Axial sections resolve generic ambiguities in Palaeogene nummulitids: Blondeauina as an Oligocene Tethyan Marker

Larger benthic foraminifera (LBF) were diverse and rapidly evolving during the Paleogene, making them important components of shallow-marine carbonates and valuable tools for biostratigraphy and reservoir correlation. Their complex internal morphology, however, requires careful taxonomic assessment. Accurate identification is particularly relevant to subsurface correlation in hydrocarbon-bearing successions of Libya, the U.A.E., Iraq, and regions. This study re-evaluates the Oligocene marker Blondeauina bouillei (De La Harpe, 1879), commonly misidentified as Nummulites bouillei when classification is based only on equatorial sections. By integrating axial and equatorial thin-section analysis, we confirm the generic distinctiveness of Blondeauina. Diagnostic features include disconnected septal filaments, absence of alar prolongations, a coiling pattern that changes from involute to complanate in mature forms, and locally kinked or anastomosing septa. Comparison with Nummulites, Assilina, Operculina, Decrouezina, Bassiounina, and Gaziryina highlights the importance of axial sections for resolving generic ambiguities among Paleogene nummulitids. Blondeauina is proposed as a reliable Rupelian marker, although its total stratigraphic range may extend from the Late Eocene to the Late Oligocene. Its palaeobiogeographic distribution suggests Tethyan dispersal, probably originating in northern Tethys, possibly Italy. Its thin, flat test and association with Nummulites and Nephrolepidina indicate a warm, normal-marine, middle-ramp habitat.http://urn:lsid:zoobank.org:pub:9AB2081A-3768–40 CD-A3B1-88965C8C3E21