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Michael Streng, Tania Hildebrand-Habel, Helmut Willems:
Cenozoic evolution of calcareous dinoflagellates in the eastern Indian Ocean (ODP Legs 120 and 122)
(Talk)

Two cores from the E (ODP Leg 122, Hole 761B) and the SE Indian Ocean (ODP Leg 120, Hole 747A) have been analysed, to study the Cenozoic evolution and morphological variability of calcareous dinoflagellates. The studied samples cover the stratigraphic interval from the Late Cretaceous to Quaternary. More than 50 morphotypes have been identified, of which five are new. Distinctive stratigraphic boundaries and times of global climatic changes, e.g. the K/T boundary and the Paleocene/Eocene boundary, were of special interest, as previous studies have shown significant shifts in calcareous dinoflagellate associations during these times (e.g. Hildebrand-Habel et al., 1999; Hildebrand-Habel & Willems, 2000). These shifts are generally reflected in changes in the dominant wall-type. Upper Maastrichtian associations are characterised by species with an oblique wall-type, in contrast to earliest Paleocene associations, which are dominated by the tangential wall-type. The Paleocene/Eocene boundary in Leg 122 is coupled with a 'revival' of the oblique wall-type, a trend which seems to continue until the Middle Eocene. The shift to modern associations is probably connected to the Miocene/Pliocene boundary. By comparing Late Miocene and Late Pliocene samples, a distinctive change in the associations of calcareous dinoflagellates, as well as a decrease of the cysts' diameter have been recognised. However, further detailed studies, which are currently in progress, have to show if this change is: 1) definitely connected to the Miocene/Pliocene boundary; 2) possibly a mid-Pliocene event; or 3) a gradual development during the Pliocene.

References

Hildebrand-Habel, T. & Willems, H. 2000. Distribution of calcareous dinoflagellates from the Maastrichtian to early Miocene of DSDP Site 357 (Rio Grande Rise, western South Atlantic Ocean). International Journal of Earth Sciences, 88: 694-707.

Hildebrand-Habel, T., Willems, H. & Versteegh, G.J.M. 1999. Variations in calcareous dinoflagellate associations from the Maastrichtian to middle Eocene of the western South Atlantic Ocean (São Paulo Plateau, DSDP Leg 39, Site 356). Review of Palaeobotany & Palynology, 106: 57-87.

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