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doi:10.2204/iodp.proc.339.103.2013

Stratigraphic correlation

The mcd scale for Site U1385 was based solely on correlation of magnetic susceptibility between holes. Because susceptibility decreases significantly below ~60 mcd and because coring gaps increase below ~110 mcd, the correlation is not as robust in the lowermost part of the section (Fig. F35). Even so, enough distinct anomalies exist to permit some confidence that coeval features are being correlated between holes. The offsets and composite depths are listed in Table T25. A growth factor of 1.07–1.10 is calculated by linear regression for the different holes at Site U1385, indicating a 7%–10% increase in mcd values relative to mbsf values (Fig. F36).

The five holes cored at Site U1385 provided ample sediment for constructing an ultracomplete spliced stratigraphic section containing no notable gaps or disturbed intervals. We refer to this splice as the “primary splice” (Fig. F37; Table T26). Two nearly complete secondary splices were also constructed, one using intervals from Holes U1385A and U1385B (the “AB splice”) and the other using intervals from Holes U1385D and U1385E (the “DE splice”) (Tables T27, T28; Fig. F37). Hole U1385C is not included in any of the splices because it is a single core from the uppermost part of the section, which is well sampled by the other holes. Where possible, we avoided including intervals in the splices that were disturbed significantly by drilling, voids, and interstitial water samples (Table T14). In addition, all magnetic susceptibility data were cleaned for the top of each section and measurement outliers (Table T29). No corrections were made for the small normal faults observed within several sections of Site U1385.

The goal of creating the primary splice was to ensure that a complete section of the most representative intervals was identified. Using this splice, nondestructive data sets collected along the cores, such as physical and magnetic properties, can be spliced into complete composite records. The two nearly complete secondary splices were constructed to maximize the material available for sampling while adhering to the IODP sampling policy, which seeks to preserve representative material from a site for future studies. Both secondary splices are complete enough that it will only be necessary to sample within the single primary splice in a few relatively narrow intervals.

Finally, a linear regression through the core tops of all holes at Site U1385 was applied to compress the expanded meters composite depth scale to the meters below seafloor scale (Fig. F38). This recalculated mbsf depth scale (mbsf*) facilitates a direct comparison of the spliced records with data plotted on the original mbsf scale. The linear regression was forced through the origin (i.e., at zero mcd and mbsf*) and gives an average compression factor of 0.9093254414.

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