Resolving views on Antarctic Neogene glacial history – the Sirius debate

ABSTRACTThe discovery of marine Pliocene diatoms in warm-based glacial deposits (now termed the Sirius Group) high in the Transantarctic Mountains in the 1980s began a three-decade-long controversy over the stability of the East Antarctic Ice Sheet. Their presence implied that this ice sheet had collapsed as recently as three million years ago to allow their deposition in shallow interior seas, followed by transport and deposition from an expanded over-riding ice sheet. Though the glacial deposits included clasts with older diatoms, no evidence of clasts with Pliocene diatoms was published, but the hypothesis gained wide acceptance. Increasing knowledge of ice sheet behaviour and the antiquity and stability of the Transantarctic Mountains, along with new techniques for dating age and denudation rates for landscapes, has led to a more likely alternative hypothesis – that the high-level Sirius Group deposits pre-date Transantarctic Mountains uplift and their Pliocene diatoms are atmospheric contaminants. Surveys have shown that marine diatoms from the Antarctic margin and the Southern Ocean are indeed reaching the surface of the ice sheet and blowing through the mountains, with permafrost processes providing opportunities for contamination. Modelling and geological evidence is now consistent with a stable East Antarctic Ice Sheet in the interior for the last 14 Ma, with some retreat around the margins and periodic collapse of the West Antarctic ice sheet in Pliocene times.