Palynology, micropalaeontology and geochemistry of the Eocene Rusayl Formation of Northern Oman

New palaeontological and geochemical data are presented for the Rusayl Formation of Northern Oman. Eocene palynomorphs (97 taxa) including many new to the Arabian Peninsula and a distinctive new ostracod assemblage (21 species including 11 new taxa) are described and key taxa illustrated. This represents the most diverse palynomorph assemblage yet recorded from the Eocene within the Arabian Peninsula area. Ostracods of this age are poorly known from the Middle East, with only one species from this area found in the Oman material, and a further three from western Pakistan. The palynology indicates a dominantly restricted shallow marine palaeoenvironment with distinct periods of strong marine influence during which dinocyst abundances increase markedly. The palynofloras are dominated by Nypa palm pollen typical of mangroves ( Spinizonocolpites and Proxapertites ). The palynofacies are dominated by cuticle and membrane material (leaf debris) and brown pseudoamorphous wood, indicating a marginal marine palaeoenvironment. The associated ostracod and foraminiferal assemblages broadly support these interpretations indicating a lagoonal to infralittoral environment of deposition. Nannofossils are recorded for the first time from the formation and support a Middle Eocene age for the upper part of the Rusayl Formation. Inorganic geochemistry indicates that the fine-grained siliciclastic intervals were largely derived from ophiolitic material and pre-Permian basement. Shales and coals contain common oil-prone lipid-rich cuticle and locally abundant gas-prone woody kerogen with pyrolysis S2 yields of up to 15.13 mg/g. Although thermally immature, the sequence is sufficiently buried by a sediment overburden exceeding 5 km in the offshore to generate hydrocarbons.