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doi:10.2204/iodp.proc.323.107.2011

Stratigraphic correlation

The composite depth scale and splice at Site U1343 are constructed from 0.0 to 269.92 m CCSF-A (as defined in "Stratigraphic correlation" in the "Methods" chapter). The splice consists of one complete and continuous interval from the mudline to 269.92 m CCSF-A. Below the splice, cores from Hole U1343E (with unknown gaps) are appended from 270.47 to 779.18 m CCSF-A.

The continuous splice ranges from the top of Core 323-U1343C-1H to interval 323-U1343E-28H-6, 79.2 cm (Tables T18, T19). The appended cores range from interval 323-U1343E-29H-1, 0 cm (270.42 m CCSF-A), to 83X-7, 31 cm (779.62 m CCSF-A), with a constant affine value of 35.62 m.

Correlations were accomplished using IODP Correlator software (version 1.656), and some intervals were checked with digital line-scan images with Corelyzer (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 (Fig. F32), WRMSL GRA bulk density (Fig. F33), whole-round NGR (Fig. F34), and color reflectance parameter b* (Fig. F35) data. Figure F36 shows the spliced composite record for Site U1343.

The CCSF-A and CCSF-D scales were constructed by assuming that the uppermost sediment (the mudline) in Core 323-U1343C-1H represents the sediment/water interface. The mudline was also recovered in Cores 323-U1343A-1H and 323-U1343B-1H, confirming the fidelity of the top of the recovered section. Core 323-U1343C-1H serves as the anchor in the composite depth scale and is the only core with depths that are the same on the mbsf, CCSF-A, and CCSF-D scales. From this anchor we worked downhole, correlating the variations in core logging data on a core-by-core basis using Correlator. All splice points in the interval of 0–269.92 m CCSF-A are clear and convincing based on multiple data types and are further supported with NGR wireline logging data (see "Downhole measurements"). Pervasive gas voids are apparent as low spikes in the GRA bulk density data and, to some extent, in other data types.

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 the mbsf and CCSF-A depth scales is nonlinear (Fig. F37). 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 U1343 between 0 and 36.4 mbsf (i.e., Cores 323-U1343A-1H through 4H, 323-U1343B-1H through 4H, and 323-U1343C-1H through 4H) is 1.03. At greater depths (all cores to 234.2 mbsf, that is, through Core 323-U1343C-26H) have an affine growth factor of 1.15. A few significant anomalies around this relatively uniform affine growth relationship are explained; relatively short cores (e.g., Cores 323-U1343C-8H and 323-U1343E-5H) typically contain significant debris that fell in the borehole at the top of each Section 1; as a result, they have artificially low apparent top depths and thus artificially low affine values. The calculation of mass accumulation rates (MARs) based on CCSF-A or CCSF-D scales should account for the affine growth factor by dividing apparent depth intervals by the appropriate growth factor for the depth interval. 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.

Cores deeper than the spliced interval—that is, intervals 323-U1343E-29H-1, 0 cm (270.42 m CCSF-A), through 83X-7, 31 cm (779.62 m CCSF-A)—were appended to the slice with a constant affine value of 35.62 m. MARs calculated in this interval should not be divided by the affine growth factor because their depths are a linear transformation of drilling depths.

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