Neogene fan deltas in the northern Guadalquivir basin (Andújar, Jaén, Spain)

Abstract

The Neogene of Andújar (Guadalquivir Basin) consists of siliciclastic aud carbonate rocks of Upper Tortonian and Messinian age. They are grouped into a laterally-related facies assemblages that form two megacycles. Ihe lower of these cycles has debris-flow, proximal and distal braided-channels and sandy plain sediments, alí them with subaerial and subaqueous features, plus marine littoral bars aud carbonate shelf deposits. Lateral arrangement of facies allow to interpret these rocks as deposited in delta settings with variable name depending on the criterion used: braided delta (McPherson et al., 1981) orfan delta (Nernec & Steel, 1988). In Postma’s (1990) proposal of classifucation the described case-study sedimented in a shallow delta system fed by alluvial systems. It is an intermediate between types A and B, with bed-load dominance at the river-mouth and shoal-water profile, developed over a carbonate shelf. Sea-level fluctuations controlled the evolution of the system as deduced from spatial arrangement of the described rocks. This fluctuation was in tum related to variations of the basin’s volume related to synsedimentary movements along the south margin (although this is a passive margin, it locates at the northem edge of a basin with a complex geodynamic behaviour during Cainozoic).