van den Akker, Theodora Johanna Hendrica Anna; (2001) Companion to palaeocene biostratigraphy and palaeoenvironments in the Foula Sub-Basin, West of the Shetland Islands (UK). Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Foula Sub-basin is part of the Faeroe-Shetland Basin, which is located on the North Atlantic margin, west of the Shetland Islands (UK). The Faeroe-Shetland Basin is a very important sea-way connecting the North Atlantic Ocean and Norwegian Sea. This basin was a major Cretaceous depocentre where thick successions of turbidite derived mudstones from the Upper Cretaceous Shetland Group accumulated. This area is of great interest due to several hydrocarbon findings. However, despite the need of a good biostratigraphic framework for dating these monotonous successions of mudstones, no biozonation scheme for the area has been published to date. In this study, ditch cuttings of four wells from the Foula Sub-basin were analysed for microfossils. Based on the succession of these microfossils, which include abundant and diverse agglutinated foraminifera, calcareous benthic and planktonic foraminifera, diatoms and radiolarians, a biozonation scheme for the Campanian to Palaeocene interval is proposed. The proposed Zonation contains 12 Zones: 1. Impoverished Zone: late Palaeocene. 2. Reticulophragmium pauperum Zone: late Thanetian. 3. Reticulophragmium pauperum - Ammoanita ruthvenmurrayi Zone: early Thanetian. 4. Spiroplectammina spectabilis Zone: Selandian. 5. Cenosphaera lenticularis Zone: Selandian. 6. Pseudotextularia elegans Zone: latest Maastrichtian. 7. Globigerinelloides volutus - Reussella szajnochae 2 Zone: late Maastrichtian. 8. Caudammina ovula - Remesella varians Zone: early - late Maastrichtian. 9. Globigerinelloides volutus - Reussella szajnochae 1 Zone: late Campanian. 10. Caudammina ovula - Caudammina ovuloides Zone: mid Campanian. 11. Fenestrella bellii Zone: early Campanian. 12. Inoceramus spp. Zone: Santonian. Despite some local differences, the biostratigraphy of the Foula Sub-basin compares well with the biostratigraphy of the Western Tethys, northern North Sea Basin and Norwegian margin, and is therefore an important link between the southern and northern areas of the North Atlantic margin. In addition to biostratigraphy, the record of microfossil assemblages is also a useful tool to give insight in the palaeobathymetric and palaeoenvironmental history of the Foula Sub-basin. The composition of the microfossil assemblages indicates that deposition of Campanian and Maastrichtian mudstones took place in a well oxygenated, lower bathyal marine environment with influxes of North Atlantic surface water masses. The occurrence of three late Campanian - late Maastrichtian calcareous foraminiferal rich intervals indicates periods of increased vertical circulation in the area during climatic maxima. A widespread early Palaeocene erosional event, which is induced by thermal uplift in the Faeroe-Shetland area in relation to the Icelandic mantle plume, results in an hiatus encompassing upper Maastrichtian to lower Palaeocene sediments. The deposition of Palaeocene sediments took place in a lower to upper bathyal environment.

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