Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1972 Physical and chemical changes related to epigenetic dolomitization David Eugene Simon Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Geology Commons Recommended Citation Simon, David Eugene, "Physical and chemical changes related to epigenetic dolomitization " (1972). Retrospective Theses and Dissertations. 6121. https://lib.dr.iastate.edu/rtd/6121 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This dissertation was produced from a microfilm copy of the original document. 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University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 A Xerox Education Company 73-9486 S DON, David Eugene, 1943- PHYSICAL AND CHEMICAL CRINGES RELATED TO EPIGENETIC DOLCMITIZATION. Iowa State University, Ph.D., 1972 Geology University Microfilms, A XEROX Company , Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. Physical and chemical changes related to epigenetic dolomitization by David Eugene Simon A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Earth Science Major: Geology Approved: Signature was redacted for privacy. in Charge of Major Work Signature was redacted for privacy. r the Major Department Signature was redacted for privacy. For the Graduate College lews State University Ames, Iowa 1972 PLEASE NOTE: Some pages may have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company i i TABLE OF CONTENTS Page TWTDon: irTT nKi i EPIGENETIC DOLOMITES 3 COMPOSITION-VCLUXE RELATIONSHIPS 8 DEVELOPMENT OF A WORKING MODEL FOR STUDY OF REPLACEMENT PROCESSES 15 i'lc inuu ùiuu! I 3 GEOLOGIC SETTING A.ND PETROLOGY 25 Ferguson Ouarr_y 25 Peloid limestone 28 Transition zone 31 Dolomite 34 Randall Quarry 34 Limestone 37 Dolomite 37 Summary of Petrography 42 Paragenesis of Ferguson Quarry Samples 42 Paragenesis of Randall Quarry Samples 43 Composition of the Carbonate Phases 44 Ferguson Quarry samples 44 Randall Quarry samples 46 Summary 47a PRESENIAII'JN UF uaim Void Volume-Pore Radii Relationships 48 Ferguson Quarry samples 48 Randall Quarry samples 51 Summary 55 i ii Page Phase and Component Relationships 57 Ferguson Quarry samples 57 Randall Quarry samples 62 DISCUSSION 68 Volume-Mass Changes of the Carbonate Phases 70 Petrogenic Models of Dolomitization 77 Ferguson Quarry 78 Randall Quarry 82 Competing Reactions and Complexity of the Process 85 Relation of Model to Nature 89 CONCLUSIONS 92 REFERENCES CITED 96 ACKNOWLEDGEMENTS 101 APPENDIX A 102 Analysis of Limestones and Dolomites 103 APPENDIX B 106 APPENDIX C 120 1 INTRODUCTION The major purpose of this study is to account for, by chemical and physical methods, the changes which occur in geological materials; specifically changes related to alteration or replacement processes. Geologic alteration or replacement generally results from reactions of minerals with components of a fluid phase flowing through the rock. Because changes in mass and pore volumes usually accompany the replace­ ments, study of associated composition and volume changes is necessary to explain how the replacement operates. This type of study requires measurement of physical and chemical changes occurring in a gradational sequence of rocks undergoing replacement; in this study epigenetic dolomitization of limestone. A majority of past studies on dolomitization have described the nature and direction of the process, but not the actual mass and volume changes which occurred. This study will utilize a model of replacement by which related mass and volume changes can be determined. Such knowledge will provide a better insight into some aspects of epi genetic dolomitization. It is generally agreed that the majority of dolomites owe their origin to replacement of pre-existing calcium carbonate material. However, the exact method by which this replacement occurs and the related composition- volume relationships are still unknown. Epigenetic dolomitization is here defined as the post-1ithification replacement of limestone, which probably includes the 1ate-diagenetic classification of some investigators (Fairbridge, 1957; Friedran and Sanders, 1967). Epigenetic dolomites comr^nly exhibit a cross-cutting relationship across bedding planes of the 9 host limestones. This parent-daughter relationship allows siucy of gains and losses of component oxides, phases and volume changes for the system, evaluation of the method by which the process operates, and to what extent local controls, if any, influence the process. Investigations by numerous people (Landes, 1946; Hewett, 1928; Levering, 1949; Murray, 1960; Weyl, 195Û) have shown that dolomitization porosity changes range from large increases in some instances to none in others and to actual decreases in still others. Usually two methods, mole-for-mole and volume-for-volume, are used to describe the colomitization process but they do not adequately explain the mass and void volume changes actually observed. However, through use of parent-daughter sample sets considered representative of epigenetic dolomitization, measurement of related mass and pore volume changes, chemical changes and pétrographie study will yield interrelated data concerning the changes associated with dolcmitization. Such an approach is undertaken in this study and makes it possible to explain how these changes occurred. The following sections will review composition-volume relationships, ep'! genetic dolomi tizati on and the proposed model of alteration or replacement processes. Following these reviews the systems selected for study, experimental methods, data obtained, and interpretations will be oresented. 3 EPÎGENETIC DOLOMITES Recent comprehensive reviews of modern and ancient dolomites indicate most moaern workers in carbonate petrology believe that mosz dolomites originate by reclacement of pre-existing calcium carbonate material by hypersaline brine: (Friedman and Sanders, 1967; Zenger, 1972; Bathurst, 1971). For detailed discussions of various aspects cf tne dolomitization, the reader is referred to the above references. In general, three types of dolomites are recognized: (1) Syngenetic dolomite-formed essentially penecontemporaneously with deposition, generally considered to be a marine evaporite basin. (2) Diagenetic dolomite-formed by replacement of calcium carbonate sediments during the period when the sediments are being consolidated. (3) Epigenetic dolomite-formed by replacement of limestone along faults, joints, bedding planes and other primary and secondary structural elements long after the sediment is lithified. usually show a cross-cuiting relationship of the dolomitized zones across the original limestone bedding. These zones generally have gradational to sharp contacts between the limestone and dolomite which allow parent- daughter sample sequences to be obtained laterally within the same bed and serve as a basis to study the alteration process. Friedman and Sanders (1957) have discussed several unsolved problems regarding the replacement of calcium carbonate by dolomite. They point out that it is not understood if the dolomite replacement occurs by the ^ 4,iiW « V./I VI I LV LV i I V* w Ciltsrf L* ^ Vv ^ I V I V/ I I ^ i 4 dolomite, or diffusion and ion exchange of Mg for Ca in the crystal or the amount and how the Mg