Neogene planktonic foraminifera of ODP Site 130-806

The Neogene biostratigraphy presented here is based on the study of 230 samples through 737 m of pelagic sediment in Hole 806B. Sediment accumulation is interrupted only once in the uppermost lower Miocene (Zone N6), apparently coincident with a widespread deep-sea hiatus. Preservation of planktonic foraminifers through the section ranges from good to moderately poor. One hundred and ten species of planktonic foraminifers were identified; taxonomic notes on most species are included. All of the standard low-latitude Neogene foraminiferal zones are delineated, with the exceptions of Zones N8 and N9 because of a high first occurrence of Orbulina, and Zones N18 and N19 because of a high first occurrence of Sphaeroidinella dehiscens. Good agreement exists between the published account of the variation in planktonic foraminiferal species richness and the rates of diversification and turnover, and measurements of these evolutionary indexes in the record of Hole 806B. The global pattern of change in tropical/transitional species richness is paralleled in Hole 806B, with departures caused by either ecological conditions peculiar to the western equatorial Pacific or by inexactness in the estimation of million-year intervals in Hole 806B. Temporal changes in the relative abundance of taxa in the sediment assemblages, considered in light of their depth habitats, reveal a detailed picture of historical change in the structure of the upper water column over the Ontong Java Plateau. The dominance of surface dwellers (Paragloborotalia kugleri, P. mayeri, Dentoglobigerina altispira, Globigerinita glutinata, and Globigerinoides spp.) throughout the lower and middle Miocene is replaced by a more equitable distribution of surface (D. altispira and Globigerinoides spp.), intermediate (Globorotalia menardii plexus), and deep (Streptochilus spp.) dwellers in the late Miocene, following the closing of the Indo-Pacific Seaway and the initiation of large-scale glaciation in the Antarctic. The shoaling of the thermocline along the equator engendered by these climatic and tectonic events persisted through the Pliocene, when initial increases in the abundance of a new set of shallow, intermediate, and deep dwelling species of planktonic foraminifers coincide with the closing of the Panamanian Seaway.

Cenozoic planktonic foraminifera in the Goban Spur Region

Cenozoic planktonic foraminiferal biostratigraphy at DSDP-IPOD Leg 80 sites documents the existence of regionwide stratigraphic gaps in the Paleocene and middle Miocene. Episodes of carbonate dissolution also occurred during the Paleocene at several sites, particularly at Site 549, where destruction of foraminiferal tests may obscure evidence of an unconformity. The middle Miocene hiatus is apparent at each site where Neogene sediments were continuously cored. Upper Miocene sediments at Site 550 (the only abyssal site) are characterized by moderate to extensive dissolution of planktonic foraminifers, but they contain abundant specimens of Bolboforma that mark this stratigraphic interval (von Daniels and Spiegler, 1974, doi:10.1007/BF02986990; Roegl, 1976, doi:10.2973/dsdp.proc.35.133.1976; Murray, 1979, doi:10.2973/dsdp.proc.48.116.1979; Müller et al., 1985, doi:10.2973/dsdp.proc.80.117.1985). Although foraminiferal evidence is not conclusive, nannofossils indicate a widespread Oligocene unconformity (Müller, 1985). Several oceanographic factors, not just simple sea-level change, probably interacted to produce these regional unconformities. There are also dramatic differences in the Cenozoic sedimentary record among Leg 80 sites, indicating that each has had a distinct geologic history. The thickness of the Cenozoic section varies from 100 m at Site 551 to 471 m at Site 548. The thickness of individual chronostratigraphic units also varies, as do the number and stratigraphic position of unconformities other than those mentioned. Differences in the stratigraphic record from site to site across the continental slope result from (1) location in separate half-graben structures, (2) varying location across the developing margin, and (3) difference in position relative to the seaward edge of the enclosing half-graben. Except for turbidites, deposition at Site 550 (abyssal) was largely independent of developments on the continental slope; but it was affected by oceanographic events widespread in the North Atlantic.