Cambrian trilobites from Reilly Ridge, northern Victoria Land, Antarctica, and their stratigraphic implications

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Abstract
Asmall trilobite faunule from the Spurs Fonnation on Reilly Ridge is described and shown to be of Mindyallan (late Middle Cambrian to early Late Cambrian) age. The trilobite locality, which was previously recorded as of “probably Tremadocian” age, contains four species of agnostids (including the genera, Hadragnostus, Formosagnostus?) and at least nine of polymerid trilobites (including Brassicicephalus sp. nov. and the genera Catillicephala, Distazeris, and Pseudokingstonia. All are recorded from the Antarctic continent for the first time. Affinities of the faunule are shared between North America and Australia. Tectonic distortion, which affects all fossils, is graphically analysed to enable the original proportions of the fossil to be determined. The structure and distribution of Bowers Supergroup units at Reilly Ridge is outlined and illusttated. The stratigraphy of the Spurs Formation is complicated by lateral facies changes and allochthonous megablocks of limestone, up to 500 m long, derived by intrabasinal gravitational sliding. Several of the previously known fossil localities at Reilly Ridge are from allochthonous blocks; that reported here is believed to be in place.