Late Eocene to Pleistocene planktonic foraminifers from Leg 120 Holes 747A and 749B on the Kerguelen Plateau were quantitatively analyzed. Microperforate tenuitellid forms dominate the Oligocene to middle Miocene, and 17 species (including the new species Tenuitella jamesi and Tenuitellinata selleyi) are recorded.A lineage zonation of tenuitellid foraminifers is proposed as an alternative scheme for refinement of the Oligocene-Miocene biostratigraphy in high latitudes. Progressive or abrupt alterations in morphological characters within this lineage, producing different morphotypes or species, coincided with prolonged or sudden changes in paleoclimate. These microperforate planktonic foraminifers thus appear to have potential as indicators of cold-water masses and temperature fluctuations in post-Eocene oceans.
Cassigerinelloita amekiensis Stolk occurs abundantly in lower middle Eocene samples from the Southern Kerguelen Plateau, drilled during Ocean Drilling Program Leg 120 (Hole 749B). It showed little morphological change during its rather short evolutionary history. Because of its microperforate, pustulate wall and a triserial, pseudoplanispiral coiling mode, C. amekiensis appears to be related closely to co-occurring Guembelitria triseriata (Terquem). These affinities indicate that the taxa are phylogenetically related and should be classified together in the family Guembelitriidae. The potential paleoceanographic importance of these forms is also discussed.
Studies of high-latitude planktonic foraminiferal faunas indicate that certain biostratigraphic problems may be resolved by the application of bioevents among the three microperforate families, Guembelitriidae, Chiloguembelinidae and Tenuitellidae. With the aid of the scanning electron microscope, these small tests appear to be useful stratigraphic markers in the condensed sequences of deep-sea cores, where their evolution can be correlated with magnetostratigraphy.In the early-mid-Eocene, the Jenkinsina-Cassigerinelloita lineage assists the recognition of zones based on the larger, muricate Acarinina. Four zones are proposed in a revised lineage zonation of the tenuitellids, presented as a complementary biostratigraphic scheme for differentiating the Eocene-Oligocene boundary interval in high latitudes: (1) the Praetenuitella insolita Zone in the late Eocene; (2) the Tenuitella gemma Zone in the early Oligocene; (3) the Tenuitella munda Zone in the mid-Oligocene; (4) the Tenuitellinata angustiumbilicata Zone in the late Oligocene.
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