El Jurásico superior de la Sierra de Aralar (Guipuzcoa y Navarra): caracterizacion sedimentológica y paleogeográfica

Abstract

Facies analysis carried out in the Upper Jurassic of the Sierra de Aralar (Eastern Basc-Cantabric Basin), give new information on the sedimentary evolution and palaeogeographic distribution of the sedimentary domains. Two depositional sequences are defined. The Lower Sequence is Oxfordian in age and ineludes two types of facies, developed in middle ramp areas. The more proximal peloidal and skeletal packstones grades to the SW into the more distal sponge, ammonite and belemnite wackestones. The Upper Sequence expands from Late Oxfordian to Kimmeridgian and consists of four types of facies. Both the sandy and the oolithic, skeletal and intraelastic facies were developed in the inner ramp areas (delta front and associated subtidal shoals). In the middle ramp areas, sedimentation was dominated by both the oolithic and peloidal and the coraline facies. The carbonate ramp was opened to the SE. The source for the elastic material, located to the N, were the elevated areas of the Ebro Massif.
The Lower Sequence shows a progradational facies arrangernent, which has been interpreted as a highstand systems tract. The Upper Sequence display a retrogradationalprogradational evolution, which would define both a transgressive and highstand systems tract. The comparison of these sequences to the ones previously defined in the Iberian basin allows to state that the driving mechanism creating the accommodation in the basin was related to regional, tectono-eustatic changes.