Bioestratigrafía y paleogeografía del Oligoceno-Mioceno del borde SO de la fosa de Ciudad Rodrigo

Abstract

During the Oligocene and Early Miocene the Arcosas de la Alamedilla Formation (Fig. 5) was deposited on the southern egde of the Ciudad Rodrigo trough (Fig. 1). 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 (Fig. 5). Pollen analysis (plate 1) suggests the existence of a temperate climate with a seasonal nature. On considering the evolution of the floristic associatgions through the stratigraphie section stratigraphie a gradual replacement of the tree taxa by those of herbaceous species may be observed (Fig. 3). This would imply a progressive degradation of the tree covering caused by a trend of the climate towards arid conditions; consequently, the seasonal character of the climate would have become more pronounced with time. Joint palynological, stratigraphie and sedimentological studies (Fig. 5) show that during the sedimentation of the Arcosas de la Alamedilla Formation the landscape was opened (Fig. 6), covered by braided fluvial systems of proximal sands and governed by a seasonal temperate climate.