Análisis sedimentológico y paleogeografía en el Mioceno del Sector de Sacramenia (Segovia)-Peñafiel (Valladolid)

Abstract

The present work is a contribution to sedimentological studies on the Miocene  facies  of the southeastern region on the Duero Basin (Sacramenia-Peñafiel zone. Fig. 1).In this area analyses were made of the clays in three profiles chosen along a study line situated between the marginal fades adjacent to the southern basement on Honrubia and the central facies of the Basin situated towards the ? (Peñafiel) (Fig. 2). The interpretation of these analyses reveals a change in the paleogeographic conditions along the section. In this sense, in the northern zone it is possible to note a predominance of inherited clays (Illita, kaolinite-chlorite, smectites), with the localized appearance of paligorskite linked to the development of carbonated crusts and intersitial gypsum (Fig. 3). In the closest zone, an association of clays with sepiolite as the major component predominates (Fig. 3); this is accompanied by a highly characteristic mineral grouping: silex (CT opal), dolomite, gypsum and celestine.The mineralogical set and the remaining sedimentological characteristics of the beds of the first zone (Bocos de Duero profile) point to a distal sinuous fluvial system originating in the East, with marked periods of drought. The lutitic-marly sediments of the area closest to the Honrubia border are characterized by the presence of a confined lacustrine environment which proves to be expansive over the fluvial system situated to the North.Finally, the results point to the existence of a paleogeographic development where sedimentation took place in subbasins which could have had autonomy during certain stages of their evolution.