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doi:10.2204/iodp.proc.303306.105.2006

Composite section

Cores were depth-shifted on the basis of magnetic susceptibility data collected with the Fast Track core logger soon after recovery. Magnetic susceptibility proved most useful for correlating between holes at Site U1305. Features in magnetic susceptibility are generally well aligned among Holes U1305A, U1305B, and U1305C (e.g., Fig. F21). The offsets and composite depths are listed in Table T18. Because of the highly disturbed nature of Core 303-U1305C-19H, which was retrieved after an incomplete stroke of the APC, it was not possible to correlate this core to the other holes.

The sections of core used for the splice are identified in Table T19. We avoided using the first (top) section of each core because it was often disturbed. The cores from Site U1305 provide a continuous stratigraphic sequence to ~295 mcd with a single problematic interval between 197.2 and 206 mcd corresponding to Core 303-U1305B-20H. All core logging properties in this interval are invariant, making it difficult to correlate among holes. Consequently, this core was appended to Core 303-U1305B-19H above and spliced to Section 303-U1305A-20H-7, 2 cm, below. We are not certain if sediment is missing at the core break between Cores 303-U1305B-19H and 20H or if the position of the splice to Section 303-U1305A-20H-7, 2 cm, is correct. Below 295 mcd, Cores 303-U1305A-29H and 303-U1305C-31H were appended to the spliced section.

A growth factor (GF) of 1.10 is calculated by linear regression for all holes at Site U1305, indicating a 10% increase in mcd relative to mbsf (Fig. F22). We used this value of GF to calculate corrected meters composite depth (cmcd) presented in Table T18 to aid in the calculation of mass accumulation rates.

We calculated sedimentation rates using paleomagnetic and biostratigraphic datums. Linear regression provides a mean sedimentation rate of 17.3 cm/k.y. for the entire section cored at Site U1305 (Fig. F23). Using only paleomagnetic datums, sedimentation rates are still relatively uniform with the exception of a greater mean sedimentation rate (29.3 cm/k.y.) between 1.07 and 1.19 Ma (from the base of the Jaramillo to the top of the Cobb Mountain Subchronozones) that averages 29.3 cm/k.y. (Fig. F23). Outside this high sedimentation rate interval, the rate varies between 13.7 and 18.5 cm/k.y. (Table T20).

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