Turbiditas calcáreas del Cretácico al norte de Vélez blanco (zona subbética): bioestratigrafía y génesis

Abstract

A stratigraphic, sedimentological and biostratigraphic study (including foraminifers, nannoplankton and radiolarians) of the Cretaceous rocks to the north of Vélez Blanco (Internal Subbetic) reveals considerable variations in the thickness, Iithology and age of the materials in many of the sections. The Iowest lithostratigraphic unit, the Carretero Formation (Upper Berriasian to upper Barremian), crops out only locally and its facies are clearly pelagic, composed by marls, marly Iimestones and limestones. The uppermost Barremian, Aptian and Albian materials of the Fardes Formation are also pelagic facies ,imd in many places have intercalations of carbonate turbidite deposits, oolitic turbidites and breccias, which in some sectors can be quite thick. Notable among these turbidites is a megabed mainly made up of variously sized fragments of middle Jurassic, shallowmarine Iimestones, redeposited in the basin during the uppermost Aptian, which are up to 60 meters in thickness in places and are interpreted as being turbidites related to a seismic event. Materials from the Cenomanian-Turonian-Coniacian-Santonian (p.p.) have been recognised in pelagic facies in two lithostratigraphic units, the Capas Blancas Formation and "Upper Cretaceous carbonate breccia': which interfinger laterally. The upper lithostratigraphic term, the Capas Rojas Formation (Santonian/upper Maastrichtian) onlaps over Jurassic rocks, which were previosly exposed upon the sea bed, and fossilizes the scarps of old faults. lntercalations of calcareous turbidites appear from place to place within these lower Senonian pelagic rocks. The carbonate turbidites were deposited in small tectonic basins bounded by normal faults, mainly in half-grabens. Sedimentary gravity flows were fed by submarine reliefs formed of both Jurassic and Cretaceous materials and the fault scarps surrounding them. They represent sedimentary bodies deposited releted to the paleofaults on an apron model, sometimes relatively thin (calcarenitic levels) and sometimes much thicker (calcareous breccias and the megabed). The turbidites beds formed mainly, or sometimes exclusively, of oolites coming from the destruction of the Camarena Formation (middle Jurassic) are of particular interest; these would have been well exposed on the sea bottom from whence the turbidity currents and mass-gravitacional flows were fed.