Estratigrafía del subsuelo en el sector noroeste de la cuenca del Duero (provincia de León).

Resumen

The Tertiary sedimentary record in the northwest area of the Duero Basin is divided into three allostratigraphic units: Vegaquemada, Candanedo and Barrillos. The deposit of the first was accomplished through a plain river furrowed by low-sinuosity channels with a wide flood plain. The second unit was formed by a set of highly efficient alluvial systems, leant to the mountainous massif that evolved sideways towards a plain river with low-sinuosity channels and a flood plain where different types of paleosols were generated. The third unit was generated by a set of highly efficient alluvial systems, built by low-sinuosity channels networks. Four seismic units are defined in the subsoil: Paleozoic (USPz), Mesozoic (USMz), Paleogene (USPg) and Neogene (USNg). Isovelocity, isochron and structural maps have been constructed for the upper and lower limits of the two tertiary units. Several well-log curves, that cross mainly the USNg are also analyzed. The study reveals that this sector of the Duero Basin constituted a foreland basin generated by the Alpine uplift of the Cantabrian Mountains. The foredeep had an east-west trend, parallel to the mountainous cantabric front and it is limited to the southwest by the peripheral threshold. The foredeep was wider than 40 km and the sediments thickness is 3,500 m. The forebulge represents a high of the basement, with a reduced thickness of the seismic units. This forebulge must have acted as a barrier for the sedimentation during the stage of the Vegaquemada allostratigraphic unit and it was exceeded by the Candanedo allostratigraphic unit.