Distribución de los Foraminíferos, Moluscos y Ostrácodos en el Neógeno de la Cuenca del Duero. aspectos más significativos

Abstract

The study of Mollusca, Foraminifera and Ostracoda in the stratigraphie sections representative of three sectors of the Neogene of the Duero Basin (Central sector), Peñafiel-Almazán and Castrillo del Val estabUshes different assembleges and the temporal and spatial changes taking place in them. Regarding the Gastropoda, the abundance of specimens contrasts with the small number of species present; in the cent-ral sector the dominant forms correspond to Valvata, Bithynia and Anisus; in the sector of Peñafiel-Almazán Hydrobia schlössen is extremely common and at Castrillo del Val, Hydrobia, Melanopsis laevigata and Potámides tricintum. The Ostracoda are represented mainly by Ilyocypris gibba, Cyprinotus salinus and Cyprideis tuberculata in the central sector; they are represented by different taxons such as Lineocypris and Subulacypris in the Peñafiel-Almazán area, and by Cyprideis torosa in Los Valles de Fuentidueña, posing problems regarding chronostratigraphy. The replacement of C tuberculata by the great predominance of Darwinula is the most sa- Hent aspect of Castrillo del Val. The changes appearing in the Ostracofauna are accompanied by the appearance and predominance of Foraminifera in several sections. Ammonia tepida appears as dominant in the central sector whereas in the sector of Castrillo del Val the assemblage of Nonion granosum and Miliolids is outstanding, together with C tuberculata, A general scheme is presented for the distribution and changes in the assemblages found in each sector and the paleoenvironmental implications are discussed.