School of Engineering and Science - Jacobs University

10 0
10 -1
Isua IF (3.8 Ga)
Kuruman IF (2.5 Ga)
10 -4
Campbellrand dolomite (2.5 Ga)
Holocene carbonate reef
La Ce Pr Nd PmSm Eu Gd Tb Dy Y Ho Er Tm Yb Lu
sample/PAAS
10 -2
10 -3
seawater x10 4
Figure 12. Distributions of the REY in average world seawater (same as Fig. 4), and various chemical
sediments that are free from contamination with Al-rich clastic detritus. Data representing the Isua IF
(Greenland) are for the IF-G reference standard analyzed at Jacobs University Bremen as discussed in
Chapter 5. Kuruman (South Africa) IF data represent the average of two analyses as reported in Bau et al.
(1997a). Campbellrand dolomite represents unpublished data from GKP-01 drillcore (Agouron-
Griqualand Paleoproterozoic Drilling Project, administered by University of Johannesburg). Holocene
(≤10,000 years old) carbonate reef data from Webb and Kamber (2000). The REY patterns of IFs and
both ancient and modern carbonates are very similar to each other and modern seawater. These
observations suggest that Archean IFs possessing seawater-like REY distributions are likely to be
excellent archives for the Nd isotopic ratios present in contemporaneous seawater.
that, as a general rule, IF samples containing more than 0.5-0.7% Al 2 O 3 are unsuitable
for reconstructing seawater Nd isotopic ratios. Additionally, the distribution of the REY
is very useful at screening potential seawater archives, as Archean marine precipitates
frequently display REY patterns that are very similar to those observed in modern
seawater.
Figure 12 shows REY patterns observed in Archean IFs and both modern and
ancient marine carbonates. The distribution of the REY is generally indistinguishable
between modern seawater and carbonate reefs, as well as Archean dolomite and IFs.
The general enrichment of the HREE over the LREE and positive La and Y anomalies
found in seawater are common to all marine precipitates shown in Fig. 12 regardless of
age. The primary differences are for Ce, which reflects the different oxidation states of
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