Contribución al conocimiento del Mioceno lacustre de la Cuenca terciaria del Duero (sector centro-oriental, Valladolid-Peñafiel-Sacramenia-Cuéllar)
The Miocene successions of the central-eastern region of Duero Basin can be grouped into five informal lithostratigraphic units, named: Marly Unit (U.l); Lutitic Unit (U.2); Marly-Gypsiferous Unit (U.3); Carbonate Unit (U.4); Carbonate-Siliciclastic Unit (US). Deposition of these successions took place in alluvial-flats with meande~gchannel(sa ssociationoff aciesA ), and lacustrine environments (associations of facies B. C and D). Association B is mostly composed of marls and represents open to semiclosed shallow lakes with moderate terrigenous influx. Association C is mostly carbonated and was formed in low-gradient ramp margins-low energy shallow lakes. Association D is gypsiferous and reflects drylsaline mud flats, playa-lake and evaporitic ponds. An ulterior alteration, related to the development of a morphological Plio-Pleistocene surface, affected the top of the Marly-gypsiferous and Carbonate Units, givingrise to two telodiagenetic faciesisHociations (El and E2). Consequently, the distribution of facies association and their general sequence enable us to recognize three depositional systems separated by discontinuities: the first contains U.l, the second assembles U.2, U.3 and U.4, and the third is formed by U.5.