Pyritized Eocene diatoms were studied in the sediments of the "Argile de Saint-Aubin" Formation in the Saint-Josse (France) borehole. A new methodology was developed in the aim to extract pyritized diatoms from any type of sediments. The methods used facilitate extraction and concentration of a good quantity and quality of diatoms from sedimentary environments previously unfeasible in diatom analysis. The degree of pyritization, which transforms siliceous frustule to internal mold of pyrite and, by epigenesis, to pyritized frustule with conservation of the ornamentations, is described. Eighteen taxa of pyritized diatoms are identified.The assemblage of pyritized diatoms of the lithostratigraphic unit studied shows that the most frequent diatom observed is Fenestrella antiqua associated with Actinoptychus senarius and Craspedodiscus moelleri. Their presences indicate that the paleoenvironment was brackish with marine influence in Lowermost Eocene.
Assemblages of brackish and marine diatoms have been examined from Upper Paleocene-Lower Eocene strata of the Belgian Basin (Knokke well) and the Dieppe-Hampshire Basin (Saint-Josse borehole and Ailly sections). The diatoms observed are invariably preserved in pyrite as internal moulds and their siliceous skeletons are completely replaced by pyrite by epigenesis. Three major diatom assemblages have been observed which can be used to approximate the position of the recently defined Paleocene-Eocene boundary (defined by the Carbon Isotope Excursion).This isotope excursion occurs just below the strong increase in the abundance of Fenestrella antiqua and in the vicinity of the abundance peak of Coscinodiscus morsianus var. moelleri. They also allow correlations of the lithostratigraphic units of the Belgian Basin with the formations of the DieppeHampshire and central North Sea Basins. For instance, investigations of diatoms recorded in the Knokke Clay Member of the Knokke well indicate that this unit corresponds to the lower units of the 'Sparnacian fades' of the Dieppe-Hampshire Basin and to the Sele Formation of the North Sea Basin.
Assemblages of brackish and marine diatoms have been examined from Upper Paleocene-Lower Eocene strata of the Belgian Basin (Knokke well) and the Dieppe-Hampshire Basin (Saint-Josse borehole and Ailly sections). The diatoms observed are invariably preserved in pyrite as internal moulds and their siliceous skeletons are completely replaced by pyrite by epigenesis. Three major diatom assemblages have been observed which can be used to approximate the position of the recently defined Paleocene-Eocene boundary (defined by the Carbon Isotope Excursion). This isotope excursion occurs just below the strong increase in the abundance of Fenestrella antiqua and in the vicinity of the abundance peak of Coscinodiscus morsianus var. moelleri. They also allow correlations of the lithostratigraphic units of the Belgian Basin with the formations of the Dieppe-Hampshire and central North Sea Basins. For instance, investigations of diatoms recorded in the Knokke Clay Member of the Knokke well indicate that this unit corresponds to the lower units of the ‘Sparnacian facies’ of the Dieppe-Hampshire Basin and to the Sele Formation of the North Sea Basin.
Background and aims -Aulacoseira sphaerica (Hérib.) Simonsen is described from samples of a boring made in a Late Pliocene freshwater maar sediments in Nogaret (Escandorgue volcanic massif, France). This species is described and compared with works of other authors. Methods -The morphology of this species is examined using light microscopy (LM) and scanning electron microscope (SEM). Key results -Our observations correspond with Héribaud's (1903) description of Melosira sphaerica. It is an initial cell of an unknown Aulacoseira that is either extinct or does not form auxospores in recent waters. But we do not agree with Loseva's (1980) identification of this species found in the upper Pliocene deposits from the locality Omara (Russia) in the Kama river (Volga's tributary) basin. Conclusion -A. sphaerica remains considered as a Late Pliocene fossil, endemic in the south of France (Massif Central, Escandorgue).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.