Pedro Farias

Emplacement of the Cuera and Picos de Europa imbricate system at the core of the Iberian-Armorican arc (Cantabrian zone, north Spain): New precisions concerning the timing of arc closure

The final stages of the Variscan orogeny (mostly Carboniferous) in the Western European Variscan belt involved the development of the Iberian-Armorican arc, which is cored by the Cantabrian zone (NW Iberia). The Cantabrian zone is the foreland of the Western European Variscan belt, and it is interpreted to record the waning stages of the closure of the Rheic Ocean. The distalmost tectonic units within the Cantabrian zone (the Cuera Unit and the Picos de Europa Province) were the last tectonic units emplaced at the core of the Western European Variscan belt orocline. Together, they form an imbricate system and associated wedge-top basins that are key to understanding the development of the orocline. The emplacement of the Cuera Unit and the Picos de Europa Province occurred in the latest Pennsylvanian, between Moscovian and Gzhelian times. New detailed mapping together with stratigraphic, sedimentologic, and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system. Our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the Cantabrian Variscan foreland fold-and-thrust belt, most probably during the oroclinal bending of the SW European Variscan belt that formed the Iberian-Armorican arc. The N-S–directed imbricate system was characterized by a shallow dip of the topographic surface (α 150 ± 15 km) and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying Gondwana lithosphere and may reflect the closure of the Iberian-Armorican arc.

Landslide development in a coastal valley in Northern Spain: conditioning factors and temporal occurrence

Abstract Sixty-five landslides have been mapped in the Meredal Valley, carved in one of the Asturian Precoastal Ranges on Mesozoic bedrock. From a genetic point of view, two groups of landslides can be distinguished: landslides developed mainly over Triassic lutites (complex movements, flows and rockslides) and landslides developed from calcareous cliffs (rock avalanches). Many of them are relict landslides, although evidence of activity can be recognized, as a result of a partial reactivation of some of the landslides. Four chronological classes have been established according to geomorphological criteria and the degree of preservation of the landslides. A lateral plugging deposit provides a minimum age of 5050±40 B.P. for the oldest class. In the same way, a stalactite gives to the third class of landslides a minimum age of 3392±128 B.P. The origin of landslides can be related to the plastic behavior of lutite and the permeability of the overlying limestone, which allows vertical seepage of water. From a regional point of view, landslides could be connected with Quaternary fluvial incision processes, as well as to Holocene high rainfall events.

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.