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doi:10.2204/iodp.proc.333.104.2012

Biostratigraphy

Preliminary analysis of the core catcher samples from Holes C0011C (Sections 333-C0011C-1H-CC to 3H-CC) and C0011D (Sections 333-C0011D-1H-CC to 52X-CC) reveals assemblages of calcareous nannofossils. Biostratigraphic datums are derived from coccoliths. According to these datum events, the composite section of Holes C0011C and C0011D has a late Pleistocene to late Miocene age.

Calcareous nannofossils

Preliminary examination of all core catcher samples from Holes C0011C and C0011D obtained well to very poorly preserved nannofossils, which occur in common abundance in most samples, and species diversity is comparatively high. However, severe dissolution also occurred, leading to coccolith-barren or very poor occurrences in some intervals. Most of the zonal markers of Martini’s zonation (1971) and Raffi et al. (2006) were identified in the sedimentary sequence. The nannofossils occurring in Holes C0011C and C0011D are listed in Tables T5 and T6.

Emiliania huxleyi and Pseudoemiliania lacunosa are absent in Sample 333-C0011C-1H-CC. The last occurrence (LO) of P. lacunosa is found in Samples 333-C0011C-1H-CC to 2H-CC. Gephyrocapsa parallela, which appears younger than 0.90 Ma, was found in Samples 333-C0011C-2H-CC to 3H-CC.

Reticulofenestra asanoi, which indicates the late Pleistocene (0.436~0.90 Ma), is found in Sample 333-C0011D-1H-CC. The first occurrence of medium Gephyrocapsa spp. (3.5~5.5 µm; 1.67 Ma) is identified in Samples 333-C0011D-3H-CC to 4H-CC. The LO of Discoaster brouweri, which defines the top of Zone NN18 (2.06 Ma), is recognized between Samples 333-C0011D-4H-CC and 5H-CC. The LO of Discoaster pentaradiatus, which indicates the top of Zone NN17 (2.50 Ma), is found below Sample 333-C0011D-7H-CC. Samples 333-C0011D-9H-CC to 14H-CC are characterized by the occurrence of Discoaster tamalis, which assigns this interval to Zone NN16 (between 2.87 and 3.79 Ma). The LO of Reticulofenestra pseudoumbilicus (3.79 Ma) is also identified between Samples 333-C0011D-16H-CC and 47X-CC. Amaurolithus spp., which indicates Zone NN14 (4.50 Ma), is found below Sample 333-C0011D-29X-CC. Discoaster quinqueramus and Discoaster berggrenii, which indicate upper Miocene Zone NN11 (5.59~8.52 Ma), are found in Samples 333-C0011D-36X-CC to 50X-CC. The paracme end (Raffi et al., 2006) of R. pseudoumbilicus (7.10 Ma) is identified in Samples 333-C0011D-47X-CC to 48X-CC.

The assemblages obtained through all the holes are characterized by the occurrence of warmer water species such as Discoaster spp. and high species diversity (Tables T5, T6).

Sedimentation rates based on biostratigraphy

The changes in sedimentation rates in Holes C0011C and C0011D, based on calcareous nannofossils, are shown in Figure F25 and Table T7. The sedimentation rate was 5.74 cm/k.y. between 0.436 and 0.903 Ma, which corresponds to Samples 333-C0011C-1H-CC to 2H-CC. In continuation, the slightly lower sedimentation rates of 2.21, 2.09, 4.22, and 2.21 cm/k.y. between 0.903 and 2.87 Ma correspond to the upper part of the sequence. The middle part of the sequence (upper depth limit 143–224.953 mbsf shows high sedimentation rates of 6.57 and 10.70 cm/k.y. from 2.87 to 4.5 Ma. Sedimentation rates in the lower part of the sequence are 4.04 and 5.89 cm/k.y. from 4.5 to 7.122 Ma (upper depth limit 224.953 mbsf to lower depth limit 359.421 mbsf). Ages and sedimentation rates obtained are consistent with Expedition 322 results, which situate the nannofossil Zone NN11a/NN10 boundary (8.54 ± 0.24 Ma) between 417.67 and 421.39 mbsf.

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