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doi:10.2204/iodp.proc.320321.110.2010

Stratigraphic correlation and composite section

Special Task Multisensor Logger data were collected at 5 cm intervals from Holes U1338B and U1338C and compared to the Whole-Round Multisensor Track (WRMST) data obtained at 2.5 cm resolution from Hole U1338A. In this way drilling was monitored in holes after Hole U1338A in real time to maximize the opportunity for the recovery and construction of a stratigraphically complete composite section. Cores from Holes U1338B and U1338C were measured on the WRMST for final correlation. After the cores were split and described, a composite section and spliced sequence were constructed.

Magnetic susceptibility, NGR, GRA bulk density, L*, and scanned images all contributed to correlation between holes at Site U1338. GRA and magnetic susceptibility are illustrated in Figures F41 and F42. Features between all records are well aligned to ~280 m CCSF-A. Ship heave of several meters during coring in Hole U1338C resulted in relatively more core disturbance in the softer sediments recovered from that hole than from other holes, and the splice was subsequently made primarily from Holes U1338A and U1338B in the upper 260 m CCSF-A (to Core 321-U1338A-27H). The remainder of the splice alternated between Holes U1338B and U1338C. Offsets and composite depths are listed in Table T23.

At the base of Core 321-U1338C-28H, overlap was lost because of poor recovery in corresponding cores from Holes U1338A and U1338B. Another gap occurred at the base of Core 321-U1338C-31H, the level of the "baby chert." Several other ties were made on the basis of short overlaps between 280 and 360 m CCSF-A. Images of cores from all three holes as well as a spliced image are presented in Figure F43. Ties below 360 m CCSF-A were generally good to 430 m CCSF-A, whereupon poor core condition and low variability in the data used for correlation left little to do but finish out the splice with the lower four cores from Hole U1338C. Splice tie points are listed in Table T24.

A growth factor of 1.11 is calculated by linear regression of CSF versus CCSF-A for all Site U1338 cores, indicating an 11% increase in CCSF-A relative to CSF depth (Fig. F44). We used this value to calculate the CCSF-B scale presented in Table T23 to aid in the calculation of sedimentation and mass accumulation rates.

Sedimentation rates

All principal biostratigraphic datums and a set of 22 tentatively interpreted paleomagnetic reversals (restricted to the APC-cored sections) (Table T25; see also "Biostratigraphy" and "Paleomagnetism") were used in establishing age control (Fig. F14). The linear sedimentation rate at Site U1338 decreases from 28.7 m/m.y. in the Miocene to 12.7 m/m.y during the Pliocene–Pleistocene (Fig. F14).

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