English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

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. INTRODUCTION Ocean 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, 1974, 1982; Manum and Cookson, 1964). These previous studies, however, were chiefly concerned with systematic descriptions, and the various zonation schemes proposed by several authors (Edgell, 1964; Evans, 1966; Morgan, 1977; among others) are based mainly on data from wells in different basins. Not until the mid-1980s was a more complete zonation scheme given by Wilson (1984) for New Zealand and by Helby et al. (1987) for Australia. These zonation schemes have provided 1 Wise, S. W., Jr., Schlich, R., et al., 1992. Proc. ODP, Sci. Results, 120: College Station, TX (Ocean Drilling Program). 2 Graduate School, China University of Geosciences, Beijing 100083, China (current address: Department of Geology, Florida State University, Tallahassee, FL 32306, U.S.A.). 3 ETH-Zürich, Geological Institute, 8092 Zurich, Switzerland. palynologists with important criteria for stratigraphic correlation. Site 748 provides a unique, nearly continuous section of Cenomanian-Maestrichtian sediments that contains nannofossils and foraminifers as well as palynomorphs. The dating of the section is, therefore, more precise, as it is based on well-documented multidisciplinary calcareous microfossil chronostratigraphy. As a result, this study will add more information to what is already known about dating and correlating dinoflagellate zones in this region and should enhance the value of the zonation schemes proposed by Wilson (1984) and Helby et al. (1987). The sediments from Hole 748C were divided into four units (Schlich, Wise, et al., 1989). A detailed description of the upper two lithologic units ranging from Pleistocene through Paleocene (Cores 120-748C-1R through 120-748C26R), the basal unit, and the basal two subunits of Unit III ranging from Cenomanian to Santonian (Core 120-748C-78R through Section 120-748C-62R-CC) is found in Schlich, Wise, et al., 1989). Samples for the present study are from the upper two Subunits IIIB and IIIA of ?Santonian through Maestrichtian age (from 407 to 740 m below seafloor (mbsf); Core 120-748C-27R through Section 120-748C-62R-4). They consist of glauconitic rudstones, packstones, and grainstones, intermittently silicified, with intervals of abundant bryozoans, inoceramid prisms, and crinoid columnals and rare red algal debris (Fig. 2). MATERIALS AND METHODS The samples studied from Core 120-748C-27R through Section 120-748C-62R-4 are mainly glauconitic sandstones, siltstones, and claystones. One or two samples were processed from each core, and about the same volume of rock was used for each processed sample. Samples were processed using standard maceration and centrifuge preparation tech-

Late Cretaceous Dinoflagellate Cysts (?Sanonian-Maestrichtian) from the Southern Indian Ocean (Hole 748C)