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doi:10.2204/iodp.proc.342.112.2014

Stratigraphic correlation

Sampling splice

We constructed a sampling splice for Site U1411 that consists of a series of floating continuous intervals from ~0 to ~20, ~100 to ~171, ~172 to ~196, and ~213 to 233 m core composite depth below seafloor (CCSF) (Fig. F27). The splice is based on a combination of shipboard physical property measurements (primarily magnetic susceptibility) for the 0 to ~108 and ~193 to ~233 m CCSF intervals and shore-based X-ray fluorescence (XRF) core scanning measurements of calcium/iron ratio for the ~108 to ~193 m CCSF interval. The large number of appended cores in the splice from ~20 to ~100 m CCSF is a result of time constraints; the drilling strategy was to advance without recovery through much of the upper ~100 mbsf of Hole U1411C to target prioritized stratigraphic intervals. The appended cores between ~171 and ~242 m CCSF are the result of a number of XCB cores with poor recovery from Holes U1411B and U1411C. Hole U1411B spans the thickest sediment column recovered at this site, with a maximum depth for the bottom of Core 342-U1411B-28X of 254.5 mbsf (274.02 m CCSF). Hole U1411C extends to a maximum depth of 223.9 mbsf (242.26 m CCSF). As a result, we append the last three cores in Hole U1411B as well as the last core in Hole U1411C at the bottom of the splice. Our correlation yields a growth rate of 8% for Hole U1411B and 9% for Hole U1411C (Fig. F28). The affine table (Table T19) summarizes the individual offsets for each core drilled.

Correlation during drilling operations

To aid correlation during drilling operations at Site U1411, we assessed magnetic susceptibility and GRA bulk density data collected at 2.5 cm resolution on the Special Task Multisensor Logger before allowing cores to equilibrate to room temperature. Magnetic susceptibility is low (<30 IU) between ~13 and 149 m CCSF, but it was still possible to guide drilling operations. From ~149 to 274 m CCSF, magnetic susceptibility is higher (~30–70 IU), which improved our ability to correlate in real time.

Hole U1411A was ended after one core because it did not recover a mudline. Hole U1411B switched to XCB coring for Core 342-U1411B-21X, but recovery for Cores 21X and 22X was <10%, leaving a large gap between ~177 and 196 mbsf.

The strategy for Hole U1411C was to drill without recovery through the upper portion of the sediment column after recovering the first two cores. As a result, Core 342-U1411C-3H is labeled in the affine table as a drilling advance of ~92 m. Recovery in Hole U1411C resumed at ~106 m CCSF, and with minor drilling adjustments, we were able to offset coring gaps across most of the EOT.

Correlation and splice construction

Shipboard stratigraphic correlation and splice construction were based on magnetic susceptibility data and verified by NGR data. These two data series generally show clear, correlatable features throughout the sediment column (see “Physical properties”). However, in order to improve confidence in the splice across the EOT for sampling, we collected Ca/Fe measurements using the Avaatech XRF core scanner at Scripps Institution of Oceanography. We scanned the archive halves of Cores 342-U1411B-12H through 20H and 342-U1411C-4H through 12X and verified and/or adjusted the shipboard composite depth scale and tie points using measured elemental ratios. Our correlation is consistent with biostratigraphic and paleomagnetic results (see “Biostratigraphy” and “Paleomagnetism”).

We defined Core 342-U1411C-1H as the anchor in our splice because it is longer than Core 342-U1411B-1H, whereas Core 342-U1411A-1H did not recover a mudline. We appended cores from Hole U1411B from ~20 to 108 m CCSF because Hole U1411C did not recover sediment in this interval. We added offsets to these cores (Table T19) to eliminate overlap between successive cores in Hole U1411B. We used XRF Ca/Fe data from ~108 to 193 m CCSF to identify ties (Fig. F29), though there are two tentative tie points in this interval based on small (~1 m or less) overlap between successive cores. The apparent gaps in the splice in Figure F27 at 119.00–120.00, 127.29–129.52, and 130.32–131.29 m CCSF are because of damage to the core liners of Sections 342-U1411C-5H-2, 6H-3, 6H-4, and 6H-7, which prevented the generation of WRMSL data. The tie points in these intervals are based on XRF elemental data. We used magnetic susceptibility to select tie points from ~193 to ~233 m CCSF where we did not collect XRF core scanner data. A tentative tie point at ~224 m CCSF is also the result of small overlap between successive cores. The large gap from ~195 to 213 m CCSF is the result of poor recovery in both holes, suggesting that this gap is attributable to the formation. Finally, data from Core 342-U1411B-27X is not shown in Figure F27 because damage to the core liner prevented collection of WRMSL magnetic susceptibility data; however, we append this core below the splice.

The Site U1411 splice (Table T20) can be used as a sampling guide across the EOT, particularly from ~108 to 171 m CCSF, which is the longest stratigraphically continuous interval in the splice.

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