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Plant Macrofossils
C Hatte´, University of Arizona, Arizona, USA
A J T Jull, University of Arizona, AZ, USA
ª 2007 Elsevier B.V. All rights reserved.
Introduction
Until the late 1980s, the majority of radiocarbon
dates for lacustrine or palustrine paleoclimatic stu-
dies from the late Pleistocene and Holocene were
obtained by beta-counting of samples of organic
lake muds or bulk peat sediment. However, since(1990). Evidence of late Pleistocene fires and eucalypt forest
from a north Queensland humid tropical rainforest site.
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Press, Chicago.
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Black carbon in soils: The use of benzenecarboxylic acids as
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Hatte´, C., Morvan, J., Noury, C., and Paterne, M. (2001). Is
classical acid–alkali–acid treatment responsible for contamina-

macrofossil material by accelerator mass spectro-
metry (AMS) (see AMS Method). This is partly
because AMS offers the possibility of dating a
much higher level of stratigraphic resolution,
since it is possible to obtain dates on very small
samples of material. It is also because of the
widely-held view that AMS dates on plant macro-
fossils are inherently more reliable than those
obtained from the sediment matrix. In such cases,
the source of the carbon is known and therefore
should not be composed of heterogeneous material
that could be of different ages. In general, it has
not been taken into account that plant macrofossils
may be species-dependent or that the plant macro-
fossils themselves may be redeposited. Consequently,
even within the plant macrofossils chronologies,
inconsistencies are still common. This suggests that
the choice of appropriate material is not trivial and
requires serious investigation.
It is evident that all warnings for paleoclimatic
studies can be extended to archeological investiga-
tions that make increasing use of plant macrofossils
for 14C dating.
Lacustrine and Palustrine Records
Algae and aquatic moss macrofossils
Aquatic cells photosynthesize subaquaticly and hence
build carbon from dissolved inorganic carbon (DIC)
into their cellular material, so they reflect the 14C : 12C
ratios of the water. The DIC is influenced by:
(1) exchange with the atmospheric CO2 reservoir;
(2) decomposition of organic matter;
(3) dissolved carbonate from surrounding limestone
catchments; and
(4) residence time of lake or peat-bog water.
Depth (cm)
eed
30 40 50 60
ulk
of r
lix l
RADIOCARBON DATING/Plant Macrofossils 2959Large numbers of terrestrial paleoclimatic stu-
dies aim to address the Last Glacial Holocene
transition. The characterization of this transition
is mostly based on lacustrine or palustrine (marsh)
records. Establishment of a reliable and accurate
chronology remains one of the major challenges in
these late glacial environments. Indeed, due to the
variations in the amount of 14C in atmospheric
CO2, this means that the measured amount of
14C is not linearly related to age, and the aging
is highly critical. This article focuses first on plant
macrofossils from these humid environments, from
algae to higher plant macrofossils. Other environ-
ments will then be considered. Finally, there will
be some reminders about sampling, storage and
pretreatments of samples and inherent possible
contaminants.
9,000
10,000
11,000
12,000
Salix leaves Carex s
14
C
yr
B
P
0 10 20
Figure 1 Radiocarbon ages obtained from macrofossil and b
(modified from Turney et al., 2000). Notice the systematic aging
Salix leaves and the age difference between Carex seeds and Sas bulk organic material
organic matter samples from Finglas River, southwest Ireland
adiocarbon ages obtained on bulk organic material compared to
eaves.This means that the 14C activity of DIC does not
reflect the 14C activity of the atmosphere, but is 14C-
depleted. This results in an artificial age, the so-
called ‘hard water effect’ inherited by algae cells,
which can show wide variation (Fontana, 2005;
Macdonald et al., 1991). See Figure 1 on bulk
organic matter.
Consequently, the AMS dating of algae macrofossils
should be avoided if possible. If there is no other
choice, an evaluation of the reservoir age should be
associated with the measurements. This could be done
by the collection, at a ‘reference’ level, of algae macro-
fossils and subaerial plant or beetle remains. Once
again, attention should be given to the choice of refer-
ence level and to the beetle species. Indeed, the level
chosen to determine the reservoir age should corre-
spond to a climatic context matching to the one for