La formación radiolarítica Jarropa: definición y significado en el Jurásico Subbético (Cordillera Bética)

Abstract

The Jarropa Radiolarite Formation is defined formally, for the first time, according to the international guide of stratigraphic nomenclature, and the holostratotype and two parastratotypes are described. This is a very characteristic Jurassic unit of the Subbetic (Betic Cordillera) in which point out the presence of radiolarite levels, together with siliceous marlstones, marls and clays. Two members are differentiated: a lower member of green, radiolarites and siliceous marls, and an upper member of red, siliceous clays and marls, both being recognizable in most of the outcrops. The age of this formation in the holostratotype, known mainly from the study of their radiolarians, is Late Callovian-Oxfordian. In other stratigraphic sections (including some parastratotype) is verified that the exact age of the bottom of the formation, and of the boundary between the two before described members are heterochronous, within the Uppermost Bajocian-Lowermost Kimmeridgian. They are pelagic sediments, deposited during the expansive phase of the Southern Iberian Continental Paleomargin, in areas far from the continent with thin continental crust. They have a great analogy with deposits outcropping in others Mediterranean Alpine domains (Apennines, Alps, Dinarids, etc.) also accumulated during Jurassic extensive phases of continental margins adjacent to the Tethys. The depositional bathymetry is estimated in a few hundreds of meters, without a necessary relation with the calcite compensation depth (CCD).