The complex evolution of the Devonian to Jurassic Transantarctic basin is still incompletely understood. In Victoria Land, the thickness and age span of the basin fill (Victoria Group) varies dramatically: several hundreds of metres of Palaeozoic glacigenic and fluviolacustrine deposits occur in southern Victoria Land and in the far north (lower Rennick Glacier area; Dow & Neall Reference Dow and Neall1974), whereas basal Beacon Supergroup strata in the Deep Freeze Range and upper Rennick Glacier area are interpreted to be Late Triassic or even Early Jurassic in age (see e.g. Goodge & Fanning Reference Goodge and Fanning2010, Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011). In the Eisenhower Range, a key area connecting southern and northern Victoria Land, fluvial conglomerates and sandstone overlying the crystalline basement have previously been interpreted as the basal part of the Triassic to Early Jurassic Section Peak Formation (Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011, Reference Elsner, Schöner, Gerdes and GauppElsner et al. In press). Here we present new palynological data indicating a Permian age for these deposits, which may be equivalent to the Takrouna Formation in northern Victoria Land and the Weller Coal Measures in southern Victoria Land.
Sample GIX-AG04/1 was collected during the Ninth German Antarctic North Victoria Land Expedition (GANOVEX IX, 2005/2006) from a c. 1 m thick lens of carbonaceous siltstone c. 35 m above the base of a section at the head of the Anderton Glacier (74°35′S, 162°15′E; see Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011 for locality details). This sample has yielded abundant wood fragments, amorphous organic matter, and a few moderately preserved palynomorphs and cuticle fragments. The palynomorph assemblage consists of monosaccate and monosulcate pollen (Cannanoropollis spp., Cycadopites cymbatus (Balme & Hennelly) Segroves, Praecolpatites sinuosus (Balme & Hennelly) Bharadwaj & Srivastava), with common occurrences of taeniate bisaccate grains (Protohaploxypinus spp., Striatopodocarpites cancellatus (Balme & Hennelly) Hart, S. fusus (Balme & Hennelly) Potonie) and unidentified trilete spores (Fig. 1).
The joint occurrence of the biostratigraphically significant S. cancellatus, S. fusus, and Praecolpatites sinuosus is indicative of the ‘Protohaploxypinus zone’ of the Transantarctic Mountains (Kyle & Schopf Reference Kyle and Schopf1982), zone APP32 of Australia (Price Reference Price1997), and the upper part of ‘zone 3’ of southern Africa (see Lindström Reference Lindström1995); although the ages of these regional zones are not precisely constrained to international stages, this indicates a Permian age possibly as old as Kungurian (late Cisuralian). A Permian age assignment is further supported by the dispersed cuticle fragments; these bear numerous small papillae per cell, which is a characteristic cuticular feature of certain species of the typically Permian seed-plant Glossopteris (Fig. 1g & h) (see Pant & Gupta Reference Pant and Gupta1968). The uniform state of preservation and the absence of any palynomorphs or cuticle fragments indicative of a younger (i.e. Triassic or Jurassic) age render significant effects of reworking unlikely.
Basal portions of sedimentary successions of nearby sections at Thern Promontory and along the Eisenhower Range escarpment have similar depositional features and comparable lithological and petrological composition (see Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011), and probably belong to the same unit. Radiometric dating of detrital zircons from a sample c. 10 m above the base of the conglomerates at the Eisenhower Range escarpment has yielded major age peaks between c. 500–550 Ma; the two youngest ages obtained are 215 ± 8 Ma (Late Triassic) and 266 ± 9 Ma (late Permian) (Reference Elsner, Schöner, Gerdes and GauppElsner et al. in press). However, these two detrital zircon ages cannot be regarded as statistically significant, and the palynological age indication is therefore considered more reliable here. The presumed Cisuralian age indicates that these deposits may represent a local equivalent of the Takrouna Formation in northern Victoria Land (Collinson et al. Reference Collinson, Pennington and Kemp1986), the Weller Coal Measures of southern Victoria Land (Isbell & Cúneo Reference Isbell and Cúneo1996), and possibly the Radok Conglomerate in the Prince Albert Mountains (Lindström & McLoughlin Reference Lindström and McLoughlin2007).
In light of this new age assignment for basal conglomerates of the Victoria Group in the Eisenhower Range, the occurrence of a < 2 m thick diamictite at the base of a section at the Eisenhower Range cliff (Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011) is of special significance. Although definite evidence for a glacial origin of this deposit has not been observed (Schöner et al. Reference Schöner, Bomfleur, Schneider and Viereck-Götte2011), the occurrence underneath the fluvial Permian conglomerates indicates that this thin bed may be a local remnant of Carboniferous/earliest Permian glacial tillites similar to the Metschel Formation in southern Victoria Land and an unnamed, presumably glacigenic unit in the lower Rennick Glacier area (see Collinson et al. Reference Collinson, Isbell, Elliot, Miller, Miller and Veevers1994, Elliot & Fleming Reference Elliot and Fleming2008).
The present description of previously unrecognized Palaeozoic deposits in the Eisenhower Range of northern Victoria Land provides an important step forward towards further identifying and interpreting correlations between individual stratigraphic units in different areas of the Transantarctic Mountains.
Acknowledgements
We thank the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR, Hannover) for the invitation to join the GANOVEX IX expedition and for a great time in the field, and Sofie Lindström (Lund), Steve McLoughlin (Stockholm), and Alan P.M. Vaughan for helpful comments. Financial support by the Alexander von Humboldt-Foundation (Feodor Lynen fellowship to BB) and the Deutsche Forschungsgemeinschaft (DFG grants SCHO 1269/1 to RS; GA 457/11+13 to Reinhard Gaupp, Jena; SCHN 408/11+13 to JWS; VI 215/6 to LV-G, and KE584/12+16 to HK; all in Priority Program SPP1158) is gratefully acknowledged.