Paleomagnetic analysis provided only one age control point at Site 1143; namely, the Brunhes/Matuyama boundary (0.78 Ma, 43.2 mcd). Thus, the age model of Site 1143 is based primarily on biostratigraphy. The combined calcareous nannofossil and foraminiferal biostratigraphy yielded 39 event levels and age assignments, using the shipboard stratigraphic framework (see "Biostratigraphy" in the "Explanatory Notes" chapter). Of those, 21 are based on nannofossils, 17 on planktonic foraminifers, and one on benthic foraminifers. Because of limited sampling (mainly core-catcher samples) and some redeposition, a certain amount of depth uncertainty is associated with the datum levels in Table T7. Particularly controversial in age are bioevents of two fossil groups near the bottom of the hole: the LO of G. mayeri (10.49 Ma) at 480.03 mcd and the FO of D. neohamatus (9.6 Ma) at 488.79 mcd. The latter is used for calculations presented in this volume.
Figure F17 (also given as Synergy Software KaleidaGraph plots and Microsoft Excel data files [see the "Supplementary Materials" contents list]) shows the linear sedimentation rate (LSR) and mass accumulation rate (MAR) curves based on calculations described in "Sedimentation and Accumulation Rates" in the "Explanatory Notes" chapter. The results show a high sedimentation rate before 6-7 Ma (60-80 m/m.y.), decreasing sedimentation rates toward the Pliocene (~30 m/m.y.), and rising sedimentation rates in the late Pleistocene (>50 m/m.y.) (Table T10). The carbonate accumulation rate decreases from nearly 4 g/cm2/k.y. ~7 m.y. ago (with relatively high values until the end of the Miocene [~2 g/cm2/k.y.]) to ~0.6 g/cm2/k.y. in the last 0.8 m.y. Noncarbonate accumulation rates show high values in the Miocene, exceeding 4 g/cm2/k.y. before 7 Ma, but they increase slightly at ~3 Ma (Fig. F17C), unlike carbonate accumulation. The remarkable variations in accumulation rates of biogenic carbonate and mainly terrigenous noncarbonate material yield significant paleoenvironmental information.
In order to understand the changes more precisely, the sum of all recognizable turbidites or slump thicknesses (see "Lithostratigraphy") is subtracted from the total sediment thickness for each time interval. The "corrected thickness" is then used for re-estimating the average accumulation rate, as well as the carbonate and noncarbonate accumulation rates (Table T11). As seen from the table, sediment redeposition is negligible (<1%) for the upper part (Pliocene and Pleistocene) but significant (~10%) for the lower part of the section (upper Miocene). This redeposition should be taken into account when the sedimentation history is interpreted.