Pliocene foraminifera and environments, Limon Basin of Costa Rica

Abstract

The sandstone facies of the Pliocene Rio Banano Formation of eastern Costa Rica contains benthic foraminifera indicative of an open marine, current-swept, neritic depositional environment. These sandstones and associated siltstones are placed in Zone N18 on the basis of overlapping ranges of planktonic foraminifera, particularly Globigerinoides obliquus extremus and G. ruber, and a short-ranging ostracode species, Radimella ovata. One hundred and eight species of benthic foraminifera have been identified from the formation. A multiple-group-component factor analysis of abundance distributions of several dominant or common species (Amphistegina gibbosa, Articulina mayori, Cassidulina laevigata, C. subglobosa, Cibicidoides floridanus, Elphidium discoidale, Hanzawaia concentrica, Pararotalia sarmientoi, Pseudononion basispinata, Quinqueloculina lamarckiana, Rosalina globularis, and Trifarina angulosa) in the type section aided in the recognition of three benthic foraminiferal assemblages related to environmental parameters. An open marine, shallow, sandy continental shelf environment is suggested by the first assemblage. This is considered the typical depositional environment of the unit. The second and the third assemblages, suggesting an inner littoral environment and the proximity to a reef, respectively, also indicate introduction of significant amount of transported material into the thanatotopes.