The recovery of complete sediment sections over APC-cored intervals was crucial to the paleoceanographic objectives of Leg 189. Drilling of multiple holes at each site ensured that intervals missing from one APC hole as a result of recovery gaps between cores were recovered in an adjacent hole. During Leg 189, as on previous ODP legs, continuity of recovery was confirmed by composite depth sections developed for all multiple cored sites. The methods used during Leg 189 were similar to those used to construct composite depth sections during Leg 138 (Hagelberg et al., 1992), Leg 154 (Curry, Shackleton, Richter, et al., 1995), Leg 162 (Jansen, Raymo, Blum, et al., 1996), and Leg 167 (Lyle, Koizumi, Richter, et al., 1997).
At each site, closely spaced (2- to 4-cm interval) measurements of magnetic susceptibility and gamma-ray attenuation (GRA) bulk density were made on the MST soon after the core sections had equilibrated to room temperature. These measurements were entered into the shipboard database and minimally processed. In addition, measurements of spectral reflectance were made at 2-cm resolution on the split cores (see "Lithostratigraphy"). Magnetic susceptibility, lightness (L*) values from the spectral reflectance measurements, and GRA bulk density measurements from each hole were compared to determine if coring offsets were maintained between holes. Integration of at least two different physical properties allowed hole-to-hole correlations to be made with greater confidence than would be possible with only a single data set.
Hole-to-hole correlations were made using interactive software developed specifically for this task. We used a software package for Unix platforms that was developed by the Borehole Research Group at LDEO and was patterned after the Leg 138 correlation software. Corresponding features in data sets from adjacent holes were aligned based on graphical and mathematical cross-correlations by using an iterative process. Features were aligned by adjusting the ODP coring depths in mbsf, measured from the length of the drill string advanced, on a core-by-core basis. No depth adjustments were made within a core. The resulting adjusted depth scale is the meters composite depth (mcd) scale.
The composite depth section for each site is presented in tabular form in the "Composite Depths" section of each site chapter. The composite depth table of Site 1171 is given as an example in Table T5. For each core, the depth adjustment required to convert from the mbsf depth scale to the mcd scale is given. The last two columns in each table give, for each core, the cumulative-depth offset added to the ODP curatorial sub-bottom depth (in mbsf) and the composite depth (in mcd), respectively. The depth-offset column facilitates conversion of sample depths that are recorded in ODP curatorial sub-bottom depth (in mbsf) to composite depth (in mcd). The equivalent depth in mcd is obtained by adding the amount of offset listed to the depth in mbsf of a sample taken in a particular core.
Adjustments to the shipboard mbsf depth scale are required for several reasons (see the short summaries in Ruddiman et al., 1987; Farrell and Janecek, 1991; Hagelberg et al., 1992; and Hagelberg et al., 1995). Rebound of the sediment following core recovery causes the cored sediment sequence to be expanded relative to the drilled interval. In addition, other factors including random variations in ship motion and heave can affect the true in situ depth of each core by introducing errors. Even between successive cores having nominally 100%, or even greater, recovery, portions of the sediment sequence are usually missing. As a result, the composite depth scale grows downhole relative to the mbsf scale, typically on the order of 10%.
The need for a composite section to verify stratigraphic continuity is illustrated in Figure F9. In the leftmost panel, GRA bulk density from three holes at Site 1171 is shown on the mbsf depth scale. In the middle panel, the same records are shown after depth scale adjustment so that correlative features are aligned.
The correlation of lithologic parameters between multiple holes and associated depth adjustments for individual cores was optimized in such a way that a single record could be sampled from the aligned cores without any additional depth scale changes. Where the amount of offset necessary to align features was ambiguous or imprecise for all lithologic parameters or where multiple hole data were unavailable, no additional depth adjustments were made. In these cases, the total amount of offset between mbsf depth and mcd is equal to the cumulative offset from the overlying cores. The composite depth section extends only to the base of multiple cored intervals, typically the APC intervals at Sites 1168-1172. Below the multiple cored intervals, cores were appended using the offset of the last core within the composite record to convert mbsf to mcd.
For each site, after the composite section was constructed, a representative record was assembled. Because the missing intervals between successive cores in the sedimentary sequence could be identified, it was possible to patch in these missing intervals with data from adjacent holes. The resulting splice provides a single representative record of each lithologic parameter (i.e., susceptibility, spectral reflectance, and GRA bulk density) for a given site. Additionally, these single records are ideally suited to serving as sampling schemes for paleoceanographic studies.
Splice tie points were made between adjacent holes at identifiable, highly correlated features. Each splice was constructed by beginning at the mudline at the top of the composite section and working downward. Typically, one hole is chosen as the backbone for the record and cores from other holes are used to patch in the missing intervals in the core gaps (Fig. F9). Intervals were chosen for the splice such that section continuity was maintained, whereas disturbed intervals were avoided. An example of a table that provides tie points for the Site 1171 splice is given in Table T6. Tables that give the tie points for construction of the spliced records are presented in each site chapter (Tables T15 in the "Site 1168" chapter, T16 in the "Site 1170" chapter, T16 in the "Site 1171" chapter, T15 in the "Site 1172" chapter).
By identifying intervals where features present in the multiple holes were most highly correlated, it was possible to construct a spliced record that avoided duplication or omission of any individual features or cycles. Splice tie points always connect features with exactly the same composite depths. As a result, the final alignment of the adjacent holes could be slightly different from the one giving the best overall visual or quantitative hole-to-hole correlation. Further adjustments to the composite depth section by expanding and compressing the depth scale within individual core intervals would be required to align all features exactly. These additional adjustments will be made as part of normal postcruise studies.