In contrast to other Leg 199 sites, the recovered sediment was only mildly affected by drilling disturbances. Under these circumstances and in the presence of high signal-to-noise ratio data sets, it was possible to direct drilling in Holes 1218B and 1218C in real time to complete the construction of the composite sediment section. MST and color reflectance data collected from cores from Holes 1218A, 1218B, and 1218C were used to construct a continuous sequence down to ~263 mbsf (~287 mcd). Hole 1218A was extended to basement at ~274 mbsf, but the two lowermost cores (Cores 199-1218A-29X and 30X) could not be bridged with data from Hole 1218B or Hole 1218C. Disturbed intervals, as determined by visual inspection of split cores, are listed in Table T10. Data from these intervals were removed prior to further correlation work. Table T11 lists the offsets that were applied to cores from each hole to create a composite depth record. This allowed the construction of a spliced record designed for sampling purposes as listed in Table T12.
On cores from Hole 1218A, MS, P-wave velocity, and color reflectance data were collected at 2-cm intervals and GRA bulk density at 4-cm intervals down to Core 199-1218A-22X, below which GRA bulk density data were acquired at 2-cm intervals. GRA bulk density data showed a strong and characteristic signal. Because of time constraints, it was desirable to obtain GRA bulk density data at a higher resolution (2-cm intervals) at the expense of P-wave velocity measurements. In addition, the P-wave whole-core logger does not operate properly in XCB-cored intervals because the core does not make full contact with the core liner. For these reasons, P-wave velocity data were not collected below Core 199-1218A-22X and then only from selected intervals from Holes 1218B and 1218C. GRA bulk density data were collected at 2-cm intervals throughout Holes 1218B and 1218C. Readings from the natural gamma ray (NGR) instrument showed only background radiation levels below ~5 mbsf. This component from the MST assemblage was only run on Hole 1218A cores. Color reflectance data were collected at 2-cm intervals on all cores.
The interval from the seafloor to ~55 mbsf was cored only in Holes 1218A and 1218B. However, a 3- to 4-m coring offset between the two holes provided complete coverage of gaps between cores. This upper section consists of clay (see "Lithostratigraphy") and has a very characteristic MS signal, whereas the GRA density data are rather featureless. The MS data allow a very clear correlation between holes in this upper interval as illustrated in Figure F14. The stratigraphic correlation in deeper intervals is supported by a strong signal in the GRA bulk density data that arises from varying proportions of CaCO3, silica, and clay end-members. GRA bulk density (Fig. F13) and MS (Fig. F14) data made the interhole correlation straightforward down to a depth of ~155 mbsf (~174 mcd), above which there is only very little stretching or squeezing observed between features that can be seen in more than one hole. An exception to this general situation is evident in Core 199-1218C-6H where, alignment of this core with equivalent sections in the other holes suggests that the core is compressed. This core disturbance is supported by the apparent misalignment of paleomagnetic reversal datums between the holes over this interval (see "Paleomagnetism"). The disappearance and reappearance of two biostratigraphic datums (see "Biostratigraphy") across Cores 199-1218A-7H and 8H indicates an additional interval with lithological disturbance that is not apparent from the MST data.
Below Core 199-1218B-21X (~220 mcd), cores from Holes 1218A and 1218B did not overlap sufficiently to cover gaps between cores. Thus, coring of Hole 1218C was designed to cover the missing intervals as well as provide additional material for high-resolution studies. The coring effort in Hole 1218C was successful at covering gaps between cores in Holes 1218A and 1218B to a depth of ~262 mbsf (287 mcd). In contrast to the overlying interval, the XCB-cored lower part of Site 1218 (below 210 mcd) shows medium to strong differential stretching and squeezing between features that are clearly recognizable in different holes. Thus, it is not always possible to align all apparently correlative features in one hole with those in other holes in the basal interval of the site.
Following construction of the composite depth section for Site 1218, a single spliced record was assembled for the aligned cores down to 263 mbsf (~287 mcd) by using cores from Holes 1218A as the "backbone" and patching across core gaps primarily with cores from Hole 1218B (Table T12). Intervals having significant disturbance or distortion (see Table T10) were avoided. The Site 1218 splice can be used as a sampling guide to recover a single sedimentary sequence between 0 and 287 mcd, although 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 T12) care was taken to align highly identifiable features from cores in each hole.
Intervals that are dominated by varying CaCO3 content show a clear cyclical signal as well as an anticorrelation between MS and GRA bulk density. The lithology-dependent correlation or anticorrelation of MS and GRA bulk density measurements is illustrated in Figure F15. Of particular interest is the transition from carbonate-poor to carbonate-rich sediments, evident as a two-step increase in GRA bulk density and decrease in MS values from 243 to 239 mcd. Based upon biostratigraphic information (see "Biostratigraphy"), this transition occurs across or just above the Eocene-Oligocene transition. In Figure F16, the spliced records of MS, GRA bulk density, and the color reflectance at Site 1218 show that this transition was preceded by an interval with large variations in MS and bulk density that correspond to five closely spaced thin chert layers between 253 and 251 mcd (the top of Cores 199-1218A-25X and 199-1218B-25X and the middle of Core 199-1218C-18X) (see "Lithostratigraphy").
Overall, the composite depth record from Site 1218 is expanded in length compared to the mbsf depth scale by ~11%. However, in detail, the expansion of the composite depth record relative to the mbsf depth measurement varies with depth as illustrated by Figure F17. Down to a depth of ~120 mbsf in Core 199-1218A-13H (~135 mcd), the relative expansion is ~14%, whereas the cores below generally only require an adjustment of ~9% with respect to their mbsf depth. This decrease in core expansion, which coincides with a change of character in the MS and GRA bulk density records, reflects a lithologic change to a stiffer, more chalklike nannofossil ooze.