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doi:10.2204/iodp.proc.323.103.2011

Stratigraphic correlation

The composite depth scale and splice at Site U1339 is complete from 0.0 to 219.06 m CCSF-A (as defined in "Stratigraphic correlation" in the "Methods" chapter). The continuous splice ranges from the top of Core 323-U1339C-1H to the bottom of Section 323-U1339D-21H-6 (Tables T18, T19). One additional core below the splice (Core 323-U1339D-22H) was included in the composite depth framework by extrapolation. Correlations were accomplished using IODP Correlator software (version 1.652, which was abandoned for version 1.65 early during coring and replaced with version 1.655 for Hole U1339D and final site compilation).

The composite (CCSF-A) and splice (CCSF-D) depth scales are based primarily on the stratigraphic correlation of STMSL magnetic susceptibility data collected at 5 cm intervals as the average of two 1 s integrations. These primary correlations were assisted and verified throughout the cored interval with STMSL GRA bulk density data (Fig. F26), NGR (Fig. F27), and STMSL magnetic susceptibility (Fig. F28) measured at 2.5 cm intervals. P-wave velocity and noncontact resistivity data were also collected with the WRMSL in part of the cores. However, these data are not illustrated here because they were not useful for correlation—either because of low signal variability or the presence of frequent gas voids (which also compromised STMSL and WRMSL GRA bulk density data). Cores 323-U1339B-1H through 4H were mostly consumed for microbiology sampling after STMSL data collection, so no WRMSL data are available for these cores. STMSL data allow us to assign composite depths to the four cores recovered from Hole U1339B, but because these cores are unavailable for future sampling, they are not included in the splice.

The CCSF-A and CCSF-D depth scales were constructed by assuming that the uppermost sediment (the mudline) in Core 323-U1339C-1H was the sediment/water interface. A mudline was also recovered in Cores 323-U1339A-1H and 323-U1339B-1H, confirming the fidelity of the top of the recovered section. Core 323-U1339C-1H was selected 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 stratigraphy on a core-by-core basis using Correlator.

The match between holes is well constrained except for two suspect intervals where overlap between holes was short: 112–123 m CCSF-A (between Cores 323-U1339D-12H, 323-U1339C-12H, and 323-U1339D-13H) and 161–168 m CCSF-A (between Cores 323-U1339D-16H and 323-U1339C-17H). However, the spliced section in these intervals is supported by wireline logging data compared to GRA bulk density core logging data (see "Downhole measurements").

The splice was constructed primarily from Holes U1339C and U1339D because these were minimally sampled at sea (Fig. F29). Two intervals from Hole U1339B were included in the splice when they were the least disturbed and most representative sections available (Table T19). 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 stretching and squeezing 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 not linear (Fig. F30). 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 U1339 is 1.10 between 0 and 100 mbsf and 1.17 between 100 and 200 mbsf. Larger growth factors in deeper intervals have been observed at other drill sites (for example, ODP Leg 202; Mix, Tiedemann, Blum, et al., 2003). At Site U1339, the larger growth factor at greater depths is consistent with more prominent gas expansion deeper in the section as well as normal expansion associated with release of overburden. Calculation of mass accumulation rates (MARs) based on the CCSF-A or CCSF-D scales should account for the expansion by dividing apparent depth intervals by the appropriate growth factor. After being divided by the growth factor (accounting for the different depth intervals), this scaled depth scale should be referred to as CCSF-B.

The deepest core at Site U1339 (Core 323-U1339D-22H) is not tied to the splice. Rather than appending this core below Core 323-U1339D-21H, we calculated its CCSF-A depth and affine value by extrapolating the value from the overlying core by a growth factor of 1.17.

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