A Review of Neogene Planktonic Foraminiferal Biostratigraphy: Applications in the Equatorial and South Pacific
M. S. Srinivasan, J. P. Kennett, 1981. "A Review of Neogene Planktonic Foraminiferal Biostratigraphy: Applications in the Equatorial and South Pacific", The Deep Sea Drilling Project: A Decade of Progress, John E. Warme, Robert G. Douglas, Edward L. Winterer
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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.
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At the present the Glomar Challenger has drilled over 500 holes over the world ocean, involving hundreds of scientists from dozens of countries. This volume is intended as a review of some of theimportant results from the most comprehensive, ambitious and successful earth-bound geologic project ever undertaken. The symposium upon which this volume originated was held April 4, 1979 at the SEPM/AAPG Annual Meeting in Houston. No comprehensive synthesis of all aspects of the DSDP has appeared, and the topic coverage in this volume is biased towards the sediments and fossils, and their significance for certain aspects of earth history – paleogeography, bathymetry, climatology, oceanography, ecology, environments – all in keeping with the audience of sedimentary geologists.