4-1. North of Oahu (PC-7 and PC-8) 　　　　　　　　　　

Objectives
PC7 and PC8 were sampled to further understanding of the timing of Nuuanu Landslide. In the 1998 cruise we recovered three cores from this area, at distances of approximately 100, 200, and 300 km from the flank of Oahu (P1, P3, and P2, respectively). Results of these cores are given in Kanamatsu et al. (2001). PC7 was recovered 400 km from Oahu, along the line formed by the previous three. PC8 was recovered 130 km west of PC7, roughly 340 km NNE of Oahu.

Lithology
Core PC7: Core was recovered from behind a small seamount. A gap was present in the coring pipe after the top 230 cm of sediment. Only the interval between 0-79 cm appeared unaffected by inflow disruption from coring, and thus may provide stratigraphic information. This interval consists of three units: 0-30cm, moderately yellowish brown clay; 30-71cm, dark yellowish brown indurate volcanic silt; 71-80 cm, volcanic sand. Much of the sediment below the gap in the coring pipe exhibits in-flow structure as well. Section 9, however, appears intact and consists of silty volcanic sand, which is incipiently indurate for the bottom 35 cm.

Core P8: This core can be divided into three units: the upper unit consists of moderately yellowish brown clay (0-64cm, sec1) and indurate fractured clay (0cm sec3-23cmsec5). The middle consists of an indurate alternation of volcanic silt and clay (23cm, sec5-88cm, sec5) above a 194-cm thick sand layer (88cm, sec5 - 93cm, sec7). Below this thick sand layer, the third unit contains moderate yellowish brown clay (93 cm, sec7-103cm, sec9) and indurated fractured clay (sec10). Section 10 exhibits inflow structure.

The thick sand layer at the base of PC7 may correlate with the sand layer in the middle of section 8, based on depth and magnetic susceptibility (MS) profiles. This layer may be a turbidite generated during the Nuuanu landslide. If so, PC8 may prove to be important in constraining the timing of this event, as it is the only core that has been recovered that contains intact pelagic sediment below the Nuuanu turbidite deposit, and thus may contain magnetic reversal events above and below the sand layer.

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