Biogeographic patterns of Pacific planktonic foraminifera have been quantitatively mapped for two time-slices in the early Miocene (22 and 16 Ma) and one in the late Miocene (8 Ma). Important differences are apparent between the early and late Miocene that resulted from changes in surface water circulation within the Pacific Ocean and between the tropical Pacific and Indian Oceans. In the early Miocene, tropical Pacific planktonic foraminifera were dominated by different taxa in the eastern and western areas, but by the late Miocene the assemblages were similar across the entire tropical Pacific. East to west faunal differences were probably due to differences in the surficial water-mass structure and temperature. It is likely that a deeper thermocline existed in the west favoring shallow water dwellers such as Globigerinoides and Globigerina angustiumbilicata, and a shallower thermocline in the east favoring slightly deeper-dwelling forms, especially Globorotalia siakensis and G. mayeri. During the late Miocene a trans-equatorial assemblage developed, dominated by Globorotalia menardii-G. limbata and Globigerinoides groups. These faunal changes are interpreted to reflect both the development, during the middle Miocene, of the Equatorial Undercurrent system when the Indonesian Seaway effectively closed and the general strengthening of the gyral circulation and Equatorial Countercurrent that resulted from increased Antarctic glaciation and high-latitude cooling during the middle Miocene. The trans-equatorial planktonic foraminiferal distribution patterns typical of the late Miocene did not persist to the present-day oceans when east-west differences are again evident. However, these differences in modern assemblages are exhibited within forms that usually inhabit deeper waters. There is a successive changing dominance from west to east of Pulleniatina obliquiloculata to Globorotalia tumida to Neoglobo-quadrina dutertrei. The modern west to east differences in these deeper-dwelling forms reflect an intensification of the Equatorial Undercurrent system and its shallowing towards the east to depths well within the photic zone. Shallow-water forms, such as Globigerinoides, maintain trans-tropical distribution patterns in the modern ocean unlike the early Miocene that lacked an effective equatorial countercurrent system in the Pacific. The distribution of faunas in the North Pacific indicates that the gyral circulation system was only weakly developed in the early Miocene, but was strong by the late Miocene. In the northwest Pacific, temperate faunas were displaced northward as the Kuroshio Current intensified in the late Miocene. In the South Pacific, more distinct latitudinal faunal provinces appeared during the middle to late Miocene along with a northward expansion of the polar-subpolar provinces and contraction of the tropical province. These faunal changes resulted from the continued areal expansion of the polar and subpolar water masses as Australia drifted northward from Antarctica and from the steepening of pole to equator thermal gradients related to increased Antarctic glaciation.

Abstract The Deep Sea Drilling Project has been fundamental in providing carbonate sedimentary sequences throughout the oceans for the study of planktonic foraminiferai biostratigraphy and evolution. We have reviewed the principal developments in the establishment of Neogene planktonic foraminiferai biostratigraphy and later applications, extensions and modifications due to deep-sea drilling. A review of the principal Neogene evolutionary lineages of planktonic foraminifera shows that only a few have formed the basis for biostratigraphic subdivision. A new Early Miocene lineage (G. kugleri-G. peripheroronda ) is reported from mid-latitude southwest Pacific DSDP Site 208. Major evolutionary lineages within the Neogene globorotaliids are recognized as separate taxonomic sub-divisions following Bandy (1972). The subgenus Globoconella Bandy, which represents the major globorotaliid lineage in temperate areas, is redefined, and we restrict the subgenus Turborotalia to Paleogene lineages. The lineage concept of taxonomy is recommended to be employed as phylogenies become well known. The southwest Pacific represents an optimal area for the study of planktonic foraminiferai biostratigraphic correlations between equatorial and temperate areas. A relatively detailed analysis of five Neogene southwest Pacific DSDP sites ranging from cool-subtropical (Sites 284, 207A) to warm-subtropical (Sites 206, 208) to tropical (Site 289), provides a strong basis for correlation between these distinct water masses. Studies of equatorial site 289 necessitate some emendments of the widely used tropical zonation of Blow (1969). Since the last appearance of G. fohsi robusta and of the entire Fohsella lineage provides an easily identifiable, useful Middle Miocene datum, it is recommended for defining the Zone N12/N13 boundary in preference to the first evolutionary appearance of S. subdehiscens (Blow, 1969). Zone N17 is subdivided into new zones, Zone N17A and N17B, based on the first appearance of Pulleniatina , a solution- resistant form occurring in deep-sea sequences from tropical to subtropical areas. A new zonation is recognized in the warm-subtropics but not for the temperate area. The warm-subtropical zones at Site 208 represent a combination of tropical and temperate zonal schemes. Because Site 208 contains a mixture of tropical and temperate elements, a greater number of faunal events is recorded compared with both tropical and temperate regions. However, faunal events at warm-subtropical Site 208 do not necessarily represent datums, since the appearance or disappearance can be diachronous with respect to either tropical or temperate regions. A zonation based on tropical species is applicable in the Early Neogene until the early Middle Miocene, after which temperate species are more valuable for biostratigraphic subdivision. This reflects global cooling related to the major development of Antarctic ice beginning in the Middle Miocene, concommitant with latitudinal shift of cool waters towards the equator. The duration of Neogene zones varies from 0.2 m.y. in the case of Zone N18 to as much as 2.7 m.y. for Zone N17 (as undivided). Only two zones have an estimated duration of less than 0.5 m.y. (Zones N13 and N18), and only two zones are longer than 2 m.y. (Zones N16 and N17). The Late Miocene exhibits zones of longest duration, the Middle Miocene zones of shortest duration and the Early Miocene, Pliocene-PJeistocene of intermediate durations. These changes in zonal duration seem to be directly related to global paleoceanographic evolution and the resultant faunal diversities in planktonic foraminifera through the Neogene.

ABSTRACT The scanning electron microscope was used to examine over 1,000 specimens of Neogloboquadrina pachyderma (Ehrenberg) and related forms from different water masses throughout the late Cenozoic to study the ancestry, evolution, and environmental relations within this species and phylogenetic relations with several other forms. Two principal surface types are distinguished: reticulate microcrystalline ultrastructure which predominates in Arctic and subant-arctic populations, and crystalline ultrastructure which dominates in populations from other areas. In subtropical populations, crystalline forms are distinguished from those of high latitudes by thinner walls, higher pore concentration, and a lack of rosette-patterned crusts. These ultrastructural differences reflect the degree of secondary calcification with reticulate microcrystalline ultrastructure representing an earlier stage. Differene in dominance of the ultrastructural types presumably reflects environmental differences associated with the various water masses. Overall similarity in ultrastructure within N. pachyderma links subtropical populations with temperate populations from the late Miocene to the Recent as one phylogenetic species that evolved from “ Globorotalia” continuosa in the late middle Miocene and early late Miocene. Neogloboquadrina acostaensis is considered to be a tropical to warm subtropical phenotypic variant of a late Miocene to early Pliocene cline with the temperate to polar variant represented by N. pachyderma. Identical surface ultrastructure and morphological intergradation between N. pachyderma and N. dutertrei dutertrei populations in subtropical sequences suggest that the two forms are genetically linked as a cline.