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During the period from November 1995 to January 1996, over 700 samples were collected for palynological study from the Shackleton Glacier area. The focus for sample collection and stratigraphic studies is to establish a more precise biostratigraphic framework for the Permian to Jurassic Victoria Group of the Beacon Supergroup in the central Transantarctic Mountains than is currently available. The fossil spores and pollen recovered from these rocks also provide information on the past vegetation and environmental history in this high paleolatitude part of Gondwanaland.
Fieldwork was carried out with helicopter support from a base camp at the junction of the Shackleton and McGregor Glaciers (SHG on (figure 1) and from camps at McIntyre Promontory and Graphite Peak. Thirty-eight sections were measured and sampled, and additional samples from other sections and sites were provided by John Isbell, David Elliot, and Greg Retallack.
Samples from the Pagoda, MacKellar, and Fairchild formations (figure 2) were collected from sites on Sullivan Ridge on the Ramsey Glacier, Reid Spur, and Mount Butters (figure 1). The Buckley Formation was sampled at McIntyre Promontory, the upper Ramsey Glacier, Graphite Peak, Mount Finley, and various sites adjacent to the McGregor and Gatlin Glaciers; the uppermost Buckley beds and the Fremouw Formation were sampled at numerous sites at and near Halfmoon Bluff, Collinson Ridge, Shenk Peak, Ellis Bluff, Schroeder Hill, Kitching Ridge, Mount Rosenwald, Layman Peak, Mount Boyd, and Graphite Peak; and the Falla Formation was sampled near Schroeder Hill and at Roberts Massif. Additional samples from the Permian formations were collected from Cape Surprise, McIntyre Promontory, Mount Heekin, and Mount Butters by John Isbell; Permo-Triassic boundary beds from Graphite Peak by Greg Retallack; and the Prebble Formation from Otway Massif and Mount Pratt by David Elliot.
In general, the level of thermal alteration of organic matter is relatively high for the Permian units and somewhat higher than experienced in much of the Beardmore area in the Triassic/Jurassic formations. Careful laboratory treatment and different types and amounts of oxidation treatment (as also found by Farabee, Taylor, and Taylor 1991) are helpful in recovering identifiable palynomorphs. Thus far, dark shale samples from the Pagoda Formation contain only traces of organic matter with no recognizable palynomorphs, the dark color probably resulting from iron-titanium oxides. Additional shaly Pagoda samples, however, as well as many samples from the overlying MacKellar and Fairchild formations are still to be processed.
The best-preserved Buckley palynomorphs obtained to date, though black in color, corroded, and barely recognizable, are from the lower part of the formation adjacent to the upper Ramsey Glacier. They appear to be Early Permian and include monosaccate pollen of Potonieisporites and Plicatipollenites, and taeniate bisaccate pollen, mainly Protohaploxypinus.
Triassic assemblages from high in the Fremouw Formation on Layman Peak and from the Fremouw and Falla Formations in the Shroeder Hill area are the best preserved from the Shackleton area thus far. The assemblages from Layman Peak, which contain relatively common lycopsid spores of Aratrisporites spp., including A. parvispinosus and A. wollariensis (figures 3C and 3D), can be included in subzone B of the Alisporites zone (Kyle 1977; Kyle and Schopf 1982) and correlated with the eastern Australian Middle Triassic Aratrisporites parvispinosus zone of Helby, Morgan, and Partridge (1987). These results are consistent with previous palynological evidence for correlation and age of the upper Fremouw Formation in the Beardmore Glacier area (e.g., Kyle and Schopf 1982; Farabee, Taylor, and Taylor 1990). The Shroeder Hill samples contain typical Middle-Late Triassic assemblages, with abundant bisaccate pollen (Alisporites) and a variety of trilete spores. One specimen of Polycingulatisporites crenulatus (figure 3B) was found in a sample (AE-12) from an unnamed ridge southeast of Shroeder Hill, suggesting correlation with antarctic subzone D and the eastern Australian P. crenulatus zone (de Jersey 1975; Helby et al. 1987), and a Late Triassic age for these beds. The samples from both Layman Peak and Shroeder Hill contain common Uvaesporites verrucosus spores (figure 3A), and these predominate in sample AE-12. Abundance of these spores, which have a probable lycopsid affinity, and other common lycopsid spores such as Aratrisporites, highlight the importance of lycopsid plants in the vegetation of this part of Antarctica during the Middle and Late Triassic.
Comparison is also possible with the New Zealand Murihiku Supergroup, where marine invertebrate faunas provide good age control for the palynomorph succession (de Jersey and Raine 1990). The New Zealand Triassic, however, includes significant hiatuses, such as most of the Ladinian (upper Middle Triassic), which complicates correlations. There are also regional differences in palynomorph assemblages across the eastern Australia-New Zealand-Transantarctic Mountains sector of Gondwanaland. An example noted by de Jersey and Raine (1990) is the rarity of A. wollariensis in New Zealand where it is restricted to one uppermost Etalian (uppermost Anisian) sample, whereas it can be common in Australian and antarctic Lower and Middle Triassic samples. In New Zealand, A. parvispinosus occurs in the Kaihikuan (uppermost Ladinian) and ranges into the Otapirian (Rhaetian or top of Triassic), appearing significantly later and disappearing slightly later than in Australia. Initial examination of the Shackleton material suggests possible variation in ranges of other forms, such as some of the apiculate spores. As laboratory processing continues on the Shackleton samples, the new data may clarify regional similarities and differences in assemblages and biostratigraphic ranges across Gondwanaland.
Special thanks go to Kevin Killilea and staff at the Shackleton base camp for logistic support, to members of Helicopters New Zealand for helicopter support, and to other geologists at the Shackleton camp for their assistance. This research was supported by National Science Foundation grant OPP 94-18093.
References
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Farabee, M.J., E.L. Taylor, and T.N. Taylor. 1990. Correlation of Permian and Triassic palynomorph assemblages from the central Transantarctic Mountains, Antarctica. Review of Palaeobotany and Palynology, 65, 257-265.
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