Keele Research Repository

Planktonic foraminifera and Radiolaria from the Middle to Late Miocene of DSDP Sites 289 and 71 in the western and central equatorial Pacific have been investigated with the aim of explaining certain changes in the biota in terms of pre-mortal (palaeoenvironmental and palaeoecological) and post-mortal (dissolution) factors.
The oceanography, planktonic ecology, pelagic (biogenic) sedimentology and Cenozoic history of the Pacific Ocean are reviewed.
A taxonomic review is presented for all forms encountered at both sites, including fifty seven planktonic foraminifera and one hundred and sixty three radiolaria, of which four new species are described and named.
A biostratigraphical analysis identifies the standard planktonic foraminiferal and radiolarian zones.
The extent of dissolution of planktonic foraminifera and radiolaria is discussed.
An interpretation of changing palaeotemperature in the epipelagic zone of the Middle to Late Miocene water column at Site 289 is attempted by reference to distributional trends in Orbullna universa, and keeled globorotaliids, including G. fohsi s.l. and G. cultrata gp.
The palaeotemperature curve suggests variation between 24*C and 29#C, fluctuations being possibly due to periodic development of upwelling in the surface waters of the western equatorial Pacific, caused by variation in the size of the Antarctic ice sheet.
Faunal trends, which are expressed by the percentage abundance of individual taxa, diversity and similarity indices of entire assemblages, and evolutionary events, were compared with palaeotemperature trends to seek correlation and thereby explain distribution. A biometric analysis of the radiolaria Stichocorys delmontensis is described to highlight an apparent relationship between abundance, morphology and palaeotemperature.
Finally, the palaeotemperature trends at Site 289 were considered in relation to previous interpretations. An overall agreement of results validates the palaeotemperature conclusions of the present study, allowing the results to be used for precise stratigraphical dating of important palaeoceanographic events, particularly in the latest Miocene (Messinian).