Beacon Supergroup

The Beacon Heights Orthoquartzite (330 m) is found in the South Victoria Land region between the Arena Sandstone and the overlying Devonian Aztec Siltstone. It is well sorted and cemented, with medium to coarse grain sizes and trough cross-beds, with Haplostigma and Beaconites remnants.^{[16][15][8][9]}

The Aztec Siltstone (125–220 m) is found both in South Victoria Land and the Darwin Mountains. The siltstone includes interbedded sandstones, fish-bearing shales,

Within the Beardmore Glacier region, the Devonian Alexandra Formation (0–320 m), which constitutes the entire Taylor Group, is a quartz sandstone to siltstone.[8]^[9][20]

Victoria Group

The Victoria Group begins with a

Trace fossils are sparse below, but become common in the Hatherton Sandstone. They change from Skolithos-dominated facies to wide diversity and abundance, including vertical and horizontal burrows and huge arthropod

• Fodinichnia: feeding burrows, probably of marine polychaetes, featuring evidence of rhythmic defecation.^[12]
  • Narrow, sinuous, near-surface forms on flat bedding surfaces
  • Longer, larger forms, reaching 13 cm across and 1 m in length.
• Walking
  Repichnia).^[12] The presence of crawling traces in such well sorted sands is problematic. The arthropod trackways are thought to have been formed in shallow water, and supersaturated sand has a shallow angle of repose. Thus either a layer of organic matter, perhaps in the form of an algal slime, must have supported the sediment,^[12] or the sediment must have been partially dry. In the context of subaerial features such as raindrop marks and desiccation cracks on associated horizons, the best explanation is that the trackways were formed on bedforms produced on a river bed, but while they were exposed by a low-flow period.^[18]
  • Beaconites antarcticus: narrow, parallel grooves, about an inch apart, disappearing into elliptical pits; created by shovelling the surface sediment aside before burrowing into the sediment.^[12] Occasionally branch.^[15]
  • Perhaps B. barretti: more widely spaced grooves (~3 cm); small footprints visible. Implies many walking limbs and an approximately rectangular shape — reminiscent of trilobites.^[12] Extend laterally up to 1.7 m; burrow deeply into sediment.^[15] Probably produced by a very different arthropod to B. antarcticus.^[15]
  • Large (~30 cm wide) trails with a scrape mark from a central tail. Three to four footprint pits diverge from these tracks at a high angle. The feet making the footprints had spines on their rears. These may have been formed by
    eurypterids but are not a perfect match to known eurypterid trails; they may also have been formed by xiphosurans^[12]
• Diplichnites trackways: double rows of fossils previously attributed to marine trilobites but now thought to perhaps be formed by annelids or myriapods.^[18] Here they appear on metre-scale crossbeds that may represent sub-fluvial dunes.^[18]

• Cruziana and Rusophycus: thought to be formed by trilobites, whose body fossils are found only in marine assemblages. Could also have been made by other arthropods, or the lower parts of the Beacon Sandstone may have been marine. They have been found in many other non-marine instances.^[18]
• Skolithos: traditionally thought to be marine; however, there are many counterexamples.^[18]

References