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doi:10.2204/iodp.proc.320321.107.2010

Stratigraphic correlation and composite section

Special Task Multisensor Logger (STMSL) data were collected at 5 cm intervals from Hole U1335B and compared to the WRMSL data obtained at 2.5 cm resolution from Hole U1335A. In this way we monitored drilling in Hole U1335B in real time to maximize the opportunity for the recovery and construction of a stratigraphically complete composite section. The overall good to excellent overlap between Holes U1335A and U1335B did not require drilling a third hole.

The correlation was refined once magnetic susceptibility and GRA density data were available at 2.5 cm resolution from the WRMSL, and NGR and color reflectance data were available from the NGR track and the SHMSL (see "Physical properties"). Visual inspection of cores, comparison with core imagery, and biostratigraphic datums were used to establish and verify hole to hole correlation where track data lacked clearly identifiable features. Magnetic susceptibility and GRA density proved most useful for correlating between holes at Site U1335 (Figs. F27, F28). Features in the magnetic susceptibility and GRA density are well aligned between Holes U1335A (337 m CSF) and U1335B (344 m CSF) to ~398 m CCSF-A. Flow-in at the bottom half of Core 320-U1335A-16H between Sections 320-U1335A-16H-4 and 16H-7 (146.4–151.46 m CSF) made it impossible to construct a complete stratigraphic section below 165.15 m CCSF-A and required appending the remainder of the section. Between ~230 and ~398 m CCSF-A, GRA density data allowed confident alignment of cores despite very low magnetic susceptibility values. The section below 398 m CCSF-A was mostly XCB-cored, lacked clearly identifiable features, and had to be appended for these reasons.

Offsets and composite depths are listed in Table T27. Following construction of the composite depth section for Site U1335, a single spliced record was assembled for the aligned cores to Section 320-U1335B-37H-6 at 398.15 m CCSF-A (top panels of Figs. F27, F28). The sections of core used for the splice are identified in Table T28 and displayed in Figures F27 and F28.

We avoided intervals with significant disturbance or distortion and missing intervals where whole-round samples for interstitial water chemistry were taken (see "Paleomagnetism;" Table T11). The Site U1335 splice can be used as a sampling guide to recover a single sedimentary sequence from 0 to 398 m CCSF-A with gaps between 165 and 166 m CCSF-A, although it is advisable to overlap a few decimeters from different holes when sampling to accommodate anticipated ongoing development of the depth scale. Stretching and compression of sedimentary features in aligned cores indicates distortion of the cored sequence. Because much of the distortion occurs within individual cores on scales of <9 m, it was not possible to align every single feature in the magnetic susceptibility, GRA, NGR, and color reflectance records. However, at crossover points along the splice (Table T28), care was taken to align highly identifiable features from cores in each hole.

A growth factor of 1.16 is calculated by linear regression for all holes at Site U1335, indicating a 16% increase in CCSF-A relative to CSF depth (Fig. F29). We used this value to calculate CCSF-B, the compressed composite depth presented in Table T27 to calculate sedimentation rates and aid in the calculation of mass accumulation rates.

Sedimentation rates

All the principal biostratigraphic datums and a set of 71 paleomagnetic reversals (restricted to the APC-cored section of the site) are defined in Holes U1335A and U1335B (Table T29; see "Biostratigraphy" and "Paleomagnetism") and were used in establishing age control (Fig. F14). Paleomagnetic reversals were used to calculate the average linear sedimentation rates (LSRs) for the upper 200 m of the section at Site U1335 on CCSF-B depth scale, as depicted in Figure F14. Below 200 m CCSF-B all available biostratigraphic datums were used to calculate the average LSRs.

LSRs at Site U1335 are high, 25 m/m.y. on the average throughout the late Oligocene and early Miocene. Sedimentation rates decrease to 17 m/m.y. in the middle early Miocene and drop to 6 m/m.y. in late to middle Miocene to recent (Fig. F14).

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