At Ocean Drilling Program Hole 748C in the Southern Indian Ocean, a total of 171 Late Cretaceous dinoflagellate taxa were encountered in 38 productive samples from Cores 120-748C-27R through 120-748C-62R (407-740 mbsf). Four provisional dinoflagellate assemblage zones and five subzones were recognized based on the character of the dinoflagellate flora and the first/last occurrences of some key species. Isabelidinium korojonense and Nelsoniella aceras occur in Zone A together with Oligosphaeridium pulcherrimum and Trithyrodinium suspect urn. Zone B was delineated by the total range of Odontochitina cribropoda. Zone C was separated from Zone B by the presence of Satyrodinium haumuriense, and Zone D is dominated by new taxa. The dinocyst assemblages bear a strong affinity to Australian assemblages. Paleoenvironmental interpretations based mainly on dinocysts suggest that during the ?Santonian-Campanian to the Maestrichtian this portion of the Kerguelen Plateau was a shallow submerged plateau, similar to nearshore to offshore to upper slope environments with water depths of tens to hundreds of meters, but isolated from the major continents of the Southern Hemisphere. Starting perhaps in the late Cenomanian (Mohr and Gee, this volume), the Late Cretaceous transgression over the plateau reached its maximum during the late Campanian. The plateau may have been exposed above sea level and subjected to weathering during the latest Maestrichtian. The studied dinocyst assemblages characterized by species of Amphidiadema, Nelsoniella, Satyrodinium, and Xenikoon together with abundant Chatangiella (the large-size species) and Isabelidinium suggest that a South Indian Province (tentatively named the Helby suite) may have existed during the Campanian-Maestrichtian in comparison with the other four provinces of Lentin and Williams. One new genus, three new species, and two new subspecies of dinocysts are described.
INTRODUCTIONOcean Drilling Program (ODP) Site 748 is located on the Southern Kerguelen Plateau (58°26.45'S, 78°58.89'E) (Fig. 1) in a water depth of 1290 m. The objective at Site 748 was to recover an expanded section of Cretaceous and Paleogene sediments to decipher the tectonic and geologic history of this part of the plateau. To achieve this goal, it is necessary to date the seismic stratigraphic section precisely by paleontologic methods. Equally important is reconstruction of the environments under which the sediments formed. Dinoflagellates have proven useful in biostratigraphy and paleoenvironmental reconstruction because of their planktonic habit and their preservable organic-walled (some with calcareous or siliceous walls) cysts.Late Cretaceous dinoflagellates from the Southern Hemisphere, especially from Australia, have been studied for almost half a century, in particular by the late Isabel Cookson, often in association with coworkers (Cookson, 1956;Cookson and Eisenack, 1958, 1960a, 1960b, 1961, 1962, 1971, 1982Manum and Cookson, 1964). These previous studies, however, were chiefly concerned with s...