Site 1053 recovered an exceptionally thick upper Eocene section consisting mainly of siliceous nannofossil ooze. This thick section might reflect periods of increased productivity in the surface waters or enhanced preservation on the seafloor.
The top of the cored interval is a 5- to 37-cm-thick layer with manganese nodules and a drilling slurry of clayey foraminifer ooze that is rich in phosphatic debris, including fish scales and vertebrae. Below this is ~12.5 m of pale yellow upper Eocene siliceous nannofossil ooze with varying amounts of foraminifers and clay. As at Sites 1050, 1051, and 1052, there is a sharp color change from pale yellow to light greenish gray. This sharp color change is time-transgressive across the four sites, and there is no discernible compositional difference in the sediment across this boundary. Green siliceous nannofossil ooze is ~126 m thick in Hole 1053A and ~114 m thick in Hole 1053B. Several ash layers are present, including a distinctive 8-cm-thick, highly altered, clay- and diatom-rich layer. At least 20 species of diatoms are present in this layer, whereas diatoms are not abundant or diverse elsewhere at Site 1053. Preservation of diatoms in this layer may have been enhanced due to leaching of silica during ash alteration. The lowermost 50 m of cored section consists of middle Eocene greenish gray chalk with varying amounts of nannofossils, siliceous microfossils, and clay. Drilling disturbance has resulted in slight to heavy biscuiting in the core.
Light/dark color alternations within the greenish sediment are often visible, with the darker intervals being more clay-rich. Correlating the two holes, however, by using magnetic susceptibility and GRAPE density data from the MST track and the Minolta color spectrophotometer proved to be difficult, as the signals were noisy mainly because of significant bioturbation. Nevertheless, the shipboard composite section shows that most likely a complete record was recovered.
Shipboard paleomagnetic results were not straightforward and need to be improved by post-cruise analysis of discrete samples. However, a detailed biostratigraphy was obtained by integration of nannofossil, planktonic foraminifer, and radiolarian datum levels. The radiolarians in particular appear to be very useful at this site. We expected to find evidence for upper Eocene meteor impacts near two well-defined extinction levels of radiolarians in the upper Eocene. The extinction levels were found, but tektites were not visible in the sediment, probably due to extensive bioturbation. We are hopeful that shore-based research will detect the tektites and other evidence for impact debris. Detailed biochronological control and excellent preservation of the calcareous microfossils make this site suitable for meeting our paleoceanographic objectives.
To 171B Conclusions