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I ABSTRACT a CONCEPTUAL MODEL of ICE SHELF i ABSTRACT A CONCEPTUAL MODEL OF ICE SHELF SEDIMENTATION Matthew Mayerle, M.S. Department of Geology and Environmental Geosciences Northern Illinois University 2014 Ross Powell, Director Sedimentation studies of polar glacimarine systems remain few relative to temperate glacimarine systems due to the problem of accessibility below ice shelves. This thesis presents a conceptual model of ice shelf sedimentation at the scale of a continental shelf, which is an update of Howat and Domack’s (2003) model. This update adds scale, a third dimension, a decade of research on new geologic/glaciological processes, depositional bias', and greater specificity to their model. The shelf-scale model groups facies into deformation till, glacigenic debris flows, shelfstone mud, and diatomaceous mud. Furthermore, the model is tested and shown to be capable of replicating the facies distribution and major landforms found in two distinctly different Antarctic paleo-ice stream troughs within time constraints dictated by radiometric dating. It is hoped that ideas and techniques presented by this conceptual model will serve as a launching pad for more advanced computational models in the future, which are badly needed in order to help constrain future behavior of ice sheets in a warming world. i NORTHERN ILLINOIS UNIVERSITY DE KALB, ILLINOIS DECEMBER 2014 A CONCEPTUAL MODEL OF ICE SHELF SEDIMENTATION BY MATTHEW WILLIAM MAYERLE ©2014 Matthew Mayerle A THESIS SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF GEOLOGY AND ENVIRONMENTAL GEOSCIENCES Thesis Director: Ross D. Powell ii DEDICATION With love to my parents William and Margaret Mayerle, whose long hours of work provided me with the gift of education. iii TABLE OF CONTENTS Page LIST OF TABLES.................................................................................................................... x LIST OF FIGURES.................................................................................................................. xi Chapter 1. AN INTRODUCTION, REVIEW, AND UPDATE OF ICE SHELF SEDIMENTATION...... 1 Introduction..................................................................................................................... 1 Background..................................................................................................................... 4 Ice Shelf Glaciology and Oceanography............................................................ 4 Previous Depositional Models............................................................................ 8 Updated Grounding Zone Model.................................................................................... 15 Stiff and Soft Till................................................................................................ 15 Mega-Scale Glacial Lineations........................................................................... 17 Grounding Zone Wedges.................................................................................... 18 Shelfstone Mud/Granulated Facies..................................................................... 22 The Null Zone..................................................................................................... 24 Updated Calving Zone Model......................................................................................... 26 Iceberg Zone....................................................................................................... 29 Polynyas.................................................................................................. 29 Iceberg Rafted Debris............................................................................. 30 Sea Ice................................................................................................................. 32 iv Open Ocean......................................................................................................... 33 Diatom Assemblages........................................................................................... 33 An Idealized Retreat Sequence....................................................................................... 34 Subglacial Environment...................................................................................... 36 Glacial Erosion Surfaces......................................................................... 36 Stiff Till................................................................................................... 37 Massive Soft Till..................................................................................... 38 Grounding-Line Proximal Environment............................................................. 39 Stratified Soft Till................................................................................... 39 Pellet-Rich Diamict................................................................................. 40 Grounding Line Proximal to Grounding Line Distal Environment................... 41 Cross Stratified Sand and Laminated Muds........................................... 41 Null Zone to Calving Line Environment............................................................ 42 Massive Sediments.................................................................................. 42 Calving Line Environment.................................................................................. 43 Dropstone Diamict.................................................................................. 43 Open Ocean Environment................................................................................... 43 Diatom Muds.......................................................................................... 43 Important Core Modifiers............................................................................................... 44 Crevasse Hydrofracture...................................................................................... 45 Ice Stream Shutdown.......................................................................................... 46 Conclusions..................................................................................................................... 49 v 2. A NEW HYPOTHETICL MODEL OF ICE SHELF SEDIMENTATION ON A CONTINENTAL SHELF SCALE.............................................................................................. 50 Introduction.................................................................................................................... 50 Model Constraints........................................................................................................... 51 Continental Shelf................................................................................................. 51 Transect Location within the Paleo-Ice Stream Trough..................................... 51 Omission of the Inner Shelf Area....................................................................... 53 Transect Dimensions Used................................................................................. 53 Reversed Shelf Gradient..................................................................................... 56 Omitted Landforms............................................................................................. 56 Glaciology........................................................................................................... 58 Depositional Caveats and Constraints............................................................................. 58 Siliceous Mud and Ooze..................................................................................... 58 Iceberg Rafted Debris......................................................................................... 61 Ice Shelf Rafted Debris/Shelfstone Mud............................................................ 62 Subglacial Deposition......................................................................................... 62 Methods........................................................................................................................... 63 Siliceous Mud and Ooze Deposition................................................................... 63 Shelfstone Mud Deposition................................................................................. 66 Grounding Zone Wedge Deposition................................................................... 67 Deformation Till and Stiff Till Deposition......................................................... 70 Iceberg Scouring................................................................................................. 71 vi Ice Shelf Model Construction and Scaling......................................................... 72 Ice Shelf Model Digitizing Process.................................................................... 73 Ice Shelf Model Setup......................................................................................... 73 Sources of Error................................................................................................. 75 Ice Shelf Model Facies and Key........................................................................ 80 The Hypothetical Ice Shelf Model.................................................................................. 81 Discussion and Future Work......................................................................................... 100 Conclusions..................................................................................................................
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