Unconformities and changes in sedimentation rate at Site 1210 are illustrated in a plot of calcareous microfossil datum ages (first and last occurrences) vs. depth (Fig. F17). These rates rely on major calcareous nannofossil and planktonic foraminiferal datums presented in Tables T3 and T4. The Pleistocene-Campanian section cored at Site 1210 is possibly punctuated by one major unconformity between the lower Miocene and lower Oligocene, as well as an interval of diastems and/or multiple condensed intervals in the middle Miocene to lower Miocene and upper to middle Eocene.
An expanded view of the Neogene (Fig. F18) shows that the upper Miocene section accumulated at rates of ~2.7-4.4 m/m.y., accelerating to 14.4-16.0 m/m.y. in the uppermost Miocene-Pleistocene. Dark-colored, clay-rich sediments in Sections 198-1210A-11H-2 through 12H-1 and Sections 198-1210B-10H-6 through 11H-3 may represent multiple condensed intervals with sedimentation rates on the order of 1.4 m/m.y. and/or the presence of one or more diastems in the middle Miocene to lower Miocene interval. The dark-colored layers in Sections 198-1210A-13H-1 through 13H-4 and Sections 198-1210B-12H-6 through 13H-1 likely correspond with a condensed section (0.2 m/m.y.) and/or major unconformity separating the lower Miocene and the lower Oligocene (Fig. F19).
The lower Oligocene accumulated at an average rate of 8.8 m/m.y. Sedimentation rates in the upper Eocene-lower Paleocene interval range between 1.6 and 7.6 m/m.y., with the lowest rates occurring in the upper middle Eocene to upper Eocene and in the basal Paleocene (Fig. F20). Shipboard biostratigraphy indicates that the Eocene/Oligocene, Paleocene/Eocene, and K/T boundary intervals are complete. Rates for the Maastrichtian-upper Campanian interval were significantly higher, ranging from 5.8 to 11.8 m/m.y., with rates as high as 31.6 m/m.y. in the mid-Campanian (Fig. F21).
Mass accumulation rates for the bulk sediment, carbonate, and noncarbonate fractions were calculated using dry bulk density (see "Physical Properties") and carbonate content (see "Organic Geochemistry") data through 13 linear sedimentation rate segments in the Cretaceous-Neogene section recovered at Site 1210 (Table T9). These segments were chosen to reflect the major changes in sedimentation rate. Physical properties and carbonate content analyses were not performed in Core 198-1210A-20H to avoid disturbing the Paleocene/Eocene boundary.
The highest rate of bulk sediment accumulation at Site 1210 occurred during the mid-Campanian, when sediment accumulated at an average rate of 3.8 g/cm2/k.y. (Fig. F22). The rate decreased through the remainder of Cretaceous interval, with jumps to 1.4 g/cm2/k.y. at 75.2 Ma and 0.7 g/cm2/k.y. at 68.6 Ma. The entire Upper Cretaceous section consists of homogeneous white calcareous ooze, and therefore the inferred changes in sediment accumulation rate do not correspond to any observed changes in lithology (see "Lithostratigraphy"). Early to late Paleocene time at Site 1210 was marked by a further decrease in the average rate of bulk sediment accumulation to 0.3 g/cm2/k.y. (Fig. F22). The rate increased to 0.9 g/cm2/k.y. at 57.5 Ma (late Paleocene). Eocene time was marked by a change in the bulk sediment accumulation rate from 0.6 to 0.2 g/cm2/k.y., with the transition occurring at 46.1 Ma (Fig. F22). The rate increased to 1.0 g/cm2/k.y. during earliest Oligocene time. Much of the lower Oligocene to lower Miocene section at Site 1210 encompasses several condensed intervals. Therefore, the corresponding bulk sediment accumulation rate estimates are extremely low, averaging 0.02 g/cm2/k.y. (Table T9). Bulk sediment accumulation rates increased gradually through the remainder of the Miocene section, from 0.15 to 0.26 g/cm2/k.y. (Fig. F22). The bulk sediment accumulation rate increased abruptly to ~1.4-1.6 g/cm2/k.y. during latest Miocene time. This rate remained relatively constant during much of the Pliocene-Pleistocene. The average rate of bulk sediment accumulation decreased significantly over the past ~400 k.y. The carbonate accumulation rate approximates that of the bulk sediment in segments 2-13 (Table T9). The noncarbonate fraction, composed largely of clay and volcanic ash, became more significant during the last 5.5 m.y., making up an average of 23 wt% of the accumulating sediment.