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doi:10.2204/iodp.proc.323.108.2011

Stratigraphic correlation

The complete and continuous composite depth scale and splice at Site U1344 is constructed from 0.0 to 332.02 m CCSF-D (as defined in "Stratigraphic correlation" in the "Methods" chapter). Cores below the splice from Hole U1344A (discontinuously with unknown gaps) are appended to the splice from 336.18 to 790.06 m CCSF-A. Specifically, the continuous splice ranges from the top of Core 323-U1344A-1H to horizon 31X-5, 50 cm (332.02 CCSF-A) (Tables T20, T21). The appended cores range from Cores 323-U1344A-32X (336.18 m CCSF-A) through 79X (790.37 m CCSF-A), with a constant affine value of 43.78 m.

Correlations were accomplished using IODP Correlator software (versions 1.656 and 1.657), 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. F35), WRMSL GRA bulk density (Fig. F36), whole-round NGR (Fig. F37), and color reflectance parameter b* (Fig. F38) data.

The CCSF-A and CCSF-D scales were constructed by assuming that the uppermost sediment (the mudline) in Core 323-U1344A-1H represents the sediment/water interface. The mudline was also recovered in Cores 323-U1344B-1H, 323-U1344C-1H, and 323-U1344D-1H, confirming the fidelity of the top of the recovered section. Core 323-U1344A-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 0–50 m CCSF-A are clear and convincing based on multiple data types. The splice tie point between interval 323-U1344A-5H-7, 40.02 cm, and 323-U1344D-6H-3, 79.90 cm (51.96 m CCSF-A), is uncertain and could be moved ~2.4 m shallower in Section 323-U1344D-6H-3 with equal uncertainty. This is a point to be checked with postcruise data. The splice tie points between intervals 323-U1344E-6H-6, 112.50 cm, and 323-U1344A-6H-4, 122.31 cm (60.38 m CCSF-A); 323-U1344E-14H-7, 12.36 cm, and 323-U1344D-14H-2, 139.17 cm (140.42 m CCSF-A); and 323-U1334A-16H-7, 85.09 cm, and 323-U1334D-17H-4, 15.30 cm (175.51 m CCSF-A), are uncertain because of low signal amplitude in magnetic susceptibility.

The splice tie points between intervals 323-U1344D-25H-3, 51.30 cm, and 323-U1344A-25H-1, 12.89 cm (264.94 m CCSF-A), and between 323-U1344A-25H-7, 41.54 cm, and 323-U1344D-27H-1, 12.07 cm (273.67 m CCSF-A), are effectively append points where there is no overlap between cores; however, they are defined here as tie points because Correlator (version 1.656) did not allow floating splice intervals below append points. The tie between intervals 323-U1344D-31H-7, 131.47 cm, and 323-U1344A-30X-5, 12.39 cm (321.49 m CCSF-A), is highly uncertain and should be considered suspect. It is included here only because Correlator allows appended cores below a tied core in the same hole.

Difficulties making many of these tie points arose because of pervasive voids that are apparent as low "spikes" in the GRA bulk density data and, to some extent, in the other data types and also because of a finding that the NGR data contain calibration artifacts within each section (low NGR values near end caps and a characteristic double-peaked pattern within most sections) that preclude the use of NGR data for detailed correlations between holes.

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 within cores from 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 roughly linear (Figs. F39, 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 U1344 is 1.18. A few significant anomalies around this relatively uniform affine growth relationship are unexplained but may indicate uncertainties in the assignment of composite depths. The calculation of mass accumulation rates (MARs) based on the CCSF-A or CCSF-D scales should account for the 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.

Cores deeper than the spliced interval (i.e., Cores 323-U1344A-32X [336.18 m CCSF-A] through 79X [790.37 m CCSF-A]) were appended to the splice with a constant affine value of 43.78 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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