Isotopic ages, magnetostratigraphy, and biostratigraphy from the early Pliocene Suva Marl, Fiji

The Suva Marl, Fiji, is early Pliocene in age from biostratigraphical data. Within the 180-m sequence occur a number of tuffaceous beds, from some of which biotite has been separated and used for K-Ar dating. The measured isotopic ages, when plotted against stratigraphic position within the Suva Marl, yield a good straight-line relation. This implies that deposition occurred at the rate of 83.2 (±5.1) m/m.y., and that the formation was deposited 5.2 to 3.2 Ma. Calcareous nannoplankton allow identification of several zonal boundaries with the following estimated ages: NN.12/NN.13 (CN10b/CN10c) = 4.82 Ma or slightly younger, NN.14/NN.15 (CN10c/CN11) = 3.86 Ma, and NN.15/NN.16 (CN11/CN12) = 3.56 Ma. Planktonic foraminiferal datum planes have proved difficult to locate closely, apart from the first coiling-direction change of Pulleniatina, which took place at ∼3.93 Ma, the base of zone N.21, the age of which we estimate to be 3.2 Ma or slightly younger, and the Sphaeroidinellopsis extinction datum, which is only marginally older.