Site 1145 yielded common to abundant, poor to moderately well-preserved upper Pleistocene through upper Pliocene calcareous nannofossils. Nannofossil biostratigraphy at this site is based on a detailed study of Hole 1145A (Tables T7, T8). All nannofossil bioevents are confirmed in Holes 1145B and 1145C without significant variations. Nannofossil preservation and abundance varies at different levels, indicating changes in calcite dissolution or dilution by other sediment components. Calcite dissolution is evident in all samples as indicated by etching on the rim of placoliths and disappearance of central structures.
Emiliania huxleyi dominates the nannofossil assemblages in the top 10 m of sediments, but its abundance decreases significantly below 22.3 mcd. Therefore, the first occurrence (FO) of "E. huxleyi increase" is tentatively drawn at 11.9 mcd. The next three Pleistocene biohorizons, the FO of E. huxleyi, the last occurrence (LO) of Pseudoemiliania lacunosa, and the LO of Calcidiscus macintyrei, occur in the correct order of succession between 53.0 and 152.8 mcd. The interval 115.0-126.0 mcd was assigned to the Gephyrocapsa (small) acme Zone based on the significant reduction in abundance of large and medium-sized Gephyrocapsa spp. Medium-sized (>4 mm) Gephyrocapsa spp. were not observed at Site 1145 below the LO of C. macintyrei. Therefore, the Pleistocene/Pliocene boundary can only be constrained by the LO of C. macintyrei (152.8 mcd) and the next lower biohorizon, the LO of Discoaster brouweri (164.9 mcd).
The LO of D. brouweri, the LO of Discoaster pentaradiatus, and the LO of Discoaster tamalis were recorded in the correct order of succession in the bottom 48 m in Hole 1145A. The LO of Discoaster surculus was not resolved at this site because of the low sampling resolution. Calcareous nannofossil preservation deteriorates significantly in the lowermost 48 m at Site 1145, which indicates severe calcite dissolution. This suggests that Site 1145 was probably below the nannofossil lysocline during the late Pliocene.
Planktonic foraminifers were also examined in all core-catcher samples from Hole 1145A and in selected core-catcher samples from Holes 1145B and 1145C. The soft clay in the samples of this site was easily removed by soaking in a warm Calgon and hydrogen peroxide solution and then washing through a 150-µm sieve. Site 1145 yields a moderate abundance of planktonic foraminifers, although their preservation degrades from good to poor downsection. This preservation was documented by an increase in fragmentation (Le and Shackleton, 1992) and a decrease of pteropod abundance with depth (see Fig. F10). In general, the upper part of Hole 1145A (above ~90 mcd) has good preservation as indicated by low fragmentation and relatively high ratios of preserved pteropods to planktonic foraminifers. Because this site is located within the modern lysocline of the South China Sea, its carbonate dissolution should be very sensitive to the changes in lysocline depth. Therefore, the high fragmentation (>15%) at ~140 mcd and below ~165 may indicate that this site was below the lysocline at that time (see Fig. F10).
The planktonic foraminiferal biostratigraphy for Site 1145 is based on Holes 1145A and 1145B (see Table T9 for details). The relatively high sedimentation rates at Site 1145 and the depth of the drilled section limit the number of biohorizons used to date the cores. The LO of Globigerinoides fistulosus (1.77 Ma) was used to mark the Pleistocene/Pliocene boundary (152.8 mcd), whereas the FO of Globorotalia truncatulinoides marked the bottom of Zone N22 (155.5 mcd) (Blow, 1969). Within Zone N22, the LO (0.12 Ma; Thompson et al., 1979) and the FO (0.40 Ma; Li, 1997) of pink Globigerinoides ruber, as well as the FO of Globorotalia crassaformis (0.75 Ma), served as three biostratigraphic control points (Table T9). The bottom of the site (212.5 mcd) was constrained by the LO of Sphaeroidinellopsis seminulina (3.12 Ma) and the FO of Globorotalia tosaensis (3.35 Ma), placing it in Zone N21.
Site 1145 yields rare to few deep-sea benthic foraminifers, but the ratio of benthic to planktonic foraminifers increases greatly in the lower part of Hole 1145A, possibly because of increased carbonate dissolution. The proportion of species indicative of high organic carbon flux (e.g., Globobulimina spp. and Uvigerina peregrina), is high above ~85 mcd and then decreases downhole. This corresponds well to changes in the group abundance of siliceous microfossils (such as radiolarians and diatoms) (Fig. F11) and in the organic carbon content in Hole 1145A. It also indicates that productivity decreases downhole. The LO of Stilostomella was observed at 94.3 mcd, placing this depth at 0.75 Ma for the latitude of this site (Schönfeld, 1996).
At Site 1145, both planktonic foraminifers and calcareous nannofossils are common to abundant, although planktonic foraminifer preservation degraded from good to poor downsection and the nannofossils were occasionally to commonly reworked. 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. F11). The age of the oldest sediments recovered at Site 1145 is ~3.12-3.35 Ma. The sedimentation rate at Site 1145, calculated based on biostratigraphic data (Table T7; Fig. F11), is 173 m/m.y. after 0.46 Ma, 28 m/m.y. before 2.0 Ma, and 55 m/m.y. in between.