Geoscience Reference
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reconstruct paleochannel activity and Eocene sea level fluctuations in this presently
semi-arid area. Alley (
1998
) and Alley et al. (
1996
;
1999
) extended this investigation
further north to include the Lake Eyre Basin and carried out detailed evaluations
of the nature and timing of major phases of deep weathering, ferricrete formation,
silicification, paleochannel aggradation and vegetation changes. They concluded that
deep weathering was prevalent before channel sedimentation and was possibly as
old as the early Mesozoic. They were able to use pollen evidence to reconstruct the
types of forests growing in central and southern Australia during the Cenozoic. Tem-
perate rainforest grew along the southern continental margin during the Palaeocene.
The rainforest was replaced by open woodland during the Oligocene-Miocene. At
this time, shallow alkaline lakes occupied parts of the paleochannels in the inland
reaches, supporting a diverse fauna, including crocodiles. By Pliocene times, some
5 million years ago, continued desiccation gave rise to an environment characterised
by chenopod shrubland and open woodland.
Helene Martin (
2006
) put together all the pollen evidence obtained in the last fifty
years from boreholes throughout Australia by herself and others and was able to
provide a comprehensive overview of the development of arid vegetation in Australia
and the associated changes in Cenozoic climates. Her conclusions were entirely
consistent with the evidence from phylogenetics and phylogeography analysed by
Byrne et al. (
2008
), which confirmed that the onset of aridity in Australia is first
evident in the mid-Miocene plant record some 15 million years ago.
In the drier mountainous regions of southern Africa, the pollen preserved in rock
hyrax dung in rock shelters has been dated by
14
C and has provided a partial but
still useful record of late Quaternary vegetation changes that was not obtainable by
other means (Scott and Woodborne,
2007
). The
13
C content of the dung has provided
additional paleoclimatic information (Scott andVogel,
2000
). Longer records of veget-
ation change have been obtained from the relatively sparse pollen preserved in lake
and pan sites in South Africa (Scott et al.,
1995
; Scott,
2002
; Scott et al.,
2003
;Scott
et al.,
2008
), including a 190 ka record for the Savanna Biome from Tswaing Crater
near Pretoria (Scott,
1999
).
The late Quaternary record of vegetation changes in semi-arid north-west Aus-
tralia comes not from deposits located on land but from marine sediment core
Fr10/95-GC17 collected about 60 km west of the Cape Range Peninsula (22
°
2.74
ʹ
S,
113
E, water depth 1,093 m) (van der Kaars and De Deckker,
2002
). The core
site is close to the present-day southern margin of the Australian summer monsoon
and at present receives 200-300 mm of annual rainfall. Pollen data from this core
provides a sensitive record of changes in the latitudinal position of the monsoon.
From 35 to 20.4 ka, herbs or small shrubs dominated the regional vegetation and there
were relatively few trees, pointing to a significant reduction in summer rainfall. This
was the driest period of the last 100 ka, which confirms previous interpretations (De
Deckkeretal.,
2002
) that the summer monsoonal regime and associated precipitation
°
30.11
ʹ
