Calcium Isotopic Variation in Marine Evaporites and Carbonates: Applications To
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UNIVERSITY OF CALIFORNIA, SAN DIEGO Calcium Isotopic Variation in Marine Evaporites and Carbonates: Applications to Late Miocene Mediterranean Brine Chemistry and Late Cenozoic Calcium Cycling in the Oceans A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Earth Sciences by Tabitha Michele Hensley Committee in Charge: J. Douglas Macdougall, Chair Chris Charles Miriam Kastner Kurt Marti Jeff Severinghaus 2006 Copyright Tabitha Michele Hensley, 2006 All rights reserved ii The dissertation of Tabitha Michele Hensley is approved, and it is acceptable in quality and form for publication on microfilm: _____________________________________________ _____________________________________________ _____________________________________________ _____________________________________________ _____________________________________________ Chair University of California, San Diego 2006 iii To my parents, Eddy and Brenda Hensley iv TABLE OF CONTENTS Signature Page …………………………………………………………………. iii Dedication ……………………………………………………………………… iv Table of Contents ………………………………………………………………. v List of Figures ………………………………………………………………….. vii List of Tables …………………………………………………………………… viii Acknowledgements …………………………………………………………….. ix Vita, Publications and Fields of Study …………………………………………. xi Abstract ………………………………………………………………………… xiii Chapter I Introduction and Ca Isotope Background ………………………….. 1 1.1 Introduction ………………………………………………………… 1 1.2 Calcium Isotope Notation and Common Standards ………………… 3 1.3 Double Spiking and TIMS Measurement …………………………... 9 1.4 Sample Preparation …………………………………………………. 12 1.5 Summary of Calcium Isotope Research ……………………………. 15 1.5.1 Temperature dependent fractionation in foraminifera …… 16 1.5.2 Global calcium cycling …………………………………... 19 1.6 Calcium Isotopes and Evaporites: Fractionation Effects in Massive Ca-Salt Deposits ……………………………………………………….. 24 Chapter II Calcium Isotopes in Evaporitic Sediments ………………………… 26 2.1 Mineralogy of Evaporitic Deposits and Mineral Stability …………. 26 2.2 Determination of a Fractionation Factor for Calcium Isotopes in Precipitated Anhydrite ………………………………………………….. 28 2.2.1 Introduction ……………………………………………….. 28 2.2.2 Experiment design ………………………………………... 29 2.2.3 δ44Ca data for precipitated anhydrite ……………………... 30 2.3 Range of Calcium Isotope Values in Evaporitic Deposits ………….. 35 v 2.3.1 Required conditions for evaporite formation and types of evaporites ………………………………………………………... 35 2.3.2 Calcium in evaporite deposits …………………………….. 37 2.3.3 δ44Ca data for evaporites and hydrothermal anhydrites …... 39 2.3.4 Conclusions ………………………………………………. 46 Chapter III Application of Calcium Isotopes to Late Messinian Mediterranean Evaporites …………………………………………. 48 3.1 Introduction to the Salinity Crisis ………………………………….. 48 3.1.1 Timing and duration of the crisis ………………………… 48 3.1.2 Causes of the Messinian Salinity Crisis …………………. 51 3.1.3 Volume and distribution of the salts …………………….. 54 3.1.4 Summary of data from four Mediterranean sites ………… 55 3.2 ODP Site 654 Tyrrhenian Basin: Calcium Isotopes and Brine Evolution ……………………………………………………………….. 58 3.2.1 General geology and mineralogy of Site 654 …………….. 58 3.2.2 Previous isotope analyses for Hole 654A ………………… 61 3.2.3 δ44Ca and 87Sr/86Sr data for Site 654 ……………………… 64 3.2.4 Testing External Precision ………………………………... 74 3.2.5 Conclusions ……………………………………………….. 76 Chapter IV A Calcium Isotope Record for Bulk Carbonates, 0-12 Ma Eastern Equatorial Pacific ………………………………………………….. 79 4.1 Introduction …………………………………………………………. 79 4.2 ODP Leg 138 Site 850 Eastern Equatorial Pacific …………………. 82 4.2.1 Overview ………………………………………………….. 82 4.2.2 The carbonate crash………………………………………. 83 4.2.3 The carbonate sedimentation maximum………………….. 85 4.3 Calcium Isotope Data for Leg 138 Site 850 and Comparisons to Other Isotope Systems ………………………………………………….. 87 4.3.1 Sample selection and Ca budget relationships ……………. 87 4.3.2 Sources of variability in the Ca budget …………………… 91 4.3.3 Site 850 δ44Ca data ……………………………………….. 95 4.3.4 The Fsed/Fw ratio and Ca concentration of the ocean ……... 105 4.3.5 Site 850 Conclusions ……………………………………… 114 References ………………………………………………………………. 118 vi LIST OF FIGURES Figure 1.2.1a δ44Ca data for a North Atlantic seawater using the 42-48 double spike ……………………………………………………… 6 Figure 1.2.1b δ44Ca data for a North Atlantic seawater and NIST SRM915a carbonate for the 42-43 spike ……………………………….…… 8 Figure 2.2.3a Rayleigh fractionation for Ca isotopes in a closed system ……... 31 Figure 2.2.3b δ44Ca data for the 40°C evaporation experiment ……………….. 33 Figure 2.3.3 δ44Ca data for 12 gypsums and anhydrites ……………………... 42 Figure 3.1.3 Satellite map of the Mediterranean region …………………….... 53 Figure 3.1.4 Summary of δ44Ca data for various Mediterranean sites ……….. 57 Figure 3.2.1 Map of the Tyrrhenian region …………………………………... 59 Figure 3.2.3a δ44Ca data for Hole 654A Tyrrhenian Sea ……………………… 67 Figure 3.2.3b Strontium isotope data for Hole 654A ………………………….. 68 Figure 3.2.3c δ44Ca and 87Sr/86Sr data for Hole 654A ………………………… 69 Figure 3.2.3d Sr and Ca isotope estimates for percentage of river water to the Tyrrhenian basin ………………………………………………... 70 Figure 3.2.3e δ18O and δ44Ca data for Hole 654A …………………………….. 73 Figure 4.3.3a Osmium, strontium, and calcium isotopic records for the past 12 Ma …………………………………………………………… 101 Figure 4.3.3b Calcium isotope data for bulk carbonate samples from Site 850 Leg 138 Eastern Equatorial Pacific …………………………….. 102 Figure 4.3.4a The Fsed/Fw ratio for the past 12 Ma ……………………………. 106 Figure 4.3.4b Ca concentrations from the Fsed/Fw ratio obtained from the δ44Ca of Site 850 carbonates ……………………………………. 113 vii LIST OF TABLES Table 1.2.1a Calcium isotopic composition of a North Atlantic seawater using the 42-48 double spike …………………………………... 5 Table 1.2.1b Calcium isotopic composition for a North Atlantic seawater using the 42-43 double spike …………………………………... 7 Table 1.2.1c Calcium isotopic composition for NIST SRM915a using the 42-43 double spike …………………………………………….. 7 . Table 1.4.2 Selected summary of previously published δ44Ca values for carbonate sediments, foraminifera, and cocolithophorid oozes .. 21 Table 2.2.3 δ44Ca data for the evaporation experiments ……………………. 32 Table 2.3.3 Mean δ44Ca values for twelve gypsums and anhydrites ….……. 40 Table 3.1.4 δ44Ca values for gypsum and anhydrite from DSDP and ODP sites in the Mediterranean ………………………………………. 56 Table 3.2.3 Hole 654A data for stable and radiogenic isotopes …………….. 63 Table 4.3.1 Summary of calcium budget variables and δ44Ca values ………. 89 44 Table 4.3.3a δ Ca and Fsed/Fw data for Leg 138 Site 850 …………………… 99 Table 4.3.3b Previously published osmium and strontium isotopes for the last 12.6 Ma …………………………………………………….. 100 Table 4.3.4a Ca concentrations for three different δw calculated from the Fsed/Fw ratio……………………………………………………………… 111 viii ACKNOWLEDGEMENTS I would first like to thank my advisor, J. Douglas Macdougall. He accepted me as a graduate student in my first year at SIO even though he had not planned to do so and allowed me to work on what would be his last research project at UCSD. Doug has allowed me to actively pursue other academic interests, specifically various teaching projects associated with the university, as I found that I greatly enjoyed the teaching aspects of being a graduate student. He has allowed me the freedom to pursue any research ideas that I wanted to explore and has always been willing to talk with me about research problems and pitfalls. Doug retired in 2005 and moved to Scotland to pursue his other career passion, writing, and even though he was overseas for long portions of my time as a graduate student, he has always been available to help me with all aspects of my research. I would also like to thank my committee members, Chris Charles, Miriam Kastner, Kurt Marti, and Jeff Severinghaus. I have benefited from their knowledge, suggestions, and encouragement throughout my time at SIO. Specifically, I would like to thank Miriam Kastner for her willingness to take me along on four different cruises even though I had no research projects on board. By including me in these oceanographic experiences, she helped to broaden my earth science background and taught me how to be a tireless scientist by example. Thanks also to Chris MacIsaac, who provided limitless support and instruction in the lab, without which I would never have been able to complete my research on time. Special thanks to the Ocean Drilling Program for providing samples for data contained in Chapter III and IV. ix Many friends have supported me throughout this long and unique process. I have greatly benefited from discussions with fellow graduate students Evan Solomon, Wei Wei, Jenna Munson, and Melissa Headley, Brian Hopkinson and Henry Ruhl regarding various aspects of my dissertation. Thanks to Christine Whitcraft who has been an unfailing friend and lent a sympathetic ear throughout our time at Scripps. Sondra Bilben, one of my best friends in San Diego and favorite bartender, has been a true friend and in every case has always looked after me as I wondered through tough times. Dominic Moreau has taught me the importance of unity and unconditional love. Lastly, I would like to thank my parents, Eddy and Brenda Hensley, who have never failed to answer the phone, listen to my insecurities and triumphs, and love me without judgment as only parents can. x VITA 1979 Born, Atlanta Georgia, USA 2000 B.S. Geology, University and Departmental Honors University of New