Outcrop Studies of Soft-sediment Deformation Features in the Navajo Sandstone by Gerald C. Bryant A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Geology University of Toronto © Copyright by Gerald C. Bryant, 2011 OUTCROP STUDIES OF SOFT-SEDIMENT DEFORMATION FEATURES IN THE NAVAJO SANDSTONE 2011 Ph.D. Thesis Gerald Craig Bryant Department of Geology University of Toronto ABSTRACT In contrast to early work establishing the importance of earthquake-induced liquefaction in producing soft-sediment deformation (SSD) of the Navajo Sandstone, this report advances the use of SSD analysis to: characterize wet climatic conditions and flood events during the depositional history of ancient eolianites; discriminate the signatures of multiple deformation events from those of complex deformation features formed in a single event; and to document the occurrence of liquefaction features unrepresented in modern Earth analogues. The diversity of deformation styles, presented here, is very unusual in a report from a single formation; yet the high resolution of interpreted time relationships between various processes of deposition, erosion, water table fluctuation, and deformation is even more notable. These exceptional features derive from the extraordinary outcrops of the Colorado Plateau, which expose many large-scale (tens of meters) features throughout their entire extent and reveal an extended history of episodic deformation through thick (hundreds of meters) sections of cross- bedded units, which frequently continue along several kilometers of cliff face. Prior studies of fluid escape from unconsolidated sand that support the present work are outlined in Chapter II. These include laboratory simulations of liquefaction and fluidization as well as analyses of analogous deposits, both ancient and modern. Chapter III provides an overview of outcrop evidence, gathered during the course of this study, for dramatic alterations in the topography and sedimentation patterns of the Navajo erg. Interpreted perturbations include: the foundering of active dunes; sediment eruptions; and the subsidence of interdune surfaces. Chapter IV constitutes an example of the detailed ii analyses that support the overview of Chapter III. Outcrop features from a site in West Canyon, Arizona provide the basis for interpreting the subsidence of a dry interdune surface to a position several meters below the contemporary water table, followed by the filling of this depression with a succession of mass flow, lacustrine, and eolian deposits. Chapter V outlines the implications of various outcrop features for the prevailing model of soft-sediment deformation in the Navajo Sandstone. Proposed modifications of this model accommodate a broader range of deformation dynamics and specifically incorporate the impact of wet climates. iii CONTENTS Outcrop Studies of Soft-sediment Deformation Features in the Navajo Sandstone ............................................................................ i ABSTRACT ................................................................................... ii CONTENTS .................................................................................. iv I. INTRODUCTION ...................................................................... 1 Focus of this Study ................................................................... 1 Eolian Facies Architecture ...................................................................... 2 Navajo Sandstone Paleohydrology ........................................................ 4 Thesis Objectives ...................................................................... 5 Collaborations ........................................................................... 6 II. BACKGROUND AND METHODS .............................................. 8 Value of this Study .................................................................... 8 Scope of this Study ................................................................... 8 Purpose of this Report ............................................................ 10 Geologic Setting ...................................................................... 10 Age .......................................................................................................... 10 Tectonic and Eustatic Context .............................................................. 11 Paleoclimate ........................................................................................... 12 Stratigraphy ............................................................................................ 14 Provenance ............................................................................................. 16 Petrology ................................................................................................. 16 Previous Work ......................................................................... 18 Early Descriptions of SSD in Colorado Plateau Eolianites ................. 18 Theoretical Milestones in Eolianite SSD Research ............................. 19 Detailed Descriptions and Paleoenvironmental Applications of Navajo SSD ............................................................................................. 20 Other Related Work on Eolianite SSD .................................................. 25 Recent Work on Navajo Sandstone SSD .............................................. 26 Methods ................................................................................... 28 Outcrop Selection .................................................................................. 28 Photographic Data Collection ............................................................... 28 Sampling and Laboratory Analyses ..................................................... 29 Chronostratigraphic and Paleoenvironmental Interpretation ............ 29 Interpretive Challenges.......................................................................... 30 Interpretive Context ................................................................ 41 General Process Implications of Navajo SSD ...................................... 41 General Paleoenvironmental Implications of Navajo SSD .................. 44 Summary .................................................................................. 48 III. DIVERSE PRODUCTS OF NEAR-SURFACE SEDIMENT MOBILIZATION IN AN ANCIENT EOLIANITE: OUTCROP iv FEATURES OF THE EARLY JURASSIC NAVAJO SANDSTONE ..................................................................................................... 49 Abstract ................................................................................... 49 Introduction ............................................................................. 50 Geologic Setting ...................................................................... 52 Observations and Interpretations .......................................... 57 Discussion ............................................................................... 73 Conclusions............................................................................. 77 IV. TOPOGRAPHIC RESPONSES TO SOFT-SEDIMENT DEFORMATION IN AN ANCIENT ERG: THE LOWER JURASSIC NAVAJO SANDSTONE ......................................... 78 Abstract ................................................................................... 78 Introduction ............................................................................. 79 General Geologic Setting ...................................................................... 79 Stratigraphy ............................................................................................ 79 Petrology ................................................................................................. 80 Typical Features of Soft-sediment Deformation in the Navajo Sandstone ........................................................................................... 82 Factors Contributing to Navajo deformation ................................... 82 Preserved Surface Effects of Large-scale Deformation Events ..... 82 Purpose of this Report........................................................................... 83 Location and Methods ............................................................ 85 Location .................................................................................................. 85 Methods .................................................................................................. 85 Architectural Relations .......................................................................... 85 Facies Succession ................................................................................. 89 Discussion ............................................................................... 92 Sinkhole Interpretation .......................................................................... 92 The unusual depression in a 1st- order boundary ................................. 94 Deformation structures that parallel the depression boundary .............. 95 The depositional geometry of units filling the depression ..................... 96 Initiation of horizontal stratification within the depression ..................... 97 Sedimentology of the Fill Succession ................................................... 97 Significance of Fracture Pattern ......................................................... 100 Volumetric Considerations .................................................................. 100 Implications for