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doi:10.2204/iodp.proc.320321.108.2010

Stratigraphic correlation and composite section

STMSL data were collected at 5 cm intervals from Hole U1336B and compared to WRMSL data obtained at 2.5 cm resolution from Hole U1336A during Expedition 320. In this way, drilling was monitored in Hole U1336B in real time to maximize the opportunity for the recovery and construction of a stratigraphically complete composite section. Cores from Hole U1336B were also measured on the WRMSL during Expedition 320 and left onboard as whole-round sections to be split and described during Expedition 321. After the cores were split and described a composite section was constructed.

Magnetic susceptibility and GRA density proved most useful for correlating between holes at Site U1336 (Figs. F27, F28). Features in the magnetic susceptibility and GRA density are well aligned between Holes U1336A and U1336B to ~94 m CCSF-A. The correlation between the two holes is presented in Figures F27 and F28. Offsets and composite depths are listed in Table T22. Below ~94 m CCSF-A, the magnetic susceptibility signal drops to very low values but density data are good enough to sustain a correlation to interval 320-U1334B-14H-4, 122 cm. At this point (138.50 m CCSF-A) sediments recovered in both holes are disturbed. Core 320-U1336B-15H was appended to the bottom of the splice (Table T23). Near the bottom of Core 320-U1336B-18H the splice shifts to Core 320-U1336A-18H and continues to the base of the hole by appending Hole U1336A cores (Table T23). A preferred splice would have been to append Core 321-U1336A-15H just above the disturbed section at the base of Core 321-U1336B-14H. However, this was not allowed by Correlator software. The critical interval from Cores 320-U1336B-14H through 320-U1336A-18H is illustrated in Figure F29.

A growth factor of 1.13 is calculated by linear regression for the top ~94 m CCSF-A of Site U1336, indicating a 13% increase in CCSF-A relative to CSF depth (Fig. F30). We used this value to calculate CCSF-B depth presented in Table T22 to aid in the calculation of sedimentation and mass accumulation rates.

Sedimentation rates

All principal biostratigraphic datums and a set of 33 tentatively interpreted paleomagnetic reversals (restricted to the APC-cored sections) (Table T24; see also "Biostratigraphy" and "Paleomagnetism") were used in establishing age control (Fig. F11). Paleomagnetic reversals were used to calculate the average LSRs for the upper 74 m CCSF-B of the section at Site U1336, as depicted in Figure F11. Below 74 m CCSF-B, only biostratigraphic datums were used to calculate the average LSRs.

The LSR at Site U1336 decreases from 15 m/m.y. in the upper Oligocene to 12 m/m.y. in the lower Miocene and stays relatively constant at 9 m/m.y. in the remainder of the section (Fig. F11).

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