Three holes were drilled with the APC at Site 1079, with a maximum penetration of 129.9 mbsf. The last sections of Holes 1079A and 1079B, as well as several sections from Hole 1079C, possessed flow-in structures, such as pseudo-bedding, parallel to the core liner and 1- to 2-cm-wide tubular structures penetrating the entire section (see barrel sheets, Section 4, this volume). Additional core disturbances caused by gas expansion are common at Site 1079.
The lithostratigraphic description for the sedimentary sequence from Site 1079 is based on data from the following sources: (1) visual core description, (2) smear-slide examination, (3) color reflectance measurements, (4) bulk calcium carbonate measurements, and (5) X-ray diffraction (XRD) measurements.
Sediments from Site 1079 form one lithostratigraphic unit composed predominantly of uniform olive-gray (5Y 4/2) silty clay with varying amounts of nannofossils and foraminifers (see Fig. 1). There are also a few discontinuous light olive-gray silt laminae (1–2 mm in thickness), which are present below 80 mbsf at all three holes. Rare gastropod shells and shell fragments in frequent abundance are disseminated throughout the uppermost seven cores of all three holes. Bioturbation is evident from numerous burrows filled with lighter colored clay. Whitish gray nodules, 1–2 mm in diameter, are present, but rare, in some of the uppermost cores. They become more frequent below 90 mbsf. Calcium carbonate content of the sediment ranges from 7 to 19 wt%, averaging about 13 wt%.
A 60-cm-thick turbidite is present in interval 175-1079C-10H-5, 35–110 cm. The base of the interval (Section 175-1079-10H-5) at 110 cm is a scoured contact (see Fig. 2). The lower part of the turbidite consists of coarse silt, which grades upward into clay. Above the turbidite sequence is a thinly laminated package of alternating layers of dark olive-gray, dark gray clay, and light olive-gray silt. Biotur-bated silty clay intervals at the top and bottom of the laminated package indicate that the low oxygen content of bottom waters may have been important in preserving laminae.
Smear-slide analyses indicate that silty clay is the dominant lithology at Site 1079. The silt component is dominated by subangular and angular mono- and polycrystalline quartz grains with subordinate amounts of detrital angular feldspar grains. Muscovite and biotite are present in trace amounts. The biogenic component is represented by frequent foraminifer fragments and nannofossils. Secondary minerals include dolomite, glauconite, and pyrite. The thin, 1- to 2-mm-thick, light olive-gray silty layers contain angular quartz and feldspar grains that are coarser than those in the clay layers.
XRD analysis of sediments from Hole 1079A reveals that the clastic fraction is dominated by smectite, kaolinite/illite, quartz, the feldspar minerals albite and microcline, and muscovite. Pyrite was identified as an accessory mineral in all samples. Other accessory phases could not be clearly identified using XRD. The smectites are generally poorly crystallized. Quartz and feldspar show comparable downcore variations, which are probably caused by grain-size variations (see Fig. 3). 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.
Color data were measured every 2 cm for Hole 1079A. Holes 1079B and 1079C were measured at 4-cm intervals. The reflectance data range between 30% and 45% throughout the column recovered from Site 1079. The red/blue (650 nm/450 nm) ratio (Fig. 4) and total reflectance (Fig. 5) data were smoothed over nine points for Hole 1079A and over five points for Holes 1079B and 1079C to remove smaller scale variability. Core disturbance makes correlation between holes difficult. After an initial high extending over 10 m, the red/blue ratio shows a low variability downcore. Comparison between the total reflectance and the red/blue ratio with calcium carbonate content and organic carbon shows no correlation (Fig. 6, Fig. 7).