Carapace Nunatak

Coordinates: 76°53′S 159°24′E / 76.883°S 159.400°E / -76.883; 159.400
Source: Wikipedia, the free encyclopedia.

Carapace Nunatak (76°53′S 159°24′E / 76.883°S 159.400°E / -76.883; 159.400) is a prominent isolated

Mount Brooke where it is visible for a considerable distance from many directions. It was so named by the New Zealand party of the Commonwealth Trans-Antarctic Expedition (1956–1958) because of the fossil carapaces of small crustaceans found in the exposed rocks.[1][2]

Geology

The Carapace Nunatak is an erosional

glacial moraines conceal the underlying Jurassic strata.[3][4]

At the base of Carapace Nunatak, about 130 m (430 ft) of cross-bedded sandstones and fine lithic

fossiliferous beds of mudstone, siltstone, and chert. The base of the Carapace Sandstone is not exposed. The Carapace Nunatak is the type locality for the Carapace Sandstone.[3][4]

Conformably overlying the Carapace Sandstone is 300 m (980 ft) of Kirkpatrick Basalt. The basalt

lava flows include a thick layer of hyaloclastite breccia with beds of pillow lava at its base. About 140 m (460 ft) above its base, a 15 m (49 ft) thick layer of volcanic breccia lies sandwiched between basaltic lava flows. The lava flows exhibit columnar jointing and, at the base of the Kirkpatrick Basalt, contain with very large (up to 2 m (6.6 ft) thick) xenoliths (rafts) of fossiliferous, laminated siltstone and chert. The upper surface of the Kirkpatrick Basalt has been long since removed by erosion.[3][4]

Fossils

The fossiliferous horizons of the Ferrar Group at Carapace Nunatak contain one of the richest and most diverse

Lagerstätten.[5][6]

In the laminated, and silicified, fine-grained lake deposits of Carapace Sandstone, fossil conchostracans (clam shrimp) are the most important in terms of number of individuals and distribution.[6][7] They consist of small, 1 to 2 cm (0.39 to 0.79 in), bivalved spinicaudatan arthropods. They are most typical of ephemeral, alkaline ponds. Associated macrofossils include notostracan branchiopods, ostracodes, insect nymphs and wings, and plant leaves. Macroscopic trace fossils are extremely rare.[5]

The lake cherts from the upper part of Carapace Sandstone contain an abundance of fusainized plant material and animal remains. This fine-grained Magadi-type chert preserves abundant plant fossils. These plant fossils include at least three conifer taxa represented by vegetative and reproductive structures, isolated ovules, a diversity of taxa of fern pinnules, rachides and rhizomes, and cycadophyte foliage. Intermixed with the plant fossils are numerous of shallow-water conchostracans and other ephemeral freshwater crustaceans.[5][8]

References

  1. ISBN 978-0-7864-3590-6
  2. ^ "Carapace Nunatak". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved 17 October 2023.
  3. ^ a b c Ballance, P.F. and Watters, W.A., 1971. The Mawson Diamictite and the Carapace Sandstone, formations of the Ferrar Group at Allan Hills and Carapace Nunatak, Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 14(3), pp.512-527.
  4. ^ a b c Bradshaw, M.A., 1987. Additional field interpretation of the Jurassic sequence at Carapace Nunatak and Coombs Hills, south Victoria Land Antarctica. New Zealand Journal of Geology and Geophysics, 30(1), pp.37-49.
  5. ^ a b c Babcock, L.E., Leslie, S.A., Elliot, D.H., Stigall, A.L., Ford, L.A. and Briggs, D.E., 2006. The “Preservation Paradox”: microbes as a key to exceptional fossil preservation in the Kirkpatrick Basalt (Jurassic), Antarctica. The Sedimentary Record, 4(4), pp.4-8.
  6. ^ a b Ribecai, C., 2007. Early jurassic miospores from ferrar group of carapace nunatak, south victoria Land, Antarctica. Review of Palaeobotany and Palynology, 144(1-2), pp.3-12.
  7. ^ Yabin, Shen, 1994. Jurassic conchostracans from Carapace Nunatak, southern Victoria Land, Antarctica. Antarctic Science, 6, pp.105–113.
  8. ^ Hieger, T.J., Serbet, R., Harper, C.J., Taylor, T.N., Taylor, E.L. and Gulbranson, E.L., 2015. Cheirolepidiaceous diversity: an anatomically preserved pollen cone from the Lower Jurassic of southern Victoria Land, Antarctica. Review of Palaeobotany and Palynology, 220, pp.78-87.
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