We built a meters composite depth (mcd) scale to Section 202-1238A-46X-1 (0.00-466.97 mcd) and a splice (as defined in "Composite Section" in the "Explanatory Notes" chapter) that documents complete recovery for the upper 225.52 mcd. The splice ranges from the top of Core 202-1238B-1H to the bottom of Section 202-1238B-22H-7 (0.00-225.52 mcd) (Tables T2, T3). All APC cores can be correlated to the splice at Site 1238.
The mcd scale and the splice are based on the stratigraphic correlation of whole-core Oregon State University Fast Track magnetic susceptibility measurements (OSUS-MS) collected at 5-cm intervals with a 10-s integration (Fig. F9; Tables T4, T5, T6). Tie points (Table T3) were then used to construct representative spliced records for multisensor track magnetic susceptibility (MST-MS), gamma ray attenuation (GRA) bulk density, natural gamma radiation (NGR) (Fig. F10), and color reflectance (L*, a*, and b*) data (Fig. F11). Magnetic susceptibility was the most useful tool for stratigraphic correlation.
We assumed that the uppermost sediment (the "mudline") in Core 202-1238B-1H was the sediment/water interface. A mudline was recovered in all three holes and this helped to confirm the fidelity of the top of the recovered section. Core 202-1238B-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.
A comparison of the mcd and mbsf depth scales (Fig. F12) shows that the mcd scale is on average 10% longer than the mbsf scale. Because the growth factor of 1.10 in the APC interval was constant and there were no obvious lithologic changes in the recovered section, we decided to place the XCB cores on an mcd scale by assuming a growth factor of 1.10 applies to the XCB cores from Hole 1238A (Fig. F12).
In order to facilitate the calculation of mass accumulation rates (MARs), we provide corrected meters composite depth (cmcd) in Table T2 and in Table T3 for depths within the composite section.
Logging operations at Site 1238 produced records of borehole density and natural gamma radiation that could be correlated to GRA density and NGR measurements in sediments from Hole 1238A (Fig. F13). An equivalent log depth (eld) (see "Composite Section" in the "Explanatory Notes" chapter) scale was produced using these correlations. This scale accounts for differential stretching and squeezing within cores as well as for the gaps between cores and is the most accurate depth scale for sediments below the spliced section and above Core 202-1238A-42X (225.52-422.13 mcd), where core recovery falls significantly. The Site 1238 eld file (see the "Supplementary Material" contents list) allows the application of the eld scale to sample depths in either the mbsf or mcd scale using the Sagan software package available from the Borehole Research Group at LDEO.