Four holes were drilled at Site 1078 with the APC/XCB to a depth of 165.2 mbsf. Several sections showed flow-in structures that were observed as pseudo-bedding parallel to the core liner and multiple stacked cones. Sedimentological data from suspect sections generally support paleomagnetic and biostratigraphic data, and affected sections were marked on the barrel sheets. In general, sections in the last cores before APC refusal (i.e., 175-1078A-7H-6, 5H-7, 6H-6, 7H-5, 8H-6, 9H-7, 11H-6, 12H-5; 175-1078C-11H-6, 13H-6; and 175-1078D-7H-4) are suspected to be affected by flow-in. Additional core disturbances were common in the uppermost 20 cm of many cores.
Sediments from Site 1078 form one lithostratigraphic unit composed predominantly of a moderately bioturbated, olive-gray (5Y 4/2) and dark olive-gray (5Y 3/2) silty clay with varying amounts of nannofossils and foraminifers (Fig. 9). Light olive-gray (5Y 6/2), 0.5- to 1.0-cm-thick, silt-rich layers with diffuse contacts are sometimes interbedded within some bioturbated intervals. Sediments in the uppermost three sections of all holes contain rare intact gastropod and mollusc shells, pteropods, and abundant shell fragments. Below 80 mbsf, all holes contain several sections with whitish gray nodules, 1-2 mm in diameter (Fig. 10). Diagenetic dolomite horizons between 3 and 7 cm in thickness are present in Sections 175-1078C-13H-1, 175-1078C-15X-3, and 175-1078D-10H-3 (Fig. 11). Calcium carbonate content ranges from 1 to 25 wt% but are typically between 17 and 20 wt% of the sediment (Fig. 9).
A 40-cm-thick laminated sequence rich in diatoms (see "Bio-stratigraphy and Sedimentation Rates" section, this chapter) is present in Sections 175-1078A-5H-3, 175-1078B-5H-4, and 175-1078C-5H-4 (Fig. 12). A comparable but less well-laminated sequence is also present in Section 175-1078D-5H-6. Stratigraphic data suggest that the laminated sediments at this depth extend laterally over some distance and are a useful marker horizon for correlation between holes. Two additional, 26- and 40-cm-thick, laminated sequences are present in intervals 175-1078C-15X-2, 114-140 cm, and 175-1078C-15X-3, 30-70 cm (Fig. 13). The laminated sequences are composed of diatom-rich, alternating dark olive-gray and dark gray layers 1-3 mm in thickness. Thinner laminae are discontinuous, extending only 5-20 mm. Bioturbated silty clay intervals are common at the top and bottom of the laminated sequences, which suggests that a lack of oxygen was crucial for the preservation of laminated intervals by the exclusion of burrowing organisms.
Laminae are well preserved inside a 7-cm-thick dolomite concretion in the top of the laminated package in Section 175-1078C-15X-2 (Fig. 11, Fig. 13). The concretion is located within a transition into an overlying interval of nonlaminated sediments. It provides an opportunity to observe the bedding style of laminated sequences before significant compaction by sedimentary loading. Figure 11 shows that within the nodule, 1- to 2-mm-thick laminae are erosively truncated by a coarse silt layer 5 mm thick, suggesting that traction currents were important for forming at least some of the laminae.
Smear-slide analyses indicate that silty clay is the dominant lithology at Site 1078. The silt fraction is composed of subangular and angular mono- and polycrystalline quartz grains with subordinate amounts of feldspar. Both potassium and sodium feldspar are present. Muscovite, biotite, and detrital apatite are present in trace amounts. The biogenic component is represented by frequent foraminifer fragments and nannofossils. Diatoms are present in laminated sequences and in nonlaminated intervals, but they are absent in the nodule found in Section 175-1078C-15X-2. Laminated sequences also show abundant diatom resting spores. Trace amounts of plant remains and amorphous organic matter are occasionally observed. Secondary minerals include glauconite peloids that commonly contain euhedral pyrite grains indicating secondary consumption of iron to form pyrite. Examination of a smear slide made from scrapings of the dolomite concretion from the top of the laminated package in Section 175-1078C-15X-2 revealed that laminae within the concretion are composed of dolomite with rare, silt-sized subangular quartz grains and are barren of siliceous microfossils.
X-ray diffraction (XRD) analysis of sediments from Hole 1078A reveals that the clastic fraction is dominated by smectite, kaolinite and/or illite, quartz, the feldspar minerals albite and microcline, and muscovite. Pyrite is present as an accessory mineral in all samples. No clear identification could be made for other accessory phases. The smectites are generally poorly crystallized. Quartz and feldspar show comparable downcore variations (Fig. 14), which is probably caused by variations in grain size. In contrast to quartz, feldspar is not supplied by the Congo River (van der Gaast and Jansen, 1984). Feldspar originates from igneous complexes in southern Africa and therefore probably represents a southern sediment source fed by the Kunene River or by eolian dust. Consequently, the feldspar/quartz ratio may indicate the contribution of sediment supplied from the south.
Samples 175-1078B-9H-5, 46-47 cm, and 175-1078B-12H-1, 46-47 cm, were specifically analyzed by XRD to determine the mineralogy of the frequently present small whitish gray nodules. These two samples show the same mineral assemblage as other samples analyzed but have lower CaCO3 contents. No additional accessory phases could be identified, suggesting that the whitish nodules are amorphous and/or are not sufficiently abundant to be detected by XRD.
Color data were obtained at 2-cm intervals for Hole 1078A. Holes 1078B, 1078C, and 1078D were measured at 4-cm intervals. The reflectance values range between 30% and 45% throughout the column recovered from Site 1078. The total reflectance (Fig. 15) and red/blue (650 nm/450 nm) ratio (Fig. 16) data were smoothed over nine points for Hole 1078A and over five points for Holes 1078B, 1078C, and 1078D to remove smaller scale variability. Total reflectance shows the same trend in the four holes, although core disturbance caused by flow-in has been observed in several cores from Site 1078 (see above). Intervals with high and low reflectance spanning over 50 m are observed and according to the ages provided in the "Biostratigraphy and Sedimentation Rates" section (this chapter), could be related to interglacial cycles. The red/blue ratio shows a low variability downcore. Comparison between the total reflectance and the red/blue ratio with calcium carbonate content and the red/blue ratio with the organic carbon content shows no correlation (Fig. 17).