Late Neogene calcareous nannofossil biostratigraphy of the Gulf of Aden region

Abstract

The hemilpelagic sedimentary sequence in the Gulf of Aden has yielded a continuous succession of relatively well preserved late Neogene nannofossils. Detailed quantitative study of the nannofossils recognized forty-two datum planes which are potentially useful in the late Neogene biostratigraphy. A high rate of sedimentation (52.2 mm/k.y.) allowed us to recognize even relatively closely spaced datum planes and locate them within the sequence. Absolute ages of the nannofossil datum planes younger than 4 Ma have been estimated by interpolation between tephra layers, for which ages were determined by correlation with paleomagnetically and radiometrically dated tephra layers exposed in East African terrestrial sequences. Ages of the older late Neogene datum planes are estimated by interpolation between the FOD of D. hamatus and the Moitu Tuff, and by extrapolation below the FOD of D. hamatus. Previously defined and newly introduced datum planes define twenty nannofossil zones, six each in the Quaternary, Pliocene and late Miocene, and two in the middle Miocene, with durations of 0.13 to 0.78, 0.37 to 0.81 and 0.14 to 2.49 m.y. in the Quaternary, Pliocene and late Miocene time period respectively. Nine new zones and five new subzones are proposed in this paper, three zones in the Pleistocene, two zones in the Pliocene, two zones and five subzones in the late Miocene, and two zones in the upper part of the middle Miocene. Six new datum planes are introduced, FOD of P. lacunosa in the Pliocene, FOD and LOD of D. neohamatus, LOD's of D. loeblichii and D. calcaris in the late Miocene and LOD of D. extensus in the latest middle Miocene.