Figure 3 presents the sediment accumulations rates in meters per million years for the last ~18 m.y. at Site 999. Rates are calculated through selected intervals bracketed by planktonic foraminifer datums using datum ages determined at Ceara Rise using the astrochronological time scale for Leg 154 sites. Datums are also plotted for both published ages and the "Ceara Rise ages" determined using the astrochronological time scales of Bickert et al. (1997), Tiedemann and Franz (1997), and Shackleton and Crowhurst (1997). All datums identified in Hole 999A are shown in Table 1. The selected datums used to construct the age/depth relationship in Figure 3 are shown in Table 2.
A short interval of low sediment accumulation is suggested in the middle Pliocene sediments between the FO of Menardella miocenica (3.6 Ma) and the LO of Dentoglobigerina altispira (3.0 Ma). However, paleomagnetic datums identified through this interval (King et al., Chap. 8, this volume) show that, in fact, M. miocenica enters the record "late" at this site, and the apparent low accumulation rate is an artifact (Fig. 4).
The interval of the "carbonate crash," a period of minimal carbonate accumulation observed at most Leg 165 sites (Sigurdsson, Leckie, Acton, et al., 1997), is partly represented by a low rate of accumulation between the FO of Neogloboquadrina acostaensis (9.8 Ma; Ceara Rise age) and the LO of Paragloborotalia mayeri (10.5 Ma; Ceara Rise age). However, these datums bracket a shorter interval of minimal carbonate accumulation as determined shipboard (Sigurdsson, Leckie, Acton, et al., 1997) and the calculated accumulation rate does not accurately reflect the period of slowest accumulation at this site.
The relatively high rate of accumulation that is calculated between the FO of Fohsella fohsi (13.4 Ma; Ceara Rise age) and LO of Catapsydrax dissimilis (17.3 Ma) is accompanied by a shift to chalk and a deterioration of foraminifer preservation at this site to "poor" and "moderate" grades.