Site 1249 was drilled near the top of the southern summit of Hydrate Ridge. Twelve holes were drilled, and eleven were cored. Hole 1249C was cored to 90.0 mbsf, with 67% core recovery of a Pleistocene-Holocene sedimentary sequence. Biostratigraphy at Site 1249 was based on the examination of diatoms and calcareous nannofossils from all core catcher samples in Hole 1249C.
Hole 1249C yielded common and moderately preserved diatoms, except for Samples 204-1249C-3H-CC and 13H-CC, where diatoms are few and poorly preserved. Diatom assemblages from Hole 1249C are dominated by such species as Stephanopyxis dimorpha, Stephanopyxis spp., Neodenticula seminae, and Thalassionema nitzschioides. Warm-water species, such as Fragilariopsis doliolus and Thalassiosira oestrupii, are sporadically present.
The interval between Samples 204-1249C-1H-CC (1.60 mbsf) and 3H-CC (7.18 mbsf) contains N. seminae but does not contain Proboscia curvirostris. These samples were assigned to North Pacific Diatom Zone (NPD) 12 (N. seminae Zone). The last occurrence (LO) of P. curvirostris was placed between Samples 204-1249C-3H-CC (7.18 mbsf) and 4H-CC (18.82 mbsf). P. curvirostris is present continuously down to the bottom of Hole 1249C, indicating that the age of the bottom is younger than 1.6 Ma.
Rare to common calcareous nannofossils were observed in almost every core catcher sample from Hole 1249C, except for Sample 204-1249C-8H-CC, where calcareous nannofossils are absent.
Common to rare Emiliania huxleyi is continuously present in the top interval of 1.42-18.82 mbsf, and this interval was assigned to Zone NN21. Sample 204-1249C-5H-CC contains neither E. huxleyi or Pseudoemiliania lacunosa and was assigned to Zone NN20. The LO of P. lacunosa in Sample 204-1249C-7H-CC (40.64 mbsf) marks the NN19b/NN20 zonal boundary for the stratigraphic level. Various small Gephyrocapsa species are common in Sample 204-1249C-7H-CC (40.64 mbsf) but are absent in the next sample below (Sample 204-1249C-8H-CC), which is barren of calcareous nannofossils. As a result, the small Gephyrocapsa spp. Acme Zone was not recognized in Hole 1249C. Sample 204-1249C-9H-CC (59.97 mbsf) and samples below it contain rare Calcidiscus macintyrei. The LO of C. macintyrei (1.59 Ma) was placed at 59.97 mbsf. Gephyrocapsa lumina is common in sediments from near the bottom of Hole 1249C (Sample 204-1249C-17H-CC [148.47 mbsf]), assigning the sample to the lower part of early Pleistocene Zone NN19, with an age of younger than 1.67 Ma.
Based on analysis of diatoms and calcareous nannofossils from the Pleistocene-Holocene sedimentary sequence in Hole 1249C, one diatom and three nannofossil events were recognized (Table T3; Fig. F12). The age of the bottom sediment of Hole 1249C was estimated to be younger than 1.6 Ma, based on the diatom assemblage, or to be younger than 1.67 Ma, based on the nannofossil assemblage. Therefore, the age of the sediment sequence in Hole 1249C is early Pleistocene-Holocene.
We estimated the linear sedimentation rates for Site 1249 using the identified events (Fig. F12). The sedimentation rates are estimated to be 9 cm/k.y. for the interval from the top of Hole 1249C to 25 mbsf, 6 cm/k.y. for the interval from 25 to 35 mbsf, and 2 cm/k.y. for the interval from 35 to 55 mbsf.