Coalsack Bluff

Hammer et al. (1986) revisited Graphite Peak during the 1985-1986 field season and collected additional specimens of tetrapod bones. Although most of these bones belonged to Lystrosaurus murrayi, the new collection also included a mandible of the carnivorous cynodont reptile Phrinaxodon (Hammer 1990b). 

The second discovery of tetrapod bones occurred 2 years later on Novanber 23,1969, at Coalsack Bluff 

The geology of Coalsack Bluff was described by Collinson and Elliot (1984) who also published a large-scale map of the nunatak which is only 5 km long and 2 km wide. The rocks exposed at Coalsack Bluff include the upper part of the Buckley Formation and the lower part of the overlying Fremouw Formation for a total thickness of approximately 500 m. The sedimentary rocks of Coalsack Bluff were intruded by three sills of Ferrar Dolerite. Four whole-rock K-Ar dates, cited by Collinson and Elliot (1984), range from 170.1 2.0 to 182.3 3.2 Ma and conhrm a Middle Jurassic age for these rocks (lUGS 2002). 

Glacial deposits of Quaternary age on the northwestern side of Coalsack Bluff contain cobbles and boulders of locally derived Ferrar Dolerite, clasts of igneous and metamorphic rocks, as well as fragments of limestone containing well-preserved archae-ocyathids of Cambrian age. These limestone clasts could have originated from an outcrop of Shackleton Fimestone that occurs at the south end of Buckley Island located about 95 km southeast of Coalsack Bluff (Section 5.3.1). 

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The Fremouw Formation in Table 10.7 is the oldest unit of Triassic age in the Beardmore area of the central Transantarctic Mountains. It was named by Barrett (1969) for Fremouw Peak which is located south of the Prebble Glacier in the Queen Alexandra Range in Fig. 10.14. The Fremouw Formation is composed of sandstones and mudstones that rest disconformably on the Buckley Formation (Barrett et al. 1986). The basal beds of the Fremouw Formation are composed of quartz sandstone and greenish-gray mudstone. This part of the formation contains vertebrate fossils that were discovered and described by Barrett et al. (1968b), Elliot et al. (1970), Kitching et al. (1972), and Hammer et al. (1986). The vertebrate fossils include bones of both reptiles and amphibians that occur as channel lag deposits in the basal Fremouw at Coalsack Bluff identified in Fig. 10.13. 

The Early Triassic Fremouw Eormation has yielded fossil bones of a wide variety of land-based amphibians and reptiles that inhabited the forests on the coastal plain of East Antarctica. The collecting sites in the Beardmore and Shackleton glacier areas of the central Transantarctic Mountains include Graphite Peak, Coalsack Bluff, the Cumulus Hills, and the Gordon Valley. The most famous Triassic reptile is Lystrosaurus which was a plump little animal about 90 cm long that seems to have been well adapted to digging burrows in the soil. 

Fig. 13.22 Mount Achernar at 84°12 S and 160°56 E contains three sills of Ferrar Dolerite which intruded srmdstones of the Permian Buckley Formation. The underlying basement rocks ace not exposed in this area. Mount Achernar is located a short distance west of Coalsack Bluff (Section 11.2.2 Fig. 11.9B) and of Mt. Sirius which contains a deposit of Neogene till on its summit Excerpt of the topographic map Buckley Island, Antarctica SV 51-60/3 published in 1967 by the US Geological Survey...

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