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doi:10.2204/iodp.proc.342.110.2014

Age-depth model and mass accumulation rates

At Site U1409, we recovered a 200 m thick sequence of Pleistocene to lower Paleocene nannofossil ooze and nannofossil clay, with foraminifers and radiolarians. Thin Pleistocene and Oligocene intervals overlie a middle Eocene through lower Paleocene succession with significant hiatuses between the lower Pleistocene and upper Oligocene (22 m.y. duration) and lower Oligocene and middle Eocene (8.3 m.y. duration). A short hiatus or condensed interval is also identified at the Paleocene/Eocene boundary. The Oligocene is highly condensed and may contain substantial hiatuses. Sedimentation rates are 0.65–1.31 cm/k.y. through the middle Eocene, 0.81–1.44 cm/k.y. through the lower Eocene, and ~0.47–1.80 cm/k.y. through the Paleocene.

Biostratigraphic datums and magnetostratigraphic datums from Hole U1409A (Table T16) were compiled to construct an age-depth model for this site (Fig. F24). A selected set of datums (Table T17) 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 T18; Fig. F31).

Age-depth model

The age-depth model is primarily tied to paleomagnetic datums in the upper 39 m of Hole U1409A, along with a single Pleistocene nannofossil datum. A nearly complete sequence of magnetochrons has been identified in the Oligocene. A lower Oligocene–upper Eocene unconformity is identified by nannofossil datums. Paleomagnetic datums provide the primary tie points in the underlying middle to upper lower Eocene interval. The remaining lower Eocene and Paleocene section is tied to radiolarian and nannofossil datums with the base of planktonic foraminifer, Morozovella angulata, providing the final tie point in the age model. All datums are in good agreement through the Eocene and Paleocene.

Linear sedimentation rates

This site has a short Pleistocene section, with a LSR of 0.32 cm/k.y. A condensed Oligocene section (LSR of < 0.5 cm/k.y.) is bounded by hiatuses. The Eocene has a relatively stable LSR that ranges from 0.65 to 1.44 cm/k.y. and averages ~0.9 cm/k.y. The Paleocene comprises a condensed upper interval (LSR of 0.21 cm/k.y.), an expanded middle interval (LSR of 1.8 cm/k.y.), and an average LSR at the base (0.47 cm/k.y.).

Mass accumulation rates

MARs at Site U1409 range from 0.1 to 0.9 g/cm²/k.y. in the Pleistocene and Oligocene to maximum values of ~2.5 g/cm²/k.y. in the middle Paleocene. In the Pleistocene sequence recovered at Site U1409, MAR is dominated by noncarbonate components. Oligocene MARs are also strongly modulated by noncarbonate components; indeed, carbonate contents are close to 0 wt% for much of the upper Oligocene. Carbonate and noncarbonated fractions are approximately equal throughout the middle Eocene, and carbonate becomes the predominant contributor to mass accumulation below the middle Eocene. A broad distinctive peak in MARs occurs in the middle Eocene; two shorter peaks, driven primarily by carbonate accumulation, occur in the early Eocene and a large and distinctive peak in MARs, also driven primarily by carbonate accumulation, occurs across the upper/middle Paleocene boundary.

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