A composite section was constructed for the upper 144 mcd of Site 1220 using multisensor track (MST) and color reflectance data to determine depth offsets between cores from Holes 1220A, 1220B, and 1220C (Figs. F11, F12). In Hole 1220A, MS and color reflectance data were collected at 2-cm intervals and gamma ray attenuation (GRA) bulk density at 4-cm intervals down to Core 199-1220A-10H, below which GRA bulk density data were acquired at 2-cm intervals. GRA bulk density data were collected at 2-cm intervals throughout cores from Holes 1220B and 1220C. P-wave velocity data were collected at 2-cm intervals through Core 199-1220A-11H and from Cores 199-1220B-4H through 13H. No P-wave data were collected in the XCB portion of Hole 1220B or in any core of Hole 1220C. Minolta spectrophotometer data were collected in all three holes at 2-cm intervals. Readings from the natural gamma ray (NGR) instrument showed only background radiation levels below ~50 mbsf. This component from the MST assemblage was only run in Hole 1220A. Disturbed intervals, as determined by visual inspection of split cores, are listed in Table T7. Data from these intervals were removed prior to correlation work. Table T8 lists the offsets that were applied to cores from each hole to create a composite depth record.
Cores from Site 1220 overlap and form a continuous sedimentary sequence down to ~144 mcd (base of Core 199-1220B-10H) (Figs. F11, F12). Between 144 and 166 mcd, cores were placed into a composite depth framework, but a continuous section could not be constructed over this interval because gaps were aligned and it was not always possible to establish the true stratigraphic position of the cores. For example, Cores 199-1220B-11H and 199-1220C-10H can be correlated to each other but not to cores above or below. Figures F11 and F12 show that in this interval, between 148 and 158 mcd, the position of these cores is not constrained with respect to Hole 1220B or Hole 1220C or with respect to other intervals above or below in either hole.
The first cores from Holes 1220B and 1220C recovered sediments from >34 and >25 mbsf, respectively, so there is no spliced record available for the interval covered by Cores 199-1220A-1H and 2H. However, this interval of predominantly radiolarian clay was recovered in the site survey piston Core EW9709-13PC (Lyle, 2000), and the bulk density and MS records between Site 1220 and the site survey core correlate well. The GRA bulk density record at Site 1220 (Fig. F11) shows several section-long intervals (~100 and 195 mcd, respectively) that have values offset from the background GRA record by 0.15 g/cm3. This offset does not correspond to any lithologic, physical, or geochemical change in the core and is an electronic artifact that occurred during data collection.
Following construction of the composite depth section for Site 1220, a single continuous spliced record was assembled for the aligned cores down to ~144 mcd by patching across cores to cover gaps with data primarily from Holes 1220A and 1220B above 95 mcd and Holes 1220B and 1220C below 95 mcd (Table T9; Fig. F13). Intervals having significant disturbance or distortion (see Table T7) were avoided. The lithology-dependent correlation or anticorrelation of MS and GRA bulk density measurements are illustrated in Figure F14. Intervals that are dominated by varying calcium carbonate (CaCO3) content show a clear cyclical signal as well as an anticorrelation between MS and GRA bulk density.
The Site 1220 splice can be used as a sampling guide to recover a continuous single sedimentary sequence down to 144 mcd. When utilizing this splice as a sampling guide, it is advisable to overlap a few decimeters from different holes when sampling in order 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 feature in the MST and color reflectance records. However, at crossover points along the splice (Table T9), care was taken to align highly identifiable features from cores in each hole. Postcruise work will establish a detailed correlation between holes by establishing a revised meters composite depth scale that allows differential stretching and squeezing within cores, following Hagelberg et al. (1992).