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modern and Archean oceans, as well as for Eu, which indicates a greater contribution to Archean seawater from high-T hydrothermal fluids (e.g., Figs. 4,5). It should be noted that the small negative Ce anomaly in the shallow water Holocene reef carbonates relative to world seawater is not inconsistent, as very shallow seawater often displays smaller negative Ce anomalies compared to bulk seawater (e.g., de Baar et al., 1983). The fact that Archean IFs commonly have seawater-like REY distributions is not consistent with REY scavenging by Fe-oxyhydroxides in a manner similar to that observed in modern oceans. As shown in Fig. 8, adsorption-desorption reactions at equilibrium strongly fractionate the REY between metal-oxides and seawater. If Archean IFs precipitated from seawater as Fe(III) minerals, then their observed REY distributions would require quantitative scavenging of all REY in solution, perhaps in a manner analogous to the laboratory co-precipitation of REE-Fe-oxide phases from seawater in early studies (e.g., Goldberg et al., 1963). However, the exact nature of the primary IF precipitate remains unresolved, though data presented in Chapter 4 suggests that initial deposition of Fe(II) mineral phases may have been important. Regardless, the seawater-like REY distributions in Archean IFs, and the lack of other suitable archives, indicates that IFs offer the best opportunity for discerning the Nd isotopic composition of >2.7 Ga seawater. 26
References Alibert, C., McCulloch, M.T., 1993. Rare earth element and Nd isotopic compositions of the banded iron-formations and associated shales from Hamersley, Western Australia. Geochim. Cosmochim. Acta 57, 187-204. Alibo, D.S., Nozaki, Y., 1999. Rare earth elements in seawater: Particle association, shale normalization, and Ce-oxidation. Geochim. Cosmochim. Acta 63, 363-372. Anders, E., Grevesse, N., 1989. Abundances of the elements: meteoric and solar. Geochim. Cosmochim. Acta 53, 197-214. Bau M. (1999) Scavenging of dissolved yttrium and rare earths by precipitating iron oxyhydroxide: Experimental evidence for Ce oxidation, Y-Ho fractionation, and lanthanide tetrad effect. Geochim. Cosmochim. Acta, 63, 67–77. Bau M. and Dulski P. (1999) Comparing yttrium and rare earths in hydrothermal fluids from the Mid-Atlantic Ridge: implications for Y and REE behaviour during nearvent mixing and for the YrHo ratio of Proterozoic seawater. Chem. Geol., 155, 77–90. Bau M., Koschinsky A., Dulski P., and Hein J.R. (1996) Comparison of the partitioning behaviours of yttrium, rare earth elements, and titanium between hydrogenetic marine ferromanganese crusts and seawater. Geochim. Cosmochim. Acta, 60, 1709-1725. Bau M., Höhndorf A., Dulski P., and Beukes, N.J. (1997a). Sources of rare-earth elements and iron in Paleoproterozoic iron-formations from the Transvaal Supergroup, South Africa: Evidence from neodymium isotopes. J. Geol. 105, 121- 129. 27
Page 1: Iron sedimentation and the neodymiu
Page 4 and 5: The process(es) by which IFs were d
Page 7: This thesis represents original and
Page 10 and 11: viii
Page 12 and 13: goal of the research is to discern
Page 14 and 15: Figure 1. Map of southern Africa sh
Page 16 and 17: appropriate to briefly discuss: 1)
Page 18 and 19: 100 10 MORB 1 0.1 raw data (mg/kg)
Page 20 and 21: 10 -2 hydrothermal fluid 10 -3 10 -
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Page 24 and 25: 100 MCO + 3 + M(CO 3 )- 2 rare eart
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Page 30 and 31: sound geochemical basis for anomalo
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Page 34 and 35: available, it should be possible to
Page 38 and 39: Bau M., Möller P., and Dulski P. (
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Page 42 and 43: Haley B.A., Klinkhammer G.P. (2003)
Page 44 and 45: Lee J.H. and Byrne R.H. (1993) Comp
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Page 52 and 53: Abstract The benefits of inductivel
Page 54 and 55: List of Figures Figure 1. Sample de
Page 56 and 57: 1. Introduction The advent of induc
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Page 64 and 65: cps, then 3000 cps must be subtract
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Page 72 and 73: 10 2 JDo-1 reference values 10 1 IF
Page 74 and 75: Figure 5. Diagram depicting various
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Page 82 and 83: For the more recent, full 32 elemen
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Table 4. Interferences observed for
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value uncertainty (as %RSD) is repr
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1.50 FeR-4 (n=2) 1.25 JUB / referen
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1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
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consistent (App. 1), and similar to
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1.50 SGR-1b (n=3) 1.25 JUB / refere
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1.50 JCh-1 (n=3) 1.25 JUB / referen
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1.50 JDo-1 (n=5) 1.25 JUB / referen
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determinations in carbonate rocks r
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1.50 JMn-1 (n=4) 1.25 JUB / referen
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eference value. The result is that
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eference value and the measured JUB
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the 32 analyzed elements, with Ti b
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Govindaraju K. (1995) 1995 working
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Appendix 1. Analytical data Appendi
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Appendix 1. Literature reference va
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Appendix 1 continued. Data in mg/kg
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the concentration of the major elem
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Potential interferences on monoisot
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1500 0.5 M HCl 4.0 interference on
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4000 0.40 0.20 3500 0.17 mg/kg 0.18
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interference on 95 Mo in sample sol
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Nd isotopes in 2.9 Ga Archean surfa
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Table 2 Trace element concentration
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Author's personal copy B.W. Alexand
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and preservation of oxide-facies IF
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TOP relative stratigraphic position
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The mechanism by which the alkali m
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6. Widdel, F. et al. Ferrous iron o
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82 PRESERVATION OF PRIMARY REE PATT
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ulk, open ocean seawater tended to
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