Radiolarian counts demonstrate that recognizable assemblages in deposits underlying Zone RP-15 are different from those in deposits overlying Zone RP-15. Furthermore, the radiolarian assemblage composition obviously changes through the diatom interval, which possibly represents a linear faunal evolution pattern.
The radiolarian assemblage beneath the diatom accumulation is a coccodiscid–theoperid–artostrobid assemblage. The radiolarian assemblage in the uppermost section of diatom-rich sediments is a theoperid–coccodiscid–actinommid assemblage. There are also distinct faunal assemblage compositions in the lowermost sediments of Zone RP-15 and at the diatom maximum in the diatomaceous interval.
The coccodiscid–theoperid–artostrobid assemblage is characterized by large coccodiscid shells, mostly represented by Lithocyclia ocellus E. and various species of Periphaena and Heliodiscus. The artostrobid group is composed of smaller and robust forms represented by Dictyoprora mongolfieri (E.).
The radiolarian assemblage from the uppermost part of the diatom interval, grading into the normal Eocene radiolarian sediment, is characterized by a reversal in the theoperid:coccodiscid ratio and a clear increase in actinommids. Artostrobids decrease above the diatom maximum.