Calcareous nannoplankton diversity varied greatly during the Paleogene. From extremely reduced values (~10 species) in the early Paleocene (circa 66.4 to 66 Ma, age estimates from Berggren, Kent and Flynn, 1985) following the terminal Cretaceous extinctions, diversity increased progressively throughout the late Paleocene and early Eocene and reached a maximum (~120 species) in the early middle Eocene (circa 52–48 Ma). This was followed by a step-like decrease until the early Oligocene (circa 35 Ma) when minimal values (~37 species) were reached once again. After a stable low during the remainder of the early Oligocene, a moderate, increase occurred near the early/late Oligocene boundary (circa 30 Ma). Temperature has been regarded as the most important factor controlling the distribution of the calcareous nannoplankton following the characterisation of five temperature-controlled assemblages of living Coccolithophoridae in the Atlantic Ocean. Studies relative to variations in diversity in the calcareous nannoplankton throughout the Mesozoic and Cenozoic and among the extinct late Paleocene to Pliocene group Discoaster , and to changing biogeographic patterns during the Cenozoic have revealed an apparent relationship between composition of calcareous nannofossil assemblages and temperature as deduced from isotopic studies. This relationship, which is currently used to infer Paleogene climatic and oceanographic evolution from quantitative analyses of calcareous nannofossil assemblages, is however not a simple one as indicated by the fact that maximum diversity during the Paleogene (i.e., the early middle Eocene) did not occur during (but subsequently to) the warmest time (i.e., the latest Paleocene-earliest Eocene). Diversity changes in the Paleogene calcareous nannoplankton are strikingly similar to diversity changes in the Paleogene planktonic foraminifera, which have been shown to reflect fluctuations in nutrient availibility as indicated by oxygen and carbon isotopes. The parallel evolution in the two groups thus suggests that trophic levels in the photic zone played an important role in the Paleogene diversification of the calcareous nannoplankton. In the present day ocean, the calcareous nannoplankton (Coccolithophoridae) dominate the phytoplankton under oligotrophic conditions and tropical waters are characterized by highly diversified associations with strong vertical specific stratification. Only few species occur under meso- and eutrophic conditions, and there is no vertical stratification. Extremely low diversity during the earliest Paleocene followed by increasing diversity through the Paleocene and earliest Eocene is interpreted as reflecting the change from an essentially mesotrophic to an oligotrophic ocean, increased rates of speciation resulting from niche partitioning occasioned by increased oligotrophy, leading to strong vertical stratification of species in the photic zone. Decrease in diversity from middle Eocene to early Oligocene reflects, on the other hand, progressive eutrophication of the ocean as a result of climatic deterioration.
Carbon isotopic studies conducted on the upper Paleocene (Thanetian) and lower Eocene (“Sparnacian"—Ypresian) of the Paris Basin allow us to place the lithostratigraphic succession of the Mont Bernon Group in a spatial and temporal framework. The d13C (negative) carbon isotope excursion (CIE) associated with the Paleocene/Eocene Thermal Maximum (PETM) in marine sections at the NP9a/b calcareous nannoplankton zonal boundary and also in terrestrial stratigraphies, occurs in the Mortemer Formation, below the Vaugirard Formation. Moreover, a characteristic isotopic signature with stratigraphically successive negative and positive peaks permits a refinement in correlation betweeen the diverse members of the Mont Bernon Group. The strongly positive values (in upper Zone NP9) are found in the Meudon Member (Conglomerat de Meudon). These results imply that: (1) the Meudon Member constitutes the base of the Vaugirard Formation, but not the base of the Sparnacian “Stage"; (2) the mammal fauna of the Meudon Member (=late Biochron NP9) is somewhat younger than that of the basal Wasatchian North American Land Mammal Age (NALMA; which is stratigraphically correlative with, or even slightly older than, mid-Biochron NP9); (3) the base of the Sparnacian “Stage" of the Paris Basin is slightly older than the base of the Wasatchian NALMA and only marginally younger than the Chron C24r/C25n boundary. Moreover, the carbon isotopic signature suggests correlation of the Reading 1 beds/facies of the London Basin with the Mortemer Formation and Reading 2 beds with the lower part of the Vaugirard Formation of the Paris Basin. With the recognition that the Sparnacian is confined to the ca. 0.85 m.y.-long stratigraphic interval between the CIE at its base and the FAD of Tribrachiatus digitalis at the base of the Ypresian, and that it is inappropriate to lower the base of the Ypresian Stage by about 1m.y., we recommend (re)insertion of the Sparnacian Stage as the basal stage of the Eocene Series.
Les nannoflores calcaires conservees dans les formations epicontinentales paleogenes du Bassin anglo-parisien sont inventoriees et leur signification biostratigraphique est soigneusement analysee. Les etages definis dans le Bassin anglo-parisien (Thanetien, Cuisien, Lutetien, Bartonien, Ludien, Stampien) sont ainsi situes par rapport aux biozones a nannofossiles calcaires standard. Les correlations sont plus ou moins precises selon l'etage considere, et des hiatus sont reconnus entre certaines unites chronostratigraphiques. Seules, les bases du Lutetien (partie superieure de la zone NP 14) et du Bartonien (partie superieure de la zone NP 16) peuvent etre situees en termes de biozones a nannofossiles calcaires. L'etude comparee de la repartition des biozones a nannofossiles calcaires dans l'ensemble de l'Europe du Nord-Ouest (Belgique, Allemagne du Nord, Danemark, Bassin anglo-parisien) revele leur inegal developpement, les unes etant tres largement developpees (NP 8, NP 11, NP 12, NP 14 a NP 16, NP 23) les autres etant mal representees (NP 9, NP 17, NP 18, NP 19-20, NP 22) ou inexistantes (NP 10, NP 13, NP 21). Cette repartition apparaissant correlable aux variations globales du niveau marin, l'histoire du Paleogene de l'Europe du Nord-Ouest est interpretee en fonction des variations eustatiques. La paleomagnetobiostratigraphie s'etant developpee au cours des dernieres annees, et la partie inferieure des formations paleogenes d'Angleterre ayant fait l'objet de recherches paleomagnetostratigraphiques, l'histoire paleogene du Bassin anglo-parisien est replacee dans un cadre synthetique global ou le paleomagnetisme constitue l'element chronologique et les variations eustatiques l'element dynamique.
While numerous studies have been devoted to the planktonic and benthic forami-nifera in the Neogene of Jamaica, little attention has been paid to the calcareous nannofossils. This contribution is thus a documentation of the calcareous nannofossils in the lower Miocene to upper Pliocene deposits of Jamaica. The Buff Bay section, the most extensive Neogene section in eastern Jamaica, is studied in great detail, and eight other sections, including the San San Bay and the Bowden type sections, are discussed as well. Current correlations between the zonal schemes established from calcareous nannofossils and planktonic foraminifera are discussed, based upon direct correlation between calcareous nannofossil and planktonic foraminiferal zones in these sections. Integration between calcareous planktonic microfossil stratigraphies, and magnetostra-tigraphy when available, leads to the delineation of regional unconformities and to the interpretation of the Neogene stratigraphic record of eastern Jamaica in terms of sequence stratigraphy. It is shown that the Buff Bay Formation, the San San Clay, and the Bowden Formation correspond to separate unconformable stratigraphic sequences. As a result, it is suggested that the San San Clay be regarded as a distinct formation rather than part of the Buff Bay or the Bowden formations as currently accepted. Several of the "holotype" and "paratype" localities that Blow (1969) designated for his Neogene planktonic foraminiferal zones (N-Zones) are located in Jamaica. Direct correlation between these and the calcareous nannofossil schemes of Martini (1971) and Okada and Bukry (1980) are established and the implications are discussed.
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