A Biostratigraphic Study of Jurassic Calcareous Nannofossils from Portugal and Great Britain.

• Main Author: Hamilton, G
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of London 1978
• Subjects: North Atlantic
• Online Access: https://discovery.ucl.ac.uk/id/eprint/1349289/1/457965.pdf; https://discovery.ucl.ac.uk/id/eprint/1349289/

It is intended that this study will contribute to the growing record of knowledge on the stratigraphic distribution of Jurassic calcareous nannofossils in order to extend their biostratigraphic and correlatory use. Over two hundred samples from six sections in Jurassic sediments from Portugal were examined in light and scanning electron microscopes. The taxonomic aspects of the flora were studied and the stratigraphic ranges of the species and their abundances were recorded. Four of the sections cover the Lower and Middle Jurassic and these are in fully marine facies. One of the Upper Jurassic sections, Torres Vedras, is also in marine sediments but the second, the Alcanede-Carvalhos Road Section reflects part of a regressive phase which culminated in the deposition of brackish water and non-marine sediments in the basin to the north of the River Tagus during the Upper Jurassic (oýr Lusitanian stage of Portuguese geology). The stratigraphic position of the two Upper Jurassic sections is not well known. It was hoped that the examination of the calcareous nannofossils in fifteen samples from a Callovian to Oxfordian section on the Isle of Skye and in 75 samples from three Upper Jurassic cores in the western North Atlantic. would enable correlation of species and thus resolve the question of the stratigraphic position of the Upper Jurassic Portuguese sections. In fact, it only proved possible to locate the Torres Vedras Section which was of Callovian to Lower Kimmeridgian age. In addition, fourteen samples from a Triassic to lowermost Jurassic (Hettangian) section from Watchet in North Somerset, England were examined in a preliminary investigation of the early calcareous nannofossil record. The group is generally accepted as first appearing in the Lower Jurassic but the Rhaetian. samples from Watchet contained a limited assemblage which showed that a pre-Jurassic record exists. Further evidence for this was found in a reconnaissance survey of Triassic sediment from Italy. finally, a biostratigraphic scheme is ...