Previous   |   Next

doi:10.2204/iodp.proc.311.104.2006

Biostratigraphy

Cores were recovered from Holes U1326B, U1326C, and U1326D. Sample 311-U1326B-1H-CC, the only sample obtained from Hole U1326B, was barren of diatoms. Holes U1326C and U1326D contain a ~270 m thick Quaternary sedimentary sequence. The biostratigraphy determined for Site U1326 was based on an examination of all core catcher samples from the three cored holes (Table T2).

Diatoms

Diatoms are generally very rare to barren and poorly preserved in most of the samples from Site U1326. Only a few samples contain common to abundant and poorly to moderately preserved diatoms. Samples 311-U1326C-2H-CC (13.62 mbsf) and 3H-CC (22.13 mbsf) contain common to abundant diatom assemblages dominated by Stephanopyxis spp. and Thalassionema nitzschioides and are accompanied by rare occurrences of Neodenticula seminae. A large number of resting spores of Chaetoceros were observed in Sample 311-U1326C-3H-CC. Samples 311-U1326C-4H-CC through 10X-CC and 311-U1326D-2X-CC through 7X-CC have rare diatoms or are barren. Common to rare diatoms from Samples 311-U1326D-8X-CC through 10X-CC (150.50–172.87 mbsf) and 19X-CC (254.44 mbsf) are characterized by dominant occurrences of Stephanopyxis spp. and T. nitzschioides and rare occurrences of N. seminae and Proboscia curvirostris. Samples 311-U1326D-8X-CC and 9X-CC (150.50–160.00 mbsf) are also characterized by rare occurrences of Thalassiosira jouseae and abundant occurrences of resting spores of Chaetoceros. All samples with common to abundant diatoms are dominated by marine diatoms (>90%), but some samples with rare diatoms (Samples 311-U1326C-1H-CC and 5H-CC and 311-U1326D-13X-CC) are dominated by nonmarine diatoms.

The interval between the shallowest sample and Sample 311-U1326C-3H-CC (3.88–22.13 mbsf) contains N. seminae but lacks P. curvirostris and is assigned to North Pacific Diatom (NPD) Zone 12 (N. seminae Zone; 0–0.3 Ma). A diatom zonal assignment is not possible for the interval between Samples 311-U1326C-4H-CC and 10X-CC or from 311-U1326D-2X-CC through 7X-CC (28.27–141.65 mbsf) because these intervals contain no diatoms or zonal marker species. The last occurrence (LO) of P. curvirostris was recognized in Sample 311-U1326D-8X-CC (150.50 mbsf), marking the NPD Zone 12/11 boundary (P. curvirostris Zone). The interval between the LO of P. curvirostris and Sample 311-U1326D-19X-CC (150.50–254.44 mbsf) contains P. curvirostris but lacks Actinocyclus oculatus and was assigned to NPD Zone 11 (P. curvirostris Zone; 0.3–1.0 Ma). Sample 311-U1326D-20X-CC (270.69 mbsf) cannot be assigned to a diatom zone because it is barren. The NPD Zone 12/11 boundary is likely within the above mentioned barren interval (28.27–141.65 mbsf), but its exact depth determination requires postcruise analysis of additional samples at more closely spaced intervals.

Top of page   |   Previous   |   Next