Joaquín García-Sansegundo

Hercynian structure of the Axial Zone of the Pyrenees: the Aran Valley cross-section (Spain-France)

Abstract In the Axial Zone of the Pyrenees Palaeozoic rocks crop out with superimposed Hercynian and Alpine deformation. The Hercynian structures present two domains: infrastructure and suprastructure. A complete crosssection of the central part of the Axial Zone of the Pyrenees is presented, in which Hercynian structures of both domains can be observed. In the Aran Valley cross-section, the infrastucture corresponds to the Garona Dome Domain, where the main Hercynian structures are north-vergent recumbent folds, with an associated, mainly flatlying, foliation (S 2 ). In the Garona Dome Domain, the peak of the medium-to-high grade metamorphism is simultaneous with the main Hercynian structures. The Aran Valley and Noguera Ribagorca areas correspond to the suprastructure. In these domains the main Hercynian structures are upright folds, with an associated, mainly steep-lying, foliation (S 3 ). In these suprastructural domains, low grade syn-S 3 metamorphism is present. This crosssection relates the structures of the infra- and the suprastructure, suggesting a deformational sequence for the Axial Zone of the Pyrenees. This sequence is deduced from the fact that the north-vergent folds observed in the Garona Dome are earlier than the main structures of the suprastructure. The boundary of the Garona Dome and the suprastructure is a decollement level observed at the base of the Silurian. The deformational sequence proposed here provides some constraints for models of Hercynian evolution and the emplacement of the Alpine structures of the Pyrenees.

Stratigraphy and structure of the southeastern Garona Dome

AbstractNorth-facing recumbent folds in the Palaeozoic rocks of the Garona Dome have been recognized, and a modified pre-Silurian stratigraphic sequence is suggested. The gradual disappearance of part of this sequence may be interpreted as a result of truncation by an unconformable late Ordovician conglomeratic unit.

Hinterland-foreland zonation of the Variscan orogen in the Central Pyrenees: comparison with the northern part of the Iberian Variscan Massif

Abstract A new sequence of Variscan deformations is proposed for the Palaeozoic rocks of the Central Pyrenees. The non-metamorphic units include south-directed thrust systems and related folds with a poorly developed cleavage. In the metamorphic units north-verging, recumbent to inclined folds (D1), associated with a subhorizontal to south dipping cleavage, are refolded by south-verging, upright to inclined folds (D2), with a subvertical to north-dipping axial plane cleavage, and offset by south-directed thrusts approximately coeval with D2. The structural evolution of these units suggests a subdivision of the Variscan Central Pyrenees into two different regions consistent with the zones known for a long time in the core of the Ibero-Armorican or Asturian arc (northern part of the Iberian Variscan Massif). The structure of the Pyrenean non-metamorphic units has foreland affinities and is comparable to that of the Cantabrian Zone, whereas the deformation observed in the Pyrenean metamorphic units is characteristic of the hinterland and is consistent with the features of the West Asturian–Leonese Zone or Central–Iberian Zone. Since the Pyrenean non-metamorphic units are located southwards of the metamorphic ones and the Variscan thrusts are south-directed, we tentatively correlate the Variscan Pyrenees with the northern branch of the Ibero-Armorican or Asturian arc.

The Pre-Andean Phases of Construction of the Southern Andes Basement in Neoproterozoic–Paleozoic Times

During the late Neoproterozoic and Paleozoic times, the southern Andes of Argentina and Chile (21o–55o S) formed part of the southwestern margin of Gondwana. During this period of time, a set of continental fragments of variable extent and allochtony was successively accreted to that margin, resulting in six Paleozoic orogenies of different temporal and spatial extension: Pampean (Ediacaran–early Cambrian), Famatinian (Middle Ordovician–Silurian), Ocloyic (Middle Ordovician–Devonian), Chanic (Middle Devonian–early Carboniferous), Gondwanan (Middle Devonian–middle Permian), and Tabarin (late Permian–Triassic). All these orogenies culminate with collisional events, with the exception of the Tabarin and a part of the Gondwanan orogenies that are subduction-related.

Geoheritage and Geodiversity Evaluation of Endokarst Landscapes: The Picos de Europa National Park, North Spain

The endokarst presents a spectacular Geoheritage involving many singular features with thousands to millions years in age. The Picos de Europa National Park has one of the most important karst landscapes in the world. The endokarst of Picos de Europa shows high natural, scientific, and cultural values mainly related to cave features, with a spectacular vertical development (14 % of known world caves deeper than 1 km), the presence of geomorphological and sedimentary records related to the Quaternary evolution of the Cantabrian Mountain Range, and the traditional and sport uses of the cavities. The aim of this work is to inventory and to evaluate the Geoheritage and Geodiversity of the endokarst of Picos de Europa National Park combining speleological data, field work, and geomorphological mapping from nine selected caves. As a result, the Picos de Europa Geodiverstiy features show a high variability: 75 different natural features have been recognized with a density ranging from 0.3 to 1.1 different features per cm2 of cave area.

The structure in the Bagneres de Luchon and Andorra cross sections (Axial Zone of the central Pyrenees)

The Subandean Basins of South America extending from Trinidad to Tierra del Fuego have been the object of intensive exploratory activities (Fig. 1). The largest amount of hydrocarbons discovered during the last 30 years in these basins was found in complex structural terrains. A total of 59 Billion Barrels of Oil Equivalent (BBOE) have been discovered in areas affected by compressional tectonics. Of these basins, the largest discoveries are in the Furrial Trend of Venezuela (24 BBOE), followed by the Chaco area in Bolivia and Argentina (13 BBOE), the Llanos Foothills of Colombia (4.4 BBOE), and the Madre de Dios Basin of Peru (4.2 BBOE).

Influence of the Rivers on Speleogenesis Combining KARSYS Approach and Cave Levels. Picos de Europa, Spain

The influence of rivers on speleogenesis is studied analyzing the cave levels located in the underground drainage areas related to two fluvial basins. Cave levels are analyzed through their vertical distribution profiles. The underground limits of the fluvial basins are defined using a 3D geometric model of the karst aquifer established according to the KARSYS approach. The aim of this work is to analyze the influence of the rivers on cave evolution using cave morphology. The study area corresponds to the Western and Central massifs of Picos de Europa (Northern Spain), with 214 km of cave conduits up to 1.6 km vertical range. As a result, we established two sequences of development of the cave levels related to the differences of the incision rate of the Cares and Dobra Rivers, and the partial capture of the Western Massif by the Cares River.

Geomorphology and Structural Control in Caves: a Research in Torca Teyera (Picos de Europa, NW Spain)

Research in caves is rare and restricted to speleological explorations. Picos de Europa Massif shows a spectacular development of vertical caves deeper than 500 m. Torca Teyera is a 738 m-deep and 4 km-long vertical cave. The aim of this work is to establish a methodology to characterize the geological and geomorphological aspects of this special group of caves, as well as to identify the factors conditioning karst development. The research involves (1) the cave survey at a 1:500 scale and the construction of a 3D model, (2) the geomorphological mapping on the topographical survey, (3) the geological mapping of the cave environment at 1:5000 and (4) the comparison in stereographic projection of the obtained survey data and joint measures.

Le Silurien supérieur et le Dévonien inférieur à faciès carbonatés du massif des Gavarres (chaînes cières catalanes, Nord-Est de l'Espagne): stratigraphie et relation structurale avec les séries sous-jacentes

Abstract The conodont biostratigraphy of the Upper Silurian and Lower Devonian carbonate facies from the Gavarres massif, the northernmost Hercynian massif of the Catalonian coastal ranges (NE of Spain), is established. This carbonate facies assemblage rests with an Hercynian thrust over a thick siliciclastic sequence of pre-Caradoc age, usually referred to as Cambro-Ordovician series. This subtractive contact has been interpreted as an Hercynian folded thrust developed in a pre folded sequence.