We built a meters composite depth (mcd) scale and a splice (as defined in "Composite Section" in the "Explanatory Notes" chapter) that ranged from the top of Core 202-1232C-1H to the bottom of Section 202-1232B-4H-7 (Tables T2, T3). The splice extends from 0.0 to 42.58 mcd. Splice construction below this interval was precluded by incomplete core recovery and by alignment of core gaps. We constructed a discontinuous ("floating") splice (see "Composite Section" in the "Explanatory Notes" chapter) for the interval 42.67-100.34 mcd (Sections 202-1232B-5H-1 through 202-1232A-9H-7). Below that interval, cores were appended according to the cored interval if nominal recovery was <100% or to the recovered interval if recovery was >100%.
The mcd scale and the splice are based on the stratigraphic correlation of whole-core OSU Fast Track magnetic susceptibility measurements (OSUS-MS) collected at 2.5-cm depth increments using 1-s integration times (Fig. F4; Tables T4, T5). Correlations were checked using multisensor track (MST) data collected at 2.5- to 5-cm depth increments. We then constructed spliced records of magnetic susceptibility (MST-MS), gamma ray attenuation (GRA) bulk density, and natural gamma radiation (NGR) data (Fig. F5).
Magnetic susceptibility was the most useful stratigraphic tool for correlation at Site 1232. GRA density was helpful in some intervals where magnetic susceptibility structure was ambiguous. Correlation between cores from different holes was poor in the top and bottom ~1 m of many cores. We interpret this lack of correlation as evidence for disturbance resulting from the effects of the coring process at Site 1232. We constructed the mcd scale by assuming that the uppermost sediment (the "mudline") in Core 202-1232C-1H was the sediment/water interface. Core 202-1232C-1H, the "anchor" in the composite depth scale, is the only core in which depths are the same on the mbsf and mcd scales. From this anchor we worked downhole, correlating the stratigraphy on a core-by-core basis.
Although cores from different holes in the interval 42.67-100.34 mcd could not be tied directly to the splice, they could be correlated with each other. We placed them on the composite depth scale by adding the cumulative offset from the splice above to the mbsf depths for Cores 202-1232B-5H through 10H except where the bottom of a core overlapped with the top of the core below. In this case, the lower core was shifted down to prevent overlap and the new cumulative offset propagated downhole. Cores from Hole 1232A were then correlated with cores from Hole 1232B. At depths >100.34 mcd, cores in Hole 1232A were assigned an mcd by adding the cumulative offset of Core 202-1232A-9H, the deepest core correlated with a core in Hole 1232B, to their mbsf depth except when the recovered interval exceeded the cored interval. In these cases, the difference (typically <0.3 m) was added to the offset to avoid stratigraphic overlap.
A comparison of the mcd and mbsf depth scales (Fig. F6) shows that within the splice the mcd scale is an average of 22% greater than the mbsf scale. In addition, Hole 1232A shows an overall step in the offsets below Core 202-1232A-6H and can be best correlated to Core 202-1232B-7H in the composite section. This additional offset reflects the fact that Core 202-1232A-5H was recovered after operational problems and contained significant flow-in. We concluded that the core, and all subsequent cores, were recovered from deeper in the section than was recorded by the driller.
To facilitate the calculation of mass accumulation rates (MARs), we provide corrected meters composite depth (cmcd) in Tables T2 and T3 for depths within the splice. A comparison of the mcd and mbsf depth scales (Fig. F6) shows that the mcd scale within the splice is an average of 22% longer than the mbsf scale.