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ABSTRACT Paleopedology of Paleo-Wetland and Barite-Bearing

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ABSTRACT Paleopedology of Paleo-Wetland and Barite-Bearing ABSTRACT Paleopedology of Paleo-wetland and Barite-bearing, Hydric Paleosols in the Morrison Formation (Upper Jurassic-Lower Cretaceous), North Central Wyoming, USA: A Multianalytical Approach Debra S. Jennings, Ph.D. Supervisor: Steven G. Driese, Ph.D. Whereas lakes and wetlands are very sensitive to changes in climate, high- resolution data in these archives are lost unless it is possible to differentiate these deposits from other “floodplain” deposits. Synthesis of micromorphological and geochemical data with facies relationships is critical to accurate interpretations of ancient wetland- lacustrine deposits. A proposed hydrogeomorphological classification and appropriate genetic terminology that is useful in the rock record is presented. Eight Morrison Formation subenvironments, including barite-bearing paleosols, within lacustrine depositional successions from north central Wyoming were delineated using micromorphology and geochemistry, combined with facies relationships. The distribution of wetland pedotypes indicates that evapotranspiration remained high, suggesting that a stable, semi-arid to arid climate dominated in this area throughout Morrison time. This study also characterizes the micromorphology, elemental trends, and stable isotope geochemistry of sulfates in a barite-bearing Morrison paleosols and a modern analog soil (Lufkin Series) using optical microscopy, XRD, ICP-MS, and stable S and O isotope data. Data indicate that barium-rich parent material provides adequate barium for barite precipitation. Barium is mobilized and concentrated in Btg horizons ~100-160 cm below the surface. The presence of humic acids in profiles lower on the landscape prevents barite precipitation and drives the precipitation of gypsum between saturated, anoxic conditions and drier, more oxic conditions. Barite precipitation is a slow, punctuated process that begins first along evacuated macropores and then in the adjacent matrix. The modern analog displays similar catenary relationships, redox features, and micromorphological characteristics compared to the Morrison paleosols, suggesting that similar pedogenic processes led to barite precipitation. Synthesized data reveal that conditions favorable to barite-bearing soil formation are low-gradient basins that have received feldspar-rich sediments (i.e. volcanically influenced basins), soils that developed near salt domes, soils that developed in exposed wetland or lacustrine sediments, and coastal plain deposits. Combined with regional paleosols, barite-bearing paleosols may document temporal changes in drainage, surface stability, and accommodation consistent with sequence boundaries/maximum flooding surfaces, and climate changes. Paleopedology of Paleo-wetland and Barite-bearing, Hydric Paleosols in the Morrison Formation (Upper Jurassic-Lower Cretaceous), North Central Wyoming USA: A Multianalytical Aproach by Debra Sue Jennings, M.S. A Dissertation Department of Geology Stacy C. Atchley, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Enter Dissertation or Thesis Committee Steven G. Driese, Ph.D., Chairperson Stacy C. Atchley, Ph. D. Stephen 1. Dworkin, Ph. D. Daniel 1. Peppe, Ph. D. Anne E. Rushing, Ph. D. Accepted by the Graduate School May 2114 1. Larry Lyon, Ph.D., Dean Page bearing signatures is kept onfile in the Graduate School Copyright © 2014 by Debra S. Jennings All rights reserved TABLE OF CONTENTS LIST OF TABLES ............................................................................................... viii LIST OF FIGURES ............................................................................................... ix CHAPTER ONE ....................................................................................................13 Introduction ............................................................................................................13 CHAPTER TWO ...................................................................................................15 Morrison Formation Paleowetland-Lacustrine Deposits and Associated Barite- bearing Paleosols ..........................................................................................15 Abstract .........................................................................................................15 Introduction...................................................................................................16 Defining Lacustrine and Wetland Settings in the Rock Record ....................20 Methods .........................................................................................................29 Stratigraphic Sections ...................................................................................29 Microscopy and Mineralogy ................................................................30 Geochemistry .......................................................................................31 Stratigraphy .........................................................................................32 Sedimentology ......................................................................................37 Pedotypes .............................................................................................43 Pedotype A. .................................................................................43 Pedotype B. .................................................................................46 Pedotype C. .................................................................................50 Pedotype D ..................................................................................56 Pedotype E. .................................................................................60 Pedotype F. .................................................................................64 Pedotype G. .................................................................................67 Pedotype H. .................................................................................70 Discussion .....................................................................................................77 Conclusions ...................................................................................................82 v REFERENCES ......................................................................................................86 CHAPTER THREE ...............................................................................................98 Abstract .........................................................................................................98 Introduction ...................................................................................................99 Previous Work ............................................................................................100 Materials and Methods ................................................................................103 Site Description ..................................................................................103 Microscopy and Clay Mineralogy .....................................................105 Elemental Analyses ............................................................................106 Stable Isotope Analysis ......................................................................106 Radiocarbon Dating...........................................................................110 Results .........................................................................................................110 Barite-bearing Profile ........................................................................110 Pond Profile .......................................................................................116 Discussion ...................................................................................................118 Acid-sulfate Soil Genesis ...................................................................118 Factors Controlling Barite Precipitation ..........................................121 Source of barium. ......................................................................121 Sources of sulfate. .....................................................................122 Sulfur Isotopic Composition. ....................................................123 Oxygen Isotopic Composition ..................................................126 Barite Precipitation ...........................................................................127 Conclusions .................................................................................................129 CHAPTER FOUR ................................................................................................142 Comparison of Modern and Ancient Barite-bearing Acid-sulfate Soils Using Micromorphology, Geochemistry, and Field Relationships .......................142 Abstract .......................................................................................................142 Introduction .................................................................................................143 Background Information .............................................................................146 Site locations and Methodology..................................................................149 Morrison Formation Paleosols ..........................................................149 Lufkin Soil ..........................................................................................151
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