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doi:10.2204/iodp.proc.311.107.2006

Biostratigraphy

Biostratigraphy determined for Site U1329 was based on an examination of all core catcher samples and several additional core samples from Hole U1329C (Table T2). Hole U1329C contains the most complete stratigraphic sequence: a 187.5 m thick upper Miocene sequence and its overlying Quaternary sedimentary section. No Pliocene sequence was recognized at this site.

Diatoms

Diatoms are rare and poorly preserved in the interval from the seafloor to ~27 mbsf, where diatom assemblages are dominated by marine diatoms Thalassionema nitzschioides and Thalassiosira spp. and the nonmarine diatom Aulacoseira granulata s.l. Diatoms are most abundant from ~37 to ~135 mbsf, where they range from mostly common to very abundant and moderately preserved. Diatoms in this interval are dominated by Neodenticula seminae, Stephanopyxis dimorpha, Stephanopyxis spp., T. nitzschioides, and Thalassiosira spp. and mostly associated with very abundant resting spores of Chaetoceros. Overall, the very abundant occurrence of diatoms along with numerous resting spores in this interval suggest they may be a product of coastal upwelling in a shelf area, which would require them to be transported by turbidites to this site. Diatoms such as Actinocyclus oculatus, Proboscia curvirostris, and Thalassiosira jouseae are rare but were recognized only in this interval. The interval from ~137 to ~177 mbsf is characterized by the lack of some of the diatoms recognized in the upper intervals, such as A. oculatus, N. seminae, P. curvirostris, and T. jouseae and are mostly dominated by T. nitzschioides. Some diatom assemblages in this interval contain diatoms such as Neodenticula kamtschatica, Thalassionema schraderi, and Thalassiosira antiqua, which are not contained in the upper intervals. Diatoms between ~179 and ~186 mbsf are generally very rare and poorly preserved and are dominated by the nonmarine diatom Aulacoseira granulata s.l.

The interval between the seafloor and Sample 311-U1329C-2H-CC (0.10–18.30 mbsf) contains N. seminae but lacks P. curvirostris and was assigned to North Pacific Diatom (NPD) Zone 12 (N. seminae Zone). The last occurrence (LO) of P. curvirostris was recognized in Sample 311-U1329C-4H-CC (37.18 mbsf), marking the NPD Zone 12/11 boundary (P. curvirostris Zone). The LO of A. oculatus was found in Sample 311-U1329C-4H-CC (37.18 mbsf). The interval between these two LOs (37.18–95.69 mbsf) was assigned to NPD Zone 11 (P. curvirostris Zone). The interval between Samples 311-U1329C-12H-CC (105.32 mbsf) and 16H-CC (135.98 mbsf) contains both P. curvirostris and A. oculatus but lacks Neodenticula koizumii and was assigned to NPD Zone 10 (A. oculatus Zone). The interval between Samples 311-U1329C-17H-1, 10–12 cm (135.70 mbsf), and 20X-3, 10–12 cm (161.20 mbsf), is characterized by rare occurrences of N. kamtschatica, Rouxia californica, and T. antiqua and the lack of N. koizumii and was assigned to NPD Subzone 7A (R. californica Zone). The LO and the first occurrence (FO) of T. schraderi were recognized in Samples 311-U1329C-20X-5, 10–12 cm (165.20 mbsf), and 21X-CC (176.98 mbsf), respectively. The interval between the LO and the FO of T. schraderi was assigned to NPD Subzone 6B (T. schraderi Zone). The interval between Samples 311-U1329C-22X-2, 10–12 cm (180.50 mbsf), and 22X-6, 10–12 cm (186.39 mbsf), might be assigned to NPD Subzone 6A (Denticulopsis katayamae Zone), but the lack of zonal diagnostic diatoms and the predominance of nonmarine diatoms makes it difficult to make a definite zonal assignment.

The upper three diatom zones in Hole U1329C are Holocene–Pleistocene in age, and the lower two (or possibly three) zones are late Miocene in age, respectively. The Pliocene is missing in this hole as a result of a hiatus at ~137 mbsf, where sediments ranging in age from 2.0 Ma (the base of NPD Zone 10) to 6.7 Ma (the top of NPD Subzone 7A) are missing. This hiatus between Pleistocene and Miocene sediments corresponds to the boundary between lithostratigraphic Units II and III (see "Lithostratigraphy").

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