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.
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.
[3][4] The fossiliferous horizons of the Ferrar Group at Carapace Nunatak contain one of the richest and most diverse freshwater Jurassic paleobiota known from Antarctica.
[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.
[5] The lake cherts from the upper part of Carapace Sandstone contain an abundance of fusainized plant material and animal remains.