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Calcite Cementation of Sixty-Five-Year-Old Aragonite Sand Dredge Pile

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Calcite Cementation of Sixty-Five-Year-Old Aragonite Sand Dredge Pile University of Mississippi eGrove Electronic Theses and Dissertations Graduate School 2011 Calcite Cementation of Sixty-Five-Year-Old Aragonite Sand Dredge Pile Nathan M. Snyder Follow this and additional works at: https://egrove.olemiss.edu/etd Part of the Geology Commons Recommended Citation Snyder, Nathan M., "Calcite Cementation of Sixty-Five-Year-Old Aragonite Sand Dredge Pile" (2011). Electronic Theses and Dissertations. 269. https://egrove.olemiss.edu/etd/269 This Dissertation is brought to you for free and open access by the Graduate School at eGrove. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of eGrove. For more information, please contact [email protected]. CALCITE CEMENTATION OF SIXTY-FIVE-YEAR-OLD ARAGONITE SAND DREDGE PILE A Thesis presented in partial fulfillment of requirements for the degree of Master of Science in the Department of Geology and Geological Engineering The University of Mississippi by NATHANIAL M. SNYDER May 2011 Copyright Nathanial M. Snyder ALL RIGHTS RESERVED ABSTRACT Dredging of the harbor at Stocking Island, Bahamas (23°31’45”N, 75°49’41”W) in 1942 produced four dredge piles of cross-bedded aragonite skeletal sand. The spoils piles are on the leeward (western) shore of the island, where they are subject to minimal wave energy. Collectively they are 350 x 50 m in plan view and 2 m high. The surface is very well cemented, which requires a hammer and chisel for sampling. Samples were collected from six sites at various locations of the dredge pile. Samples were analyzed for both chemical and physical properties using thin-section examination, X-ray diffraction, X-ray fluorescence, bulk density measurements, isotopic analyses, and scanning electron microscopy. The skeletal sands are mostly spherical to prolate shape, are reverse graded, and range in size from 0.5–2.0 mm over a depth interval of 1.5 m, with gravel to cobble- sized material dispersed intermittently throughout the interval. This deposit is capped with a 4–6 cm-thick crust of thoroughly micritized aragonite grains completely cemented with 4 micron calcite spar. Beneath this crust, micritized aragonite grains are cemented by sparry calcite cements with meniscus and isopachous textures. The amount of cement ranges from 7-16%. Cement volume decreases with depth; the deepest samples contain meniscus cements only. There are very subtle dissolution features on the surface of individual grains. ii Reverse grading caused by grainflow occurred when these micritized skeletal sands were moved from their marine setting and debauched into the meteoric vadose environment. Calcite cementation proceeded from the surface downward; meniscus cement preceded isopachous cement. The source of carbonate for the cements is internal to the spoils piles. In this example of aragonite sand in the very early stages of mineralogical stabilization in a meteoric vadose environment, rapid cementation clearly occurred first. It is anticipated that mineralogical stabilization of the grains from aragonite-to-calcite will follow. iii DEDICATION This work is dedicated to my family for the sacrifices that were made to allow me to complete this thesis. Thank you to my children, Noah and Emma, for understanding all of the times when Dad had to miss ballgames, practices, homework, and all the missed opportunities to just throw the ball or shoot hoops. To my wife and best friend, Tina, who continues to inspire, support, and encourage me after all of these years, I say, “Thank you”. You are my source of strength and you kept me focused on the “light at the end of the tunnel” when I needed you the most. Tina, I will love you more tomorrow than I do today…. iv ACKNOWLEDGEMENTS I would like to express my deepest appreciation to my advisor, Dr. Terry Panhorst for his work in helping me complete this thesis. Thank you for countless hours, emails, conferences, and advice you have provided during the entire process. I would also like to thank my committee members, Dr. Gregg Davidson for his help in simplifying subject matter that I found to be particularly difficult, and especially Mr. Lawrence Baria whose expertise and other contributions have made this study possible. Finally, I would like to thank Dr. R. P. Major, for his ideas and support that helped shape this project. v TABLE OF CONTENTS ABSTRACT ………………………………………………………………………. ………..ii DEDICATION……………………………………………………………………………… iv ACKNOWLEDGEMENTS ……………………………………………………………….. v LIST OF TABLES …………………………………………………………………………vii LIST OF FIGURES ……………………………………………………………………….viii INTRODUCTION ……………………………………………………………………………1 GEOLOGIC SETTING ……………………………………………………………………...5 PREVIOUS WORK …………………………………………………………………………9 METHODOLOGIES ……………………………………………………………………….21 RESULTS ………………………………………………………………………………….28 DISCUSSION ……………………………………………………………………………...41 SUMMARY ………………………………………………………………………………....55 REFERENCES …………………………………………………………………………....57 VITA …………………………………………………………………………………………61 vi LIST OF TABLES 1. Point count data for Stocking Island samples at various depths below surface………………………………………………34 2. X-ray Diffraction Results ………………………………………………………..35 3. Bulk Density and Porosity ………………………………………………………36 4. Major Elements…………………………………………………………………...37 5. Strontium Content………………………………………………………………..38 6. Isotopic Analyses Results ………………………………………………………39 7. Differences Between X-ray Diffraction and Point Counting Values …..…..41 8. Mineral Abundance (XRD) and Calculated Porosity Values …………….…44 9. Cementation Rates for 5 Depths at Site EB …………………………………..48 vii LIST OF FIGURES 1. Bahamas……………………………………………………………………………………3 2. Exuma and Stocking Islands …………………………………………………………….3 3. Sample locations with letter designations on dredge pile, west side of Stocking Island, Bahamas…………………………………..………..22 4. Sampling Depths at Sample Site EB ………………………………………………….23 5. Sketch Cross-section of Stocking Island Dredge Pile ……………………………….28 6. Photomicrograph of Typical Cements …………………………………………………31 7. Photomicrograph at 3 cm Depth at Site EB……………………………………………32 8. Photomicrograph at 30 cm Depth at Site EB ………………………………………….32 9. Photomicrograph at 60 cm Depth at Site EB ………………………………………….33 10. Strontium vs. Depth……………………………………………………………………….50 viii 1. INTRODUCTION Recent carbonate sediments, which all originate in an aqueous environment, remain relatively unchanged until they are exposed to meteoric waters after being subareally exposed. Once exposed to these meteoric waters, rapid dissolution of the CaCO3 begins and often precipitation of new minerals begins (James and Choquette, 1990). According to James and Choquetts (1990), this early stage of diagenesis has been studied more than any other of the diagenetic environments, but experts in the field of carbonate diagenesis are only reasonably confident in their understanding of the processes which occur above the water table. The rate of cementation and lithification has implications for sequence stratigraphy including rate of sediment shedding during sea level low-stands. Understanding the diagenetic processes which occur above the water table can lead to a better understanding of how geologically rapid the process of carbonate cementation can be. On Joulter’s Cays, in the Bahamas, a completely lithified oolite was formed in approximately 1,000 years when the shallow marine environment was subaerially exposed (Halley and Harris, 1979). If allowed to progress and exposed to many of the same climatic influences, it is possible that the same lithifying processes could accomplish similar cementation and mineralogic alteration with a recently exposed storm deposit in much the same manner and on a similar time scale. While a change in 1 sea level will result in exposing marine sediments relatively quickly, a storm could deposit and expose sediments in a matter of days, if not hours. This geologically instantaneously time frame would allow a mechanism in which these diagentic processes could begin immediately and in modern times allow for the exact dating of various diagenetic processes. An analog of a modern storm deposit could be man- made, such as a deposit of freshly dredged sands left exposed to subaerial conditions on a beach. One such example exists in the Bahamas (Kindler and Mazzolini, 2001). Personal communications with three local inhabitants of Great Exuma Island indicate that during the process of establishing a naval base in the Bahamas on Great Exuma Island in 1942, the United States Navy created three spoils piles from dredging activities on and near Great Exuma Island (Figure 1). In preparation for construction, it was necessary to dredge Great Exuma Sound, an area of current carbonate deposition. This dredging allowed for the passage of large naval warships, in particular aircraft carriers. Dredgings were deposited at several locations on both Stocking Island and Great Exuma Island (Figure 2). One site of deposition is situated on the western shore of Stocking Island as four separate piles collectively measuring approximately 350 x 50 meters in plan view and approximately 2 meters high near the centers. The dredge pile examined in the current study was deposited on Stocking Island at approximately 23° 31’ 45” N, 75° 49’ 41” W . 2 N Figure 1. Bahamas: Great Exuma Island highlighted 1 KM N B A Figure 2. Great Exuma and Stocking Islands: A) Great Exuma Island B) Stocking Island 3 In less than 65 years, the upper 100 cm of these carbonate dredgings on Stocking Island, Bahamas has lithified and exhibits significant amounts of carbonate vadose cements.
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