Interstitial water profiles document downhole sediment diagenesis. Concentrations of dissolved silica increase from 522 uM at the sea floor to a maximum of 1000 uM at 200 mbsf, reflecting dissolution of abundant silicious microfossils. Silica values then decrease from 400-999 mbsf. Below 150 mbsf, calcium and magnesium values correlate inversely suggesting diagenetic control and an unidentified Ca-rich lithology below the drilled section. The zone of low grain density at 140 mbsf may also be associated with the loss of magnetic material observed at this depth.
Darker intervals have higher densities, susceptibilities and generally higher organic carbon values.
This suggests that the color changes are caused in part by variations in sediment compositions and depositonal regimes. These step-increases are observed as reflections on seismic data. The upper limit of the logging was at 176 mbsf, where the drill pipe was placed to bypass 'bridges' in the hole. Site 1165 provides paleontologic and sedimentologic evidence that large variations in biogenic material and clay-size terrigenous debris from Antarctica have occurred here since early Miocene time. Changes in clay mineralogy indicate show that erosion of sedimentary rocks in shelf basins started in the middle Miocene.