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 Plus annual

Presents the access of premium content as premium feature

Premium Content

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 annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Site 765 contains a sequence of tropical, middle Miocene to Holocene dinoflagellate cysts. These diverse assemblages are characterized by abundant Polysphaeridium zoharyi and Spiniferites bulloideus. Abundances of Impagidinium spp. and Nematosphaeridium spp. reflect the shelf-to-slope origin of the assemblages. One new genus, Blysmatodinium, and two new species, Nematosphaeridiumi?) wrennii sp. nov. and Blysmatodinium argoi, are described. INTRODUCTION Dinoflagellate cysts are not typically abundant in deep-ocean sediments, but are normally associated with estuaries and the continental shelf and slope. The presence of rich assemblages on the Argo Abyssal Plain at Site 765 (Fig. 1) provides a good opportunity for studying outer-shelf and slope assemblages from the tropics. Comparatively few studies of Neogene dinoflagellate cysts have been done, and most of these are of Northern Hemisphere temperate and boreal assemblages. A summary of previously published Northern Hemisphere Neogene dinoflagellate data is presented in Head et al. (1989c). Published accounts from the Southern Hemisphere are limited to Deflandre and Cookson (1955) and Truswell et al. (1985) from Australia and Gamerro and Archangelsky (1981) from Argentina. Material from Leg 123 will provide data about poorly known Southern Hemisphere Neogene and tropical assemblages and will contribute to the development of a pan-Australian Neogene dinoflagellate cyst zonation (McMinn, in press, a). Two sites were drilled during Leg 123 (Sites 765 and 766); however, only Site 765 yielded Neogene dinoflagellate cyst assemblages. Site 765 is located in the eastern Indian Ocean on the Argo Abyssal Plain in a water depth of 5200 m. A 935-m-thick succession of Quaternary to Late Jurassic sediments was intersected; this has been divided into seven lithologic units. Unit I (0-190 m) consists of Quaternary to upper Miocene, redeposited, clayey calcareous sediments of pelagic origin with minor intercalated clays. Unit II (189-474 m) consists predominantly of Miocene, graded, redeposited calcareous sediment of pelagic origin. Unit III (474-591 m) consists of early Miocene to Cenomanian interbedded claystones, graded carbonate sequences, and matrixsupported carbonate conglomerates. METHODS Forty-two, approximately 20 cm, core samples were taken at approximately 10-m intervals, i.e., approximately one sample per core. Samples were initially disaggregated in HC1 and then left in HF for 8 hr. The residue underwent heavy liquid separation in zinc bromide solution (Sp. G. = 2.1) and was then sieved using a Gradstein, F. M., Ludden, J. N., et al., 1992. Proc. ODP, Sci. Results, 123: College Station, TX (Ocean Drilling Program). 2 N.S.W. Geological Survey, University of New South Wales, Kensington 2033, N.S.W., Australia. 3 Present address: Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Box 252C, Hobart 7001, Tasmania, Australia. 10-μm sieve with the aid of an ultrasonic needle. Residues were then mounted in glycerine jelly and are stored in the Micropalaeontology Collection of the N.S.W. Geological Survey. All dinoflagellate cysts in a preparation were counted, and these form the basis of the "Count" column in Table 1. Spore and pollen identification and distribution are discussed in McMinn and Martin (this volume). Complete species citations follow Lentin and Williams (1989). BIOSTRATIGRAPHY Sediments at Site 765 were initially deposited on the outer continental shelf and slope and have been redeposited at their present location on the Argo Abyssal Plain by density currents. The rapid sedimentation rate caused quick burial and thus preservation of the palynomorphs. Reworked nannoplankton and foraminifers are common (Ludden, Gradstein, et al., 1990), but little evidence exists of reworking of Tertiary dinoflagellates, although reworking from the Middle to Late Jurassic sequence is ubiquitous. Dinoflagellate ranges recorded here are consistent with those reported elsewhere, which suggests that reworking was insignificant. Rather than propose a formal zonation, which is unwarranted on the basis of a single hole, the sequence of dinoflagellate assemblages is discussed on the basis of age, as determined by comparison with the foraminifers and nannoplankton zonations (Ludden, Gradstein, et al., 1990). The ranges of individual species are then compared with their ranges documented elsewhere. Middle Miocene The oldest Tertiary assemblages recovered from Site 765 are of middle Miocene age. Compared with younger assemblages, lowermost middle Miocene samples (123-765C-9R-3, 13-14 cm, and -10R-4, 54-57 cm) are low in dinocyst abundance and diversity. Batiacasphaera micropapillata Stover, 1977 is found in both samples, with Polysphaeridium zoharyi (Rossignol 1962), Impagidinium patulum (Wall, 1967), Impagidinium paradoxum (Wall, 1967), Impagidinium aculeatum (Wall, 1967), Systematophora placacantha (Deflandre and Cookson, 1955), and Operculodinium janduchenei Head, 1989 are present in one or another of the samples. The middle Miocene assemblages from Samples 123-765C-8R-2, 61-67 cm, to -2R-3, 69-73 cm, and -39X-1, 46-52 cm, are more abundant and diverse and are typically characterized by abundant Polysphaeridium zoharyi and Spiniferites bulloideus (Deflandre and Cookson, 1955). Significant first stratigraphic occurrences include Pyxidinopsis sp., Nematosphaeropsis lemniscata Bujack, 1984, Dapsilidinium pastielsii (Davey and Williams, 1966), and Hystrichokolpoma rigaudiae (De-

Neogene Dinoflagellate Distribution in the Eastern Indian Ocean from Leg 123, Site 765