BENTHIC FORAMINIFERAL ASSEMBLAGES IN TEMPERATE CORAL-BEARING DEPOSITS FROM THE LATE PLIOCENE

Abstract

Foraminiferal and sedimentary analyses were performed on upper Pliocene exposures in the Almeria-Nijar basin of southeastern Spain to determine its depositional history. The composite stratigraphic section reveals that, during the late Pliocene, a restricted coastal bay with coral banks was being filled with the siliciclastic sediments of prograding fan deltas. In the lower part of the Rambla Quebrada section, fine-grained sediments with Cibicides refulgens , Cibicidoides pseudoungerianus , Cibicidoides bradyi , Asterigerinata spp., Lobatula lobatula , Rosalina globularis , Textularia sp., Lenticulina calcar , and carinate elphidiids indicate deposition in a distal part of the bay where water depths were relatively deeper than those along the coast, and where the marine influence was greatest. Epiphytic species (i.e., Elphidium spp., Cibicides refulgens , Lobatula lobatula , Rosalina globularis , and Asterigerinata spp.) dominate in the lower part of the section and suggest that the distal substrate was densely vegetated. In contrast, the upper part of the Rambla Quebrada section is dominated by taxa characteristic of very shallow brackish environments, notably Ammonia spp. and noncarinate elphidiids. The relative abundance of epiphytic foraminiferal species decreases considerably up-section as a consequence of fan-delta progradation, which led to an increase in water turbidity and the influence of freshwater. Mud-dwellers (i.e., Reussella spinulosa and Nonion asterizans ) inhabiting soft bottoms dominate in the middle-to-upper part of the studied sections. Here, Cancris auriculus , Nonion asterizans , and Cassidulina neocarinata are also locally abundant. These species are usually abundant on substrata with high contents of organic matter, which in this study could be attributed to the increased nutrient flow from the fan deltas prograding into the basin. Higher in the section, varve-like laminae that include species known to be tolerant of disoxia (i.e., Bulimina aculeata and Fursenkoina acuta ) indicate that geomorphic restriction of the bay weakened the mixing of marine and fresh water, which allowed its water column to stratify and develop low-oxygen bottom conditions.