An analysis of diversity and abundance trends among all benthic foraminiferal genera and species, and particularly among species of Bolivina, was carried out for 59 samples of Neogene sediment from DSDP-IPOD Site 548, Goban Spur. By correlating these census data with lithological, geophysical, geochemical, and other faunal and floral measurements in the same stratigraphic interval, a record of irregularly fluctuating cycles was compiled. We interpret them as indicators of relative sea level. High sea levels are characterized by pelagic sedimentation and by high generic and total species diversities. During low sea level, diversity values were lower, and the accumulation of terrigenous detritus was more prevalent at the site. A sequence recording five highstands and five lowstands is interrupted by four unconformities in a scenario remarkably similar to that postulated in the work of P. R. Vail and his colleagues. Bolivina species diversity also varied cyclically. We interpret diversity of Bolivina species as a measure of relative oxygen and nutrient content at the water/sediment interface; high diversity indicates the presence of an oxygen-minimum layer, accompanied by nutrient enrichment. Our data show that this property generally varied directly with sea level, but sometimes varied independently.
