Paleoenvironmental interpretations and systematics of Devonian trace fossils from the Taylor Group (lower Beacon Supergroup), Antarctica

Trace fossils are varied and abundant in the otherwise unfossiliferous Taylor Group sandstones of the lower Beacon Supergroup. Twenty-four ichnotaxa are recognised, many previously unrecorded, and these have been grouped into 7 ichnocoenoses that occur successively from the basal Windy Gully Sandstone up into the Aztec Siltstone. The trace fossils suggest that the earliest Taylor Group sediments, the New Mountain Subgroup, is a marine transgressive sequence that progressively buried an irregular Kukri Erosion Surface and which eventually overwhelmed all basement highs by the end of Altar Mountain Sandstone deposition. Both the Windy Gully Sandstone and the New Mountain Sandstone are interpreted as the nearshore deposits of wide sandy tidal bays in which bioturbation by crustaceans was intense, while trough cross-bedded channel sands bear numerous trackways of large walking arthropods. The intervening Terra Cotta Siltstone is probably the deposit of a coastal lagoon with variable salinity and a fauna of small trilobites. Towards the end of New Mountain Sandstone deposition there was local uplift and erosion in the north (Heimdall Erosion Surface) and the temporary development of Skolithos-dominated horizons throughout the general South Victoria Land area. A more open sandy coastline existed during Altar Mountain Formation deposition and trace fossils suggest a sandy bottom fauna of worms and active arthropods. Regression was initiated at the onset of Arena Sandstone deposition and a north to east paleocurrent direction that continues in the overlying 2 formations became established. Although trace fossils are less common than in older Taylor Group formations, the Arena Sandstone contains Beaconites, a burrow that is also found in fluvial deposits in Britain. The succeeding Beacon Heights Orthoquartzite is in turn overlain by the Aztec Siltstone that represents muddy alluvial plains which buried earlier sandy plains. Possible crustacean burrows suggest a fluctuating coastal margin to the north. Systematic descriptions include the following new forms: Beaconites barretti n. ichnosp.; Didymaulichnus nankervisi n. ichnosp.; Didymaulyponomos rowei n. ichnogen., n. ichnosp.; Heimdallia chatwini n. ichnogen., n. ichnosp.; Rusophycus plumei n. ichnosp.