Review of the Upper Jurassic-Lower Cretaceous stratigraphy in Western Cameros basin, Northern Spain

The Upper Jurassic-Lower Cretaceous stratigraphy of the Cameros basin has been reviewed. In Western Cameros the stratigraphic sections are condensed but they have a parallel development with the basin depocentre and the same groups have been identified. The Tera Group consists of two formations: Señora de Brezales and Magaña. The Oncala Group is represented by two formations of fluvial deposits, Jaramillo de la Fuente and Río del Salcedal and a third formation, Rupelo of lacustrine /coastal carbonates and evaporites. The Peñacoba Formation is an independent formation made of biogenic lacustrine carbonates and it is restricted to SW Cameros. The Urbión Group is represented by the Laguna Negra Formation which is the deposit of a gravelly braidplain and occurs in NW Cameros and South Demanda. The Enciso Group encompasses three formations, Río Ciruelos which is made of fluvial deposits, Hortigüela which consists of fresh water lacustrine carbonates and Golmayo representing a fluvial dominated coastal plain with marly lakes. The Oliván Group encompasses three formations of fluvial deposits: La Gallega, Castrillo de la Reina and Cuerda del Pozo. The Salas Group consists of two formations Cabezón de la Sierra and Abejar of fluvial and aeolian deposits. The basin wide distribution of the Groups evidences the synchronous development of the rifting process across the basin and supports a model of a basin compartmentalised into multiple sectors evolving simultaneously under dif ferent rates of subsidence and terrigenous supply. The onlap of the syn-rift mega-sequence on the basin margins, the extra-basinal fluvial systems and shallow carbonate lakes together with its condensed character and the preservation of pre-rift mega-sequence at the basin margins point towards a basin with low-gradient basin margins.