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86 PRESERVATION OF PRIMARY REE PATTERNS WITHOUT CE ANOMALY Deep-Sea at 2.9~2.7 Ga. Resource Geology, 52, 101-110. Kirschvink, J.L. and Weiss, B.P. (2002) Mars, panspermia, and the origin of life: Where did it all begin? Palaeontologia Electronica, 4, 8-15. Kirschvink, J.L., Gaidos, E.J., Bertani, L.E., Beukes, N.J., Gutzmer, J., Maepa, L.N. and Steinberger, R.E. (2000) Paleoproterozoic Snowball Earth: Extreme climatic and geochemical global change and its biological consequences . Proceedings of the National Acadamy of Sciences, 97, 1400-1405. Kopp, R.E., Kirschvink, J.L., Hilburn, I.A. and Nash, C.Z. (2005) The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis. Proceedings of the National Acadamy of Sciences, 102, 11131-11136. McLennan, S.M. (1989) Rare earth elements in sedimentary rocks: Influence of provenance and sedimentary processes. In: B.R. Lipin and G.A. McKay (Editors), Geochemistry and mineralogy of rare earth elements. Reviews in Mineralogy, 21, 169-200. Nothdurft, L.D., Webb, G.E. and Kamber, B.S. (2003) Rare earth element geochemistry of Late Devonian reefal carbonates, Canning basin, Western Australia: Confirmation of a seawater REE proxy in ancient limestones. Geochimica et Cosmochimica Acta, 68, 263-283. Reichardt, F.J. (1994) The Molopo Farms complex, botswana: history, stratigraphy, petrography, petrochemistry and Ni-Cu-PGE mineralization. Exploration and Mining Geology, 3, 264-284. Rye , R. and Holland , H.D. (1998) Paleosols and the evolution of atmospheric oxygen: A critical review. American Journal of Science, 298, 621–672. Schneiderhan, E.A., Gutzmer, J., Strauss, H., Mezger, K. and Beukes, N.J. (2006) The chemostratigraphy of a Paleoproterozoic MnF-BIF-dolostone sucession – the Voëlwater Subgroup of the Transvaal Supergroup in Griqualand West, South Africa. South African Journal of Geology, 109, 63-80. Siebert, C., Kramer, J.D., Meisel, Th., Morel, Ph. and Nägler, Th.F. (2005) PGE, Re-Os, and Mo isotope systematics in Archean and early Proterozoic sedimentary systems as proxies for redox conditions on the early Earth. Geochimica et Cosmochimica Acta, 69, 1787-1801. Swart, Q.D. (1999) Carbonate rocks of the Paleoproterozoic Pretoria and Postmasburg Groups, Transvaal Supergroup. Unpublished M.Sc thesis, Rand Afrikaans University, Johannesburg, South Africa, 126pp. Tanaka, K., Ohta, A. and Kawabe, I. (2004) Experimental REE partitioning between calcite and aqueous solution at 25°C and 1 atm: Constraints on the incorporation of seawater REE into seamount-type limestones. Geochemical Journal, 38, 19-32. Taylor, S.R. and McLennan, S.M. (1985) The continental crust: its composition and evolution. Oxford, Blackwell, United Kingdom, 312pp. Terakado, Y. and Masuda, A. (1988). The coprecipitation of rare-earth elements with calcite and aragonite. Chemical Geology, 69, 103-110. Tsikos, H., Moore, J.M. and Harris, C. (2001) Geochemistry of the Palaeoproterozoic Mooidraai Formation: Fe-rich limestone as end-member of iron-formation deposition, Transvaal Supergroup, South Africa. Journal of African Earth Sciences, 32, 19-27. Veizer, J. (1983a) Chemical diagenesis of carbonate rocks: Theory and application of trace element technique. In: M.A. Arthur et al. (Editors), Stable Isotopes in Sedimentary Geology, SEPM Short Course Notes, 10, III/1 – III/100. Veizer, J. (1983b) Trace elements and isotopes in sedimentary carbonates. In: E. Roedder (Editor), Carbonates: Mineralogy and Chemistry, Reviews in Mineralogy, 11, 265-300. Walraven, F., Armstrong, R.A. and Kruger, F.J. (1990) A chronostratigraphic framework for the north-central Kaapvaal craton, the Bushveld Complex and the Vredefort structure. Tectonophysics, 171, 23-48. Walraven, F. and Hattingh, E. (1993) Geochronology of the Nebo Granite, Bushveld Complex. South African Journal of Geology, 96, 31-41. Webb, G. E. and Kamber, B. S. (2000) Rare earth elements in Holocene reefal microbialites: a new shallow seawater proxy. Geochimica et Cosmochimica Acta, 64, 1557-1565. Yang, W. and Holland, H.D. (2003). The Hekpoort paleosol profile in Strata 1 at Gaborone, Botswana: Soil formation during the Great Oxidation Event. American Journal of Science, 303, 187-220. Zhong, S.Y. and Mucci, A. (1995) Partitioning of rare earth elements (REEs) between calcite and seawater solutions at 25ºC and 1 atm, and high dissolved REE concentrations. Geochimica et Cosmochimica Acta, 59, 443-453. Editorial handling: J. Gutzmer SOUTH AFRICAN JOURNAL OF GEOLOGY
Chapter 7. Concluding remarks The data presented in this thesis presumably constrain certain geochemical features of seawater for the rather narrow period of time between 2.9-3.0 Ga. Studies of seawater chemistry that focus on younger rocks benefit from both the increased preservation of potential seawater archives as well as the greater occurrences of marine carbonates. However, in many regards, the geochemistry of Archean seawater is poorly constrained, particularly for the period of time prior to ~3.0 Ga. Though rocks older than 3.0 Ga are not particularly rare, seawater archives from this time period are limited. Further work is necessary to identify seawater archives older than 3.0 Ga, and data not included in this thesis suggest that suitable material from southern Africa is available for the time period between 3.2-3.6 Ga. Neodymium isotopic studies of these samples would help refute or support the conclusion that bulk seawater Є Nd values were generally positive with values between 0 and +2 from 3.0-3.8 Ga. For younger rocks, unpublished Nd isotopic data indicates that shallow water marine carbonates from the Transvaal Supergroup in South Africa possess Є Nd (2.5 Ga) between -0.3 and -2.2, consistent with the conclusions of the Pongola IF study that weathering of continental crust significantly influenced seawater chemistry near the Kaapvaal craton after 2.9 Ga. Furthermore, Mn sediments from the ~2.25 Ga Hotazel Formation in South Africa display seawater-like REY patterns, and possess Є Nd values between -2.2 and -4.2. These data are consistent with an increasingly important flux of solutes derived from weathering of continental crust in younger marine chemical precipitates. A possible test of this hypothesis would be Nd isotopic studies on late Archean (2.5-2.9 Ga) seawater archives of well defined age and representing a variety of depositional environments. Such studies may resolve the question of whether or not 173
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Iron sedimentation and the neodymiu
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The process(es) by which IFs were d
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This thesis represents original and
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viii
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goal of the research is to discern
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Figure 1. Map of southern Africa sh
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appropriate to briefly discuss: 1)
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100 10 MORB 1 0.1 raw data (mg/kg)
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10 -2 hydrothermal fluid 10 -3 10 -
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seawater and returned to the sedime
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100 MCO + 3 + M(CO 3 )- 2 rare eart
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net effect of carbonate complexatio
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feature was not recognized in early
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sound geochemical basis for anomalo
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deviation of the 143 Nd/ 144 Nd rat
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available, it should be possible to
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modern and Archean oceans, as well
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Bau M., Möller P., and Dulski P. (
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Elderfield H. and Greaves M.J. (198
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Haley B.A., Klinkhammer G.P. (2003)
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Lee J.H. and Byrne R.H. (1993) Comp
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Piepgras D.J. and Wasserburg G.J. (
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Tosiani T., Loubet M., Viers J., Va
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Abstract The benefits of inductivel
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List of Figures Figure 1. Sample de
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1. Introduction The advent of induc
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Figure 1. Flow-chart diagram of the
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during decomposition (SiF 4 and CO
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Fractionation between the three iso
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cps, then 3000 cps must be subtract
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variety of ways. These range from r
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Table 3. Change in HFSE concentrati
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0.90, corresponding to an anomalous
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10 2 JDo-1 reference values 10 1 IF
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Figure 5. Diagram depicting various
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20 18 basalt BHVO-2 (n=5) run preci
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The method precision for elements p
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Two approaches may be utilized to d
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For the more recent, full 32 elemen
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isotopic data for geologic CRMs, av
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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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Page 132 and 133: Nd isotopes in 2.9 Ga Archean surfa
Page 136 and 137: Table 2 Trace element concentration
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Page 152 and 153: Author's personal copy B.W. Alexand
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Page 184: ulk, open ocean seawater tended to
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