A 400.7-mcd-thick (340.1 mbsf) upper Paleocene (~58 Ma) to Pleistocene pelagic sediment sequence was recovered at Site 1263. Sixty-two biostratigraphic and six magnetostratigraphic datums were selected to construct an age-depth model for this site (Table T15; Fig. F37). Linear sedimentation rates (LSRs), total mass accumulation rates (MARs), and carbonate MARs were calculated at 1-m.y. intervals (Table T16) (see "Age Model and Mass Accumulation Rates" in the "Explanatory Notes" chapter).
The main objective of Site 1263 was to recover a complete and well-resolved upper Paleocene 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 1263 is therefore characterized by a significant condensed interval comprising a major unconformity in the upper Oligocene to upper Miocene section (28-5 Ma; 49–29 mcd). Biostratigraphic and magnetic reversal data are in general agreement for the upper Paleocene to lower Oligocene section, and the age model is based on all datum types. The Pliocene–Pleistocene age model is roughly constrained by planktonic foraminifers only (Fig. F37). The most significant discrepancies between nannofossil and planktonic foraminiferal datums exist in the partly condensed middle Eocene to lower Oligocene interval, where reworking is common.
LSRs range between <1 and 29 m/m.y., and total MARs range from <0.1 to 4.1 g/cm2/k.y. Total MAR fluctuations essentially represent variations in carbonate MAR. LSRs and carbonate MARs were highest from 58 to 51 Ma (late Paleocene to early Eocene) and relatively constant from 51 to 43 Ma (middle Eocene). The rates dropped in the late Eocene to very low values and formed a moderate peak in the early Oligocene (34–29 Ma). The magnitude of the extremely low LSRs and MARs cannot be determined for the upper Oligocene to upper Miocene. The Pliocene–Pleistocene rates are generally low to moderate.
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. The moderately high noncarbonate value of 0.8 g/cm2/k.y. in the interval of 54–55 Ma is related to the presence of the carbonate-poor intervals of a few centimeters to several decimeters thickness (see "Lithostratigraphy" and "Geochemistry"). These short-term carbonate dissolution events are smoothed out in the 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.