DSDP Site 594, Chatham Rise, New Zealand - Late Neogene planktonic foraminiferal biostratigraphy revised
Abstract. A restudy of the planktonic foraminifera at DSDP Leg 90, Site 594, has been made and consequently a revised scheme of late Neogene zones has been necessary. The Globorotalia sphericomiozea Zone (including G. conomiozea) is contracted to occupy a much smaller interval just below the Miocene/Pliocene boundary and the G. puncticulata, G. inflata and G. truncatulinoides Zones have been expanded. In the uppermost Miocene and Lower Pliocene, the standard regional planktonic foraminiferal datums provide a good correlation with DSDP Leg 29 Hole 284, DSDP Leg 90 Hole 593 and with New Zealand on-land palaeomagnetically-zoned sequences. They do not, however, correlate with the magnetochronology adopted in the Leg 90 Initial Reports for this interval in Hole 594 in which Chrons 4–6 are offset downwards against the foraminiferal datums. It is possible that there are unrecognized hiatuses in the Plio-Pleistocene.
Higher in the Pliocene, very low species diversity of the cold-water faunas, scarcity of warm-water foraminiferal zonal species, and their much later appearance in Hole 594, contribute to a recognition that the Subtropical Convergence has been an effective barrier against the southwards penetration of most warmer water planktonic species.
Neoacarinina blowi Thompson and Globorotalia crozetensis Thompson, are recorded from the New Zealand area for the first time