Construction of the composite section from Holes 1128B and 1128C indicates that a nearly complete record of the Pleistocene-lower Oligocene sedimentary section at Site 1128 was recovered. Comparison of the amount of overlap between cores from adjacent holes was used to verify the degree of section continuity (see "Composite Depths" in the "Explanatory Notes" chapter). Using the Splicer software, sedimentary features and physical properties present in adjacent holes were aligned so that they occur at approximately the same depth. The alignment was performed downward from the mudline, and an offset value was added to the mbsf depth of each core to create a meters composite depth (mcd) for each core. Table T3 (also in ASCII format) relates mbsf to mcd for each core and section at Holes 1128B and 1128C and provides offset values for the conversion of mbsf to mcd.
The primary lithologic parameters used to create the composite section were magnetic susceptibility (MS) data collected by the MST on whole-round cores, gamma-ray attenuation (GRA) bulk density data (also acquired by the MST), color reflectance data (400 nm) measured on split cores, and natural gamma radiation (NGR) emissions data collected by the MST (Fig. F18). For specifics regarding these data collection procedures and parameters, see "Physical Properties". Unlike at the shallower sites of Leg 182, the MS of the sediments at Site 1128 was quite high, and the resulting data were very useful for correlation. P-wave velocity data collected by the MST were of poor quality as a result of numerous voids in the cores and, therefore, were not used for correlation purposes.
Biostratigraphic data aided in correlations by providing additional datums that were compared between holes (Table T4; see "Biostratigraphy"). Planktonic foraminifers were particularly useful in constraining correlative intervals of the recovered section. Because most biostratigraphic samples were taken from core catchers, the stratigraphic error is generally on the order of 9.5 m (the distance between core catchers in two consecutive cores). However, in some cases, more detailed investigations were performed that reduced the stratigraphic error of a biostratigraphic range and allowed for increased confidence in correlations. Occasionally, overlapping biostratigraphic ranges permitted the recognition of correlative intervals between holes to an accuracy of 1-2 m. An example is the overlap of the range of the C. macintyrei last appearance datum in the top of Core 182-1128B-3H and the bottom of Core 182-1128C-2H, which constrains the tie between these two cores, in addition to providing an excellent time-stratigraphic horizon (1.67 Ma at 17-18.75 mcd) (Table T4).
Magnetostratigraphic datums also aided in correlation between holes (see "Magnetostratigraphy"). Chron boundaries were identified throughout the recovered section except from the interval between 57 and 75 mcd where the record is disrupted by the debrite unit (Fig. F19; Table T5). The stratigraphic error on the chron boundaries is estimated to be ~±0.2 m.
Differential core distortion was not a significant problem at Site 1128, in contrast to the shallower water sites, because of the relatively low concentration of hydrocarbon and hydrogen sulfide (H2S) gas within the sediments. The data records from both holes are quite similar and easily aligned. Core overlap between holes averaged ~2 m where recovery was high and allowed for a statistical evaluation of ties used to create the composite section. However, correlations below ~160 mcd were hindered by poor core recovery, resulting from the presence of multiple chert layers interbedded with calcareous wackestone (see "Lithostratigraphy"). Recovery and correlation improved again below ~180 mcd (Fig. F18).
The Pliocene/Pleistocene boundary occurs at ~17 mcd (~15 mbsf in both holes), based upon biostratigraphic data (Fig. F19). The Pliocene/Miocene boundary occurs at ~42 mcd (39.5 mbsf in both holes). The upper Miocene-Pleistocene section corresponds to lithostratigraphic Subunit IA and is characterized by pink nannofossil ooze, interbedded with numerous turbidites consisting dominantly of planktonic foraminifers. The turbidites exhibit high color reflectance and low NGR activity and MS. These small features, ranging from tens of centimeters to >1 m thick, can be readily correlated between holes, based on the high similarity of data peak characteristics. At 40-50 mcd, a 10-m-thick high-amplitude peak doublet occurs in the NGR and MS data and corresponds to lows in the color reflectance data (Figs. F18, F19). This doublet provides a prominent correlation marker in both holes and corresponds to two layers of dark wackestone separated by a turbidite.
At 60-72 mcd, a debrite unit occurs that is prominent in all of the data and corresponds to lithostratigraphic Subunit IB. The top of the debrite is present in Core 182-1128B-7H, but it is missing between Cores 182-1128C-6H and 7H and, therefore, does not provide a useful correlative horizon. The base of the debrite occurs at 73 mcd, is present in both holes and provides a good correlation horizon. There appears to be a section within the debrite that was not recovered in either hole; therefore, correlations between holes within the debrite zone are not possible. Below the debrite bed, sediments are a more uniform calcareous clay to nannofossil ooze (lithostratigraphic Subunit IC; lower Oligocene), which grade downward to an olive green clay (lithostratigraphic Subunit IIA) at 104 mcd. These units exhibit lower amplitude, but still easily correlated, oscillations in all of the data. Another prominent, large-scale feature occurs at 146-153 mcd in both holes. This unit is a nannofossil ooze, probably a thick turbidite, exhibiting very high and uniform reflectance and density values and very low and uniform NGR and MS values. The base and top of this distinctive unit provide excellent correlation horizons.
Overall, the composite section indicates excellent agreement between the depositional records in Holes 1128B and 1128C, with the one exception being the debrite discussed above. Although there exists a small gap in the composite section within the debrite, recovery of the rest of the section is complete to 162 mcd (Fig. F19; Table T6, also in ASCII format). The composite section continues below this, but the spliced section could not be continued because of large gaps in recovery. Correlations are still readily apparent in the data to 260 mcd, the total depth of Hole 1128C. The mcd scale expansion relative to the mbsf scale is ~10%.