La sedimentación continental del Grupo Campóo (Malm-Cretácico basal de Cantabria, Burgos y Palencia): testimonio de un reajuste hidrográfico al inicio de una fase rift.

Abstract

The Campóo Group (a term introduced herein> is the oldest of the several tectonostratigraphic imits that made up the Upper Jurassic-Lower Cretaceous syn-rift succession of the western part of the Basquecantabrian Basin. Analysis carried out so far of lis fresh water ostracods of charophytes have prodir ced ambiguous resulis, although they are sufficient to prove that the age of the Carnpóo Group must be comprised witbin the Oxiordian-Berriasian time span. The Campóo Group was accumulated within a 50 Km wide semigrahen, itse]f suibdivided into separated small basins, created by the reactivation of Hercynian faults. Because of that, the Campóo Group is composed of four, laterally correlative formations: two of them (Arroyal asid Saja Fms.> are representative of fluviatiJe systems of different typc; thc other tiro <Aguilar and Cires Ems) of internál-draining aluvio-lacustrine environments. Such an array of continental systems points out to the temporal coexistence of separate drainage networks of relatively small dimensions. Such paieogeographic arrangemeiR is considered to reeord a phase of hydrographic readjustment afta the tectonie uplifting and emergence of the area. A comparison of the aboye results with published information reveals a similar situation in other contemporary basins of north Spain and Portugal. Because of that, the hydrographic readjustment deducted for the Campóo Group is considered a rule rather than an exception on Ihe initia] development of rifted basins.