The radiolarian assemblages are peculiar in that numerous common tropical forms, some of which are biomarkers, are absent or very rare. In addition, some species not usually found in tropical assemblages are present. These forms, indicative of upwelling conditions, fall into three categories: 1) endemic upwelling, 2) displaced temperate, and 3) enhanced tropical. Comparison of the Oman margin/Owen Ridge fauna with that recovered from the Peru margin upwelling area (ODP Leg 112) suggests that the assemblage may be globally diagnostic of upwelling conditions. The onset of upwelling is marked by the appearance of siliceous biota at about 11.9 Ma, and there is some indication of a decrease in the strength of the upwelling signal at about 9.6 Ma. A strong pulse in, or strengthening of, the upwelling mechanism is indicated by a marked fauna change at 4.7 Ma. There is a weaker signal, implying a change in upwelling conditions, at about 1.5 Ma.