Diatom biostratigraphy of the Cenozoic glaciomarine Pagodroma Group, northern Prince Charles Mountains, East Antarctica*

Abstract

In the northern Prince Charles Mountains glaciomarine sediments of the Pagodroma Group outcrop on Fisher Massif (Mt Johnston and Fisher Bench Formations) and at the Amery Oasis (Battye Glacier and Bardin Bluffs Formations), at locations 300 and 250 km south of the Amery Ice Shelf edge, respectively. Most of the Pagodroma Group consists of ice‐proximal glaciomarine diamict, and a much subordinate (<2%) amount of more ice‐distal mudstone. Microfossil biostratigraphy based upon in situ and glacially reworked diatoms constrains the ages of the four formations, and identifies at least six intervals of marine fjordal deposition. Sparse diatoms in Mt Johnston Formation diamicts indicate an Early Oligocene age. However, it is unclear whether these diatoms are in situ or else are glacially reworked and represent either an immediately prior or more remote past interglacial. The Battye Glacier and Fisher Bench Formations contain in situ diatoms and are broadly time equivalent, the former dating between 10.7 and 9.0 Ma and the latter between 12.1 or 10.7 Ma and 8.5 Ma. In situ diatoms indicate the Bardin Bluffs Formation to have been deposited between 2.6 and either 1.8 or 0.99 Ma. Glacially reworked diatoms in the Bardin Bluffs and Fisher Bench Formations identify four depositional intervals. The reworked taxa are sourced from Eocene–Oligocene (>30.1 Ma), Middle Miocene (14.5–12.5 Ma and 12.1–11.5 Ma), Early Pliocene (4.9–3.6 Ma) and, tentatively, Late Pliocene (3.4–2.6 Ma) strata. These microfossil data further develop the interpretation that the Pagodroma Group formed during episodes of reduced glacial extent when, in the absence of an ice shelf, marine waters penetrated far southwards into the Lambert Graben of East Antarctica.

Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica

“…Of the diverse sections documented in these efforts, only the CIROS-2 drillcore from McMurdo Sound (Winter and Harwood, 1997;Winter et al, 2012a) and possibly the Bardin Bluffs Formation of the Pagodroma Group in the Amery Oasis (Whitehead et al, 2004) overlap with the late Pliocene PRISM interval of focus. However, these proximal records are discontinuous due to sediment removal by the very glacial fluctuations we seek to reconstruct, and paleoenvironmental interpretations have been drawn from diatom-bearing mudstone, sandstone, and diamict, in contrast to the rich diatomites preserved in distal diatom-ooze belt settings (Burckle, 1984;Burckle and Cirilli, 1987;Barron, 1996b).…”

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.…”

“…Correlated using data from (Gradstein et al 2012) and benthic 18 O isotope stack LR04 (Lisiecki and Raymo 2005). Data for the Antarctic Peninsula is from Smellie et al (2006);N vlt et al (2011), Cockburn Island: (Jonkers and Kelley 1998;Pirrie et al 2011;Levy et al 2012), Vestfold Hills: (Quilty et al 1990;Quilty et al 2000;Whitehead et al 2001;Whitehead et al 2004;Whitehead et al 2006b;Cody et al 2008;Colhoun et al 2010), Larsemann Hills: (Webb 1974;Quilty et al 1990;McMinn and Harwood 1995)…”

“…The part of the Sørsdal Formation that contains abundant bivalve material has been dated to the early Pliocene (4.5-4.1 Ma) using diatom and bivalve biostratigraphic records Pickard et al 1986Pickard et al , 1988Quilty et al 2000;Harwood et al 2000) and is supported by magnetic polarity data from the site (Berggren et al 1995;Quilty et al 2000). This age has been further constrained to 4.2 to 4.1 Ma (Whitehead et al 2004;Whitehead et al 2006b). Shelly lenses within diatomaceous sandstone beds contain numerous hiatellid bivalves, dominantly of Hiatella cf.…”

Chapter 5 Cenozoic Climate History from Seismic Reflection and Drilling Studies on the Antarctic Continental Margin

“…Sediments in the Prince Charles Mountains indicate open-water fjordal environments in the Miocene to Pliocene (Hambrey and McKelvey, 2000;Whitehead et al, 2003Whitehead et al, , 2004. Lower Pliocene marine diatomite in the Vestfold Hills, on the eastern side of Prydz Bay, contains evidence of temperatures 41C warmer than today (Whitehead et al, 2001).…”