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doi:10.2204/iodp.proc.333.103.2012

Biostratigraphy

Preliminary biostratigraphy determination for Hole C0018A was based on examination of calcareous nannofossils. All core catcher samples and additional samples from sections between core catcher samples were examined. The results of nannofossil investigation are presented in Table T6. Calcareous nannofossils investigated are generally well to moderately preserved through all sections except for Samples 333-C0018A-18H-CC and 20H-CC (Table T6). The biostratigraphic results (six recognized nannofossil events) show that the entire recovered section in Hole C0018A has an age range within the Pleistocene (Fig. F24; Table T7). Two lithologic subunits have been described (see “Lithology”):

• Subunit IA: ash-bearing hemipelagic silty clay interbedded with MTDs between 0 and 190.65 mbsf, and

• Subunit IB: a sandy turbidite sequence between 190.65 and 313.66 mbsf.

Subunit IA ranges from the recent to ~1 Ma, and Subunit IB ranges from ~1 to ~1.46–1.67 Ma. Two nannofossil events in Subunit IA suggest a slightly lower sedimentation rate in the interval between 0 and 25 mbsf than the other intervals. In spite of interbedding of disturbed MTDs within Subunit IA, nannofossil analysis provides no evidence for any significant hiatus or age reversal (Table T7). Thus, it can be interpreted that no considerable erosion and overturning of sequences within Subunit IA have occurred.

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