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doi:10.2204/iodp.proc.339.205.2019

Calcareous nannofossil stratigraphy

In general, calcareous nannofossil assemblages are abundant and indicative of the early Pleistocene, corroborating the shipboard results (see the “Methods” chapter [Expedition 339 Scientists, 2013a]). Small placolith taxa (<3 µm) dominated the assemblages. Reworking of lower Neogene and Paleogene species were observed in the analyzed record but mostly in low proportion. The preservation was good to moderate with weak dissolution and overgrowth in some samples. In total, four calcareous nannofossil datums defined and calibrated by Raffi et al. (2006) were newly identified in the analyzed samples (Table T1). In the shipboard analysis, the LO of large Gephyrocapsa (>5.5 µm; 1.61 Ma) and the HO of Calcidiscus macintyrei (1.66 Ma) were identified between Samples 339-U1387C-7R-CC and 8R-CC (346.05–357.52 mbsf) (see the “Methods” chapter [Expedition 339 Scientists 2013a]). However, the significantly higher sampling resolution revealed an abundance pattern that suggests repositioning both these datums to greater depth. Thus, the LO of large Gephyrocapsa (>5.5 µm; 1.61 Ma) was identified between Samples 10R-1, 75–77 cm, and 10R-1, 48–50 cm, (367.55–367.28 mbsf), whereas the HO of Calcidiscus macintyrei (1.66 Ma) was identified between Samples 11R-2, 48–50 cm, and 11R-2, 14–16 cm (378.38–378.04 mbsf). Finally, both the LO of medium Gephyrocapsa group (1.73 Ma) and the HO of Discoaster brouweri (1.95 Ma), which during the shipboard analysis were not possible to place because of the lower sampling resolution, are now constrained. The LO of medium Gephyrocapsa group (1.73 Ma) was placed between Samples 14R-1, 88–90 cm, and 14R-1, 80–82 cm, (406.08–405 mbsf). However, this event should be taken with caution because of the irregular and intermittent record observed, sometimes related to dissolution. The HO of D. brouweri (1.95 Ma) was identified between Samples 19R-2, 88–90 cm, and 19R-2, 14–16 cm (455.38–454.63 mbsf). Between Samples 19R-3, 129–131 cm, and 19R-4, 49–51 cm (457.25–457.9 mbsf), no coccoliths were preserved.

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