The following comments are based on analysis of residues that were prepared for foraminferal study. Residues are generally large and are dominated by angular terrigenous material to a greater degree than at Sites 1165 and 1166. Residues are commonly coarse sand, and although poorly sorted, seldom show signs of bimodal size distribution; thus they are consistent (within the sample) with a single source. Detrital pyrite and traces of black coal, probably from the Permian Amery Group in the Prince Charles Mountains, are present in virtually all samples. Table AT1 summarizes our observations.
The absence of sponge spicules, except in the upper section, seems anomalous in light of their abundance in Prydz Bay sediments of similar age. Shell material abundance is also less than expected. No bone or teeth were observed. Echinoid remains are present in all slope faunas yet are rare in transported continental shelf faunas. Ostracods are rare, and no pattern can be detected in their presence. In Sample 188-1167A-25X-CC, 22-23 cm, ostracods are represented by rinds of the less soluble parts of the valves, which indicates that their absence may in part be caused by dissolution. Bivalve shell fragments are present sporadically but are small and not adequate for identification purposes.
The characteristics of sand grains in the sand beds changes downhole. The shallower samples contain very immature sands with high amounts of garnet and other diverse heavy minerals. By Sample 188-1167A-25X-CC, the content of heavy minerals has decreased markedly, and residues represent very clean, white sand. Although both shallow and deeper residues contain clasts of sandstone in the coarse fraction, these clasts are dominant below Core 188-1167A-25X. Above this core, sandstone clasts are subordinate, whereas clasts with lithologies typical of the Precambrian basement of the Lambert Graben margin are predominant. This change over time may reflect an early source of mature, well-washed, well-sorted material carried initially by water, followed by the modern interval of glacially transported, less mature detritus with less opportunity for weathering and sorting to remove the heavy minerals. The change could be from a clean sandstone source (to account for the large fragments of clean sandstone in the coarse fraction) to one more dependent on the Precambrian shield of East Antarctica, or there could have been a change in the dominance of the source.
Below Core 188-1167A-25X, other variations also occur, such as a reduction in the diversity of accessories, which is evident from Table AT1, and consistent with the change in sand type referred to above. The incidence of faunas barren of foraminifers is very obvious below that depth.