This study presents the
first detailed calcareous nannofossil assemblage data from the Late
Cretaceous succession of the subsurface Aruma Basin, north Oman. The
taxonomic description and documentation of assemblage composition are based
on extensive quantitative analysis of ditch cuttings and side-wall samples
from eight hydrocarbon exploration wells across north Oman. The samples
studied from those wells cover the Coniacian to earliest Maastrichtian deep
marine shales and marls of the subsurface Fiqa Formation. These fine-grained
siliciclastic deposits often yield moderately to well-preserved nannofossil
assemblages, especially in the Campanian intervals. Consequently, diverse
assemblages have been recorded from the Fiqa Formation, with a total
diversity of ∼200 species, including two new species,
Staurolithites ormae sp. nov. and Chiastozygus fahudensis
sp. nov., which are illustrated and described. Extensive imaging of this
diversity is provided here, as are stratigraphic distributions of the main
components from a key reference well in north Oman, W-4. Poorly described
groups such as Staurolithites are closely investigated and their
utility for stratigraphic applications is highlighted. Relative abundances of
nannofossil taxa with strong palaeoenvironmental preferences have revealed
new insights into the palaeo-productivity of the basin. High-fertility
species like Discorhabdus ignotus, Biscutum constans and
Zeugrhabdotus erectus show substantial variations in abundance
throughout the Fiqa Formation, reflecting long-term shifts in the
productivity conditions of the basin. This is supported by abundance patterns
of Watznaueria barnesiae and Micula staurophora that show a
broadly inverse correlation with the high-fertility species. The Fiqa
Formation represents a key regional seal unit for the Cretaceous hydrocarbon
reservoirs of Oman, as well as being a productive unit elsewhere in the
Arabian Peninsula. Beyond the Aruma Basin of Oman, this study will provide a
key reference point for future biostratigraphic or palaeoenvironmental
analyses of the Late Cretaceous calcareous nannofossil assemblages across the
Middle East and other southern Tethyan areas.</p