La sedimentación aluvio-lacustre de la Cuenca de Cires (Jurásico sup. - Berriasiense de Cantabria): un modelo evolutivo de las cuencas lacustres ligadas a la estapa temprana del rift noribérico.

Abstract

The Cires basin <late Jurassic-Berriasian) is situated in the NW part of the Basquecantabrian Basin, and is one of ifie numerous alluvio-lacustrine basius of small size created on the North-lberian margin durffig the earliest phase of the Late Jurassic-Early Cretaceous rifting period. An analysis of the relationship betwen lIs sedimentary infilí and fringing tectonic structures demostrates that the Ches basin was a rapidly subsiding semigraben, developed under extensional tectonic conditions. Alinvial fans were originated froin reliefs created by the action of tSe Cabuérniga Fault on ita active northem margin. The southern margin was passive, and was progresively oniapped by lacustrine carbonates. The bulk of the deposition within the semigraben occurred on a low-energy, shallow lacustrine complex. Large climatie fluctuations of the lake shoreline, favoured by a low gradient, led the development of a wide palustrine fringe, in which an extensive development of rhyzogenic caleretes look place. From a wider point of view, facies and sedimentary processes within the Cires Fm. are very similar to those recorded in other conteinporary or near contemporary alluvio-lacustrmne formations of the Basquecantabrian I3asin (Fm. Aguilar> and Cameros Basin (Señora de Brezales aud Rupelo Fms.). Because of that, the Ches Basin can be taken as a representative exmnpie depicting the tectonostratigraphic evolution of lacustrine basius developed at the onset of ifie North-Iberian rift. Key Wards: Alluvio-lacustrine basins, rhyzogenic caicretes, North-lbedan rift, Malm, Berriasian.