Secuencias de olistostromas en una cuenca de antepaís pensilvaniense (Unidad del Pisuerga-Carrión, Zona Cantábrica)

Abstract

The 5000 m-thick Pennsylvanian succession that crops out in the Pisuerga Area (PisuergaCarrión Unit, Cantabrian Zone), has been subdivided into six mappable shallowing-upward depositional sequences, ranging in thickness from 200 to 1800 m and bounded by unconformities or their correlative conformities. Each sequence begins with olistostromes, interpreted as due to gravitational collapse triggered by thrust tectonic activity in the nappe fronts. The size of boulders and olistolites, the variations in thickness of the olistostromes and the paleocurrents suggest a sediment transport form SW to NE (according to the present day geographic coordinates).The deep-water deposits with olistostromes, related with a strong flexural subsidence linked to the tectonic overload in the thrust front, pass upwards into mixed shelf deposits as accommodation space is reduced by sediment imput. These shallow water rock are organized in glacioeustatic cycles equivalent to cyclothems. The stratal patterns (onlap, wedging and truncation) observed towards the eastern sectors of the basin are related to the synsedimentary growth of fault-related folds associated to blind thrusts forming part of a piggy-back sequence.