COMPOSITE SECTION

We built a meters composite depth (mcd) scale and a splice from 0.00 to 360.36 mcd (as defined in "Composite Section" in the "Explanatory Notes" chapter) that ranges from the top of Core 202-1237B-1H to the bottom of Section 202-1237B-34H-7 (Tables T2, T3). All cores collected at Site 1237 were included in the composite.

The mcd scale and the splice are based on the stratigraphic correlation of the whole-core OSU Fast Track magnetic susceptibility data (OSUS-MS) collected at 5-cm intervals with 10-s integrations (Tables T4, T5, T6, T7). In two intervals, 119-124 and 270-275 mcd, we also used natural gamma radiation (NGR) data, collected at 2.5-cm intervals with 5-s counts, and color reflectance (L* and b*), measured at 2.5-cm intervals, to correlate between holes. Tie points were then used to construct representative spliced records for color reflectance (L*, a*, and b*) and multisensor track data (MST-MS) (Fig. F8).

We assumed that the uppermost sediment (the "mudline") in Core 202-1237B-1H was the sediment/water interface. A mudline was also recovered in Core 202-1237C-1H, and this confirmed the fidelity of the top of the recovered section. Core 202-1237B-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. The correlation between holes is not well constrained in three intervals: 120-123, 258-262, and 270-275 mcd. Final correlation of the multiple holes drilled at Site 1237 in these intervals will require additional shore-based analysis. The first interval (~121.5 mcd) includes the tie between Cores 202-1237C-12H and 202-1237B-13H (Fig. F9D). In this interval we used NGR in conjunction with OSUS-MS data to develop the composite section. The second interval (~260 mcd) in the middle of Core 202-1237C-25H was also recovered in Cores 202-1237B-25H and 26H as well as 202-1237D-9H and 10H (Fig. F9I). In this interval, the long-period variation in magnetic susceptibility was used for correlation, whereas some high-frequency spikes in magnetic susceptibility were ignored. The third interval (~273 mcd) includes the tie between the base of Core 202-1237C-26H and the top of Core 202-1237B-27H (Fig. F9I). Here, color reflectance (b*) was used to aid in correlation.

A comparison of the mcd and mbsf depth scales (Fig. F10) shows that, unlike the first five sites drilled during Leg 202, the cumulative offset between mcd and mbsf within the splice is not linear, and thus, the growth factor is not constant. The mcd growth factor for the spliced interval at Site 1237 varies between 1.09 and 1.20. In Cores 202-1237B-1H through 16H (0.00-160.91 mcd), 202-1237C-1H through 16H (0.05-167.20 mcd), and 202-1237D-1H through 8H (2.30-116.32 mcd), mcd grows 9% relative to mbsf. In Cores 202-1237B-17H through 25H (162.80-259.49 mcd), 202-1237C-17H through 25H (167.65-263.93 mcd), and 202-1237D-9H (248.65-258.55 mcd), mcd grows at a rate of 13% relative to mbsf. Finally, from Cores 202-1237B-26H to 34H (259.15-360.61 mcd), 202-1237C-26H to 33H (264.65-354.18 mcd), and 202-1237D-10H to 11H (258.90-281.44 mcd), mcd increases at a rate of 20% relative to mbsf. These three intervals are marked by the blue lines in Figure F10.

In order to facilitate the calculation of mass accumulation rates (MARs), we provide corrected meters composite depth (cmcd) (see "Composite Section" in the "Explanatory Notes" chapter), a scale that corrects for the growth factor and adjusts the mcd to the length of the drill string, the approximate in situ depth. Equations for calculating cmcd for any depth in the composite section are provided in Table T2. The equations are defined by four tie points that can be used to transfer, by linear interpolation, mcd into cmcd in three intervals. The intervals are illustrated in Figure F10 and tabulated in Table T2.

NEXT