Multisensor track (MST) and spectral reflectance (L*) data collected from Holes 1172A, 1172B, 1172C, and 1172D were used to determine depth offsets in the composite section. Magnetic susceptibility, GRA bulk density, and spectral reflectance measurements were the primary parameters used for core-to-core correlation at Site 1172. GRA bulk density and magnetic susceptibility data were collected at 2-cm intervals on all APC cores recovered from Holes 1172A, 1172B, and 1172C, except for Cores 189-1172A-23H and 24H, on which measurements were made at 3-cm intervals. Magnetic susceptibility and GRA bulk density were collected at 3-cm intervals on the XCB cores from Hole 1172A and the RCB cores from Hole 1172D. Spectral reflectance data were collected at 2-cm intervals on cores from Holes 1172A, 1172B, 1172C, and 1172D (see "Physical Properties" and "Lithostratigraphy" for details about MST and spectral reflectance data).
The data used to construct the composite section and determine core overlaps in the APC interval are presented on a composite depth scale in Figure F23. The depth offsets that comprise the composite section for Holes 1172A, 1172B, 1172C, and 1172D are given in Table T14. The composite data show that the APC cores from Site 1172 provide a continuous overlap to 146 mcd (base of Core 189-1172C-14H). Spectral reflectance and magnetic susceptibility data were the primary basis for interhole correlation. The interhole correlations (Fig. F23) show that ~50 cm to 1 m of material is missing between cores in each hole.
Cores 189-1172A-5H through 10H are severely disturbed by flow-in. These cores were not used in the composite construction and are only adjusted by the cumulative composite correction resulting from alignment of cores upsection. Below Core 14H in Holes 1172A, 1172B, and 1172C, low signal variability in the spectral reflectance, magnetic susceptibility, and GRA bulk density data precluded definitive core-to-core correlation. On the mcd scale, these cores only have a cumulative composite correction added; no further alignment was attempted.
Rotary drilling operations at Hole 1172D were designed so that an overlap of several cores occurred with the XCB-cored interval of Hole 1172A at the Eocene/Oligocene boundary. Composite alignment of the color reflectance, magnetic susceptibility, and GRA bulk density data (Figure F24) show that Cores 189-1172A-38X through 40X contain the same sedimentary horizons as Cores 189-1172D-2R and 3R. Core 189-1172D-2R spans the gap between Cores 189-1172A-38X and 39X, and Core 189-1172D-3R spans the gap between Cores 189-1172A-39X and 40X.
Stretching and compression of sedimentary features in aligned cores indicate distortion of the cored sequence. Because significant distortion occurred within individual cores on depth scales of <9 m, it was not possible to align every feature in the MST and color reflectance records accurately by simply adding a constant to the mbsf core depth. Core-scale changes will require postcruise processing to align smaller sedimentary features. Only after allowing variable adjustments of peaks within each core can an accurate estimate of core gaps be made.
Following construction of the composite depth section for Site 1172, a continuous spliced record was assembled for the aligned cores over the upper 140 mcd (base of Core 189-1172C-14H). The Site 1172 splice (Table T15) can be used as a sampling guide to recover a single sedimentary sequence between 0 and 140 mcd. The splice primarily utilizes cores from Holes 1172A as the backbone, with cores from Holes 1172B and 1172C patched in across core gaps. Intervals having significant disturbance or distortion were avoided. For example, Cores 189-1172A-5H through 10H are severely affected by flow-in. Cores from Hole 1172B and 1172C had sufficient overlap over this 50-m interval and were used to maintain a continuous splice.