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doi:10.2204/iodp.proc.342.202.2017

Results

The newly generated XRF data, together with those used for the construction of shipboard splice, enabled several revisions for the Site U1406 composite depth scale (Table T1) and splice (Tables T2 and T3). In addition, we present mapping pairs to adjust off-splice intervals to the spliced record in Table T4. Notably, we revised the first four tie points in the shipboard splice of Site U1406 (see the "Site U1406" chapter [Norris et al., 2014c]). In the shipboard splice, these revisions were solely based on physical properties data (Tables T5, T6, T7, T8) and therefore labeled as “tentative.” Additional XRF core scanning data guided our splice revisions in this interval, because the ln(Ca/K) ratio (Table T9) shows excellent correlation among the three holes. We noticed that core photos and color data plotted on the revised depth scale reveal an apparent mismatch at the top of the record (Figs. F3 and F4 at ~23 m CCSF-M). We hypothesize that a redox front reached different depths in the three holes, possibly due to variable paleobathymetry of the drift sediments (see the “Expedition 342 summary” chapter [Norris et al., 2014a]) or local variations in organic carbon supply.

Another significant revision to the composite depth scale and splice is required at ~94 m CCSF-M (uppermost Oligocene to lowermost Miocene) (see the "Site U1406" chapter [Norris et al., 2014c]). The XRF patterns of Holes U1406A and U1406B were dominant during the construction of the shipboard splice. After a thorough investigation, we present a reinterpretation in which we identify that Core 342-U1406A-9H contains a condensed interval and Core 342-U1406B-10H contains a ~2 m hiatus (Table T4; Fig. F4). Importantly, Hole U1406C contains the most suitable, and probably complete, sequence and is therefore selected for the revised splice for this interval (Tables T2, T3).

For the middle Oligocene interval, Cores 342-U1406B-15H and 342-U1406C-15H are misaligned in the shipboard composite depth model; we increased the offset between the two cores by ~1 m and added this to the revised splice. Further downhole, the shipboard lithostratigraphy (see the "Site U1406" chapter [Norris et al., 2014c]) discusses microfaults and possible slumping. This hampers the confident construction of a continuous splice for this interval, and Cores 342-U1406A-17H and 342-U1406B-18H are therefore appended (Fig. F4; Tables T2, T3).

Following the shipboard tie points from ~186 m CCSF-M downward, we extensively revised the splice for the lower Oligocene and near the Eocene–Oligocene transition (Tables T2 and T3). A distinct maximum in magnetic susceptibility at ~255 m CCSF-M is used to tie the three holes at Site U1406 together (Fig. F4). This reinterpretation results in a much better correlation for the ln(Ca/K) records from the different holes, compared to the shipboard splice. The total length of the revised splice increases by 32.17 m to a total of 340.55 m CCSF-M. This revision results in growth factors of ~1.23 for all three holes (Fig. F5).

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