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doi:10.2204/iodp.proc.323.106.2011

Stratigraphic correlation

The composite depth scale and splice at Site U1342 is complete and continuous from 0.0 to 46.54 m CCSF-A (as defined in "Stratigraphic correlation" in the "Methods" chapter). The splice ranges from the mudline at the top of Core 323-U1342D-1H to the bottom of Section 323-U1342D-5H-7 (Tables T15, T16). Sediment cores below the splice (Cores 323-U1342A-6H and 7H) are included in the composite depth framework by appending them with a constant affine value of 2.78 m. Core 323-U1342A-8D is a drilled interval with no recovery; Core 323-U1342A-9X recovered hard rock and is not included in the composite depth framework, nor are drilled interval 323-U1342D-6D and Cores 323-U1342D-7X through 19X, which had partial recovery of lithified sediments and volcanic rocks.

Correlations were accomplished using IODP Correlator software (version 1.656), and some intervals were checked with digital line-scan images with Correlyzer (version 1.3.3).

The composite (CCSF-A) and splice (CCSF-D) depth scales are based primarily on the stratigraphic correlation of WRMSL magnetic susceptibility data (Fig. F35), augmented with WRMSL GRA bulk density (Fig. F36) and NGR data (Fig. F37). Color reflectance data were also examined; the b* parameter was useful for correlation (Fig. F38), but the L* and a* parameters did not appear to correlate between holes (data not shown). GRA data from both the STMSL and WRMSL were calibrated prior to analyzing cores for each hole.

Construction of the CCSF-A and CCSF-D scales assumed that the uppermost sediment (the mudline) in Core 323-U1342A-1H was the sediment/water interface. A mudline was also recovered in Cores 323-U1342A-1H, 323-U1342B-1H, and 323-U1342C-1H, which confirmed the fidelity of the top of the recovered section. Core 323-U1342A-1H serves as the anchor in the composite depth scale and is the only core with depths that are the same on the mbsf and CCSF-A scales. However, because Core 323-U1342A-1H is a short core, we chose to start the splice with the longer Core 323-U1342D-1H, whose top starts at 0.03 mbsf. From this core we worked downhole, correlating the variations in core logging data on a core-by-core basis using Correlator. Hole U1342B was assigned affine values based on comparison of its STMSL GRA and magnetic susceptibility data to the WRMSL GRA and magnetic susceptibility data from other holes; however, Hole U1342B was largely consumed by microbiology studies, so it was excluded from the splice. All affine values that define the composite depth scale and all splice tie points are robust and well defined at Site U1342. The resulting spliced records of magnetic susceptibility, GRA bulk density, and NGR are illustrated in Figure F39.

Within the splice, the composite CCSF-A depth scale is defined as the CCSF-D depth scale. Note that CCSF-D rigorously applies only to the spliced interval. Intervals outside the splice, although available with CCSF-A composite depth assignments, should not be expected to correlate precisely with fine-scale details within the splice or with other holes because of normal variation in the relative spacing of features in different holes. Such apparent depth differences may reflect coring artifacts or fine-scale variations in sediment accumulation and preservation at and below the seafloor.

The cumulative offset between mbsf and CCSF-A depth scales is approximately linear (Fig. F40). The affine growth factor (a measure of the fractional stretching of the composite section relative to the drilled interval; see "Stratigraphic correlation" in the "Methods" chapter) at Site U1342 is 1.06 between 0 and 44.0 mbsf. Calculation of mass accumulation rates (MARs) based on the CCSF-A or CCSF-D scales should account for this affine growth factor by dividing apparent depth intervals by the appropriate growth factor. After it is divided by the growth factor (accounting for the different depth intervals), this scaled depth scale should be referred to as CCSF-B.

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