Sedimentation rates determined for the equatorial upwelling (Sites 1225 and 1226), open-ocean (Site 1231), and Peru Trench (Site 1230) sites are based on single dates for depths <23 cmbsf and assume the seafloor at 0 cm to be 0 ka. Rates calculated for these sites are 1.8, 2.4, 1.5, and 2.0 cm/k.y., respectively (Table T2). These values fit well within the average sedimentation rate range determined by Hagelberg et al. (1995) for the 0- to 5-Ma sections of cores recovered from approximately the same sites during Leg 138 (Site 1225 at Site 851 and Site 1226 at Site 846). In these cases, the sequences were determined by gamma ray attenuation density data to be stratigraphically continuous, and the ages were yielded biostratigraphically. Overall, these sedimentation rates are also comparable with those from elsewhere in the equatorial eastern Pacific, such as the 2.5- to 5.0-cm/k.y. sedimentation rates reported by Lea et al. (2000) from the Cocos Ridge just north of the equatorial upwelling zone in the eastern Pacific.
Sedimentation rates for the Peru margin sites have been calculated from linear regression fits to multiple data points where these are available (Fig. F3), and the results are summarized in Table T2.
Holocene sediments are absent in Hole 1227B, with ~15.7 k.y. of sediment missing at the top of the hole. A continuous 1500-yr section defined by five radiocarbon ages is present below 26 cmbsf (Fig. F3A). This section spans the early part of the LGIT from ~15.7 to 17.2 ka. We estimate an accumulation rate of ~265 cm/k.y., nearly three times that of late Holocene. This period of extremely high sedimentation can probably be extended back to just prior to the LGM at ~21.5 ka.
Well preserved upper Holocene sections are present at both Sites 1228 and 1229. At both they contain a sedimentation interval spanning 0 to ~2.8 ka that is characterized by sedimentation rates between 70 and 100 cm/k.y. (Fig. F3; Table T2). We are confident that in both Holes 1228B and 1229E a continuous section is present from the surface to ~2.8 ka.
In both Holes 1228B and 1229E the middle to early Holocene is represented by a much thinner stratigraphic section with fewer (Hole 1228B) or no (Hole 1229E) radiocarbon ages, and although we believe we can identify the base of the Holocene in the latter hole, we cannot be confident that unconformities are not present in this interval at both sites. Possible locations of breaks based on lithostratigraphic criteria are between 195 and 200 cmbsf in Hole 1228B and at ~250 cmbsf in Hole 1229E. With these possibilities in mind, average sediment accumulation rates over the middle–early Holocene were ~4–6 cm/k.y. at both sites.
A thin, 1000-yr duration deglaciation section at the Holocene/Pleistocene transition is present in Hole 1228B and is defined by three radiocarbon dates that yield a sedimentation rate of ~30 cm/k.y. (Table T2). This section can probably be extrapolated to ~270 cmbsf with a resultant age span increase of ~900 yr, from 10.2 to 12.2 ka.
The six late MOI Stage 3 radiocarbon ages from Hole 1228B (Fig. F3) do not represent a coherent data set for the reasons outlined above, and a repeat measurement on Sample 201-1228B-1H-3, 22–23 cm (OZG472 and OZH143), further exemplifies the problems where there is low residual modern carbon. Nevertheless, linear regression through these data points yields a sedimentation rate of ~20 cm/k.y., which is not incompatible with lithologically similar sediments from the uppermost Pleistocene deglaciation section in the same hole. We note, however, that the very high sedimentation rate early deglaciation section present in Hole 1227B is probably absent at these more southerly and shallower water sites.