The Sirius Group

The isotopic composition of strontium of mollusc shells in the early Miocene section of the CRP-1 core (46-62 mbsf) indicated dates of 16.6 0.4 and 18.7 0.3 Ma in agreement with the diatom biostratigraphy of Harwood et al. (1998). The Ar/ Ar date of a volcanic clast (18.4 1.1 Ma) measured by McIntosh (1998) confirms the early Miocene (Burdigalian) age of the sediment. 

The third and final hole was completed in 1999 and reached sandstone of the Beacon Supergroup of Devonian age. The final depth of CRP-3 was 934 mbsf. The reports arising from the study of the third 

Personnel of the Ross Ice Shelf Project melted a hole through the ice shelf at a site known as J9 (82°22.5 S, 168°87.5 S) and used it to recover several piston cores (Clough and Hansen 1979). The ice at that location is 360 m thick and is followed by 237 m of seawater. The reports arising from this project were published in Science (vol. 203, No. 4379,1979). 

The glaciation of the Transantarctic Mountains is indicated by several features that are the characteristic products of glacial ice moving over mountainous bedrock  

Deepening of stream valleys and development of U-shaped cross sections 

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The Queen Maud Formation is a coarse grained conglomeratic sandstone that lies unconformably on the rocks of the Weaver Formation. This unit is about 25 m thick and is equivalent to the basal quartz-pebble conglomerate of the Queen Maud Formation on Mt. Weaver. On Tillite Ridge in the Wisconsin Range the Queen Maud Formation is overlain by indurated till more than 30 m thick. This till is probably of Pleistocene or even of Pliocene age and thus is one of the many late Cenozoic glacial deposits in theTransantarctic Mountains that are collectively included in the Sirius Group. 

As time passed, the volume of the East Antarctic ice sheet increased sufficiently to bury the Transantarctic Mountains during the early Miocene until only the highest peaks remained ice-free as nunataks. At this time, the ice deeply eroded the valleys of the outlet glaciers and imposed on them the typical U-shaped cross-sections that are evident in the ice-free valleys of southern Victoria Land and elsewhere in the Transantarctic Mountains. More recently, the East Antarctic ice sheet thinned causing previously ice-covered areas of the Transantarctic Mountains to become ice-free and exposing till of the Sirius Group that was deposited by the ice sheet during its maximum extent. 

The till pellets also contain a varied assemblage of reworked marine microfossils some of which are depicted in Fig. 17.10b. The flora includes 23 species of diatoms, as well as silicoflagellates, ebridians, cysts, radiolarians, sponge spicules, and palynomorphs identified by D.M. Harwood (Faure and Harwood 1990). Similar assemblages of marine microfossils occur in Cenozoic till of the Sirius Group at many places in the Transantarctic Mountains. This evidence... 

Mt. Sirius in Fig. 19.5a is a steep-sided mesa composed of sandstones of the Fremouw Formation of the Beacon Supergroup overlain by a dolerite sill of the Ferrar Group which is covered by a thick deposit of the till first described by Mercer (1972) and subsequently by McKelvey et al. (1984) and by Hagen (1988). Mt. Sirius is the type locality of the Sirius Formation which was later elevated to the stams of the Sirius Group that includes the numerous small deposits of late Cenozoic till that occur in the Transantarctic Mountains from Manhaul Bay in the Allan Hills of southern Victoria Land to the Wisconsin Range in the Horlick Mountains. 

Webb et al. (1983) considered three possible explanations for how the marine microfossils in the till of the Sirius Group could have been deposited ... 

The till of the Sirius Group in the Dominion Range and at Mt. Achemar also contains detrital grains of pyrite. The isotope composition of sulfur of these grains was determined by Hagen (1988, p. 162) ... 

Beardmore Glacier to about 2,600 m at the southern end of the Upper Oliver Platform (Webb et al. 1987). The glacial deposits of the Sirius Group in Table 19.2 consist of the late Pliocene Meyer Desert Formation (150 m) and of the overlying early Pleistocene Mt. Mills Formation (50 m) (Webb and Harwood 1993). 

Fig. 19.7 The erosional remnants of the Meyer Desert Formation and the overlying Beardmore Drift of the Sirius Group are located on benches of the Dominion Erosion Surface. The glacial sediments orange) were deposited on Ferrar dolerite and Beacon sandstones (green). The Beardmore...

Fig. 19.8 The Meyer Desert Formation of the Sirius Group in the Dominion Range has a fine grained yellowish-tan matrix of sand, silt, and clay that encloses angular boulders of dolerite of the Ferrar Group and of sedimentary rocks of the Beacon Supergroup. This facies of the glacial deposits closely resembles the diamictite on Mt. Sirius in Fig. 19.5b. However, the section in the Dominion Range also includes thin bedded and well-sorted fluvial and lacustrine sandstones and sUtstones that formed in peiiglacial environments that existed between episodic advances of the East Antarctic ice sheet during the late Pliocene (Photo by G. Faure)...

The till of the Sirius Group also contains well-preserved leaves of Nothogagus in the form of dense... 

Lodgment till and associated periglacial outwash deposits occur widely in the Transantarctic Mountains. Although all of the Cenozoic glacial deposits are now included in the Sirius Group, these deposits are difficult to date because the microfossils they contain are reworked and because the various kinds of plant ronains they may contain are not sufficiently time-sensitive to determine their depositional ages. 

Fig. 19.15 Size fractions of K-feldspar and plagioclase in the till at the base of Mt. Tuatara south of the Byrd Glacier (line A) and in till of the Sirius Group on the summit of Table Mountains (line B) yield Rb-Sr dates and intercepts Line A, t = 1100 69 Ma, 0.7050 0.0021 line B, t = 524 115 Ma, 0.7132 0.0068. These results indicate that the till on Mt. Tuatara contains feldspar of Precambrian age derived from the East Antarctic craton, whereas the till on Table Mountain originated from the Granite Harbor Intrusives (Adapted from Faure and Taylor 1981)...

Heinrich MR (ed) (1976) Extreme environments Mechanisms of microbial adaptation. Academic, New York HiU RS, Harwood DM, Webb PM (1991) Last remnant of Antarctica s Cenozoic flora Nothofagus of the Sirius Group, Transantarctic Mountains. Abstracts, Eighth International Gondwana Symposium, June 24-28, Hobart, Tasmania Hirsch P, Hoffman B, Gallikowski CA, Mevs U, Siebert J, Sittig M (1988) Diversity and identification of heterotrophs from Antarctic rocks of the McMurdo Dry VaUeys (Ross Desert). Polarforschung 58 261... 

Stern TA (1984) A seismic refraction survey near the Dailey Islands, southwestern McMurdo Sound, Antarctica. New Zealand Dept Sclent Indust Res, Geophys Div, Rept 198 1-32 Stonehouse B (ed) (2002) Encyclopedia of Antarctica and the southern oceans. WUey, Chichester, UK Stott LD, McKelvey BC, Harwood DM, Webb P-N (1983) A revision of the ages of Cenozoic erratics at Mount Discovery and Minna Bluff, McMurdo Sound. Antarctic J US 18(5) 36-38 Stroeven AP (1997) The Sirius Group of Antarctica Age and environment. In Ricci CA (ed) The Antarctic region ... 

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