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doi:10.2204/iodp.proc.311.105.2006

Biostratigraphy

Hole U1327C contains the most complete stratigraphic sequence at this site: a 300 m thick Quaternary sedimentary sequence. The biostratigraphy determined for Site U1327 was based on an examination of all core catcher samples from Hole U1327C (Table T2).

Diatoms

Diatoms are mostly rare and poorly preserved in the interval from the seafloor to ~82 mbsf and very rare to abundant and poorly to moderately preserved in the interval from ~92 to ~295 mbsf. Diatom assemblages are dominated by either marine species Neodenticula seminae, Stephanopyxis spp., Thalassionema nitzschioides, and Thalassiosira spp. or the nonmarine diatom Aulacoseira granulata s.l. The abundance of the dominant species varies greatly from sample to sample. Abundant resting spores are frequently associated with the marine diatoms in this interval. The nonmarine diatom Cyclotella spp. is abundant in Sample 311-U1327C-30X-CC. Marine- and nonmarine-dominant assemblages alternate throughout this hole, suggesting intermittent terrigenous input by turbidites.

The interval between the seafloor and Sample 311-U1327C-7H-CC (0.10–55.98 mbsf) contains N. seminae but lacks Proboscia curvirostris and was assigned to North Pacific Diatom (NPD) Zone 12 (N. seminae Zone; 0–0.3 Ma). The last occurrence (LO) of P. curvirostris was recognized in Sample 311-U1327C-8H-CC (65.64 mbsf), marking the NPD Zone 12/11 boundary (P. curvirostris Zone). The interval between the LO of P. curvirostris and Section 311-U1327C-20X-CC (66.64–167.20 mbsf) contains P. curvirostris but lacks Actinocyclus oculatus and was assigned to NPD Zone 11 (P. curvirostris Zone; 0.3–1.0 Ma). The LO of A. oculatus was recognized in Sample 311-U1327C-21X-CC (178.68 mbsf), marking the NPD Zone 11/10 boundary (A. oculatus Zone). The interval between the LO of A. oculatus and Section 311-U1327C-34X-CC ((178.68–295.26 mbsf) contains both P. curvirostris and A. oculatus and was assigned to NPD Zone 10 (P. curvirostris Zone; 1.0–2.0 Ma). The three Quaternary diatom zones are recognized at both Sites U1327 and U1329, but the thickness of the three zones in Hole U1327C is almost double that of Site U1329, which might be the result of the abundant terrestrial supply by turbidites suggested by the intermittently abundant occurrences of nonmarine diatoms.