A single hole (1166A) was drilled at Site 1166 (Table T1). Recovery in the Neogene part of the hole was poor, and no pre-Neogene foraminifers were recovered. The Neogene section yielded moderate assemblages of both planktonic and benthic foraminifers from Core 188-1166A-1R to interval 12R-1, 18-20 cm, and from most section samples within that interval. Samples 188-1166A-1R-CC and 2R-CC are barren of foraminifers, as are samples including and deeper than 12R-CC. Table T4 is a range chart of species occurrence, and "Appendix B" lists barren samples.
Planktonic assemblages are dominated by N. pachyderma (Ehrenberg), indicating only that the entire section to Sample 188-1166A-12R-1, 18-20 cm, is late Miocene or younger (N. pachyderma Zone; AN7 of Berggren, 1992, and Berggren et al., 1995). Benthic assemblages, while yielding small specimen numbers, are, in total, diverse, and assemblages can be related to those identified by Quilty (1985) from the modern continental shelf in Prydz Bay. Agglutinated forms are very rare, and the assemblages are almost entirely calcareous.
Assemblages are those to be expected on an open shelf with no evidence of salinity less than fully marine. There is no evidence of dissolution, but some specimens of N. pachyderma from the shallower parts of the section show evidence of some physical abrasion. Other than the abrasion, there is no evidence of reworking or mixing of faunas.
Accessory marine biogenic components are limited to a few sponge spicules, echinoid spines, and shell fragments, but there is ample evidence of detrital black coal (probably from the Permian farther south) throughout the section and brown coal or lignite at and below Section 188-1166A-17R-CC. The presence of marine invertebrates from Section 188-1166A-13R-1 and above supports the conclusion of fully marine conditions.
At the base of Section188-1166A-2R-2, the sediment appears to have been overlain at some time by a significant overburden (e.g., by thick ice or sediment) and thus would appear to predate the Last Glacial Maximum. The sediment is not lithified through diagenetic cementation but by decreased porosity and is very compact, giving the impression of having a high clay content. An alternative explanation is that a significant unconformity exists immediately above the base of Section 188-1166A-2R-CC.
Residues generated in the search for foraminifers in the upper part of the hole (to Section 188-1166A-11R-CC) constitute a considerable volume of the sample and are very highly dominated by terrigenous debris, commonly, but not uniformly, poorly sorted. Rounded grains are present but rare in the fine to medium sand fraction but may be abundant in coarser fractions. Traces of black coal are present in most samples.
No sample was studied from Section 188-1166A-3R-CC because of very small sample recovery or from several cores deeper in the hole where the evidence is overwhelmingly of nonmarine deposition.
The presence of wood below Section 188-1166A-17R-CC and a barnacle plate in interval 188-1166A-11R-1, 47-50 cm, are significant macropaleontological records. The wood and lignite in the Paleogene part of the section are accompanied in samples by the tectin lining of a few agglutinated foraminifers, akin to Haplophragmoides and Trochammina. These are of little chronostratigraphic value but suggest that conditions were estuarine or shallow nearshore.
Planktonic foraminifers are present and relatively common (several tens of specimens) in several samples from Sections 188-1166A-1R-1 and 1R-2, but not from Section 1R-CC. They are much less abundant at the base of Section 188-1166A-3R-2, where few specimens of N. pachyderma are present, and in Section 4R-CC. They are gray and slightly abraded with the effect of removing details of surface texture, but do not show any evidence of dissolution. In each case they are accompanied by a single benthic species. Planktonic foraminifers are generally more abundant, by a factor of 1.5-4 over the benthic component, consistent with an outer continental shelf environment of deposition.
Sample 188-1166A-5R-CC contains both four- and five-chambered forms of N. pachyderma (dominant). This association is common in modern shelf assemblages in the region. Samples 188-1166A-6R-CC, 7R-CC, and 9R-CC contain N. pachyderma, with or without Globigerina falconensis, but numbers are very low. Sample 188-1166A-8R-CC is barren of any fauna. Several samples from the interval 188-1166A-5R-CC through 10R-CC contain small planktonic species in the 63- to 125-µm fraction.
Samples 188-1166A-10R-1, 11-13 cm, 10R-CC, and 11R-CC contain a relatively diverse planktonic foraminiferal assemblage, the best available in the Neogene at this site. They are dominated by the normal four-chambered form of N. pachyderma, and there are few of the five-chambered form. There is a single specimen of Globigerinita parkerae (Bermudez) in Sample 188-1166A-10R-CC. This sample also yielded a small benthic fauna significantly different from others at this site.
The deepest occurrence of planktonic species is in Sample 188-1166A-12R-1, 18-20 cm, which contains a few N. pachyderma.
It is highly likely that the records presented here understate (but only to a limited degree) the foraminifer fauna because more delicate agglutinated forms (e.g., what appears to be Haplophragmoides sp.) were observed during examination of sediment samples under hand lens and stereobinocular microscope. These would not survive vigorous processing. Only the more robust forms are therefore recorded.
Benthic assemblages are dominated by members of the Cassidulinacea—Globocassidulina, Cassidulina, and Ehrenbergina. Lagenid/nodosariid forms are lacking, and other types are rare and apparently not systematic in occurrence. Four forms of Globocassidulina are recognized here—G. crassa crassa (d'Orbigny), G. crassa biora (Crespin), G. crassa rossensis, and G. subglobosa (Brady).
Scattered specimens of Globocassidulina are present throughout Core 188-1166A-1R and can be identified at generic level with the hand lens because of their white porcellanous appearance. Selected samples from this core, such as Samples 188-1166A-1R-1, 16-21 cm; 1R-1, 117-122 cm; and 1R-2, 9-11 cm, all contained useful benthic assemblages including sporadic specimens of Trifarina angulosa. The source cannot have been far distant but must have been to the south or southeast. It is evidence of some infauna, but numbers are too low to draw meaningful conclusions about environmental significance.
Small assemblages are present in Section 188-1166A-3R-2, base of section, and in Samples 188-1166A-4R-CC, 5R-1, 26-31 cm, 5R-CC, 6R-CC, 7R-CC, 8R-1, 42-45 cm, and 9R-CC. Samples 188-1166A-10R-1, 11-13 cm, and 10R-CC contain larger, more diverse benthic faunas. Sample 188-1166A-10R-CC yielded, in addition to species discussed above, two species of Astrononion.
Enough samples contain significant assemblages to give credence to planktonic percentage as a depth indicator. Planktonic percentage is normally ~50%-80%, suggesting water depths corresponding to outer continental shelf or deeper. Assemblages with high globocassidulinid content (especially Globocassidulina) are widespread in modern Prydz Bay in shallower, better oxygenated environments such as the Four Ladies Bank (Quilty, 1985) but not in deeper parts of the region where siliceous mud and ooze (SMO of Harris et al., 1997b) dominates. SMO conditions are not indicated in any of the assemblages studied from Site 1166. The outer continental shelf association also is consistent with the Deep Shelf Calcareous Assemblage of Milam and Anderson (1981).
Two distinct lithologic associations are recorded for cores at this site. Some are massive diamicts (coarser) and silty clays (finer). An attempt was made to relate foraminifers to these different lithologies, but assemblages seem to bear little relationship to the lithologic description. Best assemblages come from dark silty clay, whether or not the overall lithology is described as fine or coarse. This may indicate that similar marine conditions held throughout this time and that the difference in lithology reflects very little change in salinity, depth, or temperature between intervals of deposition of different sediments.
The distribution of accessory components is summarized on Table T5.
Sponge spicules were consistent components of samples at Site 1165 and are conspicuous in modern sediments of Prydz Bay. With the exceptions of the 63- to 125-µm fraction in Sample 188-1166A-1R-CC, which is a sponge spicule-rich horizon with simple diactinellid monaxon spicules to ~10 mm long, and Samples 188-1166A-1R-1, 16-21 and 117-122 cm, 2R-CC, 1R-2, 9-12 cm, and 12R-CC, they are either absent or very minor constituents at this site.
Sample 188-1166A-11R-1, 47-50 cm, contains a highly fragmented barnacle plate.
Black coal fragments are present throughout the sequence, but most are genuine coal and probably originated in the Permian sequence of the Prince Charles Mountains region, 250-500 km to the south. A few trilete and bisaccate pollen or spores were recovered from diatom preparations from Sample 188-1166A-16R-2, 140-141 cm. The bisaccate forms are likely to be from the Permian, but the source of the trilete is not as clear and could be related to the presence of wood fragments in the next core.
Wood fragments, <0.5 mm long, make their appearance downhole in Sample 188-1166A-17R-CC and are present in several samples below that. Under the microscope, the small fragments are still flexible when wet and retain their orange-brown color. Details of wood and cuticle are clearly visible in mounted slides of the material. They are not to be confused with woody structure that is visible in some of the black coal fragments that accompany most samples.
In Sample 188-1166A-25R-2, 0-5 cm, there are fragments up to 8-9 mm in diameter of dark brown lignified wood, contrasting strongly with the black coal. Woody structures are essentially pristine. It also contrasts with descriptions of the Cretaceous coals recovered during Leg 119, indicating strongly that this is Tertiary material close to its origin. The wood tissue is very well preserved in many samples.
Sample 188-1166A-27R-CC consists of highly coaly sediment, almost lignite. The major constituent is wood in fragments up to 20 mm long. The rest is quartz sand and mica, consistent with deposition in a coal swamp environment. There is ample wood and diversity, and preservation seems adequate to allow reconstruction of the vegetation at the time.
The wood fragments are clear evidence of coeval terrestrial vegetation in the samples, which are dated on other bases as latest Eocene-earliest Oligocene. Results of palynological analysis of this material is the subject of Macphail and Truswell (this volume).