Calcareous nannofossil biozonation of the Miocene and revision of the helicoliths and discoasters

摘要: "Calcareous nannofossils" form a heterogeneous group of minute calcareous objects that range in size from 1 to 30 microns. The majority the fossils resemble coccoliths exterior calcareous cover (coccosphere) the Haptophyceae and therefore it is generally accepted these fossils are remains of such unicellular algae. Reviews basic information about nannofossils have been published by Hay (1977), Gartner Haq (1978), Tappan (1980) and Lord Taylor (1982). The recognition as worthwhile tool for biostratigraphic correlations credited Bramlette his coworkers Riedel, Sullivan, Martini Wilcoxon (1954-1967). Following these pioneering efforts, intensive taxonomic biostratigraphic studies of calcareous been carried out, formed the basis for several biozonal schemes Mesozoic Cenozoic Systems. The zonations far more refined than ones, mainly owing great number sections with well-preserved nannofossil content obtained coring deep ocean sediments. The two comprehensive most frequently used the compilations (1971) Bukry (1971,1975). Although both zonal so provided good working basis biostratigraphic correlations, they not applicable everywhere. Neogene Mediterranean area has proved especially hard calibrate standard Zonations open oceans. Our investigation was concentrated on Miocene Mediterranean sections, firstly because numerous land cores this interval were either available Utrecht collections or easily accessible, and secondly "standard" were inadequate Mediterranean region. As fragmentary, large number of studied order interval completely and check reproducibility our initial results. This study led composition new "Mediterranean Zonation" (fig. 44). The applicability data sections was checked some DSDP extra-Mediterranean areas. use markers combination conventional ones we found resulted general biozonal scheme: "Integrated Zonation" (fig. 45). A amount gathered during progress of investigation. all taxa encountered chose make a thorough revision taxonomy two major groups, namely helicoliths and discoasters. As findings concerning ultrastructure nannoliths groups (chapters 4 5). Both chosen their rich diverse representation in samples. In complete knowledge about these nannofossil reconstruct "evolutional patterns" expanded our incorporating pre-Miocene postMiocene sections samples 2).