Über die chemische Zusammensetzung der Flüssigkeit in den Ascidien von Nepenthes

Von Dr. A. Bölcker

Kannenblätter 3 : Sarracenia purpurea - Nepenthes wilsoni

AR

Nepenthes : neueste Novellen und Erzählungen.

Mode of access: Internet.

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.

Planktonic foraminifera at DSDP Holes 72-516 and 72-518

Quantitative analysis was performed on the Quaternary planktonic foraminiferal fauna from Site 516, near the crest of the Rio Grande Rise, and Site 518, on the lower western flank of the Rise. From Hole 516, 46 samples were taken, and from Hole 518, 80 samples were taken. The mean interval between samples is 20 to 25 cm. About 50 species of Quaternary and Pliocene planktonic foraminifers were identified. Quaternary sediments, dated by the initial evolutionary appearance of Globorotalia truncatulinoides and other criteria, have thickness, of 9.8 m in Hole 516 and 16 m in Hole 518. The Globorotalia truncatulinoides Zone is subdivided into four subzones or biostratigraphic horizons (from lower to upper): (1) Globorotalia crassaformis viola, (2) Globorotalia crassaformis hessi, (3) Globigerina calida calida, and (4) Globigerinoides ruber (pink). Thickness of these horizons in Hole 516 establishes the age of the boundaries between them as 1.47, 0.81, and 0.28 Ma, respectively. All the Quaternary planktonic foraminiferal complexes sampled are subtropical. The region of the Rio Grande Rise, therefore, has been within the southern subtropical gyre continuously for the last 2 Ma. The average annual surface water temperatures were reconstructed for the Quaternary at both sites. A micropaleontologic method for the paleotemperature analysis of the thanatocoenosis registers an average Quaternary temperature of 21.2°C at Site 516 and 21.7°C at Site 518. The temperature fluctuations increase up to 3.5°C during the accumulation of the two last horizons (since 0.81 Ma). Temperature peaks are tentatively compared with oxygen isotopic stages and with continental glaciations. Levels at which planktonic foraminiferal species disappear correspond to coldwater intervals. In the Quaternary of Site 518, some layers show signs of dissolution. Corrosive to CaCO3, the northward flow of Antarctic Bottom Water through the Vema Channel increases during the cold periods. Site 518 has two layers of redeposited foraminiferal sand with Pliocene foraminifers. The average rate of the Quaternary sedimentation in Hole 516 is 0.52 cm per thousand years, and in Hole 518 it is 0.84 cm per thousand years.

Miozene larger foraminifera in ODP Leg 133 holes

The Marion Plateau is a large carbonate platform off northeastern Queensland. Three sites (815, 816, and 826) were drilled on this platform and form the basis for this study. Larger benthic foraminifers, together with rare planktonic forms from the shallow-water carbonates that form the main part of the platform sequence, were studied to establish a biostratigraphy. The presence of Lepidocyclina (Nephrolepidiná) howchini sensu lato and Ladoronia vermicularis, together with Globorotalia (Globorotalia) praemenardii and Orbulina, indicate an early middle Miocene (N9-N12) age (i.e., lower Tf stage) for these carbonates. Dolomitization has destroyed much of the original fabric of these carbonates, making study of the larger foraminifers difficult. Sites 815 (forereef location) and 826 (backreef, lagoonal setting) provide the best faunas. However, at all sites nodular coralline algae and Halimeda are the major bioclasts; coral fragments form a major component at Sites 816 and 826. The middle Miocene neritic sequence is separated from the overlying hemipelagic sequence by an unconformity that spans much of the middle and late Miocene. At Site 815, which is in a forereef situation, the overlying hemipelagic sequence contains a Zone N17A fauna, but at Site 816, higher on the platform, a similar sequence contains a Zone N19 fauna. The faunas indicate that the platform was built up during the early middle Miocene and remained at fairly constant water depths and temperatures during this period. It was then exposed prior to subsiding rapidly during the late Miocene and Pliocene to depths similar to those of the present day.