Pleistocene sediments recovered at Site 1147 yielded common to abundant calcareous nannofossils having poor to good preservation. Variations in nannofossil preservation and abundance at different levels indicate changes in calcite dissolution caused by fluctuations of the lysocline (Fig. F6). Nannofossil biostratigraphy at this site is based on a detailed study of samples taken from core catchers and from within cores of Hole 1147A (Tables T7, T8).
Five calcareous nannofossil bioevents were documented in the 89.4-m Pleistocene sediment sequence of Hole 1147A (Tables T7, T8). The oldest bioevent, the first occurrence (FO) of the Gephyrocapsa (small) acme interval, was observed at 78.8 mcd. No Helicosphaera sellii was found below that level, which suggests that the age at the bottom of Hole 1147A (89.4 mcd, Sample 1147A-9H-CC) is older than 1.22 Ma but younger than 1.47 Ma.
Planktonic foraminifers were examined in all core-catcher samples from Hole 1147A and selected core-catcher samples from Hole 1147B (see Table T9). Site 1147 yields a moderate abundance of planktonic foraminifers although their preservation degrades from very good to moderate downsection, as documented by an increase in planktonic foraminiferal fragments (Fig. F6).
The relatively high sedimentation rates at Site 1147 and the depth of the drilled section limit the number of biohorizons used to date the cores. Because Globorotalia truncatulinoides occurs continuously down the full length of this hole, this interval is assigned to biozone N22 (Blow, 1969). The absence of Globigerinoides fistulosus constrains the age of the sediments in Hole 1147A to younger than 1.77 Ma. Within Zone N22 we used the last occurrence (LO) (0.12 Ma; Thompson et al., 1979) and FO (0.40 Ma; Li, 1997) of pink Globigerinoides ruber as two biostratigraphic control points (Table T7).
Site 1147 also yields rare to few deep-sea benthic foraminifers. One benthic foraminiferal datum, the LO of Stilostomella, was observed at 68.06 mcd and indicates an age of ~0.75 Ma based on the latitude of this site (Schönfeld, 1996).
At Site 1147, both planktonic foraminifers and calcareous nannofossils are common to abundant. Foraminiferal preservation degraded from very good to moderate downsection, whereas nannofossils exhibited poor to good preservation. Benthic foraminifers are generally few in number.
An age-depth plot of the three fossil groups shows that the biohorizons generally agree with each other (Fig. F7). The age of the oldest sediments recovered at Site 1147 is estimated at 1.22-1.47 Ma. The sedimentation rate at Site 1147, calculated based on biostratigraphic data (Table T7; Fig. F7), is 75 m/m.y. after 1 Ma and 23 m/m.y. between 1.01 and 1.22 Ma.