A reassessment of the age of the Cockburn Island Formation, northern Antarctic Peninsula, and its palaeoclimatic implications

Abstract

New constraints on the age of the Cockburn Island Formation, northern Antarctic Peninsula, resulting from whole rock laser-stepped heated 40 Ar– 39 Ar dating of associated basalt and palaeomagnetic re-calibration of the ranges of the formation’s fossil diatom taxa, suggest that interglacial conditions existed around 3 million years ago. The refined age of the deposit supports continent-wide Late Pliocene warming in Antarctica, and makes more likely the occurrence of extensive marine incursions in East Antarctica at that time.

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

“…The presence of large thick-shelled pectens, sessile barnacles and a lack of ice-rafted debris suggest deposition in a mainly ice-free environment (Jonkers and Kelley 1998), consistent with reconstructed seasonality and growth patterns from the bivalves .…”

“…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)…”

“…40 Ar/ 39 Ar ages from the underlying volcanic rocks provide a maximum age of ca. 4.9 Ma for the CIF (Jonkers and Kelley 1998). Ages determined using mean Sr isotope ratios from Dingle et al (1997); based on Howarth and McArthur (1997) and Sr isotope ratios from bivalve shells ) suggest a depositional age of 4.7 (+0.6/ −1.2) and 4.66 (+0.17/−0.24) Ma respectively (Pirrie et al 2011).…”

“…These ages are stratigraphically consistent with the 40 Ar/ 39 Ar age of the underlying volcanic rocks. In contrast a biostratigraphic age based on the diatom assemblage suggested that the deposit was formed around 3 Ma (Jonkers and Kelley 1998;Pirrie et al 2011) but an updated biostratigraphy places this at 2.8 to 2.4 Ma (Cody et al 2008;Levy et al 2012). Ages based on diatom biostratigraphy can be problematic as aeolian transportation of diatoms by wind may have occurred (e.g.…”

A diatom record of late Pliocene cooling from the Ross Sea continental shelf, AND-1B, Antarctica

“…The coastal and terrestrial Cenozoic Investigation in the Western Ross Sea (CIROS) and the Dry Valley Drilling Project (DVDP) cores from McMurdo Sound, Ross Sea, comprise truncated diatombearing early and mid-Pliocene sequences (Winter and Harwood, 1997;Winter et al, 2010a) and the Deep Sea Drilling Project (DSDP) Leg 28 Site 271 from Eastern Basin, Ross Sea comprise a sporadic late Pliocene record with only 7% recovery (Hayes et al, 1975). Some evidence for late Pliocene warm periods was encountered in Prydz Bay by Ocean Drilling Program (ODP) Legs 113 and 188 (Mahood and Barron, 1996;Whitehead et al, 2005), from an uplifted marine sequence in the Pagodroma Group, Prince Charles Mountains, East Antarctica (Whitehead et al, 2004) and Cockburn Island, Antarctic Peninsula (Jonkers and Kelley, 1998). These records are too few and sporadic to provide a comprehensive view of late Pliocene climate on the Antarctic continental shelf.…”