Distribution of calcareous nannofossils at Sites 1168, 1170, 1171, and 1172 was obtained by semiquantitative analyses. Diversity of nannofossils at Site 1168 was sufficient to allow the recognition of most Okada and Bukry (1980) Miocene zones. In comparison, at the other three sites, diversity was lower and resulted in less biostratigraphic resolution. Despite the low abundance of some marker species within the triquetrorhabdulids, ceratoliths, and sphenoliths, a reliable biostratigraphy could be generated from their abundance patterns when compared with stratigraphic data available from foraminiferal, diatom, radiolarian, and magnetostratigraphies.
Several alternative markers were used to help refine the stratigraphy of Leg 189 sites. The top and bottom of the R. pseudoumbilicus >7 µm paracme, the FO of C. premacintyrei, and the FO of C. tropicus appear to be useful events in the Tasman Seaway. Additional quantitative work would provide a detailed view of the distribution of these species.
Core disturbance and extreme bioturbation in the upper Miocene and across the Miocene/Pliocene boundary at Sites 1170, 1171, and 1172 complicated the interpretation of the sedimentary history of these regions. Overgrowth of delicate features on sphenoliths in the lower Miocene and on discoasters in the upper Miocene sections prevented the identification of the complete range of Sphenolithus disbelemnos, Sphenolithus dissimilis, D. loeblichii, and D. surculus.