Tertiary calcareous nannofossils from the central and southern North Sea Basins, and their biostratigraphical application
Material from the Tertiary of 12 released Shell/Esso exploration wells from the central and southern North Sea basins was studied (739 samples) to elucidate on the distribution and character of calcareous nannofossils in this commercially valuable area. The biostratigraphical distribution of the calcareous nannofossils is outlined, together with brief remarks on the lithology and wireline log responses in each well. Remarks on the distribution of foraminifera were supplied by G. K. Gillmore as part of a parallel study. Comparative material from sites in southern England (London Clay Formation, North London; Thanetian, Pegwell Bay; and Palaeogene of the Isle of Wight), Alabama (Lone Star Cement Quarry, St. Stephen's), New Zealand (William's Bluff near Oamaru, and Hampden Beach), South Atlantic (DSDP 36-329-29-1,36-329- 30-2), Hatton-Rockall Basin (DSDP 12-117-2-3), and Blake Plateau off Florida was also used during the study (70 samples). These localities were selected and analysed for correlation of stratigraphical levels (e. g. Late Oligocene of the Hatton-Rockall Basin), for comparison with low latitude assemblages at certain stratigraphical levels (e. g. Late Eocene of Alabama) or for close examination and scrutiny of species of Reticulofenestra (e. g. Hampden Beach, New Zealand). A brief overview of previous work in this area, the geological history of the North Sea Basin, and the development of oil exploration is given together with sampling strategies and procedures in the introductory chapter. A new method for examining the same specimen in both light and scanning electron microscopes is established which utilises materials and methodology routinely employed in nannopalaeontology, thus enabling the maximum amount of information to be derived from each specimen. Each well is discussed individually in sections relating to blostratigraphically important levels. The lithology, wireline log responses, and foraminiferal data (where available) are used to supplement and complement the calcareous nannofossil data and to build up an outline stratigraphy for each well (see Figs. 22-31). The result of the biostratigraphical study is the proposal of a biozonation scheme for the central and southern North Sea Basins (NS zones 1-23, largely based on the FDO of species) which covers more of the Tertiary, in finer detail, than any of the previously published schemes, and a tentatively proposed joint calcareous nannofossil/foraminifera b1ozonation scheme. The NS (abbreviation for North Sea) biozonation scheme is compared with the established schemes for north-west Europe and with those of supposed wider applicability. Using the scheme as a tool of correlation the extensive formations of the North Sea Basin are compared and contrasted with the restricted and often facies variable outcrops of northwest Europe. The taxonomic section is reduced in the interests of brevity, as the majority of the species encountered are established in the literature, however, a detailed examination of the Family Noelaerhabdaceae, in particular the genus Reticulofenestra, was undertaken and comment made on the taxonomy, structure and evolution of the group. The definition of this genus is emended and a comprehensive compendium of species produced to facilitate cross-referencing of forms.