The Permian-Triassic Transantarctic basin, which occupied the Panthalassan margin of the East Antarctic craton, including the present Transantarctic and Ellsworth Mountains, evolved above a mid-Paleozoic passive continental margin basement through the following stages: (1) Carboniferous/Permian extension, (2) late Early Permian back-arc basin, (3) Late Permian and Triassic foreland basin, and (4) Jurassic extension and tholeiitic volcanism. A mid-Paleozoic (Devonian) wedge of coastal-to-shallow marine quartzose sandstone developed on the eroded roots of the Late Cambrian-Early Ordovician Ross orogen. A lacuna in East Antarctica during the Carboniferous was followed by the inception of Gondwanan deposition in a wide Carboniferous/Permian extensional basin. Volcanic detritus at the base of the late Early Permian post-glacial marine(?) shale and sandstone sequence in the Ellsworth Mountains is the first sign of a volcanic arc and subduction along the Panthalassan margin. A similar but much thinner non-volcaniclastic sequence accumulated in the Transantarctic Mountains. The introduction of abundant volcanic detritus to the cratonic side of the basin and a 180° paleocurrent reversal in the Late Permian in the Beardmore Glacier area are the earliest indicators of tectonism along the outer margin of the basin and the inception of a foreland basin that accumulated thick Late Permian and Triassic braided stream deposits of mixed volcanic and cratonic provenance. The Permian sequences in the Ellsworth and Pensacola Mountains were folded in the Triassic. The foreland basin was succeeded in the Early Jurassic by extension and initial silicic and then tholeiitic volcanism that led to the breakup of Gondwanaland.

The Polarstar Formation, a 1-km-thick argillite and sandstone unit, is the uppermost part of a thick Cambrian to Permian sedimentary sequence in the Ellsworth Mountains. The formation gradationally overlies the Whiteout Conglomerate, an Upper Carboniferous-Lower Permian glacial diamictite. The lower part of the Polarstar is mostly argillite, and the middle part consists of coarsening-upward cycles of argillite to sandstone. These cycles begin with lenticular bedding overlain by wavy and flaser bedding and end with ripple-laminated, fine-grained sandstone to cross-bedded, medium-grained sandstone. The upper part of the formation consists of fining-upward cycles of channel-form, cross-bedded, medium-grained sandstone overlain by fine-grained sandstone and of Glossopteris -besaing siltstone, argillite, and coal. The sequence of facies suggests that the depositional environment changed temporally in this area from prodelta to delta and coastal plain. The occurrence of a marginal-marine trace fossil fauna in the middle of the formation and the complete absence of a marine shelly fauna suggest depositional conditions ranging from anaerobic to dysaerobic in a stratified inland sea. Detrital grains in Polarstar sandstone indicate a source terrane dominated by silicic to andesitic volcanic rocks, including tuffs, with minor mafic volcanic and low-grade metamorphic and granitic rocks. The Polarstar Formation was probably deposited in a back-arc basin between the Pacific margin of Gondwanaland and the East Antarctic craton.

Five marine biofacies based on conodont distributions are recognized for the Permian Phosphoria Formation and related rocks. They are: (1) facies with no conodonts, (2) facies with Hindeodus only, (3) facies with Hindeodus and (or) Neostreptognathodus and (or) Stepanovites and (or) Merrillina, (4) a transitional facies containing any of the components of biofacies 3 with either Neogondolella or Xaniognathus, (5) facies dominated by Neogondolella and Xaniognathus. These biofacies (1–5) represent progressive shore or nearshore to offshore differentiation of the conodont faunas. Intervals of phosphate deposition within the Phosphoria Formation correspond to shoreward encroachment of offshore biofacies during trasgressive events. Elements of these conodont faunas, including the new species Neostreptognathodus newelli , are described.

Conodonts have been described from Jurassic rocks in Japan and from Upper Cretaceous rocks in western Africa. However, both occurrences might also be interpreted as reworked faunas. Arguments in favor of the reported ages include independent interpretation of the age of the enclosing rock and apparent lack of source rocks for reworking. Opposing arguments include well-established Triassic occurrences of conodonts that appear to be identical with most of the species reported as post-Triassic.