987): El sinforme de Alcañices en la transversal de Manzanal del Barco. Stvdia Geologica Salmanticensia, 24: 151-175.
ABSTRACT: The stratigraphy and structure of the Alcañices synform are described in the cross section of the Esla valley, The sedimentary succesion, ranging from the Lower Ordovician to the Devonian, has been divided in six formations, to which local denominations have been assigned. The structure is a rather complex one, resulting from tbe superimposition of four deformation phases of hercynian age ad of a tardi hercynian faulting stage. The first phase gave rise to large recumbent folds, the second was responsible for the appearance of subhorizontal shear zones and thrust faults, the third produced steep folds approximately homoaxial with the first ones, and the fourth generated a swarm of sinistral wrench faults trending NW SE. The tardihercynian stage of faulting produced a new fault system trending NE SW as well as new movements of the fauls of the previous phase as dextral wrench ones.
Merchán, J.C., Martín-Izard, A. & Arribas, A. (1987): Geología y metalogenia de los yacimientos de Pb y Sn de la zona de Guijuelo. El caso de la Stolzita de La Tala. Stvdia Geologica Salmanticensia, 24: 177- 214.
ABSTRACT: The Pb, W and Pb W mineralizations described in this paper are situated 3 4 km east of Guijuelo, in the province of Salamanca. The host rocks are metasediments of the Monterrubio Fm., a rock assemblage occurrying in the schist greywacke complex (CEG), which underwent three Hercynian tectonic stages and one important late Hercynian fracturation The Pb ores are vein hke and hydrothermal, the W ores are disseminated in calsilicate rocks; and the Fb W ores, represented by La Tala orebody, have a mixed origin, as hydrothermal Pb rich solutions affected the stratabound W mineralizations already present in the CEG. Due to it, stolzite (PbWO4) made up most of the ore when the mine was in operation.
Jiménez Fuentes, E. & Martín-Izard, A. (1987): Consideraciones sobre la edad del Paleógeno y la tectónica alpina del sector occidental de la cuenca de Ciudad Rodrigo. Stvdia Geologica Salmanticensia, 24: 215-228.
ABSTRACT: The possible relation ship between the Tejoneras and the Ciudad Rodrigo stratigraphic units of the terciary secuence filling the western part of the Ciudad Rodrigo basin is analyced in this paper. A tectonic model is also established. According to it, the southern border of the basin is limited by a single fault, striking NNE, which has been broken and reajusted by later faults followins NNW to NW direction.
Polo, M.A., Alonso-Gavilán, G. & Valle, M.F. (1987): Bioestratigrafía y paleogeografía del Oligoceno-Mioceno del borde SO de la fosa de Ciudad Rodrigo (Salamanca). Stvdia Geologica Salmanticensia, 24: 229-245.
ABSTRACT: During the Oligocene and Early Miocene the Arcosas de la Alamedilla Formation was deposited on the southern egde of the Ciudad Rodrigo trough.
This unit is the result of a dismanteling of a granitoid source areas present day situated to the S, SW and N by large ephemeral low sinuosity fluvial systems.
Pollen analysis suggests the existencc of a temperate climate with a seasonal nature. On considering the evolution of the floristic associatgions through the stratigraphic section stratigraphic a gradual replacement of the tree taxa by those of herbaceous species may be observed. This would imply a progressive degradation of the tree covering cused by a trend of the climate towards aris conditions; consequently, the seasonal character of the climate would have become more pronounced with time.
Joint palynological, stratigraphic and sedimentological studies show that during the sedimentation of the Arcosas de La Alamedilla Formation the landscape was opened, covered by braided fluvial systems of proximal sands and governed by a seasonal temperature climate.
Alonso Gavilán, G., & Cantano Martín, M. (1987): La Formación Areniscas de Ciudad Rodrigo: Ejemplo de sedimentación controlada por paleorrelieves (Eoceno, fosa de Ciudad Rodrigo). Stvdia Geologica Salmanticensia, 24: 247-258.
ABSTRACT: In the southeastern Ciudad Rodrigo there is a conspicuous sandstone unit that has been usually refered to as "Serie" de Ciudad Rodrigo. The purpose of this paper is to define this Lithostratigraphic Unit: Ciudad Rodrigo Sanstone Formation. This Unit consist of clastic sediments derived from the weathered metamorphic and plutonic rocks placed in NW, SW and S of the basin. Paleocurrent measurement reveal a convergent pattern which coupled with the existent paleo-reliefs towards the NE, suggest and endorheic basin that was progresvely filled up by alluvials fans sediments. From the analysis of the present day distribution of deposits it is proposed that the development of alluvials fans was controlled by the paleo reliefs that closed the Noreastern edge of the basin during Eocene times.