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SUMMARY:Neogene terrestrial environment of Antarctica - Alan Ashworth (Dep
 artment of Geosciences\, North Dakota State University)
DTSTART:20091118T163000Z
DTEND:20091118T173000Z
UID:TALK20978@talks.cam.ac.uk
CONTACT:Poul Christoffersen
DESCRIPTION:The discovery of terrestrial fossil assemblages at several loc
 ations in the Transantarctic Mountains is transforming our understanding o
 f the late Cenozoic environment of Antarctica.  The most southerly fossil 
 assemblage is at lat. 85.1°S\, about 500 km from the South Pole.  The env
 ironment was an active glacial margin in which plants\, insects and freshw
 ater mollusks inhabited sand and gravel bars and small lakes on an outwash
  plain.   Initially the deposits were assigned a Pliocene age (3.5 Ma) but
  a mid- to early Miocene age is more probable (c. 14 – 25 Ma) based on c
 orrelation of fossil pollen from the deposits with 39Ar/40Ar dated pollen 
 assemblages from the McMurdo Dry Valleys.  Within the McMurdo Dry Valleys\
 , the oldest fossiliferous beds are at least 19.76 Ma based on the 39Ar/40
 Ar age of a volcanic ash bed interbedded within a valley fill of diamictit
 es\, paleosols and lacustrine deposits.  The valley floor during the non-g
 lacial phases had poorly-drained soils and the extensive development of mo
 ssy mires. Wood and leaves of Nothofagus are abundant in lacustrine deposi
 ts.  The silts of shallow fluvial channels contain abundant megaspores and
  spiky leaves of the aquatic lycopod Isoetes (Quillwort). The youngest fos
 siliferous beds within the Dry Valleys are 14.07 Ma.  The fossils are most
 ly those of freshwater organisms including numerous species of diatoms and
  an ostracod species in which the soft anatomy is preserved.   The base of
  the lake is marked by a moss bed with exceptionally well-preserved stems 
 and leaves of the extant species Drepanocladus longifolius.  Pollen eviden
 ce from marine cores in the Ross Sea basin suggests that tundra existed fr
 om the Oligocene to the Mid-Miocene.   Fossil evidence from the Dry Valley
 s locations indicates organisms with complex life histories persisted in A
 ntarctica until c. 14 Ma.  At 14 Ma there was a shift in glacial regimes f
 rom wet- to cold-based\, marking a profound and abrupt climatic shift like
 ly causing widespread extinction.  It seems probable that at least some of
  the mid-Miocene fossils had ancestors that evolved in Antarctica during t
 he Paleogene or earlier.   An important consequence of these studies is th
 at the Cenozoic climate of Antarctica was warm enough until the mid-Miocen
 e to support vascular plants and insects. 
LOCATION:Scott Polar Research Institute\, LIBRARY (1ST FLOOR)
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