Evaluation of Stromatolites from the 3.4 Ga Kromberg Formation, Barberton Greenstone Belt, South Africa

Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2014 Evaluation of Stromatolites from the 3.4 Ga Kromberg Formation, Barberton Greenstone Belt, South Africa Corey E Shircliff Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Earth Sciences Commons Recommended Citation Shircliff, Corey E., "Evaluation of Stromatolites from the 3.4 Ga Kromberg Formation, Barberton Greenstone Belt, South Africa" (2014) LSU Master's Theses 1507 https://digitalcommons.lsu.edu/gradschool_theses/1507 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons For more information, please contact gradetd@lsu.edu EVALUATION OF STROMATOLITES FROM THE 3.4 GA KROMBERG FORMATION, BARBERTON GREENSTONE BELT, SOUTH AFRICA A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics by Corey Elizabeth Shircliff B.S., Beloit College, 2011 May 2014 This thesis is dedicated to my parents, Jim and Jenny Shircliff Thank you for inspiring and encouraging me ii Acknowledgements Although it is difficult to adequately thank them, the author is extremely grateful to Dr Gary Byerly, her advisor, for the countless hours of assistance given, experience in the field, and honest guidance throughout her career as a graduate student She would also like to thank Dr Maud Walsh for valuable discussions, assistance in the field, and for the use of the samples she collected in the field Thanks are also due to Dr Sophie Warny for guidance and valuable discussion as a committee member, Dr Achimm Hermann, for use of his microscope, Jill Bambrick Banks for her helpfulness with the handheld XRF, Dr Donald Lowe for his assistance in the field, Rick Young for aid in the rock lab, Chris O’Loughlin and the LSU Raman laboratory, and to Heather Lee, who has been extremely helpful and patient with the author iii Table of Contents Acknowledgements……………………………………………………………………………… iii List of Tables………………………………………………………………………………… vi List of Figures……………………………………………………………………………………… vii Abstract…………………………………………………………………………………………………………… ix Introduction……………………………………………………………………………… Geologic Setting……………………………………………………………… ………4 2.1 Barberton Greenstone Belt…………………………………… ………… 2.2 Kromberg Formation……………… …… ……………………………… 10 Methods………………………………………………………………………………… 17 3.1 Bulk Rock X-Ray Fluorescence……… ………………………………… 17 3.2 Raman Spectroscopy………………… ………………………………… 17 3.3 ICP-Mass Spectrometry……………… ………………………………… 14 18 3.4 δ 13C Isotopes ………….……………… ………………………………….14 18 Results…………………………………………………………………………………… 19 4.1 Domical Type……………… … …………………………………… 20 4.2 Flat-Laminated Type…………… ………………………………………… 25 4.3 Bulk Rock X-Ray Fluorescence…….………………………………………25 30 4.4 Raman Spectroscopy……………… ………………………………… …27 33 4.5 ICP-Mass Spectrometry….………… …… …………………….…… 35 13 4.6 δ C Isotopes ……… …………… …………………………………… 36 39 Discussion……………………………………………………………………………… 41 5.1 Morphologic Features …………… ……………………………………… 41 5.2 Chemistry…………………………………………………………………… 47 Conclusion.……………………………………………………………………………… 54 References…………………………………………………………………………………… 56 Appendix A: Locations of Sections……………… ……………………………………… 62 iv Appendix B: Complete Measured Sections……………………………………………………… 67 63 Appendix C: Expanded Methods……….………………………………………………… 76 Appendix D: Handheld XRF Results……………………………………………………… 78 Vita………………………………………………………………………………………… 79 v List of Tables Table Methods and implications for identifying stromatolitic origin…………………………… Table Summary of results……………………………………………………………………………………… 19 Table Major element percent composition XRF…………………………………………………………… 31 Table Trace element composition in ppm (XRF)……………………………………………………………… 31 Table Trace and rare earth element amounts (ppm)…………………………………………………… 37 Table Cerium and europium anomalies………………………………………………………………………… 38 Table Ua and log FeO values for K1 samples………………………………………………………………… 39 Table Carbon and carbon isotopes…………………………………………………………………………… 40 vi List of Figures Figure Generalized geologic map of the BGB………………………………………………………………… Figure Geologic map of the field area………………………………………………………………………… Figure Generalized stratigraphic column………………………….…………………………………………… 11 Figure Generalized basal K1 lithofacies……………………………………………………………………… 13 Figure Generalized K1 measured sections…………………………………………………………………… 15 Figure Sample CES 10-13 (domical sample)………………………………………………………………… 21 Figure Raman shirft results for sample CES 10-13…………………………………………………………… 21 Figure Domical stromatolite; light microscope image………………………………………………………… 23 Figure Domical stromatolite trough; light microscope image………………………………………………… 24 Figure 10 Interior cut surfaces of flat-laminated forms………………………………………………………… 26 Figure 11 Sample CES 4-2b…………………………………………………………………………………… 27 Figure 12 Raman shift results for sample CES 4-2b……………………………………………………………… 28 Figure 13 Fine resolution Raman shift results for sample CES 4-2b………………………………… 28 Figure 14 Ripped-off laminae package in sample CES 8-4……………………………………………………… 29 Figure 15 Sample CES 8-6; light microscope image…………………………………………………………… 30 Figure 16 Uranium vs Nb, Pb, Zr, and Ti (ppm)………………………………………………………………… 32 Figure 17 TiO2 vs Nb…………………………………………………………………………………………… 32 Figure 18 Raman shift results for sample CES 8-6……………………………………………………………… 33 Figure 19 Raman shift results for sample CES 8-4……………………………………………………………… 34 vii Figure 20 Rare earth element compositions compared to the Primitive Mantle………………………………… 36 Figure 21 Spider diagram of K1 samples compared to the PM………………………………………………… 38 Figure 22 Authigenic Uranium (Ua) vs log FeO………………………………………………………………… 39 viii Abstract Silicified sedimentary rocks from the 3.4 Ga Kromberg Formation of the Barberton Greenstone Belt in South Africa contain laminated structures that have been identified as possible stromatolites in the field Morphological evaluation and a variety of chemical analyses are presented here, in an effort to describe the samples in a sedimentary context and consider biogenicity of these laminated forms Two major types of laminated structures were identified in the field – domical laminates and flat-laminated samples with little to no synoptic relief The domical sample presents the best morphological evidence for biogenicity There are several characteristics that suggest the deposition must be biologically mediated: dome slopes are greater than 40º and their crests have thickened laminae, varied fine-grained sand bimodal depositional patterns appear within the domes, with a high degree of laminae inheritance from the base of the sample to the top The flat-laminated samples, while lacking domical morphology, show high levels of lamina cohesion, mineralogic deposits in individual lamina, and, in most cases, a high degree of laminae inheritance Raman spectroscopy indicates that the laminae in the domical and flat-laminated samples are carbonaceous, with strong disordered and ordered carbon peaks appropriate for indigenous carbon in these greenschist facies Although the carbonaceous matter is less than 1% of the rock, samples from the lower K1 Member of the Kromberg Formation were analyzed for δ13C, and the values range from -29‰ to -39‰, which is consistent with the isotopic signatures of autotrophic microbes Rare earth element (REE) analyses indicate that the depositional environment was marine and anoxic With all the evidence taken together, the author suggests it is more plausible for the domical sample to be biogenic Additionally, it is ix .. .EVALUATION OF STROMATOLITES FROM THE 3.4 GA KROMBERG FORMATION, BARBERTON GREENSTONE BELT, SOUTH AFRICA A Thesis Submitted to the Graduate Faculty of the Louisiana State University... sedimentary rocks from the 3.4 Ga Kromberg Formation of the Barberton Greenstone Belt in South Africa contain laminated structures that have been identified as possible stromatolites in the field Morphological... ancient stromatolites have been reported in both the South African Barberton Greenstone Belt (BGB) as well as the Pilbara Craton of Western Australia, the focus of this research is on those from the