Late Pliocene age of glacial deposits at Heidemann Valley, East Antarctica: evidence for the last major glaciation in the Vestfold Hills

Abstract

A Pliocene (2.6-3.5 Ma) age is determined from glacial sediments studied in a 20 m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14 C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the 'Vestfold Glaciation' may have been due to lateral expansion of the Sørsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea.

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…There is, however, evidence for periods of warmth (4.6 to 3. (Pirrie et al 1997;Smellie et al 2006;N vlt et al 2011), Larsemann Hills: (Webb 1974;Quilty et al 1990;McMinn and Harwood 1995), Vestfold Hills: (Colhoun et al 2010;Quilty et al 2000;Whitehead et al 2001;Whitehead et al 2004;Whitehead et al 2006b), Wright Valley: (Prentice et al 1993), McMurdo Sound: (Eggers 1979;Leckie and Webb 1979) Fig 3 Stratigraphic setting of late Neogene successions that yield shallow marine fossils.…”

“…These deposits are nearly coeval with the Wright Valley (Dry Valleys) and probably represent the last time the area was covered by an enlarged EAIS (Colhoun et al 2010).…”

“…The Heidemann Valley deposits may correlate with a marine incursion (M10 of Whitehead et al 2006b) dated at 3.2 to 2.5 Ma that can be traced 500 km to the SW at Amery Oasis and is part of a major marine incursion onto the East Antarctic craton (Whitehead et al 2006b;Quilty 2010). The deposit at Heidemann Valley is just 4 m thick and it can only be reached by digging trenches through regolith (see Colhoun et al 2010).…”

“…These have been dated as Pliocene in age (3.5 to 2.6 Ma), determined from amino acid racemisation, diatom and foraminifera biostratigraphy and magnetic polarity data (Colhoun et al 2010). There are uncertainties associated with both the magnetic data, due to unreliable interpretation of polarity changes in the absence of absolute dating, and amino acid dating of molluscs due to assumptions about temperatures controlling the rate of amino acid diagenesis.…”

“…The foraminifera biostratigraphy only provides an upper age limit due to the absence of Ammoelphidiella antarctica and the fact that all other foraminifera reported are extant. The diatom biostratigraphy used by Colhoun et al (2010) is based on the presence of Thalassiosira insigna (Jousé) Harwood & Maruyama, 1992 and Fragilariopsis kerguelensis (O'Meara) Hasle, 1958, indicating an age of >2.6 Ma and <3.2 Ma respectively. However, using these same species and biostratigraphy from Cody et al (2008), the age range would be 2.29 to 2.19 Ma, which would not correlate with the other dating methods used.…”