Modelo sedimentario de los lagos neógenos de la Cuenca del Duero: sector Centro-Occidental

Abstract

In the inner neogene sediments of the Duero Basin, three facies associations have been identified: A, ? and C. Their vertical sucession establishes a sedimentary pattern of evolution in the Basin, which begins with fluvial facies and finishes with lacustrine faciès. The latter have post-sedimentary processes superposed, due to palustrine conditions.The association A was deposited in fluvial channels of high sinuosity and flood plains with thick caler êtes.The association ? was deposited in a mud flat. The main processes were: mud accumulation, freatic level oscillations and long periods of subaereal exposures. Two areas have been identified in this mud flat: one is quite well drained and the other is not drained in the least.The association C belonged to broad lakes, which were very shallow and which had strong oscillations of the water level. The nearshore zone is formed by two lithofacies: detrital and calcareous (wackestone). The central area is dominated by maries sedimentation.The above-mentioned conditions in the central zone are only interrupted by thin beds of packstone, which are interpreted as channel coming from the nearshore.On this depositional context palustrine facies are placed. These are characterised by vegetation colonization over nearshore lacustrine lithofacies (wackestone with roots), and by the development of intense pedogenetic processes, accompanied by the sedimentation of black claystones. With the exception of packstones, the other lacustrine lithofacies are affected by pedogenetic processes.