Characterization and Formation of High-Chroma Features in Loamy Soils of Southern Minnesota A Dissertation SUBMITTED TO THE FACULTY OF UNIVERSITY OF MINNESOTA BY Douglas Wayne Pribyl IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY James C. Bell, Adviser December 2012 © Douglas Wayne Pribyl 2012 Acknowledgements Many people both inside and outside the University of Minnesota have helped make this dissertation possible. The Department of Soil, Water, and Climate has supported me in many ways not least of which was the office staff, who were always ready with a friendly greeting, and willing and able to solve any problem: Karen Mellem, Kari Jarcho, Jenny Brand, and Marjorie Bonse. I especially want to thank my adviser, Jay Bell, for his continuous enthusiasm and encouragement. Ed Nater, together with Jay Bell, is responsible for introducing me to soil genesis and enabling me to pursue the interest they created. The rest of my committee, Paul Bloom and Carrie Jennings, have provided inspiration and motivation. Terry Cooper and John Lamb imparted wisdom and confidence in ways that only the best teachers can. I am profoundly grateful to have been their teaching assistant. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. A special thanks to the staff who trained, listened, suggested, and encouraged: Bob Hafner, Ozan Ugurlu, Jinping Dong, John Nelson, Alice Ressler, Maria Torija Juana, Fang Zhou, and Nicholas Seaton. My earliest microscopy imaging and analysis work was with Gib Ahlstrand at the Biological Imaging Center, now part of the University Imaging Centers at the University of Minnesota. Later imaging and analysis work at the Imaging Center required the able assistance of Tracy Anderson, Gail Celio, and Mark Sanders, who were most generous withe their tim and resources to help a non‐biologist in time of need. Also, I want to thank Thelma Berquó, Subir Banerjee, and others at the Institute for Rock Magnetism, Paroma Chakravarty at Dr. Raj Suryanarayanan’s Pharmaceutics Lab for use of their FT‐Raman, Roger Eliason and Russell Anderson at the University of Minnesota Soil Testing Lab, Donna Whitney in the Geology Department who made her lab available for thin sectioning and Valerie Morgan who took the time to train me. I am truly fortunate to have had the loving support of my wife, whose quiet, unwavering confidence kept me on course and whose companionship kept me grounded. Finally for my parents, who encouraged me to pursue my interests and continue my education, a more tangible acknowledgement: the choice of Palatino Linotype as the type font used for this dissertation. i Dedication This dissertation is dedicated to my parents, Vernon and Myra Pribyl, whose love of family knows no bounds. ii ABSTRACT High‐chroma features have not been adequately defined under existing terminology or classified under existing systems. The terms “masses” as a subclass of concentrations used in field definitions and “loose infillings” used in micromorpological classifications come closest but are not fully satisfactory. Defined descriptively, high‐chroma features have a typical color of 7.5YR 5/8, are usually less than 1 to 2 mm in diameter, are poorly cemented, and have a sharp external boundary with the soil matrix. They are found in well‐drained to poorly drained soils with first‐appearance typically at depths of 50 to 100 cm. A study was undertaken to more fully characterize and classify high‐chroma features and to provide more accurate interpretations of feature morphology for applications in environmental and soil quality, plant nutrition, and soil genesis. High‐chroma features found within peds having varying degrees of hydromorphic expression were assigned to classes depending on internal color and color patterns. Material removed from features, halos, and the soil matrix was analyzed using a low‐power stereomicroscope, SEM/EDS, TEM/ED, μ‐XRD, ICP, and stain tests to determine properties and composition. Four formation hypotheses are proposed: (1) a non‐pedogenic origin, features having developed from the weathering of an inherited precursor mineral; (2) a pedogenic origin resulting from the formation and infilling of vesicles that formed at depth shortly after deglaciation but are no longer actively forming; (3) a pedogenic origin but features are actively forming; (4) formation by dissolution of a soluble mineral fragment and subsequent infilling of the resulting void, analogous to the formation of a geode. Although high‐chroma features might develop by more than one pathway, a non‐pedogenic origin is favored. Non‐pedogenic hypothesis (1) and the hybrid geodic hypothesis (4) offer the most efficient explanations for the presence of silt, iron, and manganese within high‐chroma features. A proposed weathering sequence based on feature classification and evidence for the presence of manganese nodules in the till‐source bedrock also support a non‐ pedogenic origin. Pedogenic hypotheses require a sequence of events of uncertain and in some cases seemingly low probability. Existing classification systems offer little insight into genesis. Most importantly, given the evidence for a non‐pedogenic origin, high‐chroma features should not be interpreted or classified as redoximorphic features as the term is typically used in the field. Although high‐chroma features may result from alternating periods of oxidation and reduction, when used alone they are ambiguous indicators of seasonal wetness. iii Table of Contents Acknowledgements ................................................................................................................ i Dedication ................................................................................................................................ ii Abstract .................................................................................................................................... iii List of Tables ............................................................................................................................ v List of Figures .......................................................................................................................... vi Introduction ............................................................................................................................. 1 General description of high‐chroma features ........................................................ 3 Historical and interpretive sciences ........................................................................ 6 General description of the study area ..................................................................... 10 Development of the soils .......................................................................................... 17 Literature Review .................................................................................................................... 26 Part I: Further characterization of the till ............................................................... 26 Part II: Classification systems .................................................................................. 50 Part III: Properties and formation of nodules and concretions ........................... 75 Methods .................................................................................................................................... 101 Sampling methods ..................................................................................................... 102 Sample sites ................................................................................................................ 104 Initial sample preparation ........................................................................................ 109 Thin sections ............................................................................................................... 109 Characterization and analysis .................................................................................. 111 Results and Discussion .......................................................................................................... 137 Classification of peds by hydromorphology ......................................................... 137 Characterization of high‐chroma features ............................................................. 144 Classification of high‐chroma features ................................................................... 203 Classification as redoximorphic features ............................................................... 209 Comparison of data: non‐pedogenic and pedogenic hypotheses ....................... 215 Discussion of proposed formation hypotheses ..................................................... 220 Non‐pedogenic, inherited ............................................................................ 223 Pedogenic, inherited ..................................................................................... 230 Pedogenic, coeval .......................................................................................... 256 Geode hypothesis .......................................................................................... 258 Other hypotheses .......................................................................................... 261 Conclusion ..............................................................................................................................