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High-Resolution Neogene Planktonic Foraminifer Biostratigraphy of Site 806, Ontong Java Plateau (Western Equatorial Pacific)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Chaisson, William P. Leckie, Rafael M. |
| Copyright Year | 1993 |
| Abstract | 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. INTRODUCTION One of the principal objectives of Ocean Drilling Program (ODP) Leg 130 was to collect a depth transect of complete Neogene sections down the northeastern flank of Ontong Java Plateau in the western equatorial Pacific (Fig. 1). The goal was to evaluate the vertical distribution of a variety of parameters of paleoceanographic significance (Kroenke, Berger, Janecek, et al., 1991). Site 806 anchors this transect near the top of the plateau in a water depth of 2520 m. Hole 806B contains the thickest (738 m) and most complete Neogene sequence drilled during Leg 130 (Kroenke, Berger, Janecek, et al., 1991). The pelagic sediments of Hole 806B contain rich assemblages of calcareous and siliceous microfossils and represent a rare opportunity to further refine biostratigraphies and the correlation between microfossil groups in an expanded, virtually complete tropical section. The section also provides a wealth of material for high-resolution sedimentologic, isotopic, geochemical, geophysical, and physical properties analyses. The absence of a paleomagnetic stratigraphy in all but the upper 10 m (Kroenke, Berger, Janecek, et al., 1991) is the only disappointing feature of this section, particularly from a geochronologic point of view. Neogene planktonic foraminifers have been widely studied in the subtropical and tropical Pacific (e.g., Brönnimann and Resig, 1971; Jenkins and Orr, 1972; Keller, 1981a, 1981b, 1981c; Orr and Jenkins, 1980; Srinivasan and Kennett, 1981a, 1981b; Barron et al., 1985; Saito, 1985; Stone and Keller, 1985). The purpose of this study is twofold. First, we establish a high-resolution planktonic foraminiferal biostratigraphy through the Neogene of Hole 806B. This provides a 1 Berger, W.H., Kroenke, L.W., Mayer, L.A., et al., 1993. Proc. ODP, Sci. Results, 130: College Station, TX (Ocean Drilling Program). 2 Department of Geology and Geography, University of Massachusetts, Merrill Science Center, Amherst, MA 01003, U.S.A. chronostratigraphic framework for sedimentologic, geochemical, and geophysical research at this site. Second, we evaluate the species concepts and morphologic variability of low-latitude taxa, and then document taxon ranges and compare Hole 806B datums with other published records, including nearby Deep Sea Drilling Project (DSDP) Hole 289. The ranges of the 110 species encountered in this study provide a large data base for the study of species richness and rates of speciation, extinction, and turnover in the tropics. We present 228 samples from the basal Miocene through Pleistocene of Hole 806B and two additional samples from the uppermost Oligocene of Hole 806C. The Neogene (0-23.7 Ma) of Hole 806B is represented by 737.75 m of section. This translates into an average sample density of approximately 31 samples per 100 m of section with an average temporal resolution of about 104 k.y. In addition, we examined numerous additional samples to refine biostratigraphic datums. For example, in the Miocene/Pliocene boundary interval, the average temporal resolution is approximately 22.6 k.y. METHODS A total of 230 samples from Cores 130-806B-1H through -78X (0-743.1 mbsf) and Cores 130-806C-59X and -60X (740.0-759.2 mbsf) were examined in detail for planktonic foraminifers. Most cores are represented by three samples, typically from Sections 2, 5, and the core catcher (CC). Cores with poor recovery are represented by one or two samples, depending on the amount of sediment recovered. The relative abundances of planktonic foraminiferal species in these 230 samples are shown on the distribution table (Table 1, in back pocket). Additional samples, typically from Sections 1, 3, 4, and 6, were examined for key taxa or to more closely resolve the placement of biostratigraphic boundaries. These samples are not shown on the distribution table. Samples were soaked in a neutral pH mixture of diluted hydrogen peroxide and Calgon for about an hour. The samples began to get |
| File Format | PDF HTM / HTML |
| DOI | 10.2973/odp.proc.sr.130.010.1993 |
| Alternate Webpage(s) | http://www-odp.tamu.edu/publications/130_SR/VOLUME/CHAPTERS/sr130_10.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
