Clumped Isotope Analysis of Carbonates: Analytical Aspects, Calibration and Application to Silurian Brachiopod Shells and Diagenetic Phases from Gotland/Sweden
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Clumped isotope analysis of carbonates: analytical aspects, calibration and application to Silurian brachiopod shells and diagenetic phases from Gotland/Sweden Dissertation submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Institute of Geosciences Department of Paleontology Johann Wolfgang Goethe-University Frankfurt/Main 18 16 13 16 by Ulrike Wacker from Nürnberg Frankfurt (August 2014) (D30) Vom Fachbereich 11 der Johann Wolfgang Goethe-Universität als Dissertation angenommen. Dekan: Prof. Dr. Andreas Junge Gutachter: Dr. habil. Jens Fiebig Prof. Dr. Stefano M. Bernasconi Datum der Disputation: TABLE OF CONTENTS List of Figures .............................................................................................................................................. iv List of Tables................................................................................................................................................ vi Acknowledgements ..................................................................................................................................... vii Abstract ......................................................................................................................................................... 1 1 Introduction............................................................................................................................................... 3 1.1 Carbonate clumped isotope paleothermometry.................................................................................. 4 1.2 Recent developments in clumped isotope analysis and paleothermometry ....................................... 7 1.2.1 Data reduction and interlaboratory comparison...................................................................... 7 1.2.2 Calibration of the carbonate clumped isotope thermometer ................................................... 9 1.3 Acid digestion, gas preparation and clumped isotope analysis performed in Frankfurt .................. 10 1.3.1 Phosphoric acid digestion ..................................................................................................... 11 1.3.2 Purification of analyte gas..................................................................................................... 12 1.3.3 Mass spectrometric analysis.................................................................................................. 14 1.4 Application of clumped isotope thermometry to Silurian carbonates.............................................. 15 1.5 Objectives and outline of the thesis.................................................................................................. 17 2 Background effects on Faraday collectors in gas-source mass spectrometry and implications for clumped isotope measurements .............................................................................................................. 19 2.1 Introduction...................................................................................................................................... 20 2.2 Experimental .................................................................................................................................... 22 2.2.1 Mass Spectrometers .............................................................................................................. 22 2.2.2 Background determination on masses 44-49 ........................................................................ 23 2.2.3 Clumped isotope notation ..................................................................................................... 27 2.3 Results.............................................................................................................................................. 28 2.3.1 Negative backgrounds on Faraday cups................................................................................ 28 12 2.3.2 Significance of the mass 49 signal of CO2 measured through a 10 Ω resistor ................... 29 2.4 Discussion ........................................................................................................................................ 31 2.5 Background correction procedures................................................................................................... 32 2.6 Conclusions and implications .......................................................................................................... 38 2.7 Acknowledgements.......................................................................................................................... 39 2.8 Supplementary Information ............................................................................................................. 40 3 Clumped isotope analysis of carbonates: comparison of two different acid digestion techniques......... 42 3.1 Introduction...................................................................................................................................... 43 3.2 Experimental .................................................................................................................................... 45 3.2.1 Samples and sample preparation........................................................................................... 45 3.2.2 Acid digestion ....................................................................................................................... 46 3.2.3 CO2 cleaning procedure ........................................................................................................ 47 3.2.4 Measurements ....................................................................................................................... 47 3.2.5 Data processing..................................................................................................................... 48 3.3 Results.............................................................................................................................................. 50 3.4 Discussion ........................................................................................................................................ 53 3.4.1 Correlation between sample size and Δ47 values................................................................... 53 3.4.2 Potential occurrence of contaminants in sample-derived CO2.............................................. 54 3.4.3 Incomplete gas yield ............................................................................................................. 56 3.4.4 Potential variations of fractionation factors during acid digestion ....................................... 57 3.4.5 Secondary re-equilibration.................................................................................................... 59 3.4.6 Difference in the acid fractionation factors between 90 and 25 °C ...................................... 61 3.4.7 Implications for discrepant calibrations................................................................................ 62 i 3.5 Conclusions...................................................................................................................................... 63 3.6 Acknowledgments............................................................................................................................ 63 3.7 Supplementary Information ............................................................................................................. 64 4 Empirical calibration of the clumped isotope paleothermometer using calcites of various origins ....... 67 4.1 Introduction...................................................................................................................................... 68 4.2 Materials and methods ..................................................................................................................... 71 4.2.1 Sample material..................................................................................................................... 71 4.2.1.1 Eggshell of an ostrich .............................................................................................. 72 4.2.1.2 Spondylus sp. ........................................................................................................... 72 4.2.1.3 Dyscolia wyvillei...................................................................................................... 73 4.2.1.4 Cold seep carbonate................................................................................................. 74 4.2.1.5 Foraminifera ............................................................................................................ 75 4.2.2 Acid digestion, gas purification, mass spectrometric analysis and data reduction ............... 77 4.3 Results.............................................................................................................................................. 79 4.3.1 Standard materials................................................................................................................. 80 4.3.2 Regression line and statistical analyses................................................................................. 81 4.3.3 Replication of measurements ................................................................................................ 83 4.4 Discussion ........................................................................................................................................ 84 4.4.1 Comparison of our calibration with