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1 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272, USA (e-mail: gregr@darkwing.uoregon.edu)
2 2CSIRO Land and Water, Adelaide Laboratories, PMB2, Glen Osmond, South Australia 5064
3 3Department of Soil Science, University of Wisconsin, Madison, Wisconsin 53706-1299, USA
Fossil Nothofagus leaves from the Meyer Desert Formation of the Sirius Group in the central Transantarctic Mountains have been found with recycled marine diatoms indicating that they are no older than 4.1–3.1 Ma; they have been interpreted as evidence for Pliocene warming and diminution of the East Antarctic Ice Cap. In contrast, Plio-Pleistocene ice-cap stability and sustained polar palaeoclimate has been argued from landforms in Victoria Land and isotopic data from the Southern Ocean. New evidence on this question comes from fossil soils in the Meyer Desert Formation. One of these, the Siesta palaeosol, has a gypsic horizon at a depth of 85 cm as in soils of polar deserts with a mean annual precipitation (MAP) of 120–220 mm. Clastic dykes from a 60–80 cm thick permafrost active layer in the palaeosols are evidence of a mean annual temperature (MAT) of –3 to –11°C. This is warmer and wetter than the Dominion Range today (MAP 36 mm, MAT –39°C) but still a periglacial climate, cooler and drier than southern Chilean moorland and krummholz (MAP 600–7500 mm, MAT 5–8°C), or subantarctic tundra (MAP 400–2500 mm, MAT –5 to +5°C). A Pliocene age for the Nothofagus fossils and Siesta palaeosol is compatible with soil development on surfaces that bracket their enclosing deposits. The Dominion Range was significantly warmer and wetter than it is today during Pliocene (c. 3.5 Ma) growth of Nothofagus and formation of the Siesta palaeosol, but the Beardmore Glacier was still large at that time. Surface soils and palaeosols of the Meyer Desert Formation are evidence of another warmer and wetter episode earlier during the Pliocene (c. 5 Ma). Both warm intervals were separated by intervening times of glacial expansion and frigid palaeoclimate.
Keywords: Pliocene, Antarctica, Sirius Group, palaeosols, palaeoclimates.
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