A 236.4-mcd-thick (213.0 mbsf) Maastrichtian (~66 Ma) to Pleistocene pelagic sediment sequence was recovered at Site 1262. A total of 66 biostratigraphic datums and 23 magnetostratigraphic datums (Table T15) were selected to construct an age-depth model for this site (Table T16; Fig. F32). Linear sedimentation rates (LSRs), total mass accumulation rates (MARs), and carbonate MARs were calculated at 1-m.y. intervals (see "Age Model and Mass Accumulation Rates" in the "Explanatory Notes" chapter).
The main objective of Site 1262 was to recover a complete and well-resolved upper Maastrichtian to lower Eocene section, and the site was chosen to yield this critical stratigraphic interval at a relatively shallow burial depth. The sediment section at Site 1262 is therefore characterized by significant condensed intervals and unconformities throughout the upper lower Eocene to the lower upper Miocene section (51–7 Ma; 94–44 mcd). Biostratigraphic and magnetic reversal data are in general agreement for the Maastrichtian to lowermost Eocene section and the uppermost Miocene to Pleistocene section (Fig. F32). In the younger interval, the age-depth model relies primarily on paleomagnetic and nannofossil data. Below 94 mcd, we relied primarily (although not exclusively) upon calcareous nannofossil datums to define the age-depth model. The most significant discrepancy between nannofossil and planktonic foraminiferal datums exists in the condensed middle to upper Eocene interval. Apparent discrepancies in the upper Paleocene probably result from the lower resolution of shipboard studies and possible lack of intercalibration.
LSRs range between <1 and 14 m/m.y., and total MARs range from <0.1 to 1.8 g/cm2/k.y. Total MAR fluctuations essentially represent variations in carbonate MAR. LSRs and carbonate MARs show a broad peak from 65 to 50 Ma with the greatest values at 54–53 Ma and a second peak from 5 to 0 Ma with the greatest values at 2–3 Ma. Noncarbonate MARs averaged over 1-m.y. intervals are generally low (<0.2 g/cm2/k.y.) throughout the section, and the small fluctuations may be within the analytical uncertainty of the data. The Paleocene–Eocene sediment record is characterized by carbonate-poor intervals of a few centimeters to several decimeters in thickness (see "Lithostratigraphy" and "Geochemistry"). These short-term carbonate dissolution events are smoothed out in our MAR record as a result of our 1-m.y. sampling of the age-depth model, dictated by the limited resolution of the shipboard age-depth control points and density and carbonate data.