Estratigrafía y arquitectura de facies de la Formación Niebla, Neógeno superior, sector occidental de la Cuenca del Guadalquivir

Abstract

The Niebla Fm., redefined in this work, marks the beginning of the Neo gene deposition on the western edge of the Guadalquivir Basin. This unit lies unconformably on a Paleozoic-Mesozoic substrate and is truncated by a not previously identified discontinuity with subaerial exposure features. The irregular topography of the substrate and the general sedimentary trend determine a complex internal architecture in the unit, which it is made up of five main facies associations: (1) fluvial conglomerates and sandstones, (2) fan-delta conglomerate bars, (3) littoral sands and silts, locally rich in Heterostegina, (4) beach sandy calcarenites and conglomerates, and (5) shallow marine bioclastic limestones and calcarenites. All these facies were deposited on the inner part of a low gradient homoclinal ramp, under general transgressive conditions. The conclusions presented in this paper represent a significant departure from the previous chronological adscription and regional significance of the unit.