School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

The process(es) by which IFs were deposited in Archean seawater is also investigated through a study of Fe-rich shales formed in close association with the Pongola IFs. Major and trace element concentration data for these Fe-rich shales indicate post-depositional mobility and extreme loss of alkali metals and barium (Ba). Mobility of these elements in modern clastic sediments has been observed in the presence of pore water NH + + 4 , and a significant presence of NH 4 in Fe-rich Archean + sediments would strongly suggest a biologic origin for IFs. However, a conclusive NH 4 signature is not observed in the Pongola Fe-rich shales, and the behavior of the alkali metals and Ba is best explained by the presence of significant concentrations of dissolved Fe 2+ in sediment pore waters and/or bottom seawater. This suggests that precipitation of Fe(III) mineral phases, either in the water column or at the sediment water interface, was an unlikely mechanism for the deposition of the primary Fe-rich sediment. While studies of seawater prior to ~2.7 Ga are generally constrained to investigations of IFs, cherts, and rare fluid inclusions, the occurrence of carbonate rocks is extensive after 2.7 Ga. Many Archean and Paleoproterozoic carbonates are dolomitic and/or highly silicified, and the retention of primary seawater trace metal distributions in these rocks has not been conclusively demonstrated. A study of limestones and silicified dolomites from the ~2.25 Ga Mooidrai carbonates indicates that silicified dolomites retain primary trace metal signatures consistent with seawater and indistinguishable from coeval limestones. Therefore, silicified dolomites free of clastic detritus are considered suitable archives for proxies of ancient seawater. The accuracy and reproducibility of the trace metal concentration data for 32 elements are evaluated, and the inductively coupled plasma mass spectrometry (ICPMS) analytical methods used are described. The ICPMS data for Sm and Nd in IF samples are in excellent agreement with thermal ionization mass spectrometry (TIMS) measurements, supporting the accuracy of the reported REE data. The data quality is discussed in the context of repeated analyses of certified reference materials (CRMs) commonly used in geochemical research. Measured concentrations for IF and carbonate CRMs match reference data well; however, some elements suffer from major element interferences in particular rock types. This includes Co in carbonate rocks, and Nb in Fe-rich rock types. The concentrations of many trace metals in some CRMs are poorly constrained, and early published datasets appear to frequently overestimate the abundances of these elements. ii
ACKNOWLEDGEMENTS A special thank you to my family and friends for their encouragement and support, and particularly to Claudia Nitzschmann, as three years became four, and four years became five. Thanks as well to my advisor, Michael Bau, for introducing me to the numerous, endlessly fascinating topics regarding the geochemical evolution of the early Earth. I must confess a compelling attraction to a subject where it is so difficult to prove my assertions wrong… A debt of gratitude also to the many people that I came to know and appreciate within the geochemistry working group at Jacobs, including, but not limited to, faculty (A. Koschinsky), students (K. Schmidt, S. Kulaksiz), and staff (D. Meißner, J. Mawick, A. Moje). The various excursions, meetings, and long hours in the lab were much more enjoyable because of their presence. from Holland (1972) iii
Page 1: Iron sedimentation and the neodymiu
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 -
Page 22 and 23: seawater and returned to the sedime
Page 24 and 25: 100 MCO + 3 + M(CO 3 )- 2 rare eart
Page 26 and 27: net effect of carbonate complexatio
Page 28 and 29: feature was not recognized in early
Page 30 and 31: sound geochemical basis for anomalo
Page 32 and 33: deviation of the 143 Nd/ 144 Nd rat
Page 34 and 35: available, it should be possible to
Page 36 and 37: modern and Archean oceans, as well
Page 38 and 39: Bau M., Möller P., and Dulski P. (
Page 40 and 41: Elderfield H. and Greaves M.J. (198
Page 42 and 43: Haley B.A., Klinkhammer G.P. (2003)
Page 44 and 45: Lee J.H. and Byrne R.H. (1993) Comp
Page 46 and 47: Piepgras D.J. and Wasserburg G.J. (
Page 48 and 49: Tosiani T., Loubet M., Viers J., Va
Page 50 and 51: THIS PAGE INTENTIONALLY LEFT BLANK
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
Page 58 and 59:
Figure 1. Flow-chart diagram of the
Page 60 and 61:
during decomposition (SiF 4 and CO
Page 62 and 63:
Fractionation between the three iso
Page 64 and 65:
cps, then 3000 cps must be subtract
Page 66 and 67:
variety of ways. These range from r
Page 68 and 69:
Table 3. Change in HFSE concentrati
Page 70 and 71:
0.90, corresponding to an anomalous
Page 72 and 73:
10 2 JDo-1 reference values 10 1 IF
Page 74 and 75:
Figure 5. Diagram depicting various
Page 76 and 77:
20 18 basalt BHVO-2 (n=5) run preci
Page 78 and 79:
The method precision for elements p
Page 80 and 81:
Two approaches may be utilized to d
Page 82 and 83:
For the more recent, full 32 elemen
Page 84 and 85:
isotopic data for geologic CRMs, av
Page 86 and 87:
Table 4. Interferences observed for
Page 88 and 89:
value uncertainty (as %RSD) is repr
Page 90 and 91:
1.50 FeR-4 (n=2) 1.25 JUB / referen
Page 92 and 93:
1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
Page 94 and 95:
consistent (App. 1), and similar to
Page 96 and 97:
1.50 SGR-1b (n=3) 1.25 JUB / refere
Page 98 and 99:
1.50 JCh-1 (n=3) 1.25 JUB / referen
Page 100 and 101:
1.50 JDo-1 (n=5) 1.25 JUB / referen
Page 102 and 103:
determinations in carbonate rocks r
Page 104 and 105:
1.50 JMn-1 (n=4) 1.25 JUB / referen
Page 106 and 107:
eference value. The result is that
Page 108 and 109:
eference value and the measured JUB
Page 110 and 111:
the 32 analyzed elements, with Ti b
Page 112 and 113:
Govindaraju K. (1995) 1995 working
Page 114 and 115:
Appendix 1. Analytical data Appendi
Page 116 and 117:
Appendix 1. Literature reference va
Page 118 and 119:
Appendix 1 continued. Data in mg/kg
Page 120 and 121:
the concentration of the major elem
Page 122 and 123:
Potential interferences on monoisot
Page 124 and 125:
1500 0.5 M HCl 4.0 interference on
Page 126 and 127:
4000 0.40 0.20 3500 0.17 mg/kg 0.18
Page 128 and 129:
interference on 95 Mo in sample sol
Page 130 and 131:
THIS PAGE INTENTIONALLY LEFT BLANK
Page 132 and 133:
Nd isotopes in 2.9 Ga Archean surfa
Page 134 and 135:
Page 136 and 137:
Table 2 Trace element concentration
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Author's personal copy B.W. Alexand
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
and preservation of oxide-facies IF
Page 168 and 169:
TOP relative stratigraphic position
Page 170 and 171:
The mechanism by which the alkali m
Page 172 and 173:
6. Widdel, F. et al. Ferrous iron o
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
82 PRESERVATION OF PRIMARY REE PATT
Page 180 and 181:
Page 182 and 183:
Page 184:
ulk, open ocean seawater tended to
show all

School of Engineering and Science - Jacobs University

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?