Sedimentología de sucesiones sinrift tempranas en un semigraben marginal de un rift extensional: la Cuenca de Bijuesca, Jurásico superior de la Cordillera Ibérica (Zaragoza, España) Sedimentology of the early synrift record in a marginal halfgraben related to an extensional rift: Bijuesca Basin, Upper Jurassic of the Iberian Range (Zaragoza, Spain)

A detailed sedimentological study of the first synrift continental deposits recorded in the Bijuesca Halfgraben (Bijuesca and Ciria Formations), has allowed to understand the stratigraphic architecture of the sediments which record the beginning of the extension in this structure. The Bijuesca Fm consists of detrital sediments arranged in three different alluvial fan (i.e., proximal, medium and distal) facies associations. This unit is made up by two retrograding sequences that consist of siliciclastics and carbonate detrital deposits eroded from the Jurassic prerift units. These sequences record sedimentation in an alluvial fan system with low-efficiency of transport. The Ciria Fm consists of lacustrine carbonate sediments arranged in shallowing-upwards sequences. The predominance of pedogenic modifications affecting the lacustrine sediments and the absence of deep lacustrine facies, allow classifying this lake system as a low-gradient ramp margin lake with low energy. The characteristics of both depositional systems agree with the tectonic situation supposed for the early stages of a rift system.