The Miocene record of the Betic Cordillera uplift in Los Guájares valley (Granada province, S Spain)

Abstract

The Los Guájares valley is located about 35 km south of Granada in the Internal Zones of the Betic Cordillera. The Miocene deposits in this area consist of six sedimentary units separated by unconformities, which are exposed in small and laterally discontinuous outcrops overlying metamorphic rocks of the Alpujárride Complex. The lowest unit comprises upper Serravallian marls with planktonic foraminifera filling neptunian dykes and covering Triassic dolomitic marbles of the Alpujárride Complex. These marls reflect deep marine deposition on the Betic basement under a local extensional regime. Uplift of the region led to emergence and deposition of continental red alluvial-fan conglomerates and foothill breccias. The overlying unit, a shoreline conglomerate with small oyster banks, indicates relative sea-level rise. Shallow-marine conditions continued during the deposition of the following unit, early Tortonian in age, which consists of calcareous sandstones with hermatypic corals. Small patch reefs developed in the overlying unit composed of sandy limestones with corals (Porites, Tarbellastraea, Thegioastraea) and oysters, and sandy limestones with coralline algae in the most distal areas. The coral reefs in Los Guájares and some coral heads in Albuñuelas, a near locality, are the only record of early Tortonian coral buildups in the Mediterranean. The last marine unit comprises lower Tortonian conglomerates, sandstones and siltstones accumulated in the front of a small delta. Oyster banks and concentrations of Turritelines suggest high nutrient levels in the delta-front paleoenvironments. The Los Guájares valley area emerged afterwards, following the onset of a compressional geodynamic regime in the central Betic Cordillera and since the early Tortonian only small bodies of foothill and alluvial-fan deposits formed in a predominantly erosional context.