1,721,013 research outputs found
Palynological analyses of Eocene to Oligocene sediments from DSDP Site 338, Outer Voring Plateau
No full text(Appendix B) Dinoflagellate cysts occurrence in DSDP Hole 38-33
Cretaceous (Albian–?early Santonian) palynology and stratigraphy of the Abu Tunis 1x borehole, northern Western Desert, Egypt
No full textA palynological analysis has been conducted on the Cretaceous sediments of the Abu Tunis 1x borehole, in the northern Western Desert, Egypt. The palynomorphs recovered have been analysed both qualitatively and quantitatively, and permit a refinement of the original stratigraphy with the identification of four time-rock units. These have been divided into four informal sporomorph units and one dinoflagellate cyst palynozone. These biozones are, from oldest to youngest: the Afropollis jardinus-Tricolporopollenites-Elaterosporites klaszii Assemblage Zone (early–mid Albian), the Elaterosporites verrucatus-Sofrepites legouxae-Cretacaeiporites Assemblage Zone (late Albian–early Cenomanian), the Sofrepites legouxae Partial Range Zone (early–?mid Cenomanian), the Proteacidites cf. africaensis Total Range Zone (mid–late Cenomanian) and the Canningia senonica Total Range Zone (early? Santonian). A barren interzone has been identified immediately below the youngest palynozone, and this may be related to the unfavourable lithology (i.e., limestone and dolostone). The absolute abundances of spores and pollen represent the first quantitative description of an Egyptian Albian–Cenomanian palynofloral, a flora that is characteristic of the Albian–Cenomanian Elaterate Phytogeographical Province. The early Santonian palynoflora is exclusively marine phytoplankton; terrestrial palynomorphs representative of the Senonian Palmae Province are completely absent. The quantitative and semi-quantitative distributions of Afropollis jardinus are compared with similar semi-quantitative distributions of this species from other wells in the northern Western Desert of Egypt, and this permitted the identification of a mid Albian–early Cenomanian Afropollis jardinus ‘acme’ as an important local biostratigraphical event in the mid Cretaceous
Early Cretaceous palynostratigraphy of the Abu Tunis 1x borehole, northern Western Desert, Egypt, with emphasis on the possible palaeoclimatic effect upon the range of Dicheiropollis etruscusin North Africa
No full textRecent hydrocarbon exploration in the northern sector of the Western Desert in Egypt has revealed relatively rich hydrocarbon accumulations, mainly of gas, and demonstrate promising future prospects. In order to improve our understanding of this area and to provide a biostratigraphical framework for the hitherto poorly dated Lower Cretaceous successions, a palynological analysis was carried out on 57 ditch cutting samples from the Abu Tunis 1x borehole. Palynostratigraphic investigation on these samples has enabled the identification of three new palynostratigraphically defined age divisions with three corresponding palynozones defined by first uphole occurrences of gymnosperm and angiosperm pollen and dinoflagellate cysts. Spore and pollen grains recovered from the Abu Tunis 1x borehole show the characteristics of the pre-Albian Dicheiropollis/Afropollis Phytogeographical Province. Discrepancies in the reported range of Dicheiropollis etruscus, when compared with earlier (Berriasian) appearances in West Africa and later (late Hauterivian) appearances in East Africa, may be attributed to palaeoecological factors. Dicheiropollis etruscus is accepted as having a cheirolepidiacean conifer affinity and is regarded as having been produced by a thermophilous plant. Here, we suggest that Dicheiropollis etruscus was adapted to arid conditions. Dicheiropollis etruscus thus first appeared in hot, dry palaeo-subtropical African regions, but as Western Gondwana broke up and the African Plate moved northeast during/after the Late Jurassic, the region that is now present-day Egypt, Libya and Sudan had moved by the late Hauterivian into a subtropical position; the ensuing increased aridity thus allowed Dicheiropollis etruscus to migrate into these areas
The Gonyaulax spinifera (Dinophyceae) “complex”: Perpetuating the paradox?
No full textSpecimens of dinoflagellate cysts referable to the cyst-species Spiniferites ramosus (Ehrenberg 1838) Mantell 1854 and Nematosphaeropsis labyrinthus (Ostenfeld 1903) Reid 1974 have been produced in the same crossed-strain of Gonyaulax spinifera-type (Claparède and Lachmann 1857) Diesing 1866 motile cells during a routine encystment experiment. Detailed observations were made and are reported on the process of encystment, which follows a similar pattern to that already described for Lingulodinium polyedrum. Both cyst types displayed a wide range of morphological variations with respect to process length and/or trabecular development. The cysts morphology vary between “typical” S. ramosus specimens with well developed trifurcate processes with bifurcated distal ends, to specimens with abnormally developed or incomplete processes, specimens with partially developed trabecular network, to typical N. labyrinthus specimens with a complete network of trabecula joining the distal ends of the processes. The cysts were produced in salinities of 25 and 30 psu at 12 °C. Experiments in other salinities (15, 20, 35 and 40 psu) only produced cysts of S. ramosus-type. We suggest that the particular salinity conditions (25 and 30 psu) used in our experience probably triggered the expression of a particular phenotype.<br/
The composition and diversity of dinosporin in species of the Apectodinium complex (Dinoflagellata)
No full textOrganic-walled dinoflagellate cysts, produced as a result of sexual reproduction, are important tools for studies on recent and past environments. Additionally, the organic-walled cysts can be used as proxies for understanding the composition and chemical transformations of marine kerogen, the largest global organic carbon pool. However, any usage of dinoflagellate cysts in this manner is predicated on an understanding of the composition and transformations of this potential proxy. Dinoflagellate cyst walls are composed of “dinosporin”, a refractory biomacromolecule that probably represents a suite of chemically distinct biopolymers. In order to investigate both the nature of dinosporin and the extent to which the composition of this biomacromolecule may differ between dinoflagellate cyst taxa, we analyzed cyst species from the genus Apectodinium. The species defined within this genus are visually similar with several seeming to represent end-members along a continuum of morphological variation. Micro-Fourier transform infrared (FTIR) analysis was performed on three of these morphospecies (identified visually as A. paniculatum, A. parvum and A. augustum) from two regionally distinct samples. The analyses showed consistent patterns with clear differences between the species. The dinosporin of A. paniculatum closely resembles cellulose and is rich in ether bonds (Csingle bondO), while the dinosporin of A. augustum contains more carboxyl (COOH) groups. A. parvum appears intermediate in many respects, despite representing an end-member in terms of morphology. These differences are consistent regardless of the regional setting or post-depositional conditions, and strongly suggest that the original cyst wall composition of the species differed when the cysts were formed. These data are the first to clearly show differences in cyst wall composition between species of the same genus and indicate that the chemical diversity of dinosporins is greater than previously thought
Magnetostratigraphic calibration of Eocene-Oligocene dinoflagellate cyst biostratigraphy from the Norwegian-Greenland Sea
No full textThe presence of abundant age-diagnostic dinoflagellate cysts in Ocean Drilling Program (ODP) Hole 913B (Leg 151), Deep Sea Drilling Project Hole 338 (Leg 38) and ODP Hole 643A (Leg 104) has enabled the development of a new biostratigraphy for the Eocene–Oligocene interval in the Norwegian–Greenland Sea. This development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution. In parallel with this biostratigraphic analysis, we developed a magnetic reversal stratigraphy for these Norwegian–Greenland Sea sequences. This has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale (GPTS). The relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the North Sea and the North Atlantic, which allows regional correlation. Correlation of each site with the GPTS has also allowed comparison of the stratigraphic record preserved in each drill-hole. Hole 913B is the most complete and is the best-preserved record of the Eocene and Oligocene in the Northern Hemisphere high latitudes, and can serve as a reference section for palaeoenvironmental reconstructions of this age interval
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Palaeogene and Neogene cold seep communities in Barbados, Trinidad and Venezuela: an overview
No full textPalaeogene and Neogene fossiliferous carbonates from Barbados, Trinidad and northern Venezuela are interpreted to have formed at ancient cold seep sites. The hydrocarbon seepage that fuelled these chemosymbiotic ecosystems was related to tectonic activity in the southern Caribbean region, particularly the subduction of the Caribbean Plate beneath the North Atlantic Plate. The carbonates and fossils from the Scotland District, north-eastern Barbados, are Eocene–Miocene in age and are associated with two distinct tectonic units: the Sub-Oceanic Fault Zone and a diapiric mélange. The Sub-Oceanic Fault Zone is the tectonic junction between accretionary prism sediments and over-lying thrust sheets of fore-arc basin sediments. The loading of the thrust sheets caused methane-rich fluids to be expelled from the accretionary prism sediments and channelled to the sea floor via the Sub-Oceanic Fault Zone, where it supported chemosymbiotic invertebrate communities containing vesicomyid, lucinid, thyasirid, solemyid and nuculanid bivalves, a variety of gastropods and possibly vestimentiferan tube worms. The diapiric mélange is considered to represent sediment that failed under pressure in the accretionary prism and was remobilised as a diapir that extruded onto the sea floor, providing a conduit for methane and other hydrocarbons that sustained a chemosynthesis-based community of vesicomyid, lucinid and nuculanid bivalves and various gastropods. The geological setting of fossiliferous carbonates known as Freeman's Bay Limestone, in southwest Trinidad, has been less fully investigated. The Freeman's Bay Limestone is a member of the Miocene Lengua Formation, which is believed to have formed in a fore-deep basin on-lapping onto an accretionary prism formed by the subduction of proto-Caribbean crust beneath the South American Plate. The carbonates and fossils of the FBL, including the bivalves Pleurophopsis unioides Van Winkle, 1919 and Thyasira adoccasa Van Winkle, 1919, lucinids, nuculanids and bathymodiolins, and provannid and other gastropods, are interpreted to have formed at palaeo-seep sites on the accretionary prism. Little is currently known about the geological setting of the fossils collected from the Miocene Huso Member of the Pozon Formation, from northern Venezuela, but a seep origin is strongly suspected based on the taxa present. Like the fossil assemblages from Barbados and Trinidad, the Venezuelan material is dominated by vesicomyid bivalves, together with lucinid, thyasirid, bathymodiolin and solemyid bivalves and various gastropods. These taxa are characteristics of modern cold seep communities. Most comparisons between the fossil Caribbean and modern seep fauna are necessarily at the generic or family level, although in some cases, individual species are found at both ancient and modern seep sites. For example, the gastropod Cataegis meroglypta is found in seep carbonate from the SOFZ of Barbados and the FBL of Trinidad as well as at modern seeps on the Barbados Prism. At the generic level, this study has revealed the first fossil occurrences of Abyssochrysos and Provanna in the Caribbean. Such temporal and spatial links further the understanding of both local and global patterns of biogeographic distribution of cold seep fauna
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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