Marine Geology of the Western Ross Sea: Implications for Antarctic Glacial History
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RICE UNIVERSITY MARINE GEOLOGY OF THE WESTERN ROSS SEA: IMPLICATIONS FOR ANTARCTIC GLACIAL HISTORY by NATHAN CEBREN MYERS A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF ARTS APPROVED, THESIS COMMITTEE: Chairman D ohn W. \ Assistant Pr< of Geology Dr. Howard C. Clark Associate Professor of Geology HOUSTON, TEXAS APRIL, 1982 ABSTRACT MARINE GEOLOGY OF THE WESTERN ROSS SEA: IMPLICATIONS FOR ANTARCTIC GLACIAL HISTORY The stability of the Antarctic Ice Sheet has long been the subject of debate. Recently, basal till has been identified in the Ross Sea, yielding evidence for the expansion of the Antarctic Ice Sheet and its grounding in the Ross Sea. However, the sedimentologic criteria used to identify basal till may be inconclusive. Therefore, one purpose of this study is to support the validity of these sedimentologic criteria. Another goal is to determine if basal tills are present in the western Ross Sea. Marine sedimentologic processes on high latitude continental shelves are not well known. Therefore, surface sediment distributions can be used to infer marine processes active in the western Ross Sea. Three major sediment types, siliceous ooze and mud, sands, and diamictons were identified. Sands include graded volcanic sands, granitic sands, and calcareous shell hash sands. Diamictons include compound glacial marine sediment, basal till, and mass flow diamictons. Siliceous sediment distribution is controlled both by bottom currents and surface currents. Sands are found in near-coastal or ii shallow waters, or in areas of high sediment supply. The distribution of surface sediments in the western Ross Sea is controlled by thermohaline bottom currents, by surface currents, by the presence of polynyas, and by sediment gravity flow processes. Basal tills were identified as far north as Coulman Island, and as far south as Ross Island, but no basal tills were found in McMurdo Sound. A petrologic analysis of these basal tills reveals that three petrologic provinces can be recognized in the western Ross Sea and four petrologic provinces can be recognized in the central Ross Sea. The boundaries between petrologic provinces can be correlated with geologic provinces in Victoria Land and Marie Byrd Land. Paleo-ice flow paths are reconstructed based on petrologic province boundaries and bathymetry, and indicate that during the last glacial maximum ice flowed into the Ross Sea from both East and West Antarctica. The petrologic data also indicate that sedimentologic criteria used to identify basal tills are indeed valid. The marine sedimentologic record in the western Ross Sea indicates that the ice sheet which grounded there initially eroded the sea floor, and later deposited basal till except in Mcmurdo Sound where flow was restricted. Sharp contacts between basal till and compound glacial marine sediment indicate that decoupling of the Ice Sheet from its base was rapid; gradational contacts between iii compound glacial marine sediment and siliceous sediments indicate that ice-shelf retreat was slow allowing siliceous sediments to slowly dominate sedimentation. ACKNOWLEDGEMENTS The writing of this thesis would not have been possible without the assistance of many people. Dr. John Anderson deserves the most hearty thanks for inspiring and supporting, in many ways, this research. Dr. Anderson's suggestions and comments were invaluable, in the writing of this manuscript. Dr. John Valley rendered valuable assistance in interpreting microprobe results and made valuable suggestions regarding the presentation of data in this thesis. The time spent by Dr. H.C. Clark reading and editing this manuscript is greatly appreciated. Special thanks goes to my dear wife, Sherris, for spending many night-time hours typing and editing this work. Without her help this thesis would not have been finished in such timely fashion. Thanks also go to Dr. Eugene Domack for helpful suggestions, to Dave Matty for assistance with use of the microprobe, and to my officemate, Jill Singer, for bearing with me in times of stress. Barbara Ward (Victoria University of Wellington) provided some of the bathymetric data used in the construction of a bathymetric map of McMurdo Sound. Dr. Paul Ciesielski (University of Georgia) kindly examined V sediment samples and reported dates. Dennis Cassidy (Florida State University) kindly provided some of the samples analyzed in this study. This research was supported by grant number DPP79-08242 acquired by Dr. Anderson from the National Science Foundation. TABLE OF CONTENTS CHAPTER 1 PAGE INTRODUCTION 1 SETTING 5 Location 5 Bathymetry 8 Glacial Setting 15 Oceanography 21 - Geology 27 PREVIOUS WORKS 45 Historical Background 45 Geology 46 Marine Sediments 47 Heavy Minerals 51 ANTARCTIC GLACIAL HISTORY 52 THE GREAT DEBATE 55 METHODS 58 CHAPTER 2 SEDIMENTS 61 Introduction 61 Sediment Description and Distribution 62 Modern Sediment Distribution-Terra 78 Nova Bay Modern Sediment Distribution-McMurdo 88 Sound Stratigraphy 95 Conclusions 105 CHAPTER 3 MINERALOGY AND LITHOLOGY . 106 Introduction 106 Heavy Mineral Distribution 107 Coarse Sand Distribution 116 Pebbles 118 PETROLOGIC PROVINCES 122 Heavy Mineral Provinces 123 Coarse Sand Provinces 130 Heavy Mineral Source 131 Coarse Sand Source 133 Pebble Source 135 Heavy Mineral, Coarse Sand, and Pebble 136 Interpretation Discussion 136 CHAPTER 4 GLACIAL DYNAMICS 142 CONCLUSIONS 149 BIBLIOGRAPHY 151 APPENDIX I 164 APPENDIX II 181 APPENDIX III 199 APPENDIX IV 206 APPENDIX V 212 APPENDIX VI 221 APPENDIX VII 225 LIST OF FIGURES PAGE FIGURE 1 Study area location. 6 FIGURE 2 Bathymetry of the Ross Sea and present day ice-stream paths. 9 FIGURE 3 Bathymetry of the western Ross Sea. 11 FIGURE 4 Bathymetry of McMurdo Sound. 13 FIGURE 5 Depth profile in McMurdo Sound. 16 FIGURE 6 Modern Antarctic ice drainage. 19 FIGURE 7 Ross Sea surface water circulation. 22 FIGURE 8 Ross Sea water masses. 25 FIGURE 9 Place names used in this study. 34 10 Generalized geology of Victoria and FIGURE 36 Marie Byrd Lands. FIGURE 11 Outcrop map of northern Victoria Land. 40 FIGURE 12 Outcrop map of the McMurdo Sound 42 region. FIGURE 13 Sand/silt/clay ratios for basal till 63 and compound glacial marine sediment. FIGURE 14 Down-core variability of heavy 65 minerals. FIGURE 15 X-radiograph of compound glacial 68 marine sediment. FIGURE 16 Grain-size distributions for diamic- 70 tons. FIGURE 17 X-radiograph of basal till. 74 FIGURE 18 Siliceous mud distribution and thick¬ nesses for the Terra Nova Bay region. The Terra Nova Bay Polynya also shown. 79 FIGURE 19 Percent sand for the Terra Nova Bay region. 82 ii FIGURE 20 Surficial sediment in McMurdo Sound. 89 FIGURE 21 Mean grain size of surficial sediments in McMurdo Sound. 93 FIGURE 22 X-radiograph of cross-stratified sand. 96 FIGURE 23 Normal stratigraphic sequence. 98 FIGURE 24 Correlation between DF-80 cores and cores studied by Kellogg et al. 100 (1979). FIGURE 25 Seismic section across Drygalsky Trough. 103 FIGURE 26 Ternary diagrams for western Ross Sea petrology. 108 FIGURE 27 Ternary diagrams for central Ross Sea petrology. 110 FIGURE 28 Ross Sea heavy mineral and coarse sand provinces. 124 FIGURE 29 Western Ross Sea heavy mineral and coarse sand provinces. 127 FIGURE 30 Paleo-ice flow paths in the western Ross Sea. 138 FIGURE 31 Antarctic Ice Sheet maximum recon¬ struction. 140 LIST OF TABLES PAGE TABLE 1 Sedimentary criteria for the 3 recognition of marine sediments TABLE 2 Stratigraphy of Marie Byrd Land 28 and Victoria Land. TABLE 3 Geologic subprovinces. 30 TABLE 4 Characteristic heavy minerals, 112 listed in order of abundance, and inferred source rock lithology for provinces 1 through 7. TABLE 5 Characteristic lithologies, listed 114 in order of abundance, and inferred source rock lithology for provinces 1 through 7. TABLE 6 Comparison of abundances (in percent) 115 of heavy minerals in cores analyzed by Stetson and Upson (1937), to to abundances of heavy minerals in Eltanin cores analyzed in this study. TABLE 7 Compound glacial marine sediments 117 and basal till heavy mineral ratios. TABLE 8 Pebble lithologies from DF-80 cores. 119 TABLE 9 Pebble lithologies from the dry 120 valley region. TABLE 10 Pebble lithologies for Plio- 121 Pleistocene sediments at DSDP sites 270-274 (modified after Barrett, 1975a). TABLE 11 Number and type of contacts in Terra 143 Nova Bay region cores. CHAPTER 1 INTRODUCTION Since the earliest days of Antarctic exploration, scientists have theorized about the stability of the Antarctic Ice Sheet during past glacial periods. A distillation of these theories yields two opposing views plus many variants: 1) The Antarctic Ice Sheet is in a steady state condition and has never advanced beyond its present limits (Whillans, 1976; Pewe, 1960) and 2) The Antarctic Ice Sheet is a dynamic, ever-changing system, which has expanded, as grounded ice, to the continental shelf break ^(Kellogg et al., 1979, and Denton et al., 1971). Until the International Geophysical year (IGY), there was little evidence, other than theoretical, to support either view. Since the IGY, more and more land-based evidence has been compiled which supports the latter view that the ice sheet has expanded in the past. But, partly due to a lack of conclusive marine sedimentologic evidence, controversy continues over the possibilities of an expanded ice sheet having grounded on the Antarctic continental shelf. Sedimentologic criteria have been used to distinguish 1 2 high latitude marine sediment types (Table 1). Recently, cores collected on Antarctic continental shelves in the Ross Sea have been analyzed by Anderson et al. (1980). They distinguished three sediment types in the Ross Sea: 1) compound glacial marine sediments, 2) residual glacial marine sediments, and 3) basal tills. These sedimentologic studies have gone a long way toward proving that ice has grounded in the Ross Sea. However, these sedimentologic criteria, taken alone, may not be valid for the identification of basal till.