La sucesión sedimentaria siliciclástica del Cretácico superior del borde sur de la “Sierra de Guadarrama” (Madrid, España central): análisis de facies y reconstrucción paleoambiental

This study concerns the facies analysis and the reconstruction of depositional environments of the basal, terrigenous portion of the Upper Cretaceous’s sedimentary succession, located in the southern margin of the «Sierra the Guadarrama» Mountains (North of Madrid, central Spain), which is a portion of the Spanish Central Mountain Chain called «Sistema Central». The terrigenous deposits are constituted by three formations: the Arenas the Utrillas Fm (Cenomanian), the Arenas y arcillas de Castro de Fuentidueña Fm (Turonian), and the Arenas y arcillas de Segovia Fm (Early Coniacian). Six lithofacies associations where detected in the Arenas de Utrillas Fm (Cenomanian), and interpreted as low sinuosity bed-load coarse sand river’s deposits. The Arenas y arcillas de Castro de Fuentidueña Fm (Turonian) is constituted by 13 lithofacies associations. Their features support coastal depositional setting, as tidal or low energy coastal environments. This formation represented a transgressive-regressive sedimentary cycle and the autochthonous glaucony-rich deposits correspond to maximum flooding. In the Arenas y arcillas de Segovia Fm (Earliest Coniacian), 8 lithofacies associations where recognized. Two asociations, identified in the Soto del Real area, have been interpreted as fluvial deposits (located in a very distant place from the other outcrops), while the other 6 lithofacies associations matched to tidal depositional environment and represented the beginning of another sedimentary cycle, also including the immediately superposed carbonate formation (Dolomías tableadas de Caballar Fm). The acquired dates prompt to a paleoenviromental reconstruction in the study area: 1) a fluvial depositional environments, flowing from NW to SE developed during the Cenomanian; 2) a marine transgressive-regressive cycle, which flooded the all studied area, took place during Early-Middle Turonian; 3) and finally the beginning of a new transgressive cycle, characterized the Early Conician record. Moreover, a morphologic step in the basement has been identifyed, which could have strongly controlled the sedimentation