IODP

doi:10.2204/iodp.pr.320T.2009

Planktonic foraminifer biostratigraphy and sedimentation rates

Core catcher samples were examined for planktonic foraminifers from Holes U1330A and U1330B. The oldest sediments cored at this site are lower Pliocene (Zone N18–N19). Key planktonic foraminifer FO and LO datums are used to estimate sedimentation rate based on the low-resolution sampling conducted here.

Hole U1330A

The wash core (320T-U1330A-1W) and the core catchers from the two RCB cores (320T-U1330A-2R and 3R) all yield an early Pliocene age based on the presence of Globoturborotalita nepenthes (LO = 4.37 Ma) and Globorotalia tumida (FO = 5.82 Ma). The FO of Sphaeroidinella dehiscens (5.54 Ma) is a reliable proxy for some tropical regions, but earlier work on Ontong Java Plateau demonstrated that this is not a reliable datum in this area (Chaisson and Leckie, 1993). Comparison with Hole 807A indicates that the Miocene/Pliocene boundary was expected at a depth of ~125 mbsf (Kroenke, Berger, Janecek, et al., 1991).

Hole U1330B

Chronostratigraphy for Hole U1330B is tentative because of the coarse 9.5 m resolution of the core catcher samples examined here, as well as the use of a single microfossil group and lack of paleomagnetic data. The Pliocene/Pleistocene boundary is tentatively placed near the LO of Globigerinoides fistulosus (1.88 Ma) at ~27 mbsf. The lower/upper Pliocene boundary is placed near the LO of Globorotalia margaritae (3.85 Ma) at ~59 mbsf. Hole U1330B bottomed out in the lower Pliocene (>4.37 Ma) based on the presence of both G. nepenthes and G. tumida.

Sedimentation rates

Sediments accumulated at an average rate of ~26.5 m/m.y. during the Pliocene and slowed to ~16 m/m.y. during the Pleistocene based on a coarse resolution study of core catcher samples (Table T6; Fig. F8). These estimates are very similar to the rates calculated based on several microfossil groups and paleomagnetic polarity data from nearby Site 807 (Kroenke, Berger, Janecek, et al., 1991).