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Stratigraphic correlation and composite section

Special Task Multisensor Logger (STMSL) data were collected at 5 cm intervals from Holes U1332B and U1332C and compared to the WRMSL data obtained from Hole U1332A. In this way we monitored drilling in Holes U1332B and U1332C in real time to recover and construct a stratigraphically complete composite section. Several intervals between Holes U1332A and U1332B did not overlap sufficiently to cover gaps between cores. Thus, coring of Hole U1332C was designed to cover the missing intervals, as well as to provide additional material for high-resolution studies. Coring in Hole U1332C was successful at covering gaps between cores in Holes U1332A and U1332B to a depth of ~125.46 m CSF (140.38 m CCSF-A) (Fig. F34). Below ~140 m CCSF-A, recovery was poor and it was not possible to correlate features in the track data between different holes. The position of Core 320-U1332C-10H was designed to cover a gap in the composite section between the bottom of Core 320-U1332A-9H and the undisturbed part of Core 320-U1332B-10H (~83 m CCSF-A) (Fig. F34). However, the coring line parted during retrieval of the core and the impact of the subsequent fall and fishing operations left the physical properties of the entire core unsuitable for stratigraphic correlation. The correlation between the three holes for the chosen parameters was adequate to good and, in some depth intervals, excellent. The gaps between successive cores in any of the holes are on the order of 1 to 2 m, with a maximum of 3.5 m between Cores 320-U1332A-13H and 14H.

The correlation was refined once magnetic susceptibility and GRA density 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"). Magnetic susceptibility and GRA density proved most useful for correlating between holes at Site U1332. Features in the magnetic susceptibility are well aligned between Holes U1332A–U1332C to ~140 m CCSF-A, although the section below ~100 m CCSF-A is difficult to correlate because of the scarcity of characteristic features (Fig. F34). Offsets and composite depths are listed in Table T33. Strong winds and swells caused 3 m heave, which had a negative effect on the quality of the APC cores, especially on the core tops (see "Paleomagnetism;" Table T11). Chert and porcellanite layers in lithologic Unit IV (see "Lithostratigraphy") below ~130 m CSF were the main reason for poor core recovery in this interval.

Following construction of the composite depth section for Site U1332, a single spliced record was assembled for the aligned cores to 140 m CCSF-A with a gap at 83 m CCSF-A (Fig. F34). Detailed correlation and comparison with the Site 1220 magnetic susceptibility record (Shipboard Scientific Party, 2002b) suggests that the gap spans <50 cm, indicating that only a very small part of the section is missing. The sections of core used for the splice are identified in Table T34 and displayed in Figure F34. The spliced composite section consists of almost equal proportions from all three holes (Fig. F34).

Biostratigraphic and magnetostratigraphic evidence (see "Biostratigraphy" and "Paleomagnetism") suggests repetition of nannofossil Zones NP21 and NP22 (and Chrons C12r and C13n) in the early Oligocene sediments. Superposition of the duplicated section and comparison with the Site 1220 susceptibility record (Shipboard Scientific Party, 2002b) (Fig. F35) shows very good agreement and supports the hypothesis of a duplication of this sequence over a 5–7 m interval in all three drilled holes. Hole U1332A is duplicated between 73.2 and 78.1 m CCSF-A, Hole U1332B between 71.2 and 77.3 m CCSF-A, and Hole U1332C between 68.2 and 75.7 m CCSF-A (see also corresponding intervals in Fig. F34B).

We avoided intervals with significant disturbance or distortion and intervals where whole-round samples for interstitial water chemistry and microbiology were taken (see "Paleomagnetism;" Table T11). The Site U1332 splice can be used as a sampling guide to recover a single sedimentary sequence between 0 and 140 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 depth 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 T34), care was taken to align highly identifiable features from cores in each hole.

A growth factor of 1.10 is calculated by linear regression for all holes at Site U1332, indicating a 10% increase in CCSF-A relative to CSF depth (Fig. F36). We used this value to calculate the CCSF-B (see "Corrected core composite depth scale" in the "Methods" chapter) depth presented in Table T33 to aid in the calculation of mass accumulation rates.

Sedimentation rates

All the principal biostratigraphies, plus a set of ~72 paleomagnetic reversals, are defined in Holes U1332A–U1332C (Table T35; see "Biostratigraphy" and "Paleomagnetism") and were used in establishing age control (Fig. F11). Only the paleomagnetic reversals are used to calculate the average linear sedimentation rates (LSRs) for Site U1332 as depicted in Figure F11 using the CCSF-B depth scale.

Based on a simple linear interpolation from the sediment surface (assumed to be zero age) and the onset of Chron C2An.3n (Table T35), the clays of lithologic Unit I (see "Lithostratigraphy") have an LSR of 2.7 m/m.y.

The LSR at Site U1332 in the radiolarian and nannofossil oozes of lithologic Units II and III decreases from ~7 m/m.y. in the middle Eocene to 4.5 m/m.y. in the late Eocene to early Oligocene and to ~3 m/m.y. in the remainder of the section. A hiatus is present between ~20.4 and 3.6 Ma (Fig. F11) at the location of the major susceptibility peak at 11–13 m CCSF-A in Figure F34A.