We built a composite depth scale (0.00-240.39 meters composite depth [mcd]) (Table T2) and a splice (as defined in "Composite Section" in the "Explanatory Notes" chapter) that ranges from the top of Core 202-1234A-1H to the bottom of Section 202-1234B-9H-7 (0.00-94.44 mcd) (Table T3). Below Core 202-1234B-9H, we appended cores based on the assumption that the cumulative offset growth factor (see "Composite Section" in the "Explanatory Notes" chapter) for cores below the splice was the same as in the splice. The depth offsets of cores from Hole 1234B were then adjusted for optimum correlation of magnetic susceptibility with those from Hole 1234A.
The mcd scale and the splice are based on the stratigraphic correlation of whole-core OSU Fast Track magnetic susceptibility data (OSUS-MS) collected at 5-cm depth intervals using 1-s integration times. OSUS-MS data for Holes 1234A, 1234B, and 1234C and the primary splice constructed from them are presented on the primary mcd scale in Figure F5 and in Tables T4, T5, and T6. The splice tie points (Table T3) were used to construct representative spliced records for reflectance (L*), multisensor track magnetic susceptibility (MST-MS), gamma ray attenuation (GRA) bulk density, and natural gamma radiation (NGR) data (Fig. F6). Magnetic susceptibility was the most useful tool for stratigraphic correlation.
We assumed that the uppermost sediment in Core 202-1234A-1H was the sediment/water interface (the "mudline"). A mudline was also recovered in Core 202-1234B-1H, and this helped to confirm the fidelity of the top of the recovered section. Core 202-1234A-1H, the "anchor" in the composite depth scale, is the only core with depths that are the same on the mbsf and mcd scales. From this anchor, we worked downhole, correlating records on a core-by-core basis. Comparison of the mcd and mbsf depth scales (Fig. F7) shows that the mcd scale is, on average, 18% longer than the mbsf scale. Core 202-1234B-1H was assigned a negative offset of -0.19 m because the best correlation with Core 202-1234A-1H, made on the broad susceptibility maximum at ~2.5 mcd, shifts Core 202-1234B-1H up 19 cm relative to Core 202-1234A-1H. Such small differences may occur in cores that contain the mudline, which typically consists of very soupy sediment. They are most likely a result of the behavior of the sediment in response to drilling.
Continuous recovery of the sediment section at Site 1234 could not be demonstrated based on shipboard data below Cores 202-1234A-9H and 202-1234B-9H (Fig. F5D). Although cores below 94 mcd could not be tied directly to the cores within the spliced interval, most could be correlated with one or more cores in the other hole (Fig. F5D, F5E, F5F, F5G). These correlations resulted in "floating splices." First, cores with tops at depths greater than 94 mcd (starting with Cores 202-1234A-10H and 202-1234B-10H) were all assigned a depth offset based on the assumption that mcd = 1.18 (mbsf) (i.e., that the growth factor is constant). Then, cores from Hole 1234B were correlated where possible (six out of ten cases) with cores from Hole 1234A. The cumulative offsets of cores from Hole 1234B that could not be correlated were left unaltered.
To facilitate the calculation of mass accumulation rates (MARs), we provide corrected meters composite depth (cmcd) in Tables T2 and in Table T3 for depths within the splice. The mcd growth factor for the spliced interval at Site 1234 is 1.18. This growth factor was assumed to apply to the interval below the splice.