Upper Eocene-Oligocene larger Foraminifera from the westernmost Tethys (Prebetic Range, SE Iberia)

Revision of Austrotrillina and Risananeiza

Abstract

The study of upper Eocene-Oligocene larger foraminiferal assemblages in two sections of the Prebetic Range in south-eastern Iberia (Ibi and La Font Roja sections) revealed a rich diversity, including species previously known only from the Central Tethys, such as the Eocene Neorhipidionina cf. spiralis, and the Oligocene Pfendericonus globulus, Austrotrillina howchini, Idalina pignattii, and Archaias sp., as well as endemic forms such as Peneroplis peramplus, Spirolinella emmae, and Borelis sp. 1. The continuous record of Austrotrillina (Rupelian-Chattian) and Risananeiza (upper Chattian) showed evolutionary trends and allowed for a systematic revision. Austrotrillina asmariensis, A. striata, and A. brunni are considered morphotypes of a single species, A. striata, evolving anagenetically from the lower Rupelian A. paucialveolata, which originated from the Eocene A. eocaenica. The two known species of Risananeiza, R. crassaparies and R. pustulosa, were identified for the first time within the same stratigraphic section. They represent successive stages of an anagenetic species throughout the upper Chattian. The biostratigraphic results provide an improved characterization of Shallow Benthic zones SB 21 to 23 in the westernmost Tethys and allow the subdivision of SB 23 (upper Chattian) into two sub-biozones, 23A and 23B, based on the stratigraphic ranges of miogypsinids (Miogypsinella spp., Postmiogypsinella intermedia) and Risananeiza. The Priabonian-Chattian Neorotalia burdigalensis also exhibits evolutionary trends with potential biostratigraphic relevance. Overall, the biostratigraphic data obtained indicate diachronous, parallel evolution and extinction in several genera, improving our understanding of diversity patterns and migration pathways in Oligocene larger Foraminifera.