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doi:10.2204/iodp.proc.342.109.2014 Age-depth model and mass accumulation ratesAt Site U1408, we recovered a 250 m thick sequence of Pleistocene to upper Paleocene clayey nannofossil ooze with varying amounts of clay and nannofossils. A condensed Pleistocene to upper Eocene section overlies a middle Eocene through upper Paleocene succession with significant hiatuses between the Oligocene and middle Eocene (~7 m.y.) and between the middle and lower Eocene (~3 m.y.) and a minor hiatus or condensed interval around the Paleocene/Eocene boundary. Sedimentation rates are high (~1.39–3.03 cm/k.y.) through the middle Eocene, low (~0.08 cm/k.y.) through the lower Eocene, and relatively high (~1.27 cm/k.y.) through the upper Paleocene. Biostratigraphic datums and magnetostratigraphic datums from Hole U1408A (Table T15) were compiled to construct an age-depth model for this site (Fig. F15). A selected set of datums (Table T16) was used to create an age-depth correlation and calculate linear sedimentation rates (LSRs). Total mass accumulation rate (MAR), carbonate MAR (CAR), and noncarbonate MAR (nCAR) were calculated at 0.2 m.y. intervals using a preliminary shipboard splice rather than the sampling splice described in this volume (Table T17; Fig. F26). Age-depth modelThe age-depth model is tied to Pleistocene to upper Eocene nannofossil datums in the upper 38 m of Hole U1408A. Through the middle Eocene, paleomagnetic datums are used as the primary tie points. These datums are closely aligned to nannofossil datums and are also in good agreement with the more sparse radiolarian and foraminifer datums. Nannofossil datums are the primary tie points from the lower middle Eocene to Paleocene and are in good agreement with foraminifer and radiolarian datums. Linear sedimentation ratesBelow the condensed Pleistocene–Oligocene interval in the upper 38 mbsf, LSRs in Hole U1408A are high (2–3 cm/k.y.) in the middle Eocene and moderately high (1.27 cm/k.y.) in the Paleocene. The intervening Eocene section is highly condensed, with an average LSR of <0.1 cm/k.y. Mass accumulation ratesMARs range from <0.1 g/cm2/k.y. in the Pleistocene to lower Oligocene to higher values of 4.0 g/cm2/k.y. in the middle Eocene and 1.5 g/cm2/k.y. in the Paleocene. CAR and nCAR are roughly equal during the middle Eocene. Carbonate accumulation dominates mass accumulation during a peak in MAR during the Paleocene. |
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