All core photographs shown in Figures F1 and F2 have been digitally contrast enhanced using Adobe Photoshop 7.0 to highlight visible lithostratigraphy. Although the actual contrast and brightness modification applied was different for each image, they were applied uniformly to each image individually, so that relative differences within each image are retained.
Images of the four cores with single 14C ages are shown in Figure F1. Detailed high-resolution chronological division of these sections is not possible, but examination of the single age dates and their relationship to the visible lithology suggests that decimeter-scale layering is present in the uppermost parts of at least three of the four images (representing the uppermost parts of Holes 1225B, 1226C, and 1230D). At Site 1225, the banding comprises alternations of paler and darker predominantly nannofossil ooze. The boundaries between the layers are gradational, and the layers themselves are mottled, indicating bioturbation (Shipboard Scientific Party, 2003a). At Sites 1226 and 1230, the cyclicity is of the same magnitude and style, comprising alternations of nannofossil (paler color) and diatom ooze, but a higher clay content, represented by the increase in greenish gray color in the sediments, is attributed to increasing proximity to the South American continent. The layering in cores from Site 1231 is similar to that at Sites 1226 and 1230, but there is a sharp curvilinear discontinuity at 27 cm below seafloor (cmbsf) separating mottled reddish brown sediments above from gray-green ooze below. We suspect this boundary represents an unconformity. A thin, 5-cm brownish layer is present at the top of Hole 1226B, but this unit has a gradational lower boundary and is more similar to the brownish gray layers in Hole 1225B that the Shipboard Scientific Party (2003a) described as containing Mn and iron oxides, attributed to redox processes.
A 2.0- to 2.5-m Holocene section is present at Sites 1228 and 1229 (Fig. F2). Holocene sediments are absent at Site 1227. The sediments are nannofossil-bearing diatom oozes with subordinate quartz and clay (Shipboard Scientific Party, 2003b).
In both Holes 1228B and 1229E, the Holocene section is characterized by subtle, fine laminations at millimeter to submillimeter scale. The Holocene has an overall slightly darker olive green–gray color compared with underlying upper Pleistocene sediments. This subtle difference can be attributed to slightly higher total organic carbon (TOC) values in the Holocene section (Meister et al., this volume; Watson, 2003), a slightly higher clay content, and a slightly lower carbonate percentage overall, although there are significantly different values between the pale and dark laminae for each of these components in both the Holocene and upper Pleistocene deglaciation sections.
Almost 6 m of latest Pleistocene deglaciation sediments are present in Hole 1227B (Fig. F2). These strata are finely laminated at millimeter to submillimeter scale with the laminations more obvious than in the overlying Holocene section. The increased visibility of the laminations is a result of increasing contrast between the darker and lighter layers, with the latter being overwhelmingly dominated by diatom frustules (Shipboard Scientific Party, 2003b). The upper Pleistocene section overall has a paler greenish gray color compared with the overlying Holocene section, with the boundary between the two being gradational at both Sites 1228 and 1229.
A much thinner LGIT section is present in Hole 1228B, represented by <50 cm of stratigraphic section, and we cannot discount the presence of an unconformity between 2.7 and 3.0 mbsf in Hole 1228B. Such unconformities or depositional hiatuses are common throughout the Quaternary section (De Vries and Schrader, 1981; Reinhardt et al., 2002), where they are attributed by the latter authors to variations in activity of the poleward moving undercurrent on the shelf. Late Pleistocene sediment older than the LGM (i.e., MOI Stage 3) is identical in composition and stratification to post-LGM sediments, and so it is not possible to distinguish them on lithostratigraphic grounds. We believe we can extrapolate the Holocene/Pleistocene boundary in Hole 1229E to 270 cmbsf, based on the lithostratigraphic criteria described above, but would not be confident in assigning post- and pre-LGM ages to the sediment beneath this level in the absence of radiocarbon ages.