The recovery of complete sedimentary sections within APC-cored intervals was crucial to the paleoceanographic objectives of Leg 177. Drilling of multiple holes at each site ensured that intervals missing from one hole as a result of recovery gaps were recovered in an adjacent hole. During Leg 177, as with previous ODP legs, the continuity of the recovered section was confirmed by composite depth sections developed for all multihole sites. The methods used during Leg 177 were similar to those used to construct composite depth sections during Leg 138 (Hagelberg et al., 1992), Leg 154 (Curry, Shackleton, 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) wet bulk density were made using 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- to 8-cm resolution on the split cores (see "Physical Properties"). Magnetic susceptibility, spectral reflectance in the 650-700 nm band, 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 ("Splicer") for Unix platforms that was developed at the Lamont-Doherty Earth Observatory Borehole Research Group (LDEO-BRG) and that was patterned after the Leg 138 correlation software. Corresponding features in data sets from adjacent holes were aligned using graphical and mathematical cross-correlations by an iterative process. Features were aligned by adjusting the mbsf coring depths, measured from the length of advanced drill string, on a core-by-core basis. No depth adjustments were made within a core. The resulting adjusted depth scale is the mcd scale.
The composite depth section for each site is presented in tabular form in the "Chronostratigraphy" section of each site chapter. For each section in 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 section, the cumulative depth offset added to the ODP mbsf curatorial sub-bottom depth and the composite depth, respectively. The depth-offset column facilitates conversion of sample depths that are recorded in ODP mbsf curatorial sub-bottom depth to composite depth. By adding the amount of offset listed to the depth in mbsf of a sample taken in a particular core, the equivalent depth in mcd is obtained.
Adjustments to the shipboard mbsf depth scale are required for sev-eral reasons (see short summaries in Ruddiman et al., 1987; Farrell and Janecek, 1991; Hagelberg et al., 1992, 1995). Rebound of the sediment following core recovery causes the cored sedimentary 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 greater recovery, portions of the sedimentary sequence are usually missing. As a result, the mcd scale expands 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 F1. On the left panel, magnetic susceptibility from three holes at Site 1090 is shown on the mbsf depth scale. On the right 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 were 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 1088 through 1094. 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., magnetic susceptibility, color reflectance, natural gamma, and GRA bulk density) for a given site. Additionally, these single records are ideally suited to serve as sampling schemes for paleoceanographic studies.
Splice tie points were made between adjacent holes at identifiable, highly correlated features. However, because there is considerable stretching and/or compression in many sections relative to the same sedimentary interval in adjacent holes, the exact length of the splice depends on which intervals of core were selected to build it. Each splice was constructed by beginning at the mudline at the top of the composite section and working downward. An example is given in Figure F2. Tables that provide the tie points for construction of the spliced records are presented in each site chapter (see "Chronostratigraphy" sections). Intervals were chosen for the splice such that section continuity was maintained while disturbed intervals were avoided.
By identifying intervals where features present in 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 will be conducted postcruise to align all features exactly.