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doi:10.2204/iodp.proc.323.109.2011

Stratigraphic correlation

The composite depth scale and primary splice at Site U1345 is complete and continuous from 0.0 to 168.0 m CCSF-D (as defined in "Stratigraphic correlation" in the "Methods" chapter). The splice ranges from the top of Core 323-U1345A-1H (0 m CCSF-D) to horizon 323-U1345D-16H-7, 150.57 cm (168.0 m CCSF-D) (Tables T17, T18). There are no appended intervals. The splice is composed of intervals from Holes U1345A, U1345C, and U1345D. Parts of Hole U1345E were preserved as pristine whole-round sections for postcruise analyses. These cores are not included in the primary splice; however, they were considered when constructing composite depths and are thus included in the affine table (Table T17). The secondary splice at Site U1345 was constructed during the postcruise sampling party from 0.0 to 166.39 m CCSF-A, ranging from the top of Core 323-U1345C-1H (0.0 m CCSF-A) to the bottom of Core 323-U1345E-16H (166.39 m CCSF-A) (Table T19). The secondary splice is composed of intervals from Holes U1345A, U1345C, U1345D, and U1345E and includes none of the same intervals used in the primary splice. The secondary splice was constructed using a depth framework that is consistent with the primary splice, so the affine table (Table T17) is universal for both the primary and secondary splices.

Correlations were accomplished using IODP Correlator software (version 1.656), and where possible 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 data (Fig. F30). Correlations were checked with WRMSL GRA bulk density (Fig. F31), whole-round NGR (Fig. F32), and color reflectance parameter b* (Fig. F33) data. However, these data were less useful for correlation than WRMSL magnetic susceptibility data because of noise induced by extensive voids (WRMSL GRA and b*) or low signal amplitudes (NGR). In many cores, Section 1 needed to be reconstructed on the catwalk after gas expansion pushed material out of the core liner, so the intervals in Section 1 of all cores except Core 323-U1345A-1H are not included in the splice unless no other copy of the interval was available.

The CCSF-A and CCSF-D scales were constructed by assuming that the uppermost sediment (the mudline) in Core 323-U1345A-1H represents the sediment/water interface in the primary splice. The mudline was also recovered in Cores 323-U1345C-1H and 323-U1345E-1H, confirming the fidelity of the top of the recovered section. Core 323-U1345A-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.

Most of the splice points in the primary splice are clear and convincing based on multiple copies of the section recovered in five holes. The splice tie point between intervals 323-U1345A-10H-4, 48.75 cm, and 323-U1345C-10H-1, 92.95 cm (92.66 m CCSF-A), is uncertain because Core 323-U1345A-10H contains disturbed flow-in that starts approximately in the middle of Section 10H-4 and extends through the bottom of Section 10H-7. The disturbed section is not included in the splice; however, as a result of this disturbance, the composite depths in this interval could not be verified by multiple realizations. The splice tie point between horizons 323-U1345D-10H-7, 54.48 cm, and 323-U1335A-11H-3, 115.4 cm (103.02 m CCSF-A), is tentative because of low signal amplitudes in WRMSL magnetic susceptibility.

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 roughly linear (Figs. F34, F35). 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 U1345 is 1.11. A few significant anomalies around this relatively uniform affine growth relationship are unexplained but may indicate uncertainties in the assignment of composite depths. 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.

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