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doi:10.2204/iodp.proc.339.203.2017

Results

The unavoidable need for a precise age model before any reconstruction of past conditions is regularly fulfilled by a combination of dating methods. For Pleistocene sedimentary sequences, correlation of the benthic foraminifer oxygen isotopic record to the LR04 δ¹⁸O stack published by Lisiecki and Raymo (2005) is the most usual. In the absence of an isotopic record for Site U1391, a correlation to Site U1385, which has a well-established and robust chronology through a common parameter, was a possible way to circumvent the chronology problem. At Site U1385, the log(Ca/Ti) signal shows good correspondence to the planktonic δ¹⁸O record (Hodell et al., 2015) and was therefore our selected parameter.

The log for Ca/Ti and Ca/Fe measured along the cores of Holes U1391A and U1391B that compose the shipboard splice of Site U1391 revealed the existence of overlaps, offsets, and gaps. To fill in the gaps and in some cases to pinpoint the extension of some overlaps, new measurements were done on adjoining core sections and both log(Ca/Ti) and log(Ca/Fe) were used to determine the correction to apply to the mcd depth scale. Figure F1 shows the obtained log(Ca/Ti) record for Site U1391 between 81.47 and 235.53 mcd (on board) and the corrected composite depth (cmcd). Figure F2 shows the log(Ca/Ti) and log(Ca/Fe) for shipboard mcd and corrected cmcd for the two intervals where major mismatch was detected between 160 and 180 mcd (Fig. F2A, F2B) and from 230 to 250 mcd (Fig. F2C, F2D). Table T1 reports the applied correction to the shipboard defined mcd to obtain the new cmcd.

For the definition of a preliminary chronology for Site U1391, the record obtained after the mcd correction was correlated to the log(Ca/Ti) of Site U1385, which has a well-defined chronology (Hodell et al., 2015). This was performed using the Analyseries program (Paillard et al., 1996) and reveals a complete sequence between marine isotope Stages (MIS) 9 and 22. Figure F3 shows log(Ca/Ti) versus age at the two sites (U1385 and U1391) and the benthic isotopic reference record of Lisiecki and Raymo (2005). Table T2 contains the tie points used.

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