Unconformities and changes in sedimentation rate at Site 1211 are illustrated in a plot of calcareous microfossil datum ages (first and last occurrences) vs. depth (Fig. F15). These rates rely on major calcareous nannofossil and planktonic foraminiferal datums presented in Tables T2 and T3 (see "Biostratigraphy"). The Pleistocene-Maastrichtian section cored at Site 1211 is punctuated by unconformities between the upper and middle Miocene and between the upper lower Miocene and upper Oligocene. In addition, an unconformity or condensed interval is present in the middle Eocene section.
An expanded view of the Neogene (Fig. F16) shows that the upper Miocene section accumulated at rates of ~1.8 m/m.y., accelerating to 8.6 m/m.y. in the uppermost Miocene-Pleistocene. Dark-colored, clay-rich sediments in Sections 198-1211A-7H-1 and 198-1211B-6H-6 may represent an unconformity or condensed interval between upper Miocene and lower middle Miocene sediments. The sharp color change in Sections 198-1211A-7H-2 and 198-1211B-6H-7 marks the unconformity separating the upper lower Miocene and the upper Oligocene (Fig. F17).
The Oligocene section accumulated at an average rate of at least 3.4 m/m.y. Sedimentation rates in the Eocene range between 1.5 and 2.2 m/m.y., with the possibility of an unconformity or condensed interval within the middle Eocene section (Fig. F18) (see "Biostratigraphy"). Dark-colored sediments in Sections 198-1211A-11H-1 and 198-1211B-10H-4 may reflect this change in sedimentation. The upper Paleocene shows sedimentation rates of ~4.5 m/m.y., whereas much of the middle part of the Paleocene may be somewhat condensed with sedimentation rates ranging between 0.5 and 0.9 m/m.y. By contrast, the lower Danian (lowest Paleocene) is comparatively expanded with rates of 2.5 m/m.y. immediately above the K/T boundary. Shipboard biostratigraphy indicates that the E/O, Paleocene/Eocene (PETM), and K/T boundary intervals are paleontologically complete. Rates for the upper Maastrichtian interval were significantly higher, ranging between 4.5 and 29.5 m/m.y. (Fig. F19).
Mass accumulation rates for the bulk sediment, carbonate, and noncarbonate fractions were calculated using dry bulk density (see "Physical Properties") and carbonate concentration (see "Organic Geochemistry") data through 13 linear sedimentation rate segments in the Cretaceous-Neogene section recovered at Site 1211 (Table T8). These segments were chosen to reflect the major changes in sedimentation rate as shown in Figures F15, F16, F17, F18, and F19. Not all segments are represented in dry bulk density or carbonate concentration data (see Table T8).
The bulk sediment accumulation rate during much of late Maastrichtian time at Site 1211 averaged 0.5 g/cm2/k.y. (Fig. F20), slightly lower than observed for this time interval at Sites 1209 and 1210. The rate increased dramatically to an average of 3.5 g/cm2/k.y. in the ~600 k.y. preceding the K/T boundary event (Fig. F20). This phenomenon was not observed at other sites. The absence of this increase in accumulation rate at Sites 1209 and 1210, however, may be an artifact of the low density of sampling adjacent to the K/T boundary. During the early Paleocene, the average bulk sediment accumulation rate (0.1 g/cm2/k.y.) decreased to the lowest observed at Site 1211 (Fig. F20). With the exception of a short-lived rise to 0.6 g/cm2/k.y. at ~55-57 Ma, the average rate remained relatively constant (0.1-0.3 g/cm2/k.y.) throughout the Paleocene and Eocene (Fig. F20). The E/O boundary marks a rise in the bulk sediment accumulation rate to an average of 0.5 g/cm2/k.y. (Fig. F20). Much of the upper Oligocene to lower upper Miocene section at Site 1211 is represented by a condensed interval recovered in Cores 198-1211A-7H and 198-1211B-6H. Significant sedimentation resumed during late Miocene time, when the average rate at which the bulk sediment accumulated was 0.2 g/cm2/k.y. (Fig. F20). The rate increased to an average of 0.7 g/cm2/k.y. during latest Miocene time and remained constant through the remainder of the record (Fig. F20). The carbonate accumulation rate approximates that of the bulk sediment in segments 2-13 (Table T8). As at Sites 1207 to 1210, the noncarbonate fraction, composed largely of clay, volcanic ash, and minor biogenic silica, became more significant during the last 5.5 m.y., comprising, on average, 17 wt% of the accumulating sediment.