The Mawson Diamictite and the Carapace Sandstone, formations of the Ferrar Group at Allan Hills and Carapace Nunatak, Victoria Land, Antarctica

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Abstract
Four hundred feet (130 m) plus of current-bedded sandstones and fine lithic conglomerates of Jurassic age at Carapace Nunatak, formerly attributed to the Beacon Group, are shown to consist of re-derived Beacon and primary basaltic volcanic detritus. They are here named the Carapace Sandstone and referred to the Ferrar Group. They are conformably overlain by over 1,000 ft (300 m) of Kirkpatrick Basalt, including a thick hyaloclastite breccia with pillows, and a 50 ft (15 m) intercalation of what is here called Mawson Diamictite. The latter, also Jurassic in age, is also exposed extensively at nearby Allan Hills, where it fills a depression eroded several hundred feet into Permian and Triassic coal measures and sandstones of the Beacon Group. The diamictite consists, like the Carapace Sandstone, of mixed Beacon and basaltic debris, but contains more basalt, is coarser-grained, very poorly sorted, and generally unstratified. More than 1,000 ft (300 m) thick, it was originally called Mawson Tillite. The present study could not confirm the glacial origin, but located pockets of the deposit in what appear to be volcanic vents; in view of the strong evidence of contemporaneity of basaltic volcanism and emplacement of the diamictite, it is concluded that the deposit is most probably one of volcanic mudflows, and possibly explosion breccias. The formation name is therefore changed to Mawson Diamictite, and it is proposed that it be transferred from the Beacon Group to the Ferrar Group.