The Jurassic volcanic sequence at Carapace Nunatak and Coombs Hills south Victoria Land, records an initial phase of explosive volcanicity, in part acidic, that was followed by quieter, flood basalt extrusion, a pattern repeated elsewhere in the Transantarctic Mountains. The explosive phase produced poorly sorted volcanogenic material (Mawson Formation) at Coombs Hills, and this was probably contemporaneous with the deposition of coarse lake sediments (Carapace Sandstone Formation) at Carapace Nunatak. The succeeding flood basalts are known as the Kirkpatrick Basalt Group.