Ostracod assemblages and palaeoenvironmental reconstruction of a Lower Pliocene shallow marine system in the East Atlantic (Bonares-Casa del Pino, Guadalquivir Basin, Spain)

The ostracod assemblages from the Bonares - Casa del Pino Section in the Lower Guadalquivir Basin, part of the lower Pliocene Arenas de Huelva Formation, have been analysed for their palaeoenvironmental significance. These assemblages form part of a subtropical/tropical biota, consistent with findings from earlier studies on fossil remains within the Zanclean deposits in the Southwestern Iberian Peninsula.The present study marks the first application of the Specific Population Species Index Method, originally developed to distinguish autochthonous from allochthonous species in Recent assemblages, to fossil ostracods. Through quantitative and statistical analyses, the autochthonous nature of both dominant and characteristic species was recognized. The succession was deposited in the northernmost sector of the East Atlantic lower Pliocene tropical palaeoecoregion (also known as Atlantic Andalusian Pliocene Mollusc Unit 1), in shallow waters. The attribution to the Offshore Transition zone, near the boundary between infralittoral and circalittoral zones, prompted clarification of vertical zonation terminology for both the Atlantic and Mediterranean, in Recent and Pliocene marine environments.