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Ice petrofabrics, Tuktoyaktuk, N.W.T., Canada Gell, Alan William 1973

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ICE PETROFABRICS, TUKTOYAKTUK, N.W.T., CANADA by ALAN WILLIAM GELL B . S c , L i v e r p o o l U n i v e r s i t y , 1 9 7 1 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Geography We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1973 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study. I further agree that permission fo r extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by hi s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of GEOGRAPHY The University of B r i t i s h Columbia Vancouver 8, Canada Date 2 2 < t h September, 1973 ABSTRACT Th i s t h e s i s attempts to e l u c i d a t e the o r i g i n and deformation o f a f o l d e d sequence of i c e and i c y sediment i n Tuktoyaktuk, N.W.T., Canada. Tuktoyaktuk l i e s between the maximum and l a t e Wisconsin l i m i t s o f g l a c i a t i o n . Bodies of underground i c e i n permafrost have c h a r a c t e r - i s t i c Ice c r y s t a l s i z e s and shapes and i n c l u s i o n s dependent on the mode of i c e growth and subsequent d e f o r m a t i o n a l or other h i s t o r y . The i c e body which was s t u d i e d l i e s beneath 2 m of f l u v i o g l a c i a l sands and 0.6 m o f g r a v e l . The i c e - i c y sediment f o l i a t i o n has been deformed i n t o s u b h o r i z o n t a l i s o c l i n a l f o l d s , the major movement being from the SSW. Fol d s are c l a s s i f i e d i n t o t h r e e s t y l e s . F a b r i c diagrams of i c e c r y s t a l o p t i c axes are of two types. A r e l i c t e a r l y f o l d shows a c l e f t g i r d l e p a t t e r n at r i g h t - a n g l e s t o the f o l d a x i s . L a t e r f l a t t e n i n g and f o l d limb e x t e n s i o n has given r i s e to f a b r i c diagrams with s t r o n g maxima normal to the a x i a l s u r f a c e s , showing that c r y s t a l s have r o t a t e d such t h a t s l i p planes are p a r a l l e l t o the s u r f a c e o f s l i p o f the body. D i f f e r e n c e s i n d e f o r m a b i l i t i e s o f pure i c e and i c e with v a r y i n g amounts of sand have given r i s e to boudinage and t r a n s p o s i t i o n - t y p e s t r u c t u r e s . Pour types o f g r a i n t e x t u r e i n d i c a t i v e of r e c r y s t a l l i z a t i o n and dependence on sediment, are d i s t i n g u i s h e d . i i i I t i s not p o s s i b l e , with the a v a i l a b l e evidence, t o d i s t i n g u i s h between two a l t e r n a t i v e o r i g i n s o f the body as segregated ground Ice o v e r r i d d e n by an i c e - s h e e t or a remnant o f a deformed i c e - s h e e t terminus. Necessary c o n d i t i o n s f o r the s u r v i v a l o f e i t h e r body may be i n f e r r e d . P e t r o g r a p h i c c h a r a c t e r i s t i c s are l i s t e d f o r f u t u r e f i e l d r e c o g n i t i o n o f the i c e type. i v . TABLE OF CONTENTS Page ABSTRACT i i LIST OF FIGURES x LIST OF FABRIC DIAGRAMS x i i LIST OF TABLES x i v LIST OF PLATES xv ACKNOWLEDGMENTS x v i Chapter I INTRODUCTION AND STATEMENT OF THE PROBLEM 1 General Statement 1 Statement of the Problem 4 General Approach 4 O r g a n i z a t i o n o f T h e s i s 5 F i e l d Area 6 I I ICE GROWTH IN SEDIMENT AND ENTRAINMENT OF SEDIMENT IN GLACIER ICE - A LITERATURE REVIEW I n t r o d u c t i o n 9 Ice Growth i n Sediment 10 F r e e z i n g Without Overburden 10 F a b r i c of Segregated Ice 11 V . Chapter Page III (d) Application to the F i e l d Situation 31 The Effect of Inclusions 34 Deformation of the Sand-Ice System 35 (a) Physico-Chemical Properties 35 (b) S o i l Strength 36 (c) Loading 37 F i e l d Studies 39 Conclusion 40 IV METHODOLOGY Introduction 43 Chapter Outline 43 Scale Considerations 44 The Symmetry Pr i n c i p l e 44 Mapping Mesoscopic Structure 45 Fold Characteristics 46 Style 1 Folds 46 Style 2 Folds 46 Sampling Methods 47 (a) Sampling Folded Material 47 (b) Sampling of Blocks 49 Thin Section Preparation 50 Universal Stage Technique 50 Errors 50 Plo t t i n g of Optic Axis Orientation 52 Number of Points 53 Contouring 53 Interpretation 54 v i . Chapter Page IV A x i a l D i s t r i b u t i o n A n a l y s i s (A.V.A.) 56 Measurement of Ice C r y s t a l S i z e and Shape 56 Sediment Content A n a l y s i s 57 Sediment S i z e A n a l y s i s 57 Conclusion 58 V RESULTS I n t r o d u c t i o n 59 Chapter O u t l i n e 59 A. S t r u c t u r e 1. O v e r a l l Mesoscopic S t r u c t u r e 60 F o l d s o f S t y l e 1 60 Folds o f S t y l e 2 61 Folds of S t y l e 3 62 I n t e r r e l a t i o n s h i p s Among F o l d S t y l e s 62 I n t e r p r e t a t i o n o f Movements from Mesoscopic S t r u c t u r e 62 2 . M i c r o s c o p i c S t r u c t u r e 63 S t y l e 1 F o l d s 64 S t y l e 2 F o l d s 64 S t y l e 3 Folds 64 3 . M i c r o s c o p i c F a b r i c 65 General Petrography 65 O r i g i n o f F a b r i c s 66 The P e t r o f a b r i c Approach 66 (a) F i r s t S t y l e 1 F o l d 66 (b) S t y l e 2 F o l d on F i r s t S t y l e 1 F o l d 71 v i i . Chapter Page V 3. (c) I n t e r p r e t a t i o n of F a b r i c of F i r s t S t y l e 1 F o l d 71 (d) Second S t y l e 1 F o l d 72 (e) T h i r d S t y l e 1 F o l d 73 ( f ) The S t y l e 3 F o l d 74 Mode of Deformation, as i n d i c a t e d by F o l d Morphology and Optic Axis D i s t r i b u t i o n s 74 B. Ice Grain Shape I n t r o d u c t i o n 75 (a) S i n g l e Phase M a t e r i a l 76 (b) The E f f e c t of I n c l u s i o n s 78 (c) Gaseous I n c l u s i o n s 78 Observations i n s i t u 79 Thin S e c t i o n A n a l y s i s 79 Texture Types (a) Sediment-free Ice 79 1. Texture Type l a 79 2. Texture Type 2a 8l (b) The E f f e c t of Sediment 82 3. Texture Type l b 82 4. Texture Type 2b 83 Mimetic Growth 83 Mode of Deformation and R e c r y s t a l l i z a t i o n as i n d i c a t e d by C r y s t a l Shape 83 v i i i . Chapter Page V C. Ice Gr a i n S i z e I n t r o d u c t i o n 85 Problems 85 R e s u l t s 86 D. Sediment 87 (a) Sediment G r a i n S i z e 87 (b) Sediment Content A n a l y s i s 88 E. Water Q u a l i t y A n a l y s i s 89 VI CONCLUSION (a) O r i g i n o f the Bedding Sequence 92 Examination o f mechanisms 93 (b) Mode of Deformation 95 Suggested Deformation mechanism (a) 96 Suggested Deformation mechanism (b) 96 M i c r o s c o p i c S t r u c t u r e 98 Deformation mechanism (a) 98 Deformation mechanism (b) 98 Summary 98 (c) D i a g n o s t i c P e t r o g r a p h i c Features o f the Tuktoyaktuk Ice 99 I. Pure Ice 99 ( i ) Ice G r a i n shape 99 ( i i ) Ice G r a i n s i z e 1 0 0 II. Ice with sediment bands 1 0 0 ( i ) Ice Gr a i n shape 1 0 0 ( i i ) Ice G r a i n s i z e 100 i x . Chapter Page VI I I I . Optic a x i s o r i e n t a t i o n i n i c e and i c y sediment 100 (d) Suggestions f o r f u r t h e r work 101 BIBLIOGRAPHY 102 X. LIST OF FIGURES Fi g u r e Page 1 L o c a t i o n Map 111 2 Maximum and Late Wisconsin L i m i t s of 112 G l a c i a t i o n 3 (a) Kink-band i n a Deformed C r y s t a l 113 (b) Undulatory E x t i n c t i o n 4 S t r e s s - s t r a i n curves f o r pure i c e and i c e 114 with v a r i o u s sediment contents 5 Dynamic and Kinematic viewpoints of 115 Deformation 6 R e l a t i o n s h i p between S-surfaces 116 7 F o l d S t y l e s 117 8 R o o t l e s s F o l d s of S t y l e 1 118 9 S t y l e 3 F o l d 119 10 Sampling S t a t i o n s on F i r s t S t y l e 1 F o l d 120 11 The three Thin S e c t i o n O r i e n t a t i o n s 121 12 ( a ) , (b) Boudinage of sandy i c e w i t h i n i c e 122 13 T r a n s p o s i t i o n S t r u c t u r e s 123 14 Shear i n d i c a t e d by j u x t a p o s i t i o n of two 123 s y n c l i n e s 15 E f f e c t o f Sediment on G r a i n Boundary Shape 124 16 Mimetic p o s t - d e f o r m a t i o n a l c r y s t a l growth 124 i n S t y l e 3 F o l d 17 Asymmetrical S t y l e 1 F o l d 125 18 G r a i n Boundary Shapes 126 F i g u r e Page 19 G r a i n Boundary Shapes on C e l l a r w a l l 127 20 R e l i c t C r y s t a l with Deformation Bands 128 21 Frequency d i s t r i b u t i o n of boundary angles 128 o f s m a l l s t r a i n - f r e e c r y s t a l s 22 Texture Type 2a. S e r r a t e d Boundaries 129 23 P o s i t i o n s of samples f o r sediment content 130 a n a l y s i s , F i r s t S t y l e 1 F o l d 2K Sediment s i z e curves 131 x i i . LIST OF FABRIC DIAGRAMS A l l diagrams contoured at 1> 2 , 3 , 5 , 7 1 / 2 , 1 0 , 12 1 / 2 , 1 5 , 17 1 / 2 , 20% i n t e r v a l s Page DIAGRAM 1 HORIZONTAL MAX. 19% 100 CRYSTALS 1 3 2 DIAGRAM 2 VERTICAL MAX. 16% 1 0 0 CRYSTALS 133 DIAGRAM 3 VERTICAL MAX. 15% 100 CRYSTALS 134 DIAGRAM 4 HORIZONTAL MAX. 16% 1 0 0 CRYSTALS 135 DIAGRAM 5 HORIZONTAL MAX. 19% 150 CRYSTALS 136 DIAGRAM 6 VERTICAL MAX. 12% 175 CRYSTALS 137 DIAGRAM 7 VERTICAL MAX. 13% 100 CRYSTALS 138 DIAGRAM 8 VERTICAL MAX. 17% 1 0 0 CRYSTALS 139 DIAGRAM 9 HORIZONTAL MAX. 11% 75 SMALL CRYSTALS 140 DIAGRAM 10 HORIZONTAL MAX. 18% 200 LARGE CRYSTALS 141 DIAGRAM 11 VERTICAL MAX. 13% 100 CRYSTALS 142 DIAGRAM 12 HORIZONTAL MAX. 11% 2 5 0 CRYSTALS 143 DIAGRAM 13 HORIZONTAL MAX. 8% 50 CRYSTALS 144 DIAGRAM 14 HORIZONTAL MAX. 6% 50 CRYSTALS 145 DIAGRAM 15 HORIZONTAL MAX. 8% 50 CRYSTALS 146 DIAGRAM 16 HORIZONTAL MAX. 9% 1 0 0 CRYSTALS 147 DIAGRAM 17 HORIZONTAL . MAX. 13% 100 LARGE CRYSTALS 148 DIAGRAM 18 VERTICAL MAX. 16% 100 CRYSTALS 149 DIAGRAM 19 VERTICAL MAX. 12% 125 CRYSTALS 150 x i i i . D I A G R A M 20 H O R I Z O N T A L M A X . D I A G R A M 21 H O R I Z O N T A L M A X . D I A G R A M 22 H O R I Z O N T A L M A X . D I A G R A M 23 H O R I Z O N T A L M A X . D I A G R A M 24 H O R I Z O N T A L M A X . D I A G R A M 25 H O R I Z O N T A L M A X . D I A G R A M 26 H O R I Z O N T A L M A X . D I A G R A M 27 H O R I Z O N T A L M A X . D I A G R A M 28 H O R I Z O N T A L M A X . D I A G R A M 29 H O R I Z O N T A L M A X . D I A G R A M 30 H O R I Z O N T A L M A X . D I A G R A M 31 H O R I Z O N T A L M A X . D I A G R A M 32 V E R T I C A L M A X . D I A G R A M 33 V E R T I C A L M A X . Page 18% 200 C R Y S T A L S 151 11% 110 C R Y S T A L S 152 8% 47 C R Y S T A L S 153 8% 43 C R Y S T A L S 154 1838 175 C R Y S T A L S 155 19% 100 C R Y S T A L S 156 6% 40 C R Y S T A L S 157 k% 30 C R Y S T A L S 158 1S% 250 C R Y S T A L S 159 12% 130 C R Y S T A L S 160 14* 120 C R Y S T A L S l 6 l 9% C R Y S T A L S I N 162 S E D I M E N T 6% 90 C R Y S T A L S 163 12% 200 C R Y S T A L S 164 xiv-. LIST OP TABLES Table Page 1 Ice C r y s t a l S i z e 89 2 Sediment Content 89 3 Water Q u a l i t y Analyses 90 X V . LIST OF PLATES P l a t e Page 1. S t y l e 1 F o l d morphology d i s p l a y e d on 165 c o r r i d o r w a l l . 2. Boudin o f i c y sand i n i c e . 165 3. S t y l e 1 F o l d - o f f s e t t i n g o f f o l i a t i o n i n 166 f o l d c l o s u r e . .4. S t y l e 2 F o l d . A x i a l s u r f a c e o b l i q u e to 166 l o c a l bedding. 5. Etched g r a i n boundaries on c o r r i d o r w a l l . 167 x v i . ACKNOWLEDGMENTS F i e l d work was c a r r i e d out du r i n g summer 1 9 7 2 , supported by the T e r r a i n Sciences D i v i s i o n of the G e o l o g i c a l Survey o f Canada. The P o l a r C o n t i n e n t a l S h e l f P r o j e c t o f the Department of Energy, Mines and Resources and the Inuvik Research Laboratory p r o v i d e d l o g i s t i c support. Winter study at the U n i v e r s i t y o f B r i t i s h Columbia was supported by a f e l l o w s h i p from I m p e r i a l O i l L i m i t e d . Some funds f o r equipment and t r a v e l came from r e s e a r c h grants (to Dr. J.R. Mackay) from the N a t i o n a l Research C o u n c i l of Canada and the Department o f Indian A f f a i r s and Northern Development ( v i a . t h e A r c t i c and A l p i n e Committee, U n i v e r s i t y o f B r i t i s h Columbia). The author wishes t o thank Dr. J.R. Mackay who s u p e r v i s e d the f i e l d and l a b o r a t o r y work and commented on s e v e r a l stages o f the manuscript, and Dr. H.O. Slaymaker f o r comments on the manuscript. CHAPTER I INTRODUCTION AND STATEMENT OP THE PROBLEM General Statement Permafrost underlies approximately one half of the land area of Canada (Brown 1967, p. 741). Within such a zone, bodies of underground ice may exist i n a variety of forms (Mackay 1972a, p. 5) » ranging from h a i r l i n e lenses to bodies of massive ice at least 35 m thick (Mackay 1971, p. 397). Ice thus has a great areal d i s t r i b u t i o n , i t being estimated that ice-wedges alone are found i n perhaps 2,600,000 km' of the northern hemisphere (Mackay 1972a, p. 5); further, d r i l l hole records show the existence of alternating i c e and sediment layers at depth. It i s evident that a knowledge of underground ice ch a r a c t e r i s t i c s i s important for an understanding of the past, present and future geomorphic development of regions containing permafrost, and of the probable effects of proposed human a c t i v i t i e s . A review of the l i t e r a t u r e shows that geomorphological investigations i n Canada have been confined largely to studies of surface expression. Studies of subsurface structure i n the f i e l d area have been limited to d r i l l i n g of pingos, inspection of slump faces, probing of ice wedges, and analysis 2. of d r i l l h o l e r e c o r d s not prepared f o r t h a t purpose. Elsewhere d e t a i l e d s t u d i e s on s e v e r a l ground i c e types have been c a r r i e d out (Black 1953j Corte 1965). Where exposure i n the t h i r d dimension i s a v a i l a b l e , i t i s c l e a r that the morphology of the ground s u r f a c e may g i v e no i n d i c a t i o n of the presence o f , say, wedges. Mackay (1972a, p. 5) p o i n t s out that "Some (forms) are d i s t i n c t and easy to r e c o g n i z e , whereas others are t r a n s i - t i o n a l and i m p o s s i b l e to i d e n t i f y " . On t h i s p o i n t , i t i s noted t h a t the exact d i s t r i b u t i o n o f i c e bodies i s only p o o r l y known, based on a e r i a l photograph i n s p e c t i o n , a study o f shot h o l e l o g s and l i m i t e d f i e l d mapping. At t h i s macro- s c o p i c s c a l e , a mapping p r o j e c t to a s c e r t a i n the occurrence of v a r i o u s i c e types from sample l o c a t i o n s would b e n e f i t g r e a t l y from a knowledge o f the c h a r a c t e r i s t i c s of the i c e s which are r e a d i l y r e c o g n i z a b l e i n the f i e l d . Where i t i s i m p o s s i b l e t o forward f r o z e n specimens f o r l a b o r a t o r y a n a l y s i s , f e a t u r e s such as g r a i n s i z e , g r a i n shape, sediment and gas content and t h e i r d i r e c t i o n a l s t r u c t u r e s r e l a t i v e to l o c a l ground s u r f a c e are v i t a l parameters f o r t h e i r a c c u r a t e r e c o g n i t i o n . T h i s i s t r u e not only f o r the p r e p a r a t i o n o f maps of v a r i o u s s c a l e s , but a l s o f o r l o c a l knowledge o f subsurface p r o p e r t i e s of the ground, necessary i n any c o n s i d e r a t i o n s o f e n g i n e e r i n g or g e n e r a l c o n s t r u c t i o n schemes. C o n s i d e r i n g the development o f a g i v e n i c y body, growth occurs by a c c r e t i o n o f l a y e r s of c r y s t a l s , as i n the i n f i l l i n g 3. of open i c e wedges, or during the penetration of a freezing front into sediment where water i s available for freezing. "Individual increments of ice average 2 mm per cycle" i n the case of ice wedges (Brown 1966, p. 1) but a wedge does not crack every year, and individuals grow at dif f e r e n t rates. The rates quoted by Brown are considered high for the Mackenzie Delta area (Mackay, personal communication). With t h i s average of less than 2 mm i n mind, i t i s evident that inve s t i g a t i o n must be made at t h i s scale to be useful. Further s o l i d , l i q u i d and gaseous inclusions are of t h i s s i z e , and t h e i r positions r e l a t i v e to c r y s t a l s are meaningful i n terms of growth history. In t h i s area, ice bodies of several ages are known. Also, i n the outer islands of the Mackenzie Delta are exposed masses of underground ice which have been deformed by g l a c i e r ice-thrust. The p o s s i b i l i t y that remnants of the ice-sheet responsible for that deformation exist buried i n the area has not been ruled out. Thus within the f i e l d area, there may occur ices of several origins and subsequent h i s t o r i e s . As an example of the need f o r c r i t e r i a by which to distinguish i c e bodies, an ice c e l l a r i n the settlement of Tuktoyaktuk, N.W.T. was chosen f o r a detailed study of meso- scopic and microscopic form. In addition to the geocryological a t t r i b u t e s , the p a r t i c u l a r c e l l a r was chosen for l o g i s t i c reasons: (a) ease of access i n a l l weathers and (b) l o c a l e l e c t r i c i t y supply for equipment. 4. Statement o f the Problem In the Tuktoyaktuk i c e - c e l l a r a l t e r n a t i n g i c e and i c y sediment bands d i s p l a y i s o c l i n a l f o l d s with s u b - h o r i z o n t a l a x i a l s u r f a c e s and oth e r evidence o f s t r o n g deformation ( P l a t e 1 ) . Thus both the o r i g i n a l i c e growth and the s t r e s s system r e s p o n s i b l e f o r i t s subsequent deformation are of i n t e r e s t . The o b j e c t i v e s of t h i s paper a r e : (1) to e l u c i d a t e the mechanism o f i c e growth and i n c o r p o r a t i o n o f sediment (2) to de c i p h e r the mode of deformation of the sediment-ice system (3) to i n f e r the p o s t - d e f o r m a t i o n a l h i s t o r y of the body, i t s s t r a t i g r a p h i c p o s i t i o n , and the temperature requirements f o r i t s continued e x i s t e n c e (4) to a s c e r t a i n d i s t i n c t i v e f e a t u r e s of the i c e body f o r f u t u r e f i e l d r e c o g n i t i o n from l i m i t e d samples. General approach In o r d e r t o determine the d e f o r m a t i o n a l h i s t o r y of a body o f f o l d e d i c e and sediment, i t i s necessary t o determine as completely as p o s s i b l e the present c o n f i g u r a t i o n o f a l l geometric f e a t u r e s , i . e . , the f a b r i c of the body. Then, assuming an o r i g i n a l c o n f i g u r a t i o n of these f e a t u r e s , a sequence o f movements must be proposed which l e a d from the o r i g i n a l t o the observed geometry. The assumption i s made th a t the o r i g i n a l l a y e r i n g was s u b - h o r i z o n t a l . T h i s i s 5. r e a s o n a b l e , due to the presence of sedimentary s t r u c t u r e s w i t h i n the beds. For any o r i g i n a l and f i n a l c o n f i g u r a t i o n s t h e r e i s an i n f i n i t e number of s t r a i n paths which c o u l d l e a d to the observed s t r u c t u r e s . The p r a c t i c e here i s to take the s i m p l e s t as most l i k e l y . A l s o the mechanism of deformation must be m e c h a n i c a l l y and g l a c i o l o g i c a l l y f e a s i b l e . The p r i n c i p l e of symmetry p l a c e s a l i m i t a t i o n on the i n t e r p r e t a t i o n o f movements. C o n s i d e r i n g the a l t e r n a t e i c e - i c y sediment l a y e r i n g , a means of i n c l u s i o n of sediment w i t h i n i c e must be proposed. The subsequent deformation o f the body Is recorded i n the f o l d morphology and m i c r o - f a b r i c . In o r d e r to understand the meaning o f the c h a r a c t e r i s t i c f o l d forms and m i c r o s c o p i c f e a t u r e s , knowledge i s r e q u i r e d o f the d e f o r m a t i o n a l c h a r a c t e r - i s t i c s o f i c e and i c y sediment. Thus review i s made f i r s t l y of known mechanisms of i n c o r p o r a t i o n of sediment w i t h i n i c e , and secondly of l a b o r a t o r y and f i e l d s t u d i e s of i c e deformation. O r g a n i z a t i o n of T h e s i s The remainder o f the t h e s i s comprises an i n t r o d u c t i o n t o the f i e l d a r e a , f o l l o w e d by:- (a) Chapter I I - a l i t e r a t u r e review o f the mechanisms of i c e growth i n sediment with and without e x t e r n a l over- burden and the entrainment of sediment i n g l a c i e r i c e . 6. (b) Chapter I I I - a l i t e r a t u r e review of deformation o f i c e and the sand-ice system i n l a b o r a t o r y experiments, and the a p p l i c a t i o n of these r e s u l t s to the f i e l d s i t u a t i o n . (c) Chapter IV - a d i s c u s s i o n of the methods o f mesoscopic f o l d a n a l y s i s ; the methods of i c e p e t r o f a b r i c s , i n c l u d i n g s t u d i e s o f o p t i c a x i s o r i e n t a t i o n , g r a i n s i z e , shape, d i s t r i b u t i o n o f i n c l u s i o n s of gas and sediment, and t h e i r i n t e r r e l a t i o n s . (d) Chapter V - r e s u l t s ( i ) mesoscopic s t r u c t u r e s ( i i ) m i c r o s c o p i c s t r u c t u r e s ( i i i ) o p t i c a x i s o r i e n t a t i o n ( i v ) g r a i n shape (v) g r a i n s i z e ( v i ) sediment d i s t r i b u t i o n and s i z e , e f f e c t on i c e c h a r a c t e r i s t i c s ( v i i ) water q u a l i t y a n a l y s i s (e) Chapter VI - C o n c l u s i o n THE FIELD AREA F i e l d work was undertaken i n the v i c i n i t y o f Tuktoyaktuk (69°27' N; 133°00! W), N.W.T. ( F i g . 1) , and shown on map sheet 107C. The g e o g r a p h i c a l nature of the surrounding l a n d area was d e s c r i b e d by Mackay (1963) and Bouchard and Rampton (1971); some submarine f e a t u r e s have been d i s c u s s e d by Shearer et a l 7. (1971) and Mackay ( 1 9 7 2 ) . Tuktoyaktuk i s s i t e d on the P l e i s t o c e n e C o a s t a l P l a i n , i n an area o f " U n d i f f e r e n t i a t e d C o a s t l a n d s " (Mackay 1 9 6 3 , p. 1 3 7 ) . The co a s t l a n d s i n gen e r a l have over 15% of the s u r f a c e l a k e - c o v e r e d , t h i s f i g u r e r i s i n g to over 50% around Tuktoyaktuk. There a l s o are channels t e n d i n g t o produce an indented c o a s t l i n e , as at Tuktoyaktuk harbour, although s p i t growth causes some smoothing-off. C o a s t a l r e c e s s i o n i s o c c u r r i n g , causing drainage of l a k e s , i n which pingos may grow. Another major f e a t u r e i s the i n v o l u t e d h i l l , o c c u r r i n g t o the east and southwest o f the f i e l d r e g i o n . These h i l l s have r e l i e f o f 100 t o 150 f e e t , r i s i n g i n a stepped manner, there o c c u r r i n g r i d g e s on step edges. Where slumping produces an exposure, e x t e n s i v e ground i c e i s seen, o v e r l a i n by t i l l - l i k e m a t e r i a l i n which i c e wedges have grown. The Quaternary h i s t o r y o f the r e g i o n has been d i s c u s s e d by Mackay ( 1 9 6 3 ) , Mackay and Stager ( 1 9 6 6 ) , Mackay et a l ( 1 9 7 2 ) , Rampton ( 1 9 7 0 , 1 9 7 1 , 1 9 7 2 a , b) and Rampton and Mackay ( 1 9 7 1 ) . In summary, i t may be s t a t e d t h a t the m a j o r i t y o f the c o a s t a l p l a i n l i e s w i t h i n the i n f e r r e d l i m i t s o f c o n t i n e n t a l g l a c i a t i o n . A v a i l a b l e r a d i o c a r b o n dates (Mackay et a l 1 9 7 2 , p. 1321) i n d i c a t e t h a t the n o r t h e r n l i m i t of the " c l a s s i c a l " Wisconsin i c e l i e s south o f a l i n e Richards I s l a n d — n o r t h e r n Tuktoyaktuk p e n i n s u l a , and n o r t h o f S i t i d g i Lake. Mackay et a l ( 1 9 7 2 , P i g . 1) p l a c e the l i m i t approximately mid-way between S i t i d g i Lake and the settlement o f Tuktoyaktuk ( P i g . 2 ) . 8. Thus, the c h a r a c t e r i s t i c f e a t u r e s are not d i r e c t r e s u l t s of g l a c i a t i o n , but l a k e s , f o r example, are of thermokarst o r i g i n ; p o s i t i v e r e l i e f f e a t u r e s mainly r e s u l t from v a r i o u s ice-growth p r o c e s s e s , d i s c u s s e d l a t e r . The s u r f i c i a l geology o f the Tuktoyaktuk area comprises f i n e t o medium gr a i n e d P l e i s t o c e n e sands, i n t h i c k n e s s e s o f 100 f e e t and more, capped i n p l a c e s by a cl a y e y diamicton up to 25 f e e t t h i c k (Rampton and Mackay 1971, p. 5)- T h i s diamicton v a r i e s with l o c a l i t y from t i l l to mudflow o r pond- de p o s i t . S e v e r a l types of massive i c e and i c y sediments i n t h i s r e g i o n have been noted by Rampton and Mackay (1971): pingo core i c e , massive i c e i n a c o a s t a l slump, a l t e r n a t i n g i c e and i c y sediment In an underground c e l l a r . A d d i t i o n a l i c e - types have been d e s c r i b e d by Mackay (1972a) as: - t e n s i o n crack i c e , a g g r a d a t i o n a l i c e and s i l l i c e . A l s o the p o s s i b i l i t y of b u r i e d g l a c i e r i c e has not been d i s c o u n t e d (Mackay 1972a, p. 5 ) . G l a c i a l deformation o f massive ground i c e has been d i s c u s s e d by Mackay (1956, 1959, 1963, 1971); Mackay and Stager (1966); Pyles (1966); Kerfoot (1969), i n the c o a s t a l area between H e r s c h e l I s l a n d and Ni c h o l s o n P e n i n s u l a . 9. CHAPTER I I ICE GROWTH IN SEDIMENT AND THE ENTRAINMENT OP SEDIMENT IN GLACIER ICE - A LITERATURE REVIEW I n t r o d u c t i o n The i c e body under c o n s i d e r a t i o n d i s p l a y s a l t e r n a t i n g l a y e r s of i c e and i c y sediment. I t i s thus necessary to e x p l a i n the v a r i a t i o n i n sediment content and the p a r t i c u l a r g r a i n s i z e i n a given band. The mesoscopic f o l d form suggested, on the f i r s t examination, a s t r o n g s i m i l a r i t y to f o l d s d e s c r i b e d from t e r m i n a l r e g i o n s of present-day i c e sheets. A l s o the Tuktoyaktuk area has been g l a c i a t e d and the sugg e s t i o n has been made t h a t g l a c i e r remnants may u n d e r l i e p a r t s o f the area. Massive beds of segregated i c e deformed by o v e r - r i d i n g i c e sheets are known i n the a r e a . Thus an important aspect of t h i s study i s to attempt t o d i s t i n g u i s h among p o s s i b l e o r i g i n s o f the Tuktoyaktuk i c e , namely: (a) formation as p a r t of an i c e sheet, (b) segregated i c e which was l a t e r deformed, and (c) o t h e r . The present f a b r i c i s a f u n c t i o n of the o r i g i n a l f a b r i c , thus d i s c u s s i o n i s made of p o s s i b l e p r e - d e f o r m a t i o n a l geometries. 1 0 . Ice-Growth In Sediment The o r i g i n of i c e l a y e r s and cement i n sediment has been d i s c u s s e d by W i l l i a m s (1967) and a p p l i c a t i o n o f t h e o r i e s to the f i e l d s i t u a t i o n i n permafrost areas o f Western A r c t i c Canada has been made by Mackay (1971)• A d i s t i n c t i o n i s made between f r e e z i n g o f a p r e v i o u s l y u n c o n s o l i d a t e d sediment by downward p e n e t r a t i o n of a f r e e z i n g f r o n t , from the ground s u r f a c e , and the f r e e z i n g at the base of an i c e sheet, i . e . , beneath an overburden other than the s o i l and ground i c e . F r e e z i n g Without Overburden In u n c o n s o l i d a t e d sediment, segregated i c e forms when pore water p r e s s u r e i s h i g h , pore i c e when i t i s low. We have p^ = pressure of the i c e p = water p r e s s u r e w a. = ice-water s u r f a c e t e n s i o n iw r = r a d i u s of s o i l pore to permit advance of f r o s t l i n e When p. - p . < 2 g i w s e g r e g a t i o n i c e r P i - P w > ^°iw pore i c e r V a r i a t i o n s i n water supply, s o i l water movement and heat e x t r a c t i o n give r i s e to a l t e r n a t i o n s between the two types (Williams 1 9 6 7 , Mackay 1 9 7 2 a , p. 1 7 ) . 11. D i s c u s s i o n has u s u a l l y c o n s i d e r e d the downward p e n e t r a t i o n o f a f r e e z i n g f r o n t ; however l a t e r a l and upward s h i f t s are p o s s i b l e , as from the base of the a c t i v e l a y e r i n w i n t e r , and i n t o a s l i p f a c e . W i l l i a m s (1967, p. 96) a l s o examined the i n f l u e n c e of a i r on f r e e z i n g i n u n s a t u r a t e d s o i l s , whereby p e r m e a b i l i t y i s reduced and pore-water pressure i s a f f e c t e d . O b servation o f s e g r e g a t i o n i c e i n d i c a t e s gas bubbles to be p r e s e n t . Mackay and Stager (1966) noted elongated bubbles a l i g n e d normal to the l a y e r i n g of i c e l e n s e s . Elsewhere s p h e r i c a l bubbles occur. F a b r i c of Segregated Ice The i c e g r a i n f a b r i c i n segregated i c e i s a f u n c t i o n of n u c l e a t i o n and e p i t a x i a l growth. At the i n i t i a l stage of i c e c r y s t a l l i z a t i o n i n sediment, random n u c l e i form. Some grow r a p i d l y to c r i t i c a l s i z e and s u r v i v e ; others r e d i s s o l v e . Of the s u r v i v o r s , those with c-axes o r i e n t e d p a r a l l e l to the d i r e c t i o n of heat flow grow most r e a d i l y . In the case of a downward p e n e t r a t i n g f r e e z i n g f r o n t , a v e r t i c a l p r e f e r r e d o r i e n t a t i o n would be expected. I n c o r p o r a t i o n of Sediment Into Ice Sheets Weertman (1957, 1964) developed a model f o r the move- ment o f g l a c i e r s over o b s t r u c t i o n s through two p r o c e s s e s : (a) s t r e s s c o n c e n t r a t i o n on the u p - g l a c i e r s i d e l e a d i n g to 12. g r e a t e r s t r a i n r a t e s and thus a c c e l e r a t e d p l a s t i c flow, and (b) i c e m e l t i n g on the high p ressure s i d e and r e f r e e z i n g on the low pre s s u r e s i d e . Kamb and LaChapelle (1964) observed s l i d i n g at the base o f Blue G l a c i e r , and d e s c r i b e d a c l e a r , b u b b l e - f r e e i c e l a y e r up t o 3 cm t h i c k , d i s t i n g u i s h a b l e by t e x t u r e and s t r u c t u r e from the o v e r l y i n g i c e , which they r e f e r r e d t o as r e g e l a t i o n i c e . On the b a s i s o f o b s e r v a t i o n s and experiments, Kamb and LaChapelle concluded t h a t p l a s t i c flow due to s t r e s s c o n c e n t r a t i o n s i s of l i t t l e importance. F u r t h e r Barnes and Tabor (1966) i n v e s t i g a t e d the hardness o f i c e ; with s p e c i a l l y prepared bubbly i c e , the i c e i n the zone a f f e c t e d by pre s s u r e became t r a n s p a r e n t i n comparison to the surrounding bubbly i c e , s u p p o r t i n g Kamb and LaChapelle's s u g g e s t i o n . I t i s apparent t h a t r e g e l a t i o n i s e s s e n t i a l to b a s a l s l i d i n g ( i n the absence o f s u r g i n g ) . Two major hypotheses have been propounded f o r the i n c o r p o r a t i o n o f e n g l a c i a l m a t e r i a l . The Shear Hypothesis The s u g g e s t i o n i s that s h e a r i n g occurs and m a t e r i a l i s t r a n s p o r t e d along d i s c r e t e f a i l u r e s u r f a c e s . M a t e r i a l i s assumed t o be scraped i n t o shear s u r f a c e s by d i f f e r e n t i a l i c e movements. However, from d e s c r i p t i o n s o f d e b r i s b a n d s — dense l a y e r s o f sand and boulders 0.5 m t h i c k , and l a y e r s of f i n e l y disseminated sediment p a r t i c l e s 1 t o 2 m t h i c k , the suggested mode of i n c o r p o r a t i o n seems u n l i k e l y . Further, Goldthwait (1951 p. 569) d e s c r i b e d "shear p l a n e s " i n the Barnes Ice Cap which curved around boulders and t i l l c l o t s , forming a u g e n - l i k e s t r u c t u r e s . P l a s t i c deformation i s more ac c e p t a b l e than b r i t t l e f a i l u r e as an e x p l a n a t i o n of the l a t t e r f e a t u r e . Recently Gow (1972) r e p o r t e d s i m i l a r s t r u c t u r e s i n the Garwood G l a c i e r , A n t a r c t i c a . Weertman's Theory Weertman (1961 p. 968) d i s c o u n t e d the shear hypothesis on s e v e r a l grounds, i n c l u d i n g t h at of the c l o s e p r o x i m i t y of d e b r i s l a y e r s . I f the sediment h o r i z o n s are of shear o r i g i n , then c l o s e l y - s p a c e d shear s u r f a c e s must e x i s t . Simple t e c t o n i c theory p r e c l u d e s t h i s . There i s no reason why y i e l d should cease along one plane o f weakness and a new plane form l e s s than 1 cm away. F u r t h e r , i n v e s t i g a t i o n s of movement along d e b r i s s u r f a c e s exposed on t u n n e l s i d e s have p r o v i d e d no evidence o f d i s c r e t e shears. B u t k o v i t c h and Landauer (I960) r e c o r d e d no s h e a r i n g motion across d e b r i s l a y e r s , although d i f f e r e n t i a l flow o c c u r r e d i n the i c e . Abel ( i n Swinzow 1962, p. 223) found t h a t bands o f d e b r i s gave i n c r e a s e d d i f f e r e n t i a l flow. Weertman (1961, p. 270) proposed a f r e e z i n g model t o e x p l a i n T h u l e - B a f f i n moraines, a r g u i n g that water produced by m e l t i n g i n i n l a n d p a r t s of an i c e sheet moves down the p r e s s u r e g r a d i e n t t o a r e g i o n where the temperature g r a d i e n t i n the i c e can conduct away more heat than i s produced by s l i d i n g o r comes from geothermal heat. Water i s c o n s i d e r e d to r e f r e e z e onto the i c e sheet. A c c o r d i n g to t h i s t h e o r y , a s h i f t i n the amount o f heat produced due to s l i d i n g w i l l l e a d t o a f r e e z i n g - i n o f d e b r i s , as the 0°C s u r f a c e passes down. R e p e t i t i o n of the c y c l e leads to m u l t i p l e l a y e r s . However, t h i s n e c e s s i t a t e s frequent s h i f t s i n the p o s i t i o n o f the m e l t i n g p o i n t isotherm; such r a p i d changes i n the thermal regime o f the b a s a l r e g i o n are u n l i k e l y . F u r t h e r , Williams ( 1 9 6 7 , P- 108) p o i n t s out t h a t , due t o overburden pressure o f an i c e mass, sediment below an i c e sheet cannot have i c e i n i t s pores, u n l e s s t h e r e i s an a s s o c i a t e d i n c r e a s e of i c e t h i c k n e s s . Other t h e o r i e s A l a t e r theory by Boulton (1970) has as i t s b a s i s the f r e e z i n g - o n mechanism, i n t h i s case the source of sediment being an a c t i v e l y eroded rock p r o j e c t i o n where p a r t i c l e s f r e e z e with r e g e l a t i o n i c e , the bands so formed being sub- sequently f o l d e d . Souchez (1967) had p r e v i o u s l y a l l u d e d to t h i s process i n a study o f V i c t o r i a Land, but i n that case no f o l d i n g o c c u r r e d . Souchez d e s c r i b e d the g l a c i e r bed as c o n s i s t i n g o f rock fragments of d i f f e r e n t s i z e s , r a n g i n g from s i l t t o bl o c k s and s l a b s ( 1 9 6 7 , P- 841). Thus a g r a i n - s i z e s e l e c t i v e process was necessary t o e x p l a i n the 12 mm diameter s i z e i n d e b r i s bands. He suggests t h a t the 15. r e g e l a t i o n process accounts f o r t h i s . A second type o f d e b r i s band, c u t t i n g , and thus younger than the f i r s t , was d e s c r i b e d by Souchez as o b l i q u e to the g l a c i e r margin, and c o n t a i n i n g coarse m a t e r i a l , but no f i n e s . Hooke (1969) r e p o r t e d t h a t i n h i s Greenland s t u d i e s , d e b r i s l a y e r s were seen to c o n t a i n a l l s i z e s of m a t e r i a l and f l u v i a l s t r a t i f i c a t i o n was r e t a i n e d i n some c a s e s — s u c h would not be p r e s e r v e d i f b l o c k s were "sheared" i n t o the i c e . F u r t h e r , Hooke (1969, p. 351) suggested t h a t the secondary bands mentioned by Souchez were i n f a c t crevasses i n f i l l e d from above. Thus th e r e occurs i n the l i t e r a t u r e disagreement con- c e r n i n g the o r i g i n of sediment i n present-day i c e sheet and g l a c i e r bases. What i s agreed i s that sediment, u s u a l l y f i n e s , occurs, that bands may become h i g h l y f o l d e d , and shears may be p r e s e n t . A r e c e n t note by Gow (1972) c o n t a i n s a d e s c r i p t i o n of a l t e r n a t i n g l a m i n a t i o n s o f sand and dust, and d i r t - f r e e i c e i n A n t a r c t i c a . The d e b r i s was c o n s i d e r e d to be o f p e r i o d i c d e p o s i t i o n d e r i v e d by wind from sources o f exposed rock and v o l c a n i c ash. Gow (1972, p. 101) a l s o r e f e r r e d to t h i c k sand and g r a v e l sequences, which were h i g h l y f o l d e d (Gow, F i g . 2) but s t i l l e x h i b i t s i z e s o r t i n g , c r oss-bedding and l e n s i n g — c h a r a c t e r i s t i c s of water d e p o s i t i o n . Gow argued t h a t the l e v e l of occurrence i n the i c e p r e c l u d e d o r i g i n at the g l a c i e r bed, but favoured d e p o s i t i o n at the top o f the g l a c i e r . 16. C o n s i d e r i n g the f i r s t s u ggestion o f w i n d - t r a n s p o r t , l i t t l e mention has been made of t h i s by oth e r authors. Goldthwait (I960) r e c o r d e d t h a t only 0.1$ of sediment t r a n s p o r t around the i c e - c l i f f at Nunatarrsuaq (Greenland) was by wind. No sugg e s t i o n was made o f i n c o r p o r a t i o n o f such m a t e r i a l i n t o the i c e sheet t h e r e . In agreement with the case o f f l u v i a l t r a n s p o r t o f m a t e r i a l , N i c h o l s (1964) r e p o r t e d undeformed in t e r b e d d e d l a y e r s of f l u v i a t i l e cross-bedded sand and g r a v e l l e s s than 0.5 m t h i c k d e p o s i t e d i n summer on the p r e v i o u s w i n t e r ' s snow accumulation. During the course of a long-term d e t a i l e d study o f a present-day i c e - s h e e t terminus, Goldthwait (I960) c o n s i d e r e d the o r i g i n and f o l d i n g o f d i r t bands. Observations over s e v e r a l years i n a r t i f i c i a l t u n n e l s , s u b g l a c i a l caverns and stream r o u t e s i n d i c a t e d t h a t "some or a l l of the d i r t now c i r c u l a t i n g near the i c e f r o n t i s simply r e i n c o r p o r a t e d i n the b a s a l l a y e r s o f i c e as the white i c e of the g l a c i e r above advances onto i t s n e a r l y stagnant d i r t - c o v e r e d toe i c e " (Goldthwait I960, p. 71). A stream s e c t i o n e x h i b i t e d the s u c c e s s i v e i n c o r p o r a t i o n o f t h i s superimposed i c e and d i r t i n t o the body, y e a r l y accumulations being i d e n t i f i e d by "deadmen" s t a k e s . Thus a c y c l i c a l process was envisaged, whereby sediment became i n c l u d e d i n t o the i c e , then f o l d e d and sheared, moving p r o g r e s s i v e l y t o the c l i f f face t o f a l l t o the toe and r e s t a r t the c y c l e . A c c o r d i n g t o Goldthwait the c y c l e might take as l i t t l e as 25 years o r as much as 17- 12 c e n t u r i e s . The e x i s t e n c e of i s o c l i n a l f o l d s i n the t e r m i n a l r e g i o n was noted by Goldthwait (I960, p. 68) and by M e r r i l l (1957) t o occur on s e v e r a l s c a l e s . Studies of the motion of the c l i f f r e v e a l e d t h a t the upper p a r t moved twice as f a s t as the lower, s h e a r i n g motion being l a r g e l y c o n c e n t r a t e d at the base of a v e r t i c a l c l i f f . D e spite s t r o n g s h e a r i n g , the i c e surrounding the rocks on the g l a c i e r bed had not moved i n l e s s than 200 y e a r s , as moss, l i c h e n and v a s c u l a r p l a n t s of that age were p e r f e c t l y p r e s e r v e d . While one l a y e r becomes f o l d e d w i t h i n the a c t i v e l y deforming i c e subsequent l a y e r s are added below. Thus a l l stages o f f o l i a t i o n geometry would be expected at a given time, from sub-planar beds through open f o l d s to more t i g h t l y appressed limbs. T h i s c o u l d occur while the i c e sheet was s t a t i o n a r y or moving (Boulton 1970). F a b r i c of undeformed b a s a l i c e In the s t u d i e s reviewed above, no c o n s i d e r a t i o n was g i v e n to i c e t e x t u r e s . Kamb and LaChapelle (1964) mentioned that r e g e l a t i o n i c e was d i s t i n g u i s h a b l e from o v e r l y i n g i c e by s t r u c t u r e and t e x t u r e , but d i d not say how. Other workers ig n o r e d the t o p i c . By analogy with s e g r e g a t i o n i c e growth i t i s suggested t h a t , as a body o f i c e i s present as a n u c l e u s , new g r a i n s w i l l grow with c-axes approximately p a r a l l e l to the d i r e c t i o n of l o c a l heat flow. T h i s assumes the absence 18. of s t r e s s . Under a c t i v e s t r e s s b a s a l planes would be o r i e n t a t e d to accommodate t h a t s t r e s s . C o n c l u s i o n S e v e r a l mechanisms have been propounded t o account f o r the presence o f extended sediment l a y e r s i n undeformed and i n deformed i c e . In the case o f rhythmic i c e banding i n s o i l s , a l t e r n a t e bands of h i g h i c e content and h i g h sediment content r e s u l t from l o c a l v a r i a t i o n s i n i c e n u c l e a t i o n and growth, the a v a i l a b i l i t y o f water and i t s flow to the f r e e z i n g f r o n t , and the removal of heat. Such a theory would e x p l a i n the v e r t i c a l changes i n sediment content i n the p r e d e f o r m a t i o n a l s t a t e of the Tuktoyaktuk i c e . L a t e r a l changes i n bed t h i c k n e s s would a l s o be expected. In t h i s case the sediment s i z e would be a f u n c t i o n of p r e - f r e e z i n g d e p o s i t i o n . The f r e e z i n g process would not be g r a i n - s i z e s e l e c t i v e , although sandy l a y e r s would be separated by i c e l e n s e s along s i l t y laminae. C o n s i d e r i n g sediment entrainment i n i c e sheets, s e v e r a l t h e o r i e s have been advanced. The shear hypothesis i s d i s c o u n t e d , as shears separated by only a few centimeters are u n l i k e l y , but t h i s does not mean that shears do not occur. Freezing-on of f i n e - g r a i n e d sediment at g l a c i e r bases has been d e s c r i b e d from areas w i t h d i f f e r e n t s i z e d fragments at the bed. Thus a g r a i n - s i z e s e l e c t i v e process i s p o s s i b l e . In t h i s case w a t e r - q u a l i t y would be expected to be s i m i l a r to that o f l o c a l ground water, i n c o n t r a s t to water chemistry i n i c e 19. at upper l e v e l s on the same g l a c i e r where f i n e g r a i n e d m a t e r i a l c o u l d be of wind-blown o r i g i n . Thus i n a d d i t i o n to the p a t t e r n o f sediment i n the i c e , c o n s i d e r a t i o n must be given t o g r a i n s i z e , t o determine i t s mode of t r a n s p o r t , and water q u a l i t y i n comparison t o c h a r a c t e r - i s t i c p r o p e r t i e s o f i c e of known g l a c i e r o r i g i n , and other i c e bodies i n the Tuktoyaktuk area. 20. CHAPTER III DEFORMATION OF ICE AND THE SAND-ICE SYSTEM Introduction The i c e body beneath Tuktoyaktuk contains layers of ice with dispersed sediment, and other layers with high sediment content. These bands vary i n thickness and i n l a t e r a l extent i n t h e i r present state, and i n some cases 2 or more layers merge into one. Under conditions of deformation the several types of material would be expected to behave d i f f e r e n t l y . As pressure and temperature fluctuated so would the r e l a t i v e "competences" change. The o r i g i n a l pre-deformational f o l i a t i o n i s assumed as sub-parallel ice and i c y sediment bands. The f o l i a t i o n attitude i s considered to have been sub-horizontal, evidence being the orientation of retained sedimentary structures r e l a t i v e to the p r e v a i l i n g f o l i a t i o n . A deformational path from the o r i g i n a l geometry to the presently observed f a b r i c must be proposed. The deformation mechanisms must be not only geometrically r e a l i s t i c , but also g l a c i o l o g i c a l l y f e a s i b l e . Thus consideration must be given to the known properties of ice under varying conditions of loading. Sediment occurs i n some of the i c e , thus the r e l a t i v e deformabilities of sediment-free and sediment-rich ice must be investigated. The deformation ceased thousands of years 2 1 . ago, thus p o s t - d e f o r m a t i o n a l processes l n Ice r e q u i r e i n v e s t i - g a t i o n , and means o f r e c o g n i t i o n of a s s o c i a t e d p r o p e r t i e s enumerated. Chapter O u t l i n e I t i s thus necessary t o c o n s i d e r the r e p o r t e d r e s u l t s of l a b o r a t o r y and f i e l d s t u d i e s on i c e deformation. D i s c u s s i o n i s i n t r o d u c e d by a l i t e r a t u r e review of s i n g l e - c r y s t a l response to l o a d i n g . T h i s i s f o l l o w e d by a summary of the deformation p r o p e r t i e s of pure i c e c r y s t a l aggregates under c o n d i t i o n s of t e n s i o n , compression and s h e a r i n g f o r v a r y i n g s t r e s s e s , times and temperatures. The m i c r o s c o p i c f e a t u r e s i n d i c a t i v e of such deformation are d i s c u s s e d , based on Gold's work (Gold 1 9 6 3 ) . I n v e s t i g a t i o n i s then made of the a d d i t i o n a l e f f e c t o f i n c l u d e d sediment i n v a r y i n g p r o p o r t i o n s . Review of Experimental Deformation of Ice Por a study of a deformed body such as i s under c o n s i d e r - a t i o n , knowledge Is r e q u i r e d of the d e f o r m a t i o n a l c h a r a c t e r i s t i c s of pure i c e and i c e c o n t a i n i n g v a r i o u s p r o p o r t i o n s of sediment. I n v e s t i g a t o r s have s t u d i e d both a c t i v e l y deforming g l a c i e r s and prepared samples i n the l a b o r a t o r y . T h i s review w i l l d i s c u s s the r e s u l t s of c o n t r o l l e d experiments, separate c o n s i d e r a t i o n being given to d e f o r m a t i o n a l p r o p e r t i e s of s i n g l e c r y s t a l s and of p o l y c r y s t a l l i n e i c e . (a) S i n g l e C r y s t a l s McConnell ( 1 8 9 1 ) e s t a b l i s h e d t h a t s i n g l e c r y s t a l s deform p l a s t i c a l l y by g l i d e on the b a s a l plane. The m a j o r i t y o f evidence i n d i c a t e s that t h i s i s the only e f f e c t i v e s l i p s u r f a c e (Glen and Perutz 1 9 5 4 ; Steinemann 1 9 5 4 ; Kamb 1 9 6 1 ) ; however, Muguruma et a l (1966) r e p o r t e d non-basal g l i d e , r e q u i r i n g a s t r e s s 20 times g r e a t e r than f o r b a s a l g l i d e . C o n s i d e r i n g the b a s a l s l i p p l a n e s , Nakaya ( 1 9 5 8 ) demonstrated t h a t s l i p bands are c o n c e n t r a t e d i n t o a s e r i e s of zones approximately 0.06 mm apart and p a r a l l e l t o the b a s a l plane. P r e v i o u s l y Steinemann ( 1 9 5 4 ) had found no d i r e c t i o n o f e a s i e s t g l i d e w i t h i n the g l i d e plane. Other workers (Griggs and Coles, ( 1 9 5 4 ) ; Steinemann ( 1 9 5 4 ) ; J e l l i n e k and B r i l l ( 1 9 5 6 ) ) concluded from measurements of s i n g l e c r y s t a l creep t h a t f o r a given s t r e s s , the r a t e o f s t r a i n i n c r e a s e s with time, and the i c e i s s a i d to be s o f t e n e d . (b) P o l y c r y s t a l l i n e Ice On the b a s i s o f s i n g l e c r y s t a l r e s u l t s i t f o l l o w s t h a t i n a p o l y c r y s t a l l i n e aggregate where i n d i v i d u a l g r a i n o r i e n t a t i o n i s random ( i n the present argument) m a t e r i a l c o n t i n u i t y demands t h a t other mechanisms operate to permit contiguous g r a i n s to conform to a r b i t r a r y shape changes. G r a i n boundaries i n t r o d u c e c o n s t r a i n t s to d i s l o c a t i o n w i t h i n a g i v e n g r a i n . I f g r a i n i n t e g r i t y i s to be p r e s e r v e d , each must deform i n a manner compatible with i t s immediate neighbours. G r a i n o r i e n t a t i o n determines the c o n s t r a i n t , thus the observed deformation i n p o l y c r y s t a l l i n e i c e r e s u l t s from i n d i v i d u a l g r a i n s attempting to deform s i n g l y , but being compromised by o t h e r s . Analogies between s i n g l e c r y s t a l deformation and p o l y c r y s t a l l i n e behaviour are not of great v a l u e . Laboratory o b s e r v a t i o n s on i c e creep have shown a dependence on s t r e s s o r i e n t a t i o n , temperature, time and i m p u r i t i e s . ( i ) S t r e s s O r i e n t a t i o n In an e a r l y study, Bader et a l ( 1 9 3 9 ) deformed i c e b l o c k s , then measured the o r i e n t a t i o n of up t o 40 g r a i n s per sample. (For comments on v a l i d i t y o f such sample s i z e , see Chapter I V ) . Samples were deformed: (a) i n compression; (b) i n t e n s i o n ; and (c) i n shear. A compressed sample showed p r e f e r r e d o r i e n t a t i o n with a l l 26 g r a i n s w i t h i n a g i r d l e 2 0 ° to 4 5 ° from the unique s t r e s s . Deformation i n t e n s i o n of another sample f o r 49 days l e d to a x i a l groupings w i t h i n 4 5 ° of the i n f e r r e d t e n s i o n a l a x i s . Shearing of a specimen f o r 6 days at 4 kg cm produced an a x i a l d i s t r i b u t i o n diagram showing 4 p r e f e r r e d d i r e c t i o n s , 2 i n the plane c o n t a i n i n g the shear. The authors concluded t h a t the t r a n s l a t i o n plane f o r i c e i n compression i s normal to the s t r e s s a x i s , i n t e n s i o n i t i s p a r a l l e l t o the t e n s i o n a x i s , and i n shear p a r a l l e l t o the shear plane. C o n s i d e r i n g c r y s t a l o r i e n t a t i o n , Steinemann ( 1 9 5 8 , p. 48) found a f a b r i c s i m i l a r t o t h a t of Bader f o r a sample i n compression, most axes b e i n g 2 0 ° t o 5 0 ° from the unique a x i s . Stanley (1965) experimented with i c e i n compression, and produced diagrams f o r specimens r e c r y s t a l l i z e d under s t r e s s , showing maxima i n a 30°- 50° s m a l l c i r c l e c e n t r e d on the s t r e s s a x i s , with maxima of 3 t o 5%> S t a n l e y argued that i n c l i n a t i o n s o f 45° to the s t r e s s a x i s would r e s u l t i f g r a i n s c r y s t a l l i z e d with b a s a l planes p a r a l l e l i n g the plane o f maximum shear s t r e s s , but found t h a t i n p r a c t i c e , planes o f f a i l u r e are at l e s s than the 45° angle p r e d i c t e d . Were b a s a l planes p a r a l l e l t o such f a i l u r e s u r f a c e s , the c-axes should be at i n c l i n a t i o n s of 45° t o 75° from the s t r e s s a x i s . S t a n l e y (1965, p. 158) e x p l a i n e d the c - a x i s i n c l i n a t i o n by assuming the b a s a l planes t o be s u b p a r a l l e l t o s u r f a c e s o f r h e i d flow. For i c e r e c r y s t a l l i z e d i n t e n s i o n experiments, c-axes tend to be i n c l i n e d at high angles t o the t e n s i o n a x i s . However, few f a b r i c s have been determined f o r t h i s c o n d i t i o n . Bader et a l (1939) made the f i r s t attempt at c o r r e l a t i o n between s t r e s s and o r i e n t a t i o n o f i c e c r y s t a l s , and i n d i c a t e d c r y s t a l growth o c c u r r e d i n i c e under shear. Perutz (1940, p. 133) s t a t e d that an i n c r e a s e i n g r a i n s i z e i s the i n e v i t a b l e r e s u l t of s t r a i n , thus c o r r o b o r a t i n g the ob s e r v a t i o n s o f Bader et a l . The experiments of Steinemann (1958) i n d i c a t e d the occurrence of "primary parakinematic r e c r y s t a l l i z a t i o n " , i . e . , an i n c r e a s e i n g r a i n s i z e d u r i n g l o a d , i n a d d i t i o n t o the normal i n c r e a s e i n s i z e on l o a d r e l e a s e ("postkinematic r e c r y s t a l l i z a t i o n " ) . The above agreement on the r o l e o f s t r e s s i n c r y s t a l growth i s not u b i q u i t o u s i n the l i t e r a t u r e . In the experiments o f Shumskii (1958, p. 2 4 6 ) , r e c r y s t a l l i z a t i o n under s t r e s s r e s u l t e d i n a r e d u c t i o n o f average g r a i n s i z e . From work on the Blue G l a c i e r , Kamb (1959) r e l a t e d f i n e l a y e r s to h i g h s t r e s s zones, and coarse l a y e r s t o zones of very weak s t r e s s . F u r t h e r , Glen (1958) and Seligman (1949) suggested a c l o s e r e l a t i o n s h i p between s m a l l g r a i n s and h i g h s t r e s s . ( i i ) Temperature The disagreements i n o b s e r v a t i o n s are probably r e l a t e d t o the i c e temperature d u r i n g deformation. Near 0°C, i c e r e c r y s t a l l i z e s so that a r a p i d i n c r e a s e i n g r a i n s i z e occurs (Rigsby I960, p. 606). I t i s noted t h a t the experiments r e p o r t e d above i n which a p p l i e d s t r e s s r e s u l t e d i n g r a i n s i z e i n c r e a s e , were not temperature c o n t r o l l e d . In the work o f Bader et a l (1939, p. 53) the i c e was s u b j e c t e d -2 to average s t r e s s e s of 4.5 kg cm at c o l d room temperatures of -4°C t o -5°C. I t may be argued t h a t temperature was of more importance than s t r e s s . Rigsby ( I 9 6 0 , p. 604) found t h a t " R e c r y s t a l l i z a t i o n a f t e r deformation i s much r e t a r d e d at lower temperatures, and i s extremely slow below about -5°C. Below about -10°C, r e c r y s t a l l i z a t i o n appears t o have almost stopped". However, these experiments were o f shor t d u r a t i o n — e x t r a p o l a t i o n t o the g e o l o g i c a l time s c a l e i s not n e c e s s a r i l y j u s t i f i e d . ( i i i ) S t r e s s - r e l e a s e C o n s i d e r i n g the r o l e o f s t r e s s - r e l e a s e i n c r y s t a l growth, Seligman (1950) r e p o r t e d an 8 - f o l d i n c r e a s e i n c r y s t a l s i z e i n i c e b l o c k s removed from a g l a c i e r t u n n e l i c e - f a c e and l e f t t o stand. Although s u g g e s t i n g s t r e s s r e l e a s e t o be the dominant mechanism, he d i d not r u l e out the p o s s i b i l i t y t h a t the temperature f a c t o r c o n t r i b u t e d i n the form o f a i r c i r c u l a t i o n . In an experimental attempt t o e s t a b l i s h a r e l a t i o n s h i p between g r a i n s i z e and s t r e s s r e l e a s e , Glen (1955) s u b j e c t e d i c e t h i n s e c t i o n s to s t r e s s e s , and found t h a t under 8.5 kg —2 —2 cm s t r e s s s m a l l e r c r y s t a l s r e s u l t e d than under 3.6 kg cm Ice s u b j e c t e d t o 5 kg cm r e c r y s t a l l i z e d i n the s e c t i o n , i n d i c a t i n g the t r a p p i n g of l a r g e s t r e s s e s . ( i v ) H y d r o s t a t i c S t r e s s Rigsby (1958) concluded t h a t temperature i s f a r more important than h y d r o s t a t i c p r e s s u r e i n both r e g u l a t i o n of deformation r a t e , and r a t e of r e c r y s t a l l i z a t i o n . Glen (1958, p. 26l) r e p o r t s the unpublished work o f Steinemann who s t u d i e d the e f f e c t of h y d r o s t a t i c p r e s s u r e s up to 80 kg _2 cm on the r a t e o f shear s t r a i n o f ring-shaped specimens. No d e f i n i t e e f f e c t was found; t h i s , i n c o n j u n c t i o n w i t h Rigsby's experiments f o r s i n g l e c r y s t a l s , i s evidence that h y d r o s t a t i c p r e s s u r e has no d i r e c t e f f e c t on the p l a s t i c p r o p e r t i e s of i c e . 27. (v) Time The importance of the time f a c t o r i n the s t r a i n and growth o f i c e i s p o o r l y understood. A p r o p o s a l by Demorest ( i n Knopf, 1953) t h a t c r y s t a l deformation leads to an unstable l a t t i c e which r e c r y s t a l l i z e s i n s t a n t a n e o u s l y was r e f u t e d by Glen ( i n Knopf 1953, p. 219). The c o n d i t i o n s assumed by Demorest l e a d t o a d e f i n i t e but sometimes slow growth r a t e . Knopf claime d t h a t r e c r y s t a l l i z a t i o n o c c u r r e d w i t h i n "a few minutes" i n Ice near the m e l t i n g p o i n t ; hence again the r o l e o f temperature i s i n d i c a t e d . (c) M i c r o s c o p i c f e a t u r e s i n d i c a t i v e o f Deformation As d i s c u s s e d e a r l i e r s i n g l e c r y s t a l s o f i c e deform by s l i p on the b a s a l planes o f the l a t t i c e . At g r a i n c o n t a c t s ( i . e . , boundaries) changes occur, g r a i n s r i g i d l y s l i p p i n g past one another, independently o f t r a n s l a t i o n g l i d i n g which may or may not be o c c u r r i n g w i t h i n a g i v e n g r a i n . L i t t l e movement can occur on g r a i n boundaries b e f o r e i r r e g u l a r i t i e s on the boundary prevent movement, thus s t r a i n accumulates w i t h i n the g r a i n s . In t h i s case, the p r o b a b i l i t y o f r e c r y s t a l l i z a t i o n , i . e . , o f both the n u c l e a t i o n o f new g r a i n s and t h e i r subsequent growth, i n c r e a s e s as the i n t e r n a l s t r e s s b u i l d s up. The new r e c r y s t a l l i z e d m a t e r i a l which w i l l appear c o n t i n u a l l y w i l l be f r e e from i n t e r n a l s t r a i n at the i n s t a n t of formation. Glen (1955) suggested t h a t the mechanisms of g r a i n boundary m i g r a t i o n and r e c r y s t a l l i z a t i o n allow, g r a i n s to conform to 2 8 . the imposed deformation. Gold ( 1 9 6 3 ) observed and d e s c r i b e d deformation mechanisms In i c e under a compressive l o a d . The mechanisms are enumerated below, i n c h r o n o l o g i c a l order of occurrence, ( i ) S l i p bands S l i p occurs when one p a r t of a c r y s t a l s l i d e s over another p a r t without l o s s of cohesion, the l a t t i c e o r i e n t a t i o n i n each p a r t being s i m i l a r l y o r i e n t a t e d b e f o r e and a f t e r the movement. In i c e the s l i p bands are p a r a l l e l t o the b a s a l plane, and thus at r i g h t angles to the o p t i c a x i s . More work has been done on metals than on i c e . Gold draws an analogy w i t h hexagonal metals. ( i i ) G r a i n boundary m i g r a t i o n G r a i n boundary m i g r a t i o n i s one of the f i r s t s i g n s of change i n the g r a i n boundary c o n f i g u r a t i o n , o c c u r r i n g i n " p r a c t i c a l l y every boundary" (Gold 1 9 6 3 , p. 1 3 ) . In a d i s - c u s s i o n of rock deformation, F l i n n ( 1 9 6 5 ) d i s t i n g u i s h e s between such m i g r a t i o n at low and h i g h temperatures. Atomic t r a n s f e r from a r e l a t i v e l y s t r a i n e d g r a i n or p a r t of a g r a i n on one s i d e of a boundary to a r e l a t i v e l y u n s t r a i n e d g r a i n or p a r t of a g r a i n , on the other s i d e , occurs at low temperatures. Thus u n s t r a i n e d m a t e r i a l i s b u i l t up at the expense of s t r a i n e d l a t t i c e , r e s u l t i n g i n s u t u r e d g r a i n boundaries ( F i g . 18 and 2 2 ) which are common i n q u a r t z i t e s . MacGregor ( 1 9 5 1 , 1 9 5 2 ) d i s c u s s e d the s i m i l a r i t y between i c e and quartz deformation. At h i g h e r temperatures, a tendency f o r g r a i n s t o minimize t h e i r area o c c u r s , boundaries m i g r a t i n g toward t h e i r c e n t r e s of c u r v a t u r e , r e s u l t i n g i n equiangular aggregates o f e q u i a x i a l g r a i n s . S e c t i o n s o f such m a t e r i a l show networks o f n e a r l y s t r a i g h t g r a i n boundaries meeting i n t r i p l e p o i n t s . Such networks were shown by V o l l ( I 9 6 0 , p. 529) to be c h a r a c t e r - i s t i c o f monomineralic r o c k s . ( i i i ) Kink-Bands The f o r m a t i o n of kink-bands, which have been r e p o r t e d i n metals, e s p e c i a l l y o f hexagonal symmetry (Hauser et a l 1955) i s a mechanism by which a bending moment, t r a n s v e r s e to the s l i p d i r e c t i o n , can be r e l i e v e d i n c r y s t a l s with only one or two p o s s i b l e s l i p d i r e c t i o n s ( P i g . 3). ( i v ) D i s t o r t i o n of G r a i n Boundaries Increased deformation i n Gold's compressive t e s t s l e d to d i s t o r t e d g r a i n boundaries. When the s l i p planes o f adjacent g r a i n s were s u i t a b l y o r i e n t e d , the boundary developed a stepped appearance. With o t h e r o r i e n t a t i o n s , s m a l l cracks appeared. Such d i s t o r t i o n s would disappear d u r i n g r e c r y s t a l - l i z a t i o n . (v) Crack Formation Gold (I960) showed t h a t cracks may be i n t e r c r y s t a l l i n e or t r a n s c r y s t a l l i n e , t h a t they propagate i n the d i r e c t i o n o f 3 0 . the g r a i n long a x i s , and t h e i r plane p a r a l l e l s the s t r e s s d i r e c t i o n . Gold ( 1 9 6 3 ) summarized other l i t e r a t u r e , s t a t i n g t h a t d i s l o c a t i o n s a s s o c i a t e d with creep are b l o c k e d , cracks n u c l e a t i n g at c o n c e n t r a t i o n s o f such d i s l o c a t i o n s which cause l o c a l s t r e s s exceeding the m a t e r i a l s t r e n g t h . ( v i ) C a v i t i e s C a v i t i e s were observed i n r e g i o n s of g r a i n boundaries, boundary t r i p l e p o i n t s , and i n t e r s e c t i o n s of s l i p planes and sub-boundaries, l a t e r becoming i n f i l l e d . ( v i i ) Recovery and R e c r y s t a l l i z a t i o n A d i s t i n c t i o n i s made between these two p r o c e s s e s . Recovery i s where d i s l o c a t i o n s w i t h i n g r a i n s migrate by d i f f u s i o n i n t o a r r a y s of lower f r e e energy. D i s l o c a t i o n s accumulating as a network o f sub-boundaries leads to p o l y g o n i z a t i o n (Cahn 1 9 4 9 ) . E l i m i n a t i o n of s t r a i n from the g r a i n s by r e c o v e r y and g r a i n boundary m i g r a t i o n may be o f s u f f i c i e n t magnitude to p r e c l u d e subsequent r e c r y s t a l l i z a t i o n by n u c l e a t i o n and g r a i n growth. R e c r y s t a l l i z a t i o n i s the s o l i d s t a t e process whereby new c r y s t a l s n u c l e a t e , a c t i v a t e d by s t r a i n energy. N u c l e i with mobile boundaries may grow through o l d s t r a i n e d g r a i n s . The new g r a i n s are c h a r a c t e r i s t i c a l l y s t r a i n - f r e e and thus may be d i s t i n g u i s h e d from r e l i c t g r a i n s . I f s u f f i c i e n t s t r a i n energy i s a v a i l a b l e the process may continue u n t i l the new 31. g r a i n s meet; otherwise remnants of o l d s t r a i n e d g r a i n s are found. In the experiments of Gold (1963), no s u r f a c e evidence o f r e c r y s t a l l i z a t i o n d u r i n g deformation was observed, but a f t e r removal o f the compressive l o a d , both recovery and r e c r y s t a l l i z a t i o n o c c u r r e d at the s u r f a c e and i n t e r n a l l y . Gold produced photographic evidence of i r r e g u l a r g r a i n boundaries and a s s o c i a t e d p o l y g o n i z a t i o n , and of a sub- boundary t e r m i n a t i n g at a s l i p plane. A comparison of t h i n s e c t i o n s showed a tendency f o r columnar g r a i n s t r u c t u r e to be transformed i n t o a g r a n u l a r one. F u r t h e r , Steinemann (1958) showed t h a t i f t h i n s e c t i o n s are cut immediately a f t e r experiments and others l a t e r , then complex intergrowths have vanished i n the l a t t e r , but the shape of g r a i n s i s f a r from i s o m e t r i c . In h i s study i t was noted t h a t deformation i n t e n s i o n and compression gave the same r e s u l t s . (d) A p p l i c a t i o n to F i e l d S i t u a t i o n The s t u d i e s r e p o r t e d above have been c o n f i n e d t o c o n d i t i o n s of l a b o r a t o r y deformation. R e c o g n i t i o n of micro- s c o p i c f e a t u r e s c h a r a c t e r i s t i c o f the s e v e r a l stages o f deformation and p o s t - d e f o r m a t i o n a l recovery and r e c r y s t a l l i z a - t i o n i s important f o r an understanding o f the h i s t o r y o f the i c e at Tuktoyaktuk. Thus c o n s i d e r a t i o n i s given to p e t r o - f a b r i c i n d i c a t o r s of deformation. 32 . Accommodation t o the imposed s t r e s s should r e s u l t i n both p r e f e r r e d o p t i c a x i s o r i e n t a t i o n and p r e f e r r e d dimen- s i o n a l o r i e n t a t i o n . There are s e v e r a l s t r e s s - c o n t r o l l e d mechanisms p r o d u c t i v e o f p r e f e r r e d l a t t i c e ( o p t i c ) o r i e n t a t i o n s . During g l i d i n g , i c e c r y s t a l s r o t a t e u n t i l the s i n g l e s l i p planes are p a r a l l e l t o each other and p e r p e n d i c u l a r t o the p r i n c i p a l s t r e s s a x i s i n n o n - r o t a t i o n a l s t r a i n , or p a r a l l e l to the movement s u r f a c e i n simple shear. During r e c r y s t a l - l i z a t i o n , p r e f e r r e d l a t t i c e o r i e n t a t i o n s may be produced by: (a) an i n c r e a s e d p r o p o r t i o n of c r y s t a l s with f a v o u r a b l e o r i e n t a t i o n s t o accommodate t o imposed s t r e s s (b) a reduced p r o p o r t i o n of c r y s t a l s with unfavourable o r i e n t a t i o n s . (c) changing o r i e n t a t i o n s from unfavourable to f a v o u r a b l e . Stanley (1965, p. 164) argued t h a t i f "unfavourable g r a i n s are e l i m i n a t e d , and t h e i r ions " t r a n s f e r r e d " t o o t h e r g r a i n s , f a v o u r a b l y o r i e n t e d g r a i n s should become p r o g r e s s i v e l y l a r g e r " . However, he goes on t o p o i n t out that i c e movement i s probably one o f c o n t i n u a l r e c r y s t a l l i z a t i o n . Shumskii (1958) proposed t h a t the l e a s t s t r e s s e d g r a i n s r e p l a c e the more h i g h l y s t r e s s e d c r y s t a l s which d i s i n t e g r a t e by a process o f p o l y g o n i z a t i o n , or by migratory r e c r y s t a l l i z a t i o n . The n u c l e a t i o n and o r i e n t a t i o n o f c r y s t a l s i n s t r e s s f i e l d s has been gi v e n t h e o r e t i c a l c o n s i d e r a t i o n by Kamb (1959)» Brace (I960) and MacDonald ( I 9 6 0 ) . Both Kamb (1959a, p. 160) and Brace ( I 9 6 0 , p. 15) have noted the s i m i l a r i t y between 3 3 . p r e f e r r e d o r i e n t a t i o n s expected to r e s u l t from d i f f e r e n t mechanisms. The t o t a l energy of p o l y c r y s t a l l i n e aggregates with an a p p r o p r i a t e p r e f e r r e d o r i e n t a t i o n i s lower than that o f a random aggregate. The mechanisms which may g i v e r i s e to a thermodynamically s t a b l e o r i e n t a t i o n are g r a i n boundary m i g r a t i o n e l i m i n a t i n g g r a i n s i n an unfavourable o r i e n t a t i o n , and n u c l e a t i o n c r e a t i n g new g r a i n s i n a thermodynamically f a v o u r a b l e a t t i t u d e . E l a s t i c s t r a i n i n g i s necessary f o r the processes to occur ( F l i n n 1 9 6 5 ) . For i c e i n shear, Rigsby ( I 9 6 0 , p. 6 0 3 ) o b t a i n e d a f a b r i c with a weak maximum i n the t h e o r e t i c a l l y p r e d i c t e d p o s i t i o n ; most other i n v e s t i g a t o r s r e p o r t f a b r i c s d i s p l a y i n g two or more maxima i n c l i n e d from the pole to the shear plane. Reid ( 1 9 6 5 , p. 2 5 8 ) suggested the " i d e a l f a b r i c " should c o n t a i n f o u r maxima arranged i n a diamond p a t t e r n around the pole. Kamb ( 1 9 5 9 ) argued t h a t i n s t r e s s e d i c e , the c-axes are a l l normal to the shear plane, but on s t r e s s r e l e a s e the o r i e n t a t i o n changes to a diamond p a t t e r n . Such a change has not been proven t o occur. F u r t h e r , Rigsby ( 1 9 6 8 , p. 2 5 0 ) concluded from a study o f c r y s t a l shapes from g l a c i e r s t h a t many axes p l o t t e d i n one maximum r e a l l y r epresent a s i n g l e c r y s t a l , thus throwing some doubt on many p u b l i s h e d f a b r i c diagrams. Hooke ( 1 9 6 9 a ) suggested t h a t such diagrams may be accepted at face v a l u e . Thus c - a x i s f a b r i c s are known to take on s e v e r a l c h a r a c t e r i s t i c p a t t e r n s , but the mechanics of formation are 3 4 . not well understood. Most f i e l d studies on g l a c i e r s record only optic axis orientation, but Anderton (1969) considered other petro- graphic data. Considering undulatory extinction, on t h e o r e t i c a l grounds i t i s due to the permanent bending of a c r y s t a l , with a resultant change i n o p t i c a l properties (Fig. 3 b ) . Steinemann (1958) showed that i t occurs for inhomogeneous deformation, and not for homogeneous. Rigsby ( I 9 6 0 ) reports that s t r a i n shadows are rarely seen i n temperate g l a c i e r s , but frequently i n polar g l a c i e r ice and laboratory deformed specimens. The Ef f e c t of Inclusions The above review of laboratory experiments i s r e s t r i c t e d to work on pure i c e . In the natural state, ice may contain impurities i n the l i q u i d , s o l i d and gaseous phase, but work on ice containing such materials i s l i m i t e d . Rigsby (I960, p. 602) suggested that bubbles i n h i b i t c r y s t a l growth by absorb- ing s t r a i n and preventing grain boundary migration. Weertman (1968, p. 155) discussed bubble coalescence as a t o o l for measuring active deformation. However, no detailed study of the effect of gaseous inclusions on laboratory controlled deformation has been made. Of more importance to t h i s study are the r e l a t i v e deformabilities of pure ice and ice loaded with varying proportions of sand. 35. In the f o l l o w i n g review, p h y s i c o - c h e m i c a l p r o p e r t i e s o f f r o z e n s o i l s are c o n s i d e r e d , f o l l o w e d by mention of changes i n s o i l s t r e n g t h on f r e e z i n g dependent on s a t u r a t i o n and temperature. Loading o f f r o z e n s o i l s i s d i s c u s s e d i n terms of changes i n ice-sediment r e l a t i o n s h i p s . Subsequent to the review of l a b o r a t o r y s t u d i e s , f i e l d evidence o f r e l a t i v e p r o p e r t i e s of i c e and i c e with d e b r i s i s examined. Deformation of the Sediment-Ice System The l i t e r a t u r e concerning sediment-ice deformation i s l e s s voluminous than that f o r pure i c e . However, work on the p r o p e r t i e s of f r o z e n ground has been r e p o r t e d , e a r l y s t u d i e s being c a r r i e d out i n Russia by T s y t o v i c h and Sumgin (1937). Before d i s c u s s i o n i s made of the mechanical p r o p e r t i e s of f r o z e n s o i l s , the s t r u c t u r e of the m a t e r i a l i n the undeformed s t a t e w i l l be d e s c r i b e d . We are c o n s i d e r i n g a 4-phase system; s o l i d m i n e r a l p a r t i c l e s , i c e matrix, water, and a i r . (a) Physico-chemical p r o p e r t i e s The s t r u c t u r e and mechanical p r o p e r t i e s of the mass are s i g n i f i c a n t l y i n f l u e n c e d by the p h y s i c o - c h e m i c a l p r o p e r t i e s of the s o i l . The r e s i s t a n c e to shear developed by g r a n u l a r m a t e r i a l s i s l a r g e l y due to f r i c t i o n between s o l i d p a r t i c l e s ; i n a d d i t i o n , c l a y p a r t i c l e s possess cohesion. Pine g r a i n e d s o i l s c o n t a i n i n g p a r t i c l e s with h i g h s p e c i f i c s u r f a c e area may r e t a i n an a p p r e c i a b l e percentage 36. o f water unfrozen at temperatures below the f r e e z i n g p o i n t o f o r d i n a r y water (Williams 1964, p. 239) . T h i s unfrozen water which surrounds the c l a y p a r t i c l e s i s a f u n c t i o n of the s p e c i f i c s u r f a c e a r e a , c o l l o i d a l a c t i v i t y of c l a y m i n e r a l and temperature ( D i l l o n and Andersland, 1966). On f r e e z i n g , bulk s o i l volume may i n c r e a s e , with i n m i g r a t i o n of water to the f r e e z i n g f r o n t . The d i s t r i b u t i o n of i c e i n the s o i l i s a f u n c t i o n of the d i r e c t i o n o f f r e e z i n g s o i l p e r m e a b i l i t y , and time. Even with an e x t e r n a l source o f water, the i n c r e a s e of volume of a s a t u r a t e d sand on f r e e z i n g i s only a s m a l l percentage o f t o t a l bulk volume ( T s y t o v i c h , 1963). Ice lens development i n f i n e g r a i n e d m a t e r i a l causes a c o n s i d e r a b l e volume i n c r e a s e . (b) S o i l s t r e n g t h The s t r e n g t h of a l l s a t u r a t e d s o i l s i n c r e a s e s on f r e e z i n g , due t o adhesion between i c e and s o i l p a r t i c l e s . Frozen s a t u r a t e d sand may have a s t r e n g t h s e v e r a l times that of c l a y at the same temperature because a c o n s i d e r a b l e amount of the water i n c l a y s remains unfrozen. In p a r t l y s a t u r a t e d s o i l s , f r o z e n s t r e n g t h i n c r e a s e with h i g h e r water content up to a l i m i t c l o s e t o the f u l l s a t u r a t i o n p o i n t . For h i g h e r water c o n t e n t s , s t r e n g t h f a l l s o f f and approaches t h a t of pure i c e ( T s y t o v i c h , 1963). A temperature r i s e produces a v a r i a t i o n i n s t r e n g t h a s s o c i a t e d w i t h i c e q u a l i t y and i c e - p a r t i c l e adhesion changes 37. (c) Loading An e x t e r n a l l o a d produces s t r e s s c o n c e n t r a t i o n s at m i n e r a l - i c e contact p o i n t s , r e s u l t i n g i n p l a s t i c flow and pressure m e l t i n g o f the i c e (Barnes and Tabor, 1966). T s y t o v i c h (1937) r e p o r t e d that meltwater migrates down the pres s u r e g r a d i e n t . R e c r y s t a l l i z a t i o n at a p o i n t o f lower s t r e s s occurs with the b a s a l plane p a r a l l e l t o the s l i d e d i r e c t i o n thus r e d u c i n g the s h e a r i n g r e s i s t a n c e . Simultane- o u s l y a denser packing o f m i n e r a l p a r t i c l e s occurs s i n c e vacant l o c a t i o n s r e s u l t i n g from moisture displacement are f i l l e d w i t h s o l i d p a r t i c l e s . T h i s g i v e s r i s e t o molecular cohesion between p a r t i c l e s (Vyalov 1963). Thus t h e r e occur two opposed phenomena i n f r o z e n s o i l s under p r e s s u r e : (a) weakening due to g r a d u a l r e - o r i e n t a t i o n of i c e c r y s t a l s , and (b) s t r e n g t h e n i n g due t o i n c r e a s e d molecular cohesion caused by c l o s e r packing of m i n e r a l p a r t i c l e s . Under l o a d i n g s u f f i c i e n t t o produce deformation, but below a c e r t a i n t h r e s h o l d v a l u e , s o f t e n i n g w i l l be com- pensated by hardening, and a s t e a d y - s t a t e deformation r a t e w i l l r e s u l t . However, i f the t h r e s h o l d value i s exceeded, s o f t e n i n g overcomes hardening, and undamped flow takes p l a c e . T h i s t h r e s h o l d value d e f i n e s the long-term s t r e n g t h o f the s o i l (Vyalov 1963). That i c e s t r u c t u r e changes as deformation proceeds has been e s t a b l i s h e d above. The i n i t i a l volume i n c r e a s e f o r such samples i s c o n s i d e r e d t o be a s s o c i a t e d with d i s r u p t i o n 3 8 . of i n t e r g r a n u l a r c o n t i n u i t y by g r a i n boundary s l i d i n g . A d d i t i o n of sand to the system may act as a key to impede g r a i n boundary s l i d i n g . Goughnour and Andersland ( 1 9 6 8 ) prepared sand-ice systems i n which "sand p a r t i c l e s are d i s p e r s e d u n i f o r m l y through the f r o z e n mass". They found that at low volume c o n c e n t r a t i o n s of sand the i n c r e a s e i n shear s t r e n g t h was a simple l i n e a r r e l a t i o n to r e l a t i v e p r o p o r t i o n s of sand and i c e . I t appears that the m a j o r i t y of p l a s t i c deformation i s accommodated by the i c e , thus the e f f e c t i v e deformation r a t e f o r the i c e may be c o n s i d e r a b l y g r e a t e r than the observed gross sample deformation r a t e . The keying e f f e c t of sand g r a i n s may occur, dependent only on the volume c o n c e n t r a t i o n of sand p a r t i c l e s , being m o b i l i z e d at a l l s t r a i n s . Hooke et a l ( 1 9 7 2 ) i n d i c a t e t h a t sand g r a i n s i n deforming i c e may be surrounded by clouds of d i s l o c a t i o n s which impede the passage of primary g l i d e d i s l o c a t i o n s . Such a c l o u d was observed by Kuroiwa and Hamilton ( 1 9 6 3 ) . Above a c r i t i c a l sand volume of k2%, Goughnour and Andersland ( 1 9 6 8 ) noted a r a p i d i n c r e a s e i n shear s t r e n g t h , which they presumed to be caused by f r i c t i o n between sand p a r t i c l e s , and d i l a t a n c y , the l a t t e r a c t i n g a g a i n s t cohesion of the i c e matrix and adhesion between sand g r a i n s and i c e . Assuming s a t u r a t e d s o i l c o n d i t i o n s , the degree of d i s p e r s i o n i n f r o z e n sand-ice samples depends on: (a) o r i g i n a l v o i d r a t i o ; (b) p e r m e a b i l i t y o f the s o l i d s o i l systems; (c) e f f e c t i v e 39. s t r e s s on the s o l i d s o i l s k e l e t o n d u r i n g f r e e z i n g , which may change as pore water i s l o s t t o i c e l e n s e s , and v a r i e s w i t h c r y s t a l o r i e n t a t i o n ; (d) r a p i d i t y o f f r e e z i n g . I n i t i a l l o a d i n g l e d to a s m a l l volume decrease equal to the volume o f s m a l l a i r bubbles. A volume i n c r e a s e on continued deformation was c o n s i d e r e d by Goughnour and Andersland (1968) to be r e l a t e d to d i l a t a n c y o f sand p a r t i c l e s . The i c e matrix e f f e c t i v e l y e x e r t s a c o n f i n i n g pressure on the sand p a r t i c l e s which i n c r e a s e s as the volume i n c r e a s e takes p l a c e . T h i s c o n f i n i n g p r e s s u r e grows u n t i l e i t h e r no more increment i n volume i s experienced, or the l i m i t i n g cohesion of the i c e i s overcome. S t r e s s - s t r a i n curves are shown i n P i g . 4. F i e l d S t u d i e s Evidence from f i e l d s t u d i e s a l s o suggests t h a t i c e c o n t a i n i n g a s m a l l percentage of d e b r i s deforms more r e a d i l y than c l e a n i c e . Abel ( i n Swinzow 1962, p. 223) recorded i n c r e a s e d d i f f e r e n t i a l movement ac r o s s c e r t a i n bands of i n c l u d e d m a t e r i a l . Swinzow (1962, p. 226) compares the deformation o f d e b r i s bands with v a r y i n g sediment content with that of surrounding c l e a r i c e . Bands wit h a s m a l l percentage of f i n e d e b r i s a c t as zones of weakness while h i g h e r c o n c e n t r a t i o n s of coarse m a t e r i a l l e a d to l e s s o v e r a l l deformation. Swinzow (1962, p. 225) suggested a change i n the flow law dependent on the i n c l u d e d d e b r i s percentage. 40. Por a g i v e n s t r e s s , the s t r a i n r a t e i s to be m u l t i p l i e d by a f a c t o r " i " which i n c r e a s e s as the sediment i n c r e a s e s , p r o v i d e d i n c l u d e d p a r t i c l e s are not t o u c h i n g . Thus . = . i f o r a s p e c i f i e d e e s i l t y i c e i c e s t r e s s . Swinzow argued t h a t p a r t i c l e c o n t a c t s serve to r e i n f o r c e the mass, the s t r a i n r a t e becoming l e s s than t h a t f o r pure i c e . A f u r t h e r p o i n t i s the p o s s i b i l i t y o f i n c r e a s e d deforma- t i o n due to changes i n the l i q u i d l a y e r at g r a i n boundaries. Nakaya and Matsumoto (1953) demonstrated the presence of a l i q u i d - l i k e l a y e r on i c e . T h i s was confirmed by H o s i e r et a l (1957) and J e l l i n e k (1965). M o r a i n a l m a t e r i a l might a f f e c t the t h i c k n e s s of the l a y e r , the more s o l u b l e components being c o n c e n t r a t e d at g r a i n boundaries. An i n c r e a s e i n i n t e r g r a n u l a r movements i s to be expected under the above c o n d i t i o n s . C o n c l u s i o n Prom the above review, i t i s evident t h a t pure i c e and i c e with sediment have d i f f e r e n t d e f o r m a t i o n a l p r o p e r t i e s . Evidence from l a b o r a t o r y and f i e l d s t u d i e s support t h i s c o n c l u s i o n . Thus i n the study o f the f o l d e d i c e i n Tuktoyaktuk, separate c o n s i d e r a t i o n must be given t o i c e s with d i f f e r e n t sediment conte n t s , the g r a d a t i o n s between s e d i m e n t - r i c h and sediment-free i c e b e i n g of p a r t i c u l a r i n t e r e s t . C o n s i d e r i n g the p r e - d e f o r m a t i o n a l s t a t e of the bedding as p a r a l l e l banding o f i c e and i c y sediment, suggestions may be made concerning the response of the body t o an imposed s t r e s s . In the r e l a t i v e l y pure i c e , some c r y s t a l s accommodate the s t r e s s by b a s a l s l i p , i f s u i t a b l y o r i e n t e d . Others may r o t a t e , s u f f e r s t r a i n b u i l d up, become p o l y g o n i z e d , or crack. I f r o t a t i o n o f many c r y s t a l s i s p o s s i b l e , l a t t i c e p r e f e r r e d o r i e n t a t i o n s occur, p r o d u c t i v e of maxima on f a b r i c diagrams. Build - u p o f s t r a i n i s c h a r a c t e r i z e d by strain-shadows and deformation bands, where i n d i v i d u a l segments of c r y s t a l s show s l i g h t l y d i f f e r e n t o p t i c a l o r i e n t a t i o n s . Cracking has been r e c o g n i z e d i n l a b o r a t o r y experiments but has not been r e p o r t e d from g l a c i e r s t u d i e s . In dead i c e , cracks would be o b l i t e r a t e d by r e c r y s t a l l i z a t i o n . The process of r e c r y s t a l - l i z a t i o n i s a c t i v e throughout deformation ( s y n t e c t o n i c r e c r y s t a l - l i z a t i o n ) and l a t e r ( p o s t - t e c t o n i c r e c r y s t a l l i z a t i o n ) . Where contiguous s t r a i n e d g r a i n s r e c r y s t a l l i z e without the form a t i o n o f new n u c l e i , mutual outgrowths of u n s t r a i n e d m a t e r i a l g i v e s sutured g r a i n boundaries. I f n u c l e i grow to g i v e new g r a i n s these are c h a r a c t e r i s t i c a l l y s t r a i n - f r e e and may embay o l d s t r a i n e d g r a i n s . In the presence of d i r e c t e d s t r e s s d u r i n g p o s t - t e c t o n i c r e c r y s t a l l i z a t i o n new g r a i n s w i l l tend to be equant, i n c o n t r a s t to the o l d g r a i n s which show d i m e n s i o n a l l y p r e f e r r e d o r i e n t a t i o n s due to flow. The presence o f i n c l u s i o n s , n o t a b l y sediment, i n an i c e specimen leads t o i n c r e a s e d deformation o f the i c e , volume 4 2 . f o r volume. Thus i n a sequence sediment-free i c e / i c y sediment, d i f f e r e n t deformation r a t e s would be expected f o r a constant imposed s t r e s s . In the f i e l d c o m p l i c a t i o n s a r i s e due to f l u c t u a t i o n s i n temperature, s t r e s s value and s t r e s s d i r e c t i o n . I t i s expected that a p p l i c a t i o n of the above p r i n c i p l e s to the body of i c e under i n v e s t i g a t i o n may a l l o w r e c o g n i t i o n of d i f f e r i n g g e n e r a t i o n s of c r y s t a l s and e l u c i d a t i o n o f the o v e r a l l mode o f deformation. CHAPTER IV METHODOLOGY I n t r o d u c t i o n The major o b j e c t i v e s of t h i s study are to analyze the mechanism o f deformation o f the f o l d e d sand-ice sequence and to i n f e r the p r e - d e f o r m a t i o n a l growth o f th a t sequence. Other purposes are to i n f e r the p o s t - d e f o r m a t i o n a l h i s t o r y of the body and to a s c e r t a i n d i s t i n c t i v e f e a t u r e s of the i c e and con t a i n e d sediment f o r f u t u r e f i e l d r e c o g n i t i o n o f the i c e type from l i m i t e d core samples. Chapter O u t l i n e I t was necessary t o map the mesoscopic s t r u c t u r e to e l u c i d a t e the f o l d geometry at th a t s c a l e . Thin s e c t i o n s of known o r i e n t a t i o n were prepared from the a v a i l a b l e exposure, n e c e s s i t a t i n g a m u l t i - s t a g e sampling p l a n : (a) sampling o f f o l d e d m a t e r i a l ; (b) sampling of blo c k s from (a) f o r t h i n s e c t i o n p r e p a r a t i o n ; and (c) sampling t h i n s e c t i o n s . The e r r o r s o f the U n i v e r s a l Stage technique are examined and i n a d d i t i o n those p e c u l i a r t o i c e s t u d i e s are enumerated. D i s c u s s i o n i s made o f the p l o t t i n g o f o p t i c a x i s o r i e n t a t i o n s , the number of p o i n t s necessary and c o n t o u r i n g methods f o r s c a t t e r diagrams. The i n t e r p r e t a t i o n o f diagrams and t e s t s 44. of s i g n i f i c a n c e of minor c o n c e n t r a t i o n s s u i t a b l e f o r f i e l d use are c o n s i d e r e d . A x i a l D i s t r i b u t i o n A n a l y s i s (A.V.A.) i s d e s c r i b e d . Scale C o n s i d e r a t i o n s The d e t e r m i n a t i o n of the f a b r i c of a body begins at the s c a l e o f the exposure, c a l l e d mesoscopic s c a l e (Turner and Weiss 1963). The p r i n c i p a l f a b r i c elements on t h i s s c a l e are f o l i a t i o n a t t i t u d e s , f o l d s and l i n e a t i o n s . A s e r i e s of mesoscopic s t u d i e s i s then s y n t h e s i z e d i n t o the o v e r a l l f a b r i c o f the b o d y — t h e macroscopic s c a l e . In the Tuktoyaktuk i c e c e l l a r the macroscale cannot be c o n s i d e r e d as a n a l y s i s Is c o n f i n e d to one major exposure; e x t r a p o l a t i o n to a l a r g e r body i s not j u s t i f i e d . However, the l a t e r a l e x t e n s i o n of the body has been mentioned by Rampton and Mackay (1971) on the b a s i s of a i r photographs a f t e r a storm. The body i s a l s o s t u d i e d on the m i c r o s c o p i c s c a l e — p r i n c i p a l elements are shape and c r y s t a l l o g r a p h i c o r i e n t a t i o n s . The Symmetry P r i n c i p l e The concept of symmetry i n the i n t e r p r e t a t i o n of deformed rocks was e s t a b l i s h e d and developed by Sander (1930). Paterson and Weiss (196l) reviewed the concept of symmetry i n p h y s i c s and r e l a t e d s c i e n c e s and have p l a c e d the a p p l i c a t i o n o f the concept t o t e c t o n i t e s on a r i g o r o u s b a s i s (p. 841): "Whatever the nature o f the f a c t o r s c o n t r i b u t i n g to a deformation may be, the symmetry t h a t i s common to them cannot be high e r than the symmetry of the deformed f a b r i c , and symmetry elements absent i n t h i s f a b r i c must be absent i n at l e a s t one of the c o n t r i b u t i n g f a c t o r s " . The symmetry of a homogeneous s t r e s s cannot be lower than orthorhombic and the symmetry of d i s t o r t i o n i n a homo- geneous s t r a i n must have orthorhombic or hi g h e r symmetry. Mapping o f a v a i l a b l e exposure In order t o determine the d e f o r m a t i o n a l h i s t o r y o f the body, i t i s necessary t o a s c e r t a i n as completely as p o s s i b l e the present c o n f i g u r a t i o n o f a l l exposed f e a t u r e s . At the mesoscale t h i s r e q u i r e s measurement of a t t i t u d e s of f o l i a t i o n , l i n e a t i o n s and f o l d axes i n the f i e l d . The exposure with i t s f o l i a t i o n s was mapped at the s c a l e 1 cm re p r e s e n t s 1 0 cm. A f o l i a t i o n i s a r e c o g n i z a b l e d i s c o n t i n u i t y or l a y e r e d s t r u c t u r e i n the i c e mass. The major f o l i a t i o n i n t h i s study i s the com p o s i t i o n a l l a y e r i n g e x h i b i t e d by d i f f e r i n g sediment content. The f o l d form and oth e r s t r u c t u r e s and t h e i r i n t e r r e l a t i o n s h i p s were analyzed and f o l d s c l a s s i f i e d by s t y l e . On t h i s b a s i s , a sampling p l a n f o r m i c r o s c o p i c study was prepared. With the u s u a l g e o l o g i c a l nomenclature, s u r f a c e s are designated S Q , S^, S 2 , e t c . i n the f o l l o w i n g d i s c u s s i o n . Here SQ i s taken t o be the p r e - d e f o r m a t i o n a l bedding; i s the a x i a l s u r f a c e ( F i g . 6 ) . 46. Fold c h a r a c t e r i s t i c s Folds are characterized by:- 1. S i m i l a r i t y i n shape from one layer to another 2. Persistence of the f o l d through appreciable s t r a t i - graphic thickness 3. Relative lengths of limbs 4. Attitude of a x i a l surfaces r e l a t i v e to the pre- v a i l i n g attitude of s t r a t i f i c a t i o n 5. Closeness of appression of limbs 6. Relative bed thickness around the f o l d closure. From a preliminary reconnaissance of the f o l d morphology throughout the c e l l a r , folds were categorized into three styles (Fig. 7). Style 1 Folds These folds have clo s e l y appressed limbs, dihedral angles being less than 30°, thus the folds are tight to i s o c l i n a l (Fig. 7a, 8) (terminology a f t e r Fleuty 1964, p. 470). Axial surfaces are p a r a l l e l to the general attitude of the compositional f o l i a t i o n . Bed thickness varies, thickening occurring at f o l d closures. In some cases attenuation of limbs i s extreme, leading to "rootless" folds where f o l d closures remain (Fig. 8). Style 2 Folds These folds are asymmetrical, one limb being long, the other short. Axial surfaces are i n c l i n e d to the p r e v a i l i n g compositional layering. The folds are not p e r s i s t e n t through much s t r a t i g r a p h i c t h i c k n e s s . Minor v a r i a t i o n s i n bed t h i c k n e s s occur around the f o l d ( F i g . 7 b ) . F o l d s occur i n beds which were t r a c e a b l e over d i s t a n c e s many times the f o l d limb l e n g t h . S t y l e 3 Folds Only one example o f t h i s f o l d type was found ( F i g . 9). The f o l d i s c h a r a c t e r i z e d by i t s more open nature than the S t y l e 1 f o l d s i n t o which i t passes v e r t i c a l l y and l a t e r a l l y . I t s a x i a l s u r f a c e i s at approximately 45° to the g e n e r a l c o m p o s i t i o n a l l a y e r i n g . Exposure of limbs to depth i s l a c k i n g , but t h e r e i s a r e c o g n i s a b l e t h i c k e n i n g i n the f o l d c l o s u r e . There i s a marked asymmetry i n terms of limb l e n g t h . Sampling Methods Having mapped the exposures, the next o b j e c t i v e was a d e t a i l e d p e t r o g r a p h i c study of the i c e body, i n c l u d i n g the p r o d u c t i o n of f a b r i c diagrams o f o p t i c axes of c r y s t a l s , and a n a l y s i s of g r a i n s i z e and shape c h a r a c t e r i s t i c s . For these i n v e s t i g a t i o n s , r e p r e s e n t a t i v e t h i n s e c t i o n s were t o be produced, n e c e s s i t a t i n g a s e v e r a l - s t a g e sampling method. (a) Sampling f o l d e d m a t e r i a l The l i m i t a t i o n of exposure to c e l l a r w a l l s l e d to the c e l l a r being c o n s i d e r e d as a p o p u l a t i o n i n i t s e l f and r e q u i r i n g as complete sampling as p o s s i b l e . Having d e f i n e d t h i s p o p u l a t i o n , 4 8 . the next step was to devise a sampling p l a n f o r f o l d e d m a t e r i a l . F o l d hinges i n such h i g h l y deformed m a t e r i a l ( i s o c l i n a l with extended limbs) have much s m a l l e r volumes and areas exposed than the corresponding limbs, so the use o f a r e g u l a r system of sample p o i n t s would g i v e few measurements of hinges. These l a t t e r are o f e s p e c i a l importance as the r e l a t i o n s h i p s o f S-surfaces are most r e a d i l y i n v e s t i g a t e d t h e r e ; a l s o bed t h i c k n e s s e s have g r e a t e s t v a r i a t i o n s , compared w i t h more uniform t h i c k n e s s on limbs. Whitten (1966) r e f e r s t o the d e s i r a b i l i t y o f s t r a t i f y i n g the sample on the b a s i s o f l i t h o - l o g i c type or the t h i c k n e s s of members. F u r t h e r i t i s argued t h a t a p l a n c o u l d be based on m a t e r i a l types d e f i n e d by d i f f e r e n t metamorphic grades or z o n a t i o n s . However, as p o i n t e d out above, the a v a i l a b l e sample i s l i m i t e d i n the v e r t i c a l dimension, where g r e a t e s t v a r i a t i o n would be expected. On the b a s i s of the map o f f o l d geometry, f o l d s were grouped by s t y l e , as d e s c r i b e d above. From each sampled f o l d , s e v e r a l blocks of known o r i e n t a t i o n were cut as i n d i c a t e d i n F i g . 10. The b l o c k s were sawn from the f a c e , g e o g r a p h i c a l o r i e n t a t i o n b e i n g denoted by c h a r a c t e r i s t i c marks on each s u r f a c e . A l s o the s t r i k e and d i p of each face was measured by compass- c l i n o m e t e r , and recorded, with a sketch or photograph of each sample. 49. (b) Sampling of Blocks From each sample b l o c k , s e v e r a l t h i n s e c t i o n s were cut at v a r i o u s o r i e n t a t i o n s . S e q u e n t i a l s e c t i o n s p a r a l l e l t o the c o m p o s i t i o n a l f o l i a t i o n were taken on f o l d limbs and at f o l d c l o s u r e s . V e r t i c a l s e c t i o n s i n 2 planes were prepared throughout the body ( F i g . 11). From the f i r s t b l o c k a randomly o r i e n t e d s e c t i o n was cut, and o p t i c axes p l o t t e d t o give an i n d i c a t i o n of any p r e f e r r e d o r i e n t a t i o n s . Conclusions drawn from t h i s diagram f a c i l i t a t e d p l a n n i n g subsequent s e c t i o n o r i e n t a t i o n s to reduce e r r o r s due to equipment (Langway 1958, p. 8; Bader 1951). I t was found p r a c t i c a l t o cut h o r i z o n t a l s e c t i o n s , and v e r t i c a l s e c t i o n s both p a r a l l e l and p e r p e n d i c u l a r to the f o l d a x i s . Thus, as shown i n F i g . 11, from each sampling s t a t i o n , s e c t i o n s o f three d i f f e r e n t o r i e n t a t i o n s were employed; a l s o random s e c t i o n s were produced and r o t a t e d i n t o the h o r i - z o n t a l or v e r t i c a l plane t o t e s t homogeneity at a given p o i n t . In many cases, a given s e c t i o n c o n t a i n e d over 100 g r a i n s . However, where s e v e r a l s e c t i o n s were cut c l o s e to each o t h e r at a given s t a t i o n , the chance of repeated measurement of one i c e g r a i n was e i t h e r avoided by c u t t i n g h o r i z o n t a l s e c t i o n s i n the same plane; or minimized by c u t t i n g h o r i z o n t a l s e c t i o n s at a v e r t i c a l s e p a r a t i o n of 5 cm. F u r t h e r checks were to observe g r a i n boundary o u t l i n e s d u r i n g m e l t i n g , and to cut v e r t i c a l s e c t i o n s mutually p e r p e n d i c u l a r and observe c r y s t a l p a t t e r n s . No complicated i n t e r l o c k i n g shapes such as d e s c r i b e d by Rigsby (1968) were found. 50. Thin S e c t i o n P r e p a r a t i o n A given s e c t i o n of known o r i e n t a t i o n was smoothed on one side and then frozen onto a t h i n p l a t e and melted on i t s upper surface u n t i l i n d i v i d u a l c r y s t a l s were e a s i l y v i s i b l e . As the work was c a r r i e d out below -10°C, i n an i c e house and a l s o i n a deepfreezer, s e c t i o n t h i c k n e s s was e a s i l y c o n t r o l l e d . Prepared s e c t i o n s were mounted on a Rigsby u n i v e r s a l stage, and f u r t h e r thinned i f necessary to maximize accuracy of e x t i n c t i o n angle measurement. Some workers mounted specimens between p l a s t i c d i s c s to prevent movement. This adds an e r r o r due to the r e f r a c t i v e index of p l a s t i c sheets; a l s o such s e c t i o n s d i s i n t e g r a t e d , which may have lead to i n c o r r e c t readings. U n i v e r s a l stage technique D e s c r i p t i o n of the standard technique of o r i e n t a t i n g c r y s t a l s on the U n i v e r s a l Stage may be found elsewhere (Emmons 1942; Langway 1958). E r r o r s Langway (1958, p. 8) enumerates four sources of e r r o r i n measuring c-axes. Further e r r o r s reported by other workers, and those found i n t h i s study are l i s t e d . (1) Measurement of exact e x t i n c t i o n p o s i t i o n at high angles (2) P a r a l l a x e f f e c t when the eye i s not normal to the measured g r a i n 51. (3) Operator e r r o r i n r e a d i n g o r i e n t a t i o n d i a l s (4) Inherent mechanical e r r o r s i n the stage i t s e l f ( r e p r o d u c i b i l i t y o f readings from the same g r a i n i s u s u a l l y between 1° and 2°). (5) Measurement of c r y s t a l s i n the e q u a t o r i a l p o s i t i o n where e x t i n c t i o n i s l e s s d i s t i n c t than i n the p o l a r p o s i t i o n . (6) P e r f e c t o r i e n t a t i o n o f the t h i n s e c t i o n may not be maintained due to i n a c c u r a c i e s o f c u t t i n g b l o c k s from the i c e f a c e , and s e c t i o n i n g o f the b l o c k s . A t e s t of such accuracy i s the c o m p a r a b i l i t y o f diagrams. (7) The p r o b a b i l i t y o f m u l t i p l e measurements o f a s i n g l e c r y s t a l has been reduced, as d i s c u s s e d p r e v i o u s l y . (8) Work on temperate g l a c i e r s n e c e s s i t a t e s the use of t h i c k s e c t i o n s of the order o f 1/16", as uncon- t r o l l e d m e l t i n g continues d u r i n g the measurement of only 10 to 20 g r a i n s per s e c t i o n , before d i s i n t e - g r a t i o n . Thus many s e c t i o n s were necessary t o produce a given diagram, f u r t h e r i n c r e a s i n g e r r o r s . In the present study, s e c t i o n s c o u l d be reduced t o approximately 0.5 mm (estimated from i n t e r f e r e n c e c o l o u r s ) thus a l l o w i n g more accurate measurement of e x t i n c t i o n . A l s o , a l l g r a i n s i n a given s e c t i o n c o u l d be measured as d i s i n t e g r a t i o n was imp o s s i b l e at the p r e v a i l i n g temperature. 52. (9) Due to the hig h sediment content i n some s e c t i o n s , i r r e g u l a r m e l t i n g o c c u r r e d ; thus some s m a l l c r y s t a l s among sediment g r a i n s were not measurable. A l l o w i n g f o r equipment e r r o r s , f a b r i c diagrams are c o n s i d e r e d r e p r e s e n t a t i v e . A l l s e c t i o n s were photographed both with and without p o l a r o i d s ; a l l were s t o r e d f o r f u t u r e r e f e r e n c e , f o r example checking some p o i n t s a f t e r p l o t t i n g . P l o t t i n g of Opt i c Axis O r i e n t a t i o n A l l o r i e n t a t i o n s , p o l a r and e q u a t o r i a l , are c o r r e c t e d f o r r e f r a c t i o n at the i c e - a i r i n t e r f a c e (Langway 1958, p. 7) . No hemispheres were used on the stage. C o r r e c t e d readings were p l o t t e d on the Schmidt e q u a t o r i a l equal area n et. A u n i t area anywhere on t h i s net corresponds to a u n i t area on the sphere from which the net was d e r i v e d , but with d i s t o r t i o n of shape. P e t r o f a b r i c diagrams i l l u s t r a t e the 3-dimensional o r i e n t a - t i o n s o f f a b r i c elements i n a complete and co n c i s e manner. C o n v e n t i o n a l l y , o r i e n t a t i o n s are shown r e l a t i v e to a r e f e r e n c e plane (the plane of the diagram) i n lower hemisphere equal area p r o j e c t i o n . In many cases the p o i n t p a t t e r n i s obvious, a p o i n t c o n c e n t r a t i o n or g i r d l e , and c o n t o u r i n g i s unnecessary. Although such s t r o n g groupings were found i n t h i s study, c o n t o u r i n g was c a r r i e d out f o r comparison with many p u b l i s h e d diagrams from g l a c i e r s showing m u l t i p l e maxima, and those from ground i c e . The l i t e r a t u r e of g l a c i o l o g y and of meta- morphic p e t r o f a b r i c s i n g e n e r a l abounds with d i s c u s s i o n concerning the number of p o i n t s necessary, how they should be contoured, what c o n s t i t u t e s a p r e f e r r e d o r i e n t a t i o n , and the v a l i d i t y of A x i a l D i s t r i b u t i o n A n a l y s i s . ( i ) Number o f P o i n t s The number of g r a i n s measured has ranged from about 25 (Bader et a l 1939) to 300 ( K i z a k i 1969a) most workers p l o t t i n g over 100. ( i i ) C ontouring A s c a t t e r diagram may be contoured t o emphasize the o r i e n t a t i o n p a t t e r n . G e n e r a l l y contours are based on the number of p o i n t s per u n i t area o f the net, u s u a l l y i n percentages. A c o u n t i n g area c o r r e s p o n d i n g to 1% of the area o f the Schmidt net i s centered on the i n t e r s e c t i o n s of a predetermined g r i d , and the number of p o i n t s i n that area are recorded. A contour surrounds a g i v e n d e n s i t y o f p o i n t s . An e r r o r e n t e r s i n the arrangement of the c o u n t i n g g r i d , and i n the s u b j e c t i v e nature of c o n t o u r i n g and i n t e r p r e t a t i o n o f contour shapes. Only the centre of g r a v i t y o f a maximum, or the t r e n d of a g i r d l e can be c o n s i d e r e d meaningful; l o c a l v a g a r i e s o f contours i n many p u b l i s h e d diagrams are not o f s i g n i f i c a n c e . In t h i s study, a s e q u e n t i a l sampling technique was used, 54. p l o t t i n g c o n t i n u i n g during g r a i n measurements, u n t i l no s i g n i f i c a n t d i f f e r e n c e ensued from p l o t t i n g the l a t e s t axes. In general approximately 100 grains produced s i n g l e maxima of 15% or over. In such eases, 100 g r a i n s , 125, 150, e t c . were measured f o r ease of percentage contouring. Sections of s e v e r a l o r i e n t a t i o n s were analyzed at each sampling p o i n t , and by r o t a t i o n t o a common plane, a composite diagram of s e v e r a l hundred grains was prepared. A l s o , synoptic diagrams from s e c t i o n s around a given minor f o l d were drawn. ( i i i ) I n t e r p r e t a t i o n The f i r s t problem i n the i n t e r p r e t a t i o n of contoured diagrams i s to decide whether the diagram shows a p r e f e r r e d o r i e n t a t i o n , i . e . , that i t d i f f e r s from that expected f o r an i s o t r o p i c o r i e n t a t i o n of grains i n the parent m a t e r i a l . F l i n n (1958, 1963) examined s e v e r a l of the widely-used t e s t s of s i g n i f i c a n c e and found them u n s u i t a b l e . The s t a t i s t i c a l ( r a t h e r than g l a c i o l o g i c a l ) s i g n i f i c a n c e of c l u s t e r s and g i r d l e s of p o i n t s may be t e s t e d against n u l l hypotheses. The usual n u l l hypothesis i s that of complete randomness. F l i n n (1958, p. 533) prepared a random diagram. Comparison with the diagrams constructed i n t h i s study i n d i c a t e s that they a l l e x h i b i t p r e f e r r e d o r i e n t a t i o n . The p r o b a b i l i t y that p o i n t diagrams co n t a i n con- c e n t r a t i o n s d e v i a t i n g from a random d i s t r i b u t i o n i s approximated by the Poisson d i s t r i b u t i o n . The p r o b a b i l i t y P of o b t a i n i n g 5 5 . at l e a s t x p o i n t s i n any 1% area of a f a b r i c diagram i s expressed by: N = number of p o i n t s sampled p = p r o b a b i l i t y t h a t 1 p o i n t occurs i n a given 1% a r e a x=x t (here 0.01) When Np = 1, P r o b a b i l i t y % c o n c e n t r a t i o n c-axes/1% area 0.63 1 0.26 2 0.08 3 0.02 4 0.004 5 0.0006 6 0.0001 7 Thus f o r a 100 p o i n t sample (Np = 1 ) the chance of a 1% con- c e n t r a t i o n i s 1 i n 10,000. The above concerns s t a t i s t i c a l , not g l a c i o l o g i c a l s i g n i - f i c a n c e . For example, minor c o n c e n t r a t i o n s w i t h i n a g e n e r a l p a t t e r n such as a g i r d l e may have no s i g n i f i c a n c e . In the present study, the l i s t e d p r o b a b i l i t i e s were used f o r com- p a r i s o n with c o n c e n t r a t i o n s obtained, r a t h e r than to a t t a c h a s i g n i f i c a n c e l e v e l t o a l o c a l c o n c e n t r a t i o n w i t h i n a given o r i e n t a t i o n p a t t e r n . 56. A x i a l D i s t r i b u t i o n A n a l y s i s (A.N.A.) Having e s t a b l i s h e d t h a t the diagrams p r o v i d e evidence t h a t p r e f e r r e d o r i e n t a t i o n s e x i s t i n the body, i t i s necessary t o determine whether or not g r a i n s of d i f f e r e n t o r i e n t a t i o n are homogeneously or inhomogeneously d i s t r i b u t e d w i t h i n the body. The method i s c a l l e d A x i a l D i s t r i b u t i o n A n a l y s i s (A.V.A.). In t h i s study, the method was a p p l i e d t o s m a l l f o l d s c o n t a i n e d w i t h i n a t h i n s e c t i o n . A drawing was made, and the f o l d s d i v i d e d i n t o f i e l d s c orresponding to (a) f o l d h i n g e s , and (b) f o l d limbs. Optic axes from c r y s t a l s w i t h i n g i v e n f i e l d s were p l o t t e d on separate diagrams and compared f o r homogeneity. I t was found t h a t diagrams from component f i e l d s were i d e n t i c a l to those o f the composite f i e l d , w i t h i n the degree o f r e p r o - d u c i b i l i t y o f the diagrams. Measurement of Ice C r y s t a l S i z e and Shape Although g r a i n s i z e s i n the i c e are on average much l a r g e r than g r a i n s i n many rock and metal t h i n s e c t i o n s , a c c u r a t e measurement d i r e c t l y on the U n i v e r s a l Stage i s i m p o s s i b l e . Thus photographic s l i d e s were prepared f o r s e c t i o n s and p r o j e c t e d onto g r i d d e d paper. Measurements were made of area and major and minor axes, t o gi v e 2-dimensional s i z e i n 3 mutually p e r p e n d i c u l a r planes and thus an o v e r a l l p i c t u r e of dimensional p r e f e r r e d o r i e n t a t i o n i n r e l a t i o n to f o l i a t i o n , and i n f e r r e d d e f o r m a t i o n a l d i r e c t i o n s . Records of c r y s t a l s i z e i n the l i t e r a t u r e are o f t e n based on the product of 2 major axes averaged over 100 g r a i n s ; these measurements were taken here f o r comparison. In a d d i t i o n t o s i z e c a l c u l a t i o n s , g r a i n shape c h a r a c t e r - i s t i c s were s t u d i e d from the s l i d e s . T r i p l e - p o i n t s o f g r a i n boundaries were measured, to g i v e an estimate of thermodynamic e q u i l i b r i u m . Sediment Content A n a l y s i s Prom f i g u r e s of f o l d s and t h i n s e c t i o n s ( P i g s . 8, 9, 10) i t i s evident t h a t sediment content v a r i e s g r e a t l y . The amount of sediment i n a t h i n s e c t i o n i s i n s u f f i c i e n t f o r e s t i m a t i o n of d i r t content by a r e a l measurement. Thus a s e r i e s of b l o c k s was cut i n a v e r t i c a l l i n e from the core of a f o l d , and the volume of excess i c e c a l c u l a t e d . T o t a l weight of a sediment-ice sample was measured, then the weight o f i c e and of dry s o i l c a l c u l a t e d to g i v e the i c e content by percent o f dry s o i l . Sediment S i z e A n a l y s i s Analyses were made of the sediment obtained from samples taken f o r sediment content a n a l y s i s , and from samples removed from beds, boudins and l e n s e s . The l a t t e r i n c l u d e d beds con- t a i n i n g sedimentary s t r u c t u r e s . Standard s i e v i n g and hydro- meter methods were employed. 58. C o n c l u s i o n The methodology employed has been designed to sample a l l f a b r i c elements i n the a v a i l a b l e exposure. Prom f o l d morphology, i n f e r e n c e s may be drawn concerning the mode of deformation to produce the g e o m e t r i c a l c o n f i g u r a t i o n at the mesoscopic s c a l e . On the m i c r o s c o p i c s c a l e , f e a t u r e s may be r e l a t e d to the mesoscopic f o l i a t i o n s . These f e a t u r e s are i c e g r a i n o p t i c a x i s o r i e n t a t i o n , dimensional o r i e n t a t i o n , g r a i n s i z e and shape. Prom the d i s c u s s i o n of d e f o r m a t i o n a l and recovery p r o p e r t i e s g i v e n i n Chapter I I I , the p e t r o f a b r i c f e a t u r e s i n d i c a t e modes and d i r e c t i o n s of deformation. A l s o age r e l a t i o n s of mesoscopic and m i c r o s c o p i c forms may be i n f e r r e d from i n d i c a t o r s of i n t e n s i t y of deformation, such as f o l d s t y l e , symmetry of f a b r i c diagrams, and from p e r i o d s of c r y s t a l growth. 59. CHAPTER V RESULTS I n t r o d u c t i o n C o n s i d e r a t i o n has been given to the known d e f o r m a t i o n a l c h a r a c t e r i s t i c s o f i c e with v a r y i n g sediment contents. R e s u l t s o f a p p l y i n g the methodology o f Chapter IV are d i s c u s s e d i n t h i s chapter, the aim being t o e l u c i d a t e the mechanism of deformation o f the i c e i n Tuktoyaktuk. Chapter O u t l i n e T h i s chapter deals f i r s t l y with mesoscopic s t r u c t u r e , and then the mi c r o s c o p i c aspects o f the deformed i c e . The o v e r a l l mesoscopic s t r u c t u r e i s s u b d i v i d e d i n t o three f o l d s t y l e s i n t r o d u c e d i n Chapter IV. Each s t y l e i s c o n s i d e r e d s e p a r a t e l y i n d e t a i l , then i n t e r r e l a t i o n s h i p s among f o l d s t y l e s are d i s c u s s e d and an o v e r a l l i n t e r p r e t a t i o n o f deforma- t i o n a l movements from mesoscopic s t r u c t u r e i s given. Then, the r e s u l t s o f m i c r o s c o p i c s t u d i e s are d i s c u s s e d . O p t i c a x i s d i s t r i b u t i o n s from t h i n s e c t i o n s from around i n d i v i d u a l f o l d s are r e l a t e d t o mesoscopic f o l i a t i o n s , and d e t a i l s o f the mode and d i r e c t i o n o f deformation i n f e r r e d f o r i n d i v i d u a l f o l d s and the o v e r a l l f o l d form. G r a i n shape c h a r a c t e r i s t i c s 6 0 . from the s e v e r a l f o l d s t y l e s and the two f o l i a t i o n s are compared, and l o c a l v a r i a t i o n s of deformation and r e c r y s t a l - l i z a t i o n i n f e r r e d . Ice g r a i n s i z e i s determined from t h r e e mutually p e r p e n d i - c u l a r t h i n s e c t i o n s , v a r i a t i o n s i n s i z e b e i ng r e l a t e d t o l o c a l changes i n f o l i a t i o n . Because o f the i r r e g u l a r i t y o f g r a i n shape, only average measurements o f g r a i n s i z e are p o s s i b l e . Sediment g r a i n s i z e , shape and c o n c e n t r a t i o n s are d i s c u s s e d . Water q u a l i t y a n a l y ses are t a b u l a t e d and i n f e r e n c e s made. An o v e r a l l i n t e r p r e t a t i o n o f the p r e - d e f o r m a t i o n a l s t a t e o f the bedding and i t s subsequent f o l d i n g i s given. A. STRUCTURE 1. O v e r a l l Mesoscopic S t r u c t u r e F o l d s of S t y l e 1 These f o l d s dominate the s t r u c t u r a l geometry, o c c u r r i n g throughout the a v a i l a b l e exposure. I n d i v i d u a l f o l d s are t r a c e a b l e f o r lo n g d i s t a n c e s , the a x i a l s u r f a c e s b e i n g sub- h o r i z o n t a l and thus p a r a l l e l to the f l o o r o f the c e l l a r . F o l d amplitudes reach s e v e r a l metres and wavelengths up to 1 m occur. Bed t h i c k n e s s v a r i e s c o n s i d e r a b l y i n a given bed, and from bed to bed. In the more r e g u l a r f o l d s the t h i c k n e s s r a t i o o f limbs t o hinges measured r a d i a l l y i s 2/9 on t h i r t y beds. The complete t h i n n i n g out of beds on limbs occurs i n many p l a c e s ( F i g . 8). The p o s s i b l e reasons are t w o - f o l d : (a) p r e - d e f o r m a t i o n a l s t a t e o f the bedding, and (b) a f e a t u r e o f deformation. As the t h i n n i n g occurs i n beds which are t h i c k at f o l d c l o s u r e s i t i s reasonable to suppose t h a t the f e a t u r e i s a d e f o r m a t i o n a l product, otherwise "limbs" would occur with no c l o s u r e s . Such are not common. However, t r a n s p o s i t i o n s t r u c t u r e s and boudinage occur ( F i g s . 12, 13). Boudinage i s common i n s t r o n g l y deformed r o c k s , i n which an o r i g i n a l l y continuous competent l a y e r between l e s s competent l a y e r s has been s t r e t c h e d , t h i n n e d and s u b d i v i d e d i n t o bodies elongated p a r a l l e l to the bedding (Fig.12a, b ) . In t h i s study the boudins have rounded o u t l i n e s , i n d i c a t i n g t h a t under the c o n d i t i o n s o f deformation, the competencies o f the beds i n v o l v e d were not very d i s s i m i l a r , but the boudinaged l a y e r having l e s s c a p a c i t y f o r s t r e t c h i n g . The boudins are not completely separated from the i n i t i a l bedding ( P l a t e 2 ) . Fol d s of S t y l e 2 . These f o l d s are c o n f i n e d between plane or unf o l d e d s e c t i o n s o f f o l d limbs, and are asymmetrical ( F i g . 7 ) . They are thus drag f o l d s , formed by the r e l a t i v e movement of the e n c l o s i n g l a y e r s . The short limb was r o t a t e d from i t s o r i g i n a l p o s i t i o n , the sense o f r o t a t i o n i n d i c a t i n g the sense o f movement i n the e n c l o s i n g l a y e r s . A x i a l s u r f a c e s are o b l i q u e to the c o m p o s i t i o n a l f o l i a t i o n and thus t o the a x i a l s u r f a c e s of S t y l e 1 F o l d s . F o l d axes are p a r a l l e l t o those o f S t y l e 1 F o l d s . F o l d s o f S t y l e 3 Only one example of t h i s F o l d S t y l e occurs a s s o c i a t e d with a lensose sand body which reaches over 40 cm t h i c k n e s s i n a d i r e c t i o n at r i g h t angles to l o c a l bedding. The l a t e r a l and v e r t i c a l g r a d a t i o n of t h i s f o l d i n t o f o l d s of S t y l e 1 i n d i c a t e s t h a t the sandy body absorbed much o f the deforma- t i o n a l s t r a i n , a l l o w i n g the S t y l e 3 F o l d to r e t a i n i t s observed morphology ( F i g . 9). I n t e r r e l a t i o n s h i p among F o l d S t y l e s W i t h i n the l i m i t e d exposure the v a r i o u s F o l d S t y l e s can be r e l a t e d . S t y l e 2 F o l d s occur as drag f o l d s on extended limbs o f S t y l e 1 F o l d s . I t i s argued that they developed e a r l y i n the deformation and became.flattened with the S t y l e 1 F o l d s . The S t y l e 3 F o l d i s unique. I t s continued e x i s t e n c e i n i t s present o r i e n t a t i o n , with the a x i a l s u r f a c e at the high angle of 45° t o the o v e r a l l s u b h o r i z o n t a l s t r u c t u r a l p a t t e r n , i n d i c a t e s t h a t i t has s u r v i v e d the f l a t t e n i n g and s t r e t c h i n g episode r e c o r d e d i n the S t y l e 1 F o l d s . I t i s thus a r e l i c t o f an e a r l y stage of deformation. The p o s i t i o n of the f o l d c l o s e to the l a r g e sand lens ( F i g . 9) suggests t h a t l a t e r s t r a i n s were l a r g e l y absorbed by t h a t sandy body. I n t e r p r e t a t i o n of Movements from Mesoscopic S t r u c t u r e s From the o v e r a l l mesoscopic s t r u c t u r a l p a t t e r n , i t i s evident t h a t the S t y l e 3 F o l d i s r e p r e s e n t a t i v e of an e a r l y stage of the deformation. I t s more open mesoscopic form and the o r i e n t a t i o n o f i t s a x i a l s u r f a c e r e l a t i v e to the l o c a l s t r u c t u r e s are evidence o f t h i s . F u r t h e r , the marked change i n f o l d s t y l e i n a l a t e r a l d i s t a n c e of 2.0 m and a l e s s e r v e r t i c a l d i s t a n c e , from S t y l e 3 to S t y l e 1 f o l d s i n d i c a t e s the p r o t e c t i v e i n f l u e n c e of the sand lens i n abs o r b i n g s t r a i n . In c o n t r a s t t o the S t y l e 3 F o l d s , S t y l e 1 F o l d s have t i g h t l y appressed limbs, i n d i c a t i n g h i g h d u c t i l i t y at the time o f f o l d i n g . The recumbent a t t i t u d e with a x i a l s u r f a c e s p a r a l l e l to the p r e v a i l i n g f o l i a t i o n suggests s t r o n g f l a t t e n i n g from the e a r l y S t y l e 1 form i n t o the p r e s e n t l y observed s t y l e . S t y l e 2 Fo l d s formed d u r i n g the development of S t y l e 1 Fol d s by drag o f r e l a t i v e l y moving limbs. Some f l a t t e n i n g has a l s o o c c u r r e d . A p o s t - f o l d i n g shear i s shown i n F i g . 14. W i t h i n the lower limb o f the major f o l d , i n t e r g r a i n f r i c t i o n reduced deformation, whereas at the i n t e r f a c e between predominantly sandy and predominantly i c y beds, motion was favoured, g i v i n g r i s e t o S-shaped s t r u c t u r e s w i t h i n the sandy bed. A f t e r f o l d f o r m a t i o n , a shear developed above the s y n c l i n e , as i n d i c a t e d by the j u x t a p o s i t i o n o f two s y n c l i n e s . 2. M i c r o s c o p i c S t r u c t u r e F u r t h e r study o f f o l d s t r u c t u r e was made on t h i n s e c t i o n s . S t y l e 1 F o l d s One such f o l d was s u b j e c t e d to d e t a i l e d s e c t i o n i n g f o r the purpose of determining o p t i c a x i s d i s t r i b u t i o n s . These s e c t i o n s were a l s o analysed f o r f o l d s t y l e . Bedding f o l i a t i o n was found t o be continuous around the f o l d c l o s u r e i n t h i s case, no major o f f s e t t i n g b e i n g d i s p l a y e d ( F i g . 10). A second f o l d of S t y l e 1 showing asymmetrical form was s t u d i e d . In t h i s case, o f f s e t t i n g o f t h i c k e n e d bedding i n the f o l d c l o s u r e i s evident ( P l a t e 3 ). O f f s e t t i n g occurs p a r a l l e l to the a x i a l s u r f a c e . T h i s i s i n agreement with the s u g g e s t i o n , based on mesoscopic s t r u c t u r e , that s t r e t c h i n g o f f o l d s o c c u r r e d , movement o c c u r r i n g p a r a l l e l to a x i a l s u r f a c e s . S t y l e 2 F o l d s These f o l d s are mainly of m i c r o s c o p i c s c a l e , i n d i v i d u a l f o l d s b e i n g c o n t a i n e d w i t h i n a g i v e n s e c t i o n . From P l a t e 4 i t i s evident that a x i a l s u r f a c e s are o b l i q u e to l o c a l bedding, s e v e r a l c r e s t s o c c u r r i n g c l o s e t o g e t h e r . S t y l e 3 F o l d s S e v e r a l s e c t i o n s cut at r i g h t angles t o the f o l d a x i s were analy s e d . On the m i c r o s c o p i c s c a l e , the boundary between sandy and i c y l a y e r s i s abrupt. I n d i v i d u a l sediment bands may s u b d i v i d e as shown i n F i g . 10, and show t h i c k n e s s v a r i a t i o n s not r e l a t e d to the present s t a t e of f o l d i n g . 65. 3. M i c r o s c o p i c F a b r i c Deformational movements i n the body have been i n f e r r e d from the a n a l y s i s o f mesoscopic and m i c r o s c o p i c s t r u c t u r e s , assuming i d e a l i z e d mechanisms of f o l d i n g and f l a t t e n i n g . In order t o g a i n a b e t t e r understanding of the a c t u a l deformation mechanism, m i c r o s c o p i c f a b r i c s of s e l e c t e d specimens were s t u d i e d . These specimens were c o l l e c t e d on the b a s i s o f the sampling p l a n d i s c u s s e d i n Chapter IV. General Petrography A simple s u b d i v i s i o n was made on the b a s i s o f the composition of l a y e r s . Ice bands are f a i r l y pure, with d i s p e r s e d sediment. 2 2 C r y s t a l s i z e v a r i e s from 0.06 cm to over 20 cm . Dimensional p r e f e r r e d o r i e n t a t i o n p a r a l l e l t o the f o l d a x i a l s u r f a c e o c c u r s . Strong undulatory e x t i n c t i o n i s common, a l s o s m a l l e r u n s t r a i n e d g r a i n s with r e g u l a r o u t l i n e s . S e v e r a l t e x t u r e s , i n c l u d i n g h i g h l y s u t u r e d g r a i n boundaries and mimetic r e c r y s t a l - l i z a t i o n are found ( F i g s . 15, 16). Sediment bands have high sediment content (Table 2.) and i c e c r y s t a l s i z e i s l i m i t e d by sp a c i n g o f sediment g r a i n s . The d i f f i c u l t y o f producing t h i n s e c t i o n s i n the m a t e r i a l meant shapes and e x t i n c t i o n c h a r a c t e r i s t i c s were l e s s w e l l s t u d i e d than i n predominantly i c e bands. Contacts between i c e and sediment bands are i r r e g u l a r and o c c a s i o n a l l y g r a d a t i o n a l . A more d e t a i l e d d i s c u s s i o n o f t e x t u r e s i s giv e n l a t e r . 66. O r i g i n of F a b r i c s The o r i g i n of a p r e f e r r e d o r i e n t a t i o n of c r y s t a l s d u r i n g deformation i s a t t r i b u t e d to r e o r i e n t a t i o n i n t o supposed s l i p d i r e c t i o n s i n the deforming body as a whole. A given t h i n s e c t i o n does not c o n t a i n a f o l d , but sampling techniques made i t p o s s i b l e to r e l a t e f a b r i c s from s e c t i o n s to f e a t u r e s of the major s t r u c t u r e s . The P e t r o f a b r i c Approach The work of Sander (1930, 1948, 1950) and Schmidt (1932) e s t a b l i s h e d the concept o f m i n e r a l o r i e n t a t i o n symmetry, i . e . , o p t i c a l or dimensional o r i e n t a t i o n i s r e l a t e d to major s t r u c t u r e s i n deformed g e o l o g i c a l b o d i e s . The term f a b r i c (Gefuge) comprises a l l s p a t i a l data; i t was found p r a c t i c a l (Sander and Schmidegg 1926) to r e f e r these data t o 3 mutually p e r p e n d i c u l a r axes, a, b, c. Sander (1930, p. 56) d e f i n e d the axes with r e s p e c t to r e l a t i v e move- ments; thus a r e p r e s e n t s the d i r e c t i o n of g r e a t e s t displacement i n the s l i p p l ane; b i s p e r p e n d i c u l a r to a and c o n t a i n e d i n the s l i p plane; c i s p e r p e n d i c u l a r to the ab p l a n e . (a) F i r s t S t y l e 1 F o l d The f i r s t major f o l d t o be sampled i s shown i n F i g . 10. F i v e i c e b l o c k s were removed from around the hinge zone as i n d i c a t e d ; f u r t h e r b l o c k s were cut on the limbs where S Q and S^ are s u b - p a r a l l e l , to study any changes i n f a b r i c throughout. 67. C o n s i d e r i n g b l o c k 1, t h i s was cut so as to c o n t a i n both r e l a t i v e l y c l e a r i c e above, and s e v e r a l sediment bands below. To mai n t a i n o r i e n t a t i o n s , measurements were taken of s t r i k e and d i p of a l l f a c e s , a l s o a N - l i n e and s e v e r a l h o r i z o n t a l marks were made as a f u r t h e r check. From t h i s b l o c k , m u l t i p l e s e c t i o n s were prepared, i n both h o r i z o n t a l and v e r t i c a l o r i e n t a t i o n s , i n which a t o t a l o f approximately 400 c-axes were measured. The f a b r i c diagrams are drawn i n t h e i r o r i g i n a l plane. As p r o j e c t i o n s are mutually at r i g h t a n g l e s , i t i s easy t o p i c t u r e mentally the r o t a t i o n of one diagram i n t o the plane of another. Diagram 1 r e p r e s e n t s 100 g r a i n s from the upper r e l a t i v e l y c l e a n i c e o f the b l o c k , i n a h o r i z o n t a l p r o j e c t i o n . A s i n g l e broad c o n c e n t r a t i o n i s i n d i c a t e d , with a maximum of 19% axes per 1% area, centered approximately 13° from the pole o f the plane of p r o j e c t i o n , which c o i n c i d e s w i t h the c - a x i s of the f o l d In the f i e l d . Minor c o n c e n t r a t i o n s of no g r e a t e r than 2% at 60° to 80° t o the c - a x i s can be given no s i g n i f i c a n c e . C o n t i n u i n g the study o f the upper i c e , a f u r t h e r s e c t i o n was cut p a r a l l e l to the bc_ plan e . In t h i s case (Diagram 2) the c o n c e n t r a t i o n p a r a l l e l t o c p e r s i s t s , with a maximum of 16%, but secondary maxima appear, l y i n g a p p r o x i - mately i n the bc_ plan e . These represent c r y s t a l s measured i n the e q u a t o r i a l e x t i n c t i o n p o s i t i o n , which i s co n s i d e r e d to be su b j e c t t o some e r r o r ; however the s t r e n g t h of the 68. c o n c e n t r a t i o n , and the c o i n c i d e n c e with minor maxima i n other diagrams suggests g e o l o g i c a l s i g n i f i c a n c e . T h i s i s d i s c u s s e d l a t e r . In o r d e r to i n v e s t i g a t e any f a b r i c changes a s s o c i a t e d with the sediment bands, a v e r t i c a l s e c t i o n was cut below the p r e v i o u s , i n the same plane. T h i s s e c t i o n i n c l u d e d sediment bands. F a b r i c diagram 3 again shows the c h a r a c t e r i s t i c maximum of 15% per u n i t area, from a t o t a l o f 100 l a r g e c r y s t a l s , between the sediment l a y e r s . C r y s t a l s w i t h i n the sediment bands were of diameter s m a l l e r than c o u l d be measured due t o the d i f f i c u l t y of t h i n n i n g the i c e between sediment g r a i n s . Minor c o n c e n t r a t i o n s occur approximately i n the same plane as b e f o r e . Block 2 was cut from the hinge zone of the f o l d , and s e c t i o n s prepared i n the h o r i z o n t a l p l a n e, i . e . p a r a l l e l t o the a x i a l plane, at s e v e r a l l e v e l s , a l s o v e r t i c a l s e c t i o n s p a r a l l e l t o the f o l d a x i s , at r i g h t angles to that a x i s , and o b l i q u e to t h a t a x i s . Diagram 4 r e p r e s e n t i n g a h o r i z o n t a l t h i n s e c t i o n shows 3 maxima arranged i n p a r t o f a s m a l l c i r c l e c e n t r e d approximately 10° from the v e r t i c a l a x i s i n the f i e l d . A f u r t h e r h o r i z o n t a l s e c t i o n from below the pre v i o u s shows a broader c o n c e n t r a t i o n surrounding the v e r t i c a l a x i s with maxima o f 20% and 9% (Diagram 5). 6 9 . V e r t i c a l s e c t i o n s were produced i n order to i n v e s t i g a t e the v a r i a t i o n i n the 2 h o r i z o n t a l s e c t i o n s . Diagram 6 r e p r e s e n t s 175 c r y s t a l s measured i n a v e r t i c a l s e c t i o n p a r a l l e l t o the f o l d a x i s . The dominant c h a r a c t e r i s t i c s are 2 maxima of 10% and 12% c l o s e l y a s s o c i a t e d with the pole to the a x i a l p l a n e . A weak g i r d l e of 1% t o 2% t r a v e r s e s the diagram, i n d i c a t i n g axes i n a v e r t i c a l plane p e r p e n d i c u l a r to the l o c a l f o l d a x i s . These are c o n s i d e r e d to r e p r e s e n t the i n f l u e n c e of l o c a l bedding around the hinge. A v e r t i c a l s e c t i o n o b l i q u e t o the f o l d a x i s was prepared, t h i s again showed a maximum of 12$ (from 100 c r y s t a l s ) i n a c o n c e n t r a t i o n around the p o l e to the a x i a l s u r f a c e . A g i r d l e with l o c a l grouping o f up to 7% was found, a f t e r r o t a t i o n o f the s e c t i o n i n t o p a r a l l e l i s m t o the f o r e g o i n g (Diagram 7 ) - Diagram 8 r e p r e s e n t s 100 c r y s t a l s i n a v e r t i c a l s e c t i o n p e r p e n d i c u l a r to the f o l d a x i s . Two maxima occur w i t h i n one major c o n c e n t r a t i o n s i g n i f y i n g c-axes at r i g h t angles to the l o c a l a x i a l plane. No g i r d l e i s seen comparable to those i n diagrams 6 and 7 , as the f o l d hinge i n sediment i s not i n c l u d e d . Block 3 was removed from the i c e - f a c e at the p o s i t i o n shown i n F i g . 1 0 . Three h o r i z o n t a l s e c t i o n s were cut at v e r t i c a l s e p a r a t i o n s o f 7 .5 cm, from which measurements o f 300 g r a i n s were taken. Small c r y s t a l s a s s o c i a t e d with a minor sediment 70. band were p l o t t e d separately from the remaining l a r g e c r y s t a l s . The diagrams (9, 10) show a strong concentration around the pole to the a x i a l s u r f a c e ; the small grains have axes d i s t r i - buted i n a cone of 15-20° rad i u s around the pole (Diagram 9). Such an arrangement has a l s o been found i n r e c r y s t a l l i z i n g quartz by V o l l (I960, p. 520). A v e r t i c a l s e c t i o n p a r a l l e l t o the f o l d a x i s gave 100 a x i a l o r i e n t a t i o n s p l o t t e d i n diagram 11. A small c i r c l e of 20° passes through the maxima. During the course of a n a l y s i s of the i c e blocks discussed above, i t became apparent that sediment bands exerted some c o n t r o l over c r y s t a l a x i s o r i e n t a t i o n . Thus block 4, from the lower limb of the f o l d was subjected to successive h o r i z o n t a l s e c t i o n i n g at 5 cm v e r t i c a l i n t e r v a l s , from a pure i c e l a y e r down to a sand band. The composite diagram and component diagrams are presented i n Diagrams 12-16. The s e v e r a l concentrations i n the composite diagram are broken down among the s e r i a l s e c t i o n s , f o r example one of the maxima at 40° t o the pole of the f o l i a t i o n i s absent from the f i n a l diagram. The maximum i s the major feature of the upper s e c t i o n . Although the sample s i z e i n some component diagrams i s l i m i t e d , the change i n d i s t r i b u t i o n of concentrations i s systematic. F u r t h e r , i t i s pointed out that such changes might not appear on composite diagrams from g l a c i e r s t u d i e s where component f a b r i c s are not p l o t t e d s i n g l y . The f i n a l b l ock i n the f o l d hinge a r e a , b l o c k 5, c o n t a i n e d a narrow sediment band near the top. H o r i z o n t a l s e c t i o n s were prepared from t h r e e p o s i t i o n s , one above and two below the sediment. A 13% maximum shows i n the f a b r i c diagram (17) at the po l e to the a x i a l plane. But t h e r e i s a c o m p l i c a t i n g f a c t o r i n the presence o f a s u b - h o r i z o n t a l sediment band on which r e l a t i v e movement would occur. Secondary maxima of up to 1% and 9% occur on a p a r t i a l g i r d l e c o n t a i n i n g the f i r s t maximum. Large c r y s t a l s i n the upper s e c t i o n are d i s t r i b u t e d evenly among the th r e e c o n c e n t r a t i o n s . Both l a r g e and s m a l l c r y s t a l s i n the lower s e c t i o n s have axes o r i e n t e d approximately v e r t i c a l l y . (b) S t y l e 2 F o l d on F i r s t S t y l e 1 F o l d A f u r t h e r s e c t i o n was taken, shown i n p l a t e 4, and o r i e n t e d v e r t i c a l l y , p e r p e n d i c u l a r t o the f o l d a x i s . As the diagram (18) of the s e c t i o n shows, minor f o l d s occur on the s u b - h o r i z o n t a l sediment bands, with t h i c k e n i n g on c r e s t s , r e l a t i v e t o "limbs". These are S t y l e 2 F o l d s . The f a b r i c diagram has a broad c o n c e n t r a t i o n c o n t a i n i n g s e v e r a l maxima, o f up to 12% at r i g h t angles t o the f o l i a t i o n . (c) I n t e r p r e t a t i o n o f F a b r i c o f F i r s t S t y l e 1 F o l d C o n s i d e r i n g f i r s t l y the f a b r i c s where no sediment o c c u r s , the i c e s u b f a b r i c s are homogeneous throughout the f o l d . That i s , the p a t t e r n s are i d e n t i c a l , w i t h i n the degree of r e p r o d u c i b i l i t y expected, r e g a r d l e s s o f p o s i t i o n on the 72. f o l d . The symmetry type i s a x i a l , and at the lowest degree, orthorhombic. The symmetry a x i s c o i n c i d e s with the pole t o the a x i a l s u r f a c e , t h i s s u r f a c e being a symmetry plane. But the bedding f o l i a t i o n i s i n c l i n e d t o t h i s plane throughout the hinge area. The i n f l u e n c e o f sediment bands i s seen i n other f a b r i c diagrams, namely the presence o f minor g i r d l e s c o r r e s p o n d i n g to bedding (Diagrams 6 , 7 ) . Thus e a r l i e r p r e f e r r e d o r i e n t a t i o n s are maintained by some g r a i n s , whereas the e a r l i e r o r i e n t a t i o n s were o b l i t e r a t e d where the c o n s t r a i n t o f sediment was not o p e r a t i v e . The symmetry suggests t h a t maximum compressive s t r e s s and the a x i s of g r e a t e s t s h o r t e n i n g was p e r p e n d i c u l a r to the a x i a l s u r f a c e s , r e s u l t i n g i n a p p r e s s i o n o f the f o l d limbs to t h e i r present i s o c l i n a l c h a r a c t e r . T h i c k e n i n g o f l a y e r s i n hinge r e g i o n s i s c o n s i s t e n t with t h i s i n t e r p r e t a t i o n . (d) Second S t y l e 1 F o l d As F i g . 17 shows, the p r o g r e s s i v e development of a f o l d can be f o l l o w e d ; t h i s area was s t u d i e d i n the p r e v i o u s manner. There again o c c u r r e d a c o n c e n t r a t i o n of s u b - v e r t i c a l c-axes as shown i n diagrams 20-23 , where > 1 maxima occur. C o n s i d e r i n g a h o r i z o n t a l s e c t i o n on the lower limb o f the f o l d i n F i g . 1 7 , axes were p l o t t e d s e p a r a t e l y , sub- d i v i s i o n b e i n g made on the b a s i s of p o s i t i o n r e l a t i v e to sediment bands. No s i g n i f i c a n t change i s apparent, other than the presence of a 6% c o n c e n t r a t i o n of axes i n one s e c t i o n p a r a l l e l t o the f o l d a x i s , but i n the h o r i z o n t a l plane. T h i s 73. i s concomitant with movement i n the d i r e c t i o n of major t r a n s - p o r t , but i n a v e r t i c a l p l a n e . However no such s t r u c t u r e was evident i n the f i e l d o r i n the s e c t i o n . The p a r t i c u l a r g r a i n s are not p a r t s o f one l a r g e c r y s t a l , but are d i s t i n c t e n t i t i e s , d i s t r i b u t e d along a sediment band. T h i s i s a l o c a l f e a t u r e , not repeated on ot h e r diagrams. A second s e r i e s o f h o r i z o n t a l s e c t i o n s produced the f a b r i c s shown i n Diagrams 24-27» s e p a r a t e l y p l o t t e d on the b a s i s o f p o s i t i o n r e l a t i v e t o l o c a l sediment bands. The composite diagram i n d i c a t e s a s m a l l c i r c l e d i s t r i b u t i o n , r a d i u s approximately 20° around the v e r t i c a l f i e l d o r i e n t a t i o n , i n c l u d i n g 3 maxima of 8, 13, 18% r e s p e c t i v e l y . The p a t t e r n i s repeated i n two of the component diagrams, and suggests a r e c r y s t a l l i z a t i o n f a b r i c , as p o i n t e d out above. (e) T h i r d S t y l e 1 F o l d A f u r t h e r s e r i e s o f s e c t i o n s was prepared from a t h i r d S t y l e 1 F o l d . A t o t a l o f 250 g r a i n o r i e n t a t i o n s from 4 s e c t i o n s gave r i s e t o the f a b r i c i n diagram 28. T h i s composite diagram i s broken down i n t o 2 components, each of 2 adjacent s e c t i o n s i n 2 h o r i z o n t a l planes 5 cm a p a r t . The same broad p a t t e r n e x i s t s i n each. A f u r t h e r f a b r i c comprises g r a i n s i n a sediment l a y e r c o n t a i n e d i n the lower s e c t i o n ; the diagram shows l e s s a r e a l spread, and the absence o f a p r e v i o u s maximum. Although the l a t t e r diagram (31) i s based on only 35 c r y s t a l s , the c o n c e n t r a t i o n i s marked and tends towards a s m a l l c i r c l e p a t t e r n . 7 4 . ( f ) The S t y l e 3 F o l d The open f o l d s and the l a t e r a l and v e r t i c a l g r a d i e n t s i n t o t i g h t s t r u c t u r e s have been r e f e r r e d to p r e v i o u s l y ( F i g . 9). The f a b r i c s r e p r e s e n t a t i v e of these open s t r u c t u r e s are markedly d i f f e r e n t from those of e a r l i e r s e c t i o n s . The s e v e r a l v e r t i c a l s e c t i o n s p e r p e n d i c u l a r to the f o l d a x i s show c l e f t g i r d l e s i n the plane of the diagram. The p a t t e r n o f p r e f e r r e d o r i e n t a t i o n f o r a l l s e c t i o n s and p a r t s o f the f o l d i s s i m i l a r ; thus the f a b r i c i s homogeneous throughout the f o l d (Diagrams 3 2 , 3 3 ) . Mode of Deformation, As I n d i c a t e d by F o l d Morphology and Optic Axis D i s t r i b u t i o n s Thus the p a t t e r n o f deformation throughout the body i s co n s i d e r e d t o be s i m i l a r to t h a t of the s m a l l open f o l d , i . e . , S t y l e 3 F o l d , with g i r d l e - t y p e f a b r i c i n the e a r l y stages, the limbs then becoming h i g h l y s t r e t c h e d , and brought i n t o p a r a l l e l i s m with an a x i a l p l a n a r " s c h i s t o s i t y " . R o t a t i o n of g r a i n s d u r i n g accommodation to the imposed s t r e s s has changed the f a b r i c of o p t i c axes to one of maximal o r i e n t a t i o n p e r p e n d i c u l a r to a x i a l planes throughout the body. At hinge zones o f f s e t t i n g o f bedding p a r a l l e l to the a x i a l s u r f a c e i s i n d i c a t e d ( P l a t e 3 ) , and the l a t t i c e f a b r i c at hinge s t a t i o n s shows the c h a r a c t e r i s t i c form, but with r e l i c t f e a t u r e s from an e a r l i e r stage i n the deformation, namely a minor g i r d l e as shown i n diagrams 6 and 7. 75. Some r e l a t i v e movement oc c u r r e d w i t h i n some of the sediment bands, depending on p a r t i c l e content; t h i c k e n i n g o f f o l d hinges occurs i n p l a c e s . Boudinage wi t h l e n s o i d o u t l i n e s and deformed sedimentary s t r u c t u r e s have been d i s - cussed, and are i n d i c a t i v e o f i n t e n s e s t r e t c h i n g . Such are the c o n c l u s i o n s drawn from an i n s p e c t i o n of f o l d morphology and o p t i c a x i a l d i s t r i b u t i o n o f the s e c t i o n s d e s c r i b e d . The next s e c t i o n deals with g r a i n shape, s i z e , d imensional o r i e n t a t i o n , evidence o f s t r a i n i n g , and the i n f l u e n c e o f sediment bands, d i s p e r s e d sediment and gaseous i n c l u s i o n s on those c h a r a c t e r i s t i c s . B. ICE GRAIN SHAPE I n t r o d u c t i o n Grain shape i n p o l y c r y s t a l l i n e aggregates i s an important parameter i n the study o f the body's h i s t o r y . In the case of a monomineralic m a t e r i a l such as an i c e body devoid o f sediment, the e x i s t e n c e of the g r a i n boundaries i s i n d i c a t i v e o f d i f f e r i n g l a t t i c e o r i e n t a t i o n s o f the g r a i n s on each s i d e . Knowledge o f a b s o l u t e and r e l a t i v e s i z e s o f contiguous c r y s t a l s i n a deformed mass, and the curvature of t h e i r mutual boundary and s t r a i n w i t h i n the i n d i v i d u a l c r y s t a l s allows i n f e r e n c e s to be made concerning the occurrence o f g r a i n boundary m i g r a t i o n , r e c r y s t a l l i z a t i o n and o v e r a l l deformation o f the body. The presence o f other phases, such as sediment, In the i c e ex e r t s 7 6 . c o n t r o l s on g r a i n shape. In the deformed body under c o n s i d e r - a t i o n , there e x i s t volumes of i c e e f f e c t i v e l y devoid of sediment while elsewhere sediment i s h e a v i l y d i s p e r s e d both i n t e r - g r a n u l a r l y and i n t r a g r a n u l a r l y , or occurs i n r e c o g n i z a b l e bands. Under a given t e m p e r a t u r e - s t r e s s system, d i f f e r e n t i a l m o b i l i z a t i o n and complicated flow p a t t e r n s r e s u l t . (a) S i n g l e Phase M a t e r i a l C o n s i d e r i n g f i r s t l y a s i n g l e phase aggregate, the i n f l u e n c e of sediment i s i g n o r e d . C h a r a c t e r i s t i c s o f g r a i n shapes i n monomineralic m a t e r i a l s have been s t u d i e d by m etal- l u r g i s t s , g e o l o g i s t s (notably on q u a r t z i t e s ) and l a t e r by g l a c i o l o g i s t s . A c l a s s i f i c a t i o n has been e s t a b l i s h e d : s t r a i g h t , curved, sutured, cuspate, e t c . , as shown i n P i g . 1 8 . MacGregor ( 1 9 5 1 ) p o i n t e d out t h a t s u t u r e d boundaries o c c u r r i n g between s l i g h t l y undulose and s t r a i n e d quartz ( r e s u l t i n g from s t r a i n - i n d u c e d boundary m i g r a t i o n , a c c o r d i n g t o P l i n n ( 1 9 6 5 , p. 5 5 ) ) a l s o occurs i n i c e . In the case of s t r a i g h t boundaries, thermodynamic e q u i l i b r i u m i s suggested, but where unequal angles occur at t r i p l e p o i n t s s t a b i l i t y has not been reached. This a l s o a p p l i e s to curved boundaries which t y p i f y t e x t u r e s l o c k e d w h ile mutually a d j u s t i n g . As p o i n t e d out p r e v i o u s l y r e c r y s t a l l i z a t i o n i s a time-dependent pr o c e s s . At any stage dur i n g the e v o l u t i o n of the f i n a l t e x t u r e , g r a i n boundary types d i f f e r . The f o l l o w i n g may occur: 77. (a) e a r l y boundaries, which are normally destroyed d u r i n g metmorphism. (b) a r r e s t e d boundaries, where e q u i l i b r i u m has not been achieved. A temperature decrease causes reduced g r a i n boundary m o b i l i t y , l e a v i n g a curved, s u t u r e d or i r r e g u l a r shape. (c) e q u i l i b r i u m boundaries i n d i c a t e low f r e e energy, and are s t r a i g h t or s l i g h t l y curved. Thus the t e x t u r e d i s p l a y e d i n a g i v e n s e c t i o n i s a f u n c t i o n of e a r l i e r t e x t u r e s , the laws of n u c l e a t i o n , growth and c e s s a t i o n of growth. Shapes are s u b j e c t t o the requirements of space f i l l i n g without gaps. There are a l s o r u l e s i n v o l v i n g the c o n f i g u r a t i o n which an aggregate o f g r a i n s must adopt i n o r d e r t o be i n e q u i l i b r i u m under the i n f l u e n c e of i n t e r f a c i a l e n e r g i e s of g r a i n s . I f thermal energy i s a v a i l a b l e , d i f f u s i o n t r a n s f e r o c c u r s . Free energy must tend to a minimum, so g r a i n shapes and boundary r e l a t i o n s h i p s must a l t e r t o make t h i s p o s s i b l e . The d i r e c t i o n o f boundary m i g r a t i o n depends on the a v a i l a b i l i t y o f s t r a i n . A s t r a i n - i n d u c e d boundary m i g r a t i o n moves from an u n s t r a i n e d i n t o a s t r a i n e d r e g i o n . Movement of the curved boundary i s away from i t s c e n t r e of c u r v a t u r e , l e a v i n g behind i t s t r a i n - f r e e m a t e r i a l of the same o r i e n t a t i o n as the parent g r a i n , with an a s s o c i a t e d i n c r e a s e i n s u r f a c e a r e a . 78. Conversely, d u r i n g the l a t e stages o f a n n e a l i n g , adjustments take p l a c e i n u n s t r a i n e d g r a i n s ; boundaries migrate towards t h e i r c e n t r e s of c u r v a t u r e , and s t r a i g h t e n , r e d u c i n g t h e i r s u r f a c e a r e a , and s u r f a c e energy. (b) E f f e c t o f I n c l u s i o n s The i n t r o d u c t i o n of i n c l u s i o n s i n t o the pure i c e system a f f e c t s the shape of c r y s t a l s , the d i s t r i b u t i o n o f the secondary phase ( i n t h i s case sediment and gas) determining the r e l a t i v e m o b i l i t i e s of the boundaries. C o n s i d e r i n g the ice-sediment system, sediment bands e f f e c t i v e l y p i n down i c e - i c e boundaries. Where a given c r y s t a l encounters one such sediment band, the c r y s t a l i s elongated p a r a l l e l t o t h a t band, and the g r a i n boundary meets t h a t band at r i g h t angles ( P i g . 15); the r e s u l t i s exaggerated where c o n t a c t s are made with two such bands. Thus a dimensional o r i e n t a t i o n o f i c e s u b - p a r a l l e l to the a l r e a d y e s t a b l i s h e d sediment s u r f a c e r e s u l t s . (c) Gaseous I n c l u s i o n s Bubble coalescence as a measure of deformation i n i c e sheets was g i v e n t h e o r e t i c a l c o n s i d e r a t i o n by Weertman (1968); t h i s i s not a p p l i c a b l e i n the dead i c e under study. Gow (1968, p. l8l) found t h a t bubbles i n A n t a r c t i c g l a c i e r i c e showed no tendency to be swept towards g r a i n boundaries d u r i n g r e c r y s t a l l i z a t i o n of the i c e . Langway (1970, p. 28) mentioned the tendency f o r bubbles t o "become s m a l l e r , more 79. s p h e r i c a l , and more u n i f o r m l y d i s t r i b u t e d ( s p a t i a l l y ) with depth" i n a deep i c e core from Greenland. Observations i n s i t u An i n d i c a t i o n of two-dimensional c r y s t a l shape was obtained from a study o f etched g r a i n boundaries on the t u n n e l w a l l s ( P l a t e 5 ) . The r e s u l t s of a p e n c i l r u b b i n g are shown i n F i g . 19. General r e l a t i o n s h i p s among the f a c t o r s o f i n f e r r e d i c e flow d i r e c t i o n , sediment l a y e r s and g r a i n s i z e , e l o n g a t i o n and i n t e r c r y s t a l l i n e j u n c t i o n s are e v i d e n t . T h i n - S e c t i o n A n a l y s i s For more q u a n t i t a t i v e knowledge of these r e l a t i o n s h i p s , t h i n s e c t i o n s were analysed f o r the above-mentioned c h a r a c t e r - i s t i c s , w h i le o p t i c a x i s o r i e n t a t i o n s were measured. S e c t i o n s were photographed to p r o v i d e s l i d e s from which t r i p l e - p o i n t angles and c r y s t a l s i z e were measured, g i v i n g a g r e a t e r degree of accuracy than i s p o s s i b l e with d i r e c t readings from the s e c t i o n . Texture Types S e v e r a l d i f f e r e n t c h a r a c t e r i s t i c t e x t u r e s were found. (a) Sediment-Free Ice 1. Texture Type l a Remnants of an e a r l y t e x t u r e are seen i n the p form of l a r g e (1-2 cm ) c r y s t a l s which were l a r g e r than at 80. present but s u f f e r e d r e c r y s t a l l i z a t i o n , with the growth of sm a l l c r y s t a l s . These l a r g e c r y s t a l s show undulatory e x t i n c t i o n and deformation bands; i r r e g u l a r l y curved undulatory e x t i n c t i o n i n d i c a t e s c r y s t a l bending. Deformation bands show a l l stages of development, from i n c i p i e n t t o w e l l - d e f i n e d ; i n the l a t t e r case i n d i v i d u a l bands have e x t i n c t i o n angles v a r y i n g by as much as 10°, and are separated by approximately s t r a i g h t l i n e sub-boundaries ( F i g . 20). Superimposed on the above t e x t u r e i s a r e c r y s t a l - l i z a t i o n t e x t u r e . As shown i n F i g . 20, zones of f i n e - g r a i n e d mosaics surround and embay the l a r g e n o n - r e c r y s t a l l i z e d g r a i n s . Elsewhere, s t r i n g s o f f i n e g r a i n s t r a v e r s e the l a r g e r , which r e t a i n t h e i r e a r l y d e f o r m a t i o n a l f e a t u r e s . There i s no evidence of s t r a i n w i t h i n the f i n e r g r a i n s , they are approximately e q u i g r a n u l a r , and t h e i r boundaries meet at c l o s e t o 120° at t r i p l e p o i n t s . Embayment of e a r l y l a r g e g r a i n s by s m a l l g r a i n s i s conc e n t r a t e d at the aforementioned i n t e r - d e f o r m a t i o n band boundaries again at 120°. That the s m a l l e r g r a i n s grew l a t e r than the l a r g e r i s shown by the occurrence o f u n s t r a i n e d f i n e c r y s t a l s t r a v e r s i n g l a r g e g r a i n s ; thus the t e x t u r e i s due t o r e c r y s t a l l i z a t i o n , and not t o o r i g i n a l p o r p h y r i t i c g r a i n growth. Had deformation o c c u r r e d a f t e r g r a i n growth, s m a l l c r y s t a l s would show some s t r a i n ; deformation band boundaries would be independent o f t r i p l e p o i n t s . Recovery from p l a s t i c deformation i s thus i n d i c a t e d , r e c r y s t a l l i z a t i o n o c c u r r i n g i n the s o l i d s t a t e . As p o i n t e d out above r e c r y s t a l - 81. l i z a t l o n tends to reduce the s u r f a c e f r e e energy, and recovery absorbs the s t r a i n energy, thus t h e r e i s a tendency towards thermodynamic e q u i l i b r i u m . The f a i l u r e t o reach complete e q u i l i b r i u m i s i n d i c a t e d by departure from the 120° angle i n some cases, although the frequency d i s t r i b u t i o n o f 800 g r a i n boundary angles i s unimodal and symmetrical about a peak at 120° ( P i g . 21). F u r t h e r evidence i s the e x i s t e n c e of curved g r a i n boundaries. Such curved boundaries occur mainly i n the l a r g e c r y s t a l s , where i n d i v i d u a l bands act as s i n g l e g r a i n s , both at i n d e n t a t i o n s and at p r o j e c t i o n s . Thus i n summary, Texture Type l a shows t h a t deformation banding was produced p r i o r to recovery and a n n e a l i n g r e c r y s t a l l i z a t i o n , and thus i s a s s o c i a t e d with the deformation. Measurement of c-axes o f the g r a i n s i n d i c a t e d the e f f e c t on f a b r i c diagrams of the r e c r y s t a l l i z a t i o n p r o c e s s . R e f e r r i n g to the o p t i c a x i s diagrams d i s c u s s e d p r e v i o u s l y , i t was found t h a t s m a l l g r a i n s change o r i e n t a t i o n p r o g r e s s i v e l y with d i s t a n c e away from the l a r g e r r e l i c t c r y s t a l s . Those nearest the r e l i c t s show o r i e n t a t i o n c l o s e to t h a t of the o r i g i n a l c r y s t a l ; r o t a t i o n i n c r e a s e s with d i s t a n c e , thus e x p l a i n i n g new o r i e n t a t i o n s i n the o p t i c a x i s diagrams. 2. Texture Type 2a A second t e x t u r e type i s shown i n F i g . 22. T h i s Is termed s t r a i n - i n d u c e d boundary m i g r a t i o n , i n which s t r a i n e d g r a i n s form n u c l e i from which u n s t r a i n e d outgrowths 8 2 . p r o j e c t i n t o adjacent g r a i n s . The absence o f s t r a i n i n the outgrowth shows t h a t the m i g r a t i o n i s p o s t - d e f o r m a t i o n a l , the process u s i n g the energy o f the s t r a i n e d l a t t i c e . The shape of such outgrowths i s o f t e n curved, where m i g r a t i o n occurs away from the centre of c u r v a t u r e , elsewhere, s t r a i g h t p a r t s of otherwise s e r r a t e d boundaries i n d i c a t e the e x i s t e n c e of a c r y s t a l l o g r a p h i c plane. Intense s u t u r i n g i s evidence f o r l o c a l s t r a i n . inhomogeneities, these o c c u r r i n g i n those c r y s t a l s with o p t i c axes f a r from the p r e f e r r e d o r i e n t a t i o n . A g i v e n g r a i n may d i s p l a y s u tured, s t r a i g h t and curved p a r t s to i t s boundary, depending on the r e l a t i v e l a t t i c e o r i e n t a t i o n of i t s neighbours. M o b i l i t y of a p a r t i c u l a r boundary segment i s reduced between g r a i n s of s i m i l a r o r i e n t a t i o n . (b) E f f e c t o f Sediment Sediment occurs i n d i s c r e t e bands, and as a d i s p e r s e d phase. C o n s i d e r i n g f i r s t l y the d i s p e r s e d g r a i n s , the sediment content i n such l a y e r s i s show i n t a b l e 2 . L i n e a r t r a v e r s e s o f s l i d e s , random samples, and t r a c i n g of g r a i n boundaries showed no s i g n i f i c a n t tendency f o r sediment to be found w i t h i n g r a i n s r a t h e r than at boundaries, or v i c e v e r s a , thus there i s no c o n t r o l on i c e c r y s t a l shape. 3. Texture Type l b Sediment bands had a d e f i n i t e e f f e c t on t e x t u r e . As p o i n t e d out above, such bands e f f e c t i v e l y p i n down moving i c e - i c e boundaries, Ice c r y s t a l s becoming elongated p a r a l l e l 83. to the band. Compared wi t h i c e - i c e i n t e r f a c e s , the i n t e r - f a c i a l t e n s i o n o f i c e with a sediment band i s very h i g h , so the i c e - i c e boundaries t r e n d normal to the sediment band. Within these d i r t l a y e r s , i c e c r y s t a l s were c h a r a c t e r i s t i c a l l y l e s s than 1 mm i n diameter. Due to the d i f f i c u l t y o f m e l t i n g evenly between sediment g r a i n s , the shape of the s m a l l c r y s t a l s was not r e a d i l y e v i d e n t , nor was the o p t i c a x i s o r i e n t a t i o n e a s i l y measured. 4. Texture Type 2b Mimetic Growth A more extreme type o f g r a i n growth i s e x h i b i t e d i n the S t y l e 3 F o l d ( F i g . 16). Here the p o s t - f o l d i n g g r a i n growth has produced g r a i n shapes mimetic of the sediment-ice f o l i a t i o n . Thus the s y n t e c t o n i c c r y s t a l l i z a t i o n t e x t u r e has been o v e r p r i n t e d by l a t e r growth, i n which s t r a i n energy o f the l a t t i c e i s reduced. Thus the p o s t - t e c t o n i c c r y s t a l l i z a t i o n i s analogous to the process o f a n n e a l i n g a l r e a d y d e s c r i b e d . Mode of deformation and r e c r y s t a l l i z a t i o n as i n d i c a t e d by c r y s t a l shape Four major t e x t u r e types have been found, two a s s o c i a t e d with sediment-free i c e , and two with sediment c o n c e n t r a t i o n s . In the sediment-free bands, some r e l i c t c r y s t a l s show evidence of bending, these c r y s t a l s having been i n o r i e n t a t i o n s which c o u l d not accommodate the imposed s t r e s s by s l i p on b a s a l 8 4 . p l a n e s . Other c r y s t a l s r o t a t e d Into o r i e n t a t i o n s f a v o u r a b l e f o r such s l i p and became extended p a r a l l e l t o the b a s a l p lane. The bent c r y s t a l s have become embayed by s m a l l e r , s t r a i n - f r e e g r a i n s which grew i n a stage of r e c r y s t a l l i z a t i o n . R e c r y s t a l l i z a t i o n a l s o o c c u r r e d i n r o t a t e d c r y s t a l s , l e a d i n g to s u t u r e d g r a i n boundaries through mutual i n t e r g r o w t h o f adjacent g r a i n s . I t i s probable t h a t where adjacent g r a i n s were of s i m i l a r o r i e n t a t i o n , the d i v i d i n g g r a i n boundary disappeared to give one l a r g e g r a i n . There i s no evidence f o r t h i s o t h e r than the presence of l a r g e g r a i n s which show s l i g h t v a r i a t i o n s i n e x t i n c t i o n angle without any i n d i c a t i o n o f i n t e r n a l s t r a i n . A c o n t r a s t i n g t e x t u r e i s found i n the S t y l e 3 F o l d , i . e . , mimetic growth. In t h i s case the f a b r i c diagrams show a g i r d l e at r i g h t angles to the g e n e r a l f o l d a x i s , and are homogeneous throughout the f o l d . Both the r e l i c t - type and sutured g r a i n boundaries are absent, the g r a i n s having grown p o s t - d e f o r m a t i o n a l l y p a r a l l e l to the bedding f o l i a t i o n . Thus there has a r i s e n no o p t i c or dimensional p r e f e r r e d o r i e n t a t i o n a s s o c i a t e d with s l i p p a r a l l e l t o the a x i a l s u r f a c e s of the S t y l e 1 F o l d s . The o p t i c a x i s d i s t r i - b u t i o n i n d i c a t e s an e a r l y stage of deformation. Any s t r a i n energy was used i n mimetic r e c r y s t a l l i z a t i o n . The remaining t e x t u r e type i s a f u n c t i o n of r e l a t i v e p r o p e r t i e s of i c e and i c y sediment, g r a i n shape i n d i c a t i n g t h a t i n t e r f a c i a l t e n s i o n s between i c e and sediment i s g r e a t e r 8 5 . than at i c e - i c e boundaries. The i n f e r r e d d e f o r m a t i o n a l p a t t e r n i s t h a t an e a r l y stage o f f o l d i n g o c c u r r e d i n which no major g r a i n shape p a t t e r n was developed. The S t y l e 3 F o l d i s a r e l i c t from t h i s stage, mimetic r e c r y s t a l l i z a t i o n having s i n c e o c c u r r e d . Elsewhere, the f o l d form was m o d i f i e d by a f l a t t e n i n g p r o c e s s , g i v i n g r i s e t o a dimensional o r i e n t a t i o n of g r a i n s , p a r a l l e l t o the s l i p s u r f a c e of the body. Superimposed on t h i s o r i e n t a - t i o n are r e c r y s t a l l i z a t i o n t e x t u r e s of sutured g r a i n boundaries and r e l i c t bent g r a i n s . This, mode of deformation agrees with that i n f e r r e d from mesoscopic f o l d form and from o p t i c a x i s o r i e n t a t i o n s . C. ICE GRAIN SIZE I n t r o d u c t i o n The presence o f mimetic c r y s t a l s such as those i n F i g . 16 i n d i c a t e s the problems o f making u s e f u l measurements of g r a i n s i z e . The mimetic c r y s t a l s c o n t r a s t markedly with the elongated shapes between sediment bands and those elsewhere with long axes p a r a l l e l t o the flow d i r e c t i o n . Problems I t i s e v i d e n t from the above d i s c u s s i o n of g r a i n shape c h a r a c t e r i s t i c s t h a t the s i z e o f a given c r y s t a l seen i n s e c t i o n w i l l have v a r i e d with time. Measurements of c r y s t a l 86. area give only an estimate o f the two-dimensional s i z e o f th r e e - d i m e n s i o n a l o b j e c t s which have not n e c e s s a r i l y reached e q u i l i b r i u m . The i r r e g u l a r i t i e s o f g r a i n shape make estimates of volume of l i t t l e v a l u e . Using three mutually p e r p e n d i c u l a r s e c t i o n s at a g i v e n sampling p o i n t i t was p o s s i b l e t o study any tendency f o r elongate shape produced d u r i n g flow, or due to the presence of sediment bands. S e c t i o n s were photo- graphed on a measured g r i d and s l i d e s p r o j e c t e d on t o gr i d d e d paper to make a r e a l measurements o f g r e a t e r accuracy than i s p o s s i b l e d i r e c t l y on the U n i v e r s a l Stage. In a d d i t i o n t o the problems o u t l i n e d above, a given s e c t i o n through a sphere, say, w i l l r a r e l y g i v e a maximal s e c t i o n a l a r e a . The problems are m u l t i p l i e d i n an aggregate o f v a r i o u s l y s i z e d and shaped p a r t i c l e s , and where i n c l u s i o n s g i v e r i s e t o marked changes i n g r a i n s i z e . R e s u l t s I t i s found from the l i t e r a t u r e t h a t Ostrem (1963) and T a y l o r (1962) gave estimates o f g r a i n s i z e based on measurements of long and short axes. Axis lengths were m u l t i p l i e d t o g e t h e r and averaged f o r 100 g r a i n s . Por com- p a r i s o n with p u b l i s h e d r e s u l t s , the present author measured area and l o n g and short a x i s l e n g t h from p r o j e c t e d photographic s l i d e s . The r e s u l t s are p l o t t e d i n Table 1. From i n s p e c t i o n of the t a b l e i t can be seen that areas measured i n h o r i z o n t a l s e c t i o n s are g r e a t e r than those from 8 7 . v e r t i c a l s e c t i o n s , as would be expected due to el o n g a t i o n p a r a l l e l to flow. This was seen i n v e r t i c a l s e c t i o n s at r i g h t angles to the f o l d a x i s . But i t i s a l s o noted that the h o r i z o n t a l s e c t i o n s i n the second f o l d show markedly 2 2 d i f f e r e n t g r a i n s i z e s , 0.340 cm , 0.492 cm due to the presence of a sediment band, as discussed i n the s e c t i o n concerning o p t i c a x i s o r i e n t a t i o n . These s e c t i o n s were prepared to show the i n f l u e n c e of such sediment. In summary, only the general conclusion can be made that three-dimensional shapes of Ice c r y s t a l s i n the i c e body d i s p l a y a strong tendency f o r elongation p a r a l l e l to the a x i a l s u r f a c e , longest axes being i n the flow d i r e c t i o n . L o c a l l y sediment bands c o n t r o l i c e g r a i n s i z e w i t h i n those bands, and enhance the dimensional o r i e n t a t i o n i n adjacent i c e c r y s t a l s . As i s the case i n metamorphic petrology i n general, no method i s a v a i l a b l e f o r the e s t i m a t i o n of g r a i n s i z e of such i r r e g u l a r l y shaped m a t e r i a l s . In l e s s deformed m a t e r i a l the more equant shapes lend themselves to comparison wi t h standard c i r c l e s f o r a r e a l measurements. D. SEDIMENT (a) Sediment Grain S i z e Samples were taken from the p o s i t i o n s shown i n F i g . 23 f o r which the g r a i n s i z e d i s t r i b u t i o n s are p l o t t e d i n F i g . 24, on the ba s i s of the r e s u l t s of s i e v i n g . As the lenses and boudins contain sedimentary s t r u c t u r e s , samples 8 8 . from them must c o n t a i n g r a i n s from more than one l a y e r . However, the cumulative d i s t r i b u t i o n curves show no pronounced " k i c k " , P i g . 24. Cross bedding s t r u c t u r e s are present i n the study area and are s i m i l a r t o those found i n f l u v i a l sands found i n the Tuktoyaktuk area (Rampton 1 9 7 0 , 1 9 7 1 ) . (b) Sediment Content A n a l y s i s Prom f i g u r e s o f f o l d s and t h i n s e c t i o n s i t i s evid e n t t h a t sediment content v a r i e s g r e a t l y . Amounts of d e b r i s i n a t h i n s e c t i o n are i n s u f f i c i e n t t o estimate d i r t content by an a r e a l measurement. Thus a s e r i e s o f b l o c k s was cut i n a v e r t i c a l l i n e from the core of the " F i r s t S t y l e 1 F o l d " o f the s t r u c t u r e a n a l y s i s , see F i g . 23 and Table 2 , The number of samples i s i n s u f f i c i e n t t o make any c o n c l u s i o n other than that a wide v a r i e t y o f sediment contents e x i s t s . A value o f 80% excess i c e by t o t a l volume was found by Rampton and Mackay ( 1 9 7 1 » p. 8) on the b a s i s o f a v e r t i c a l channel sample. Due to the complex f o l d i n g , i t i s l i k e l y t h a t a bed may have been sampled more than once i n th a t sample. 8 9 . TABLE 1 S e c t i o n Average Average Number Sample O r i e n t a t i o n s i z e l o n g , C r y s t a l s cm^ short a x i s cm F o l d 1 Block 1 H o r i z o n t a l V e r t i c a l 0 . 5 0 8 0 . 8 x 0 . 6 100 p a r a l l e l a x i s 0 . 3 4 3 0 . 6 x 0 . 5 150 Block 2 H o r i z o n t a l V e r t i c a l 0 . 7 6 0 . 9 x 0 . 8 90 p a r a l l e l a x i s 0 . 8 4 1 . 0 x 0 . 8 80 V e r t i c a l p e r p e n d i c u l a r to a x i s 0 . 5 5 0 . 9 x 0 . 6 1 0 0 Block 3 H o r i z o n t a l V e r t i c a l 0 . 5 8 7 0 . 8 x 0 . 7 215 p a r a l l e l a x i s 0 . 4 3 2 0 . 8 x 0 . 5 95 Block 4 H o r i z o n t a l 0 . 5 1 4 0 . 8 x 0 . 7 80 Block 5 H o r i z o n t a l 0 . 7 5 2 1 . 0 x 0 . 7 80 F o l d 2 H o r i z o n t a l 0 . 3 4 0 0 . 6 x 0 . 6 106 H o r i z o n t a l 0 . 4 9 2 0 . 7 x 0 . 7 1 0 5 V e r t i c a l p a r a l l e l a x i s 0 . 3 0 7 0 . 6 x 0 . 5 1 0 0 t TABLE 2 Samples from t h i s study Sediment as % T o t a l Weight F i r s t S t y l e 1 F o l d S i t e Sample 1 Sample (a) 3 . 2 5 4 . 1 9 (b) 2 3 . 3 1 2 4 . 3 8 (c) 1 0 . 9 7 8 . 3 5 (d) 9 . 1 8 6 . 7 7 (e) 2 4 . 1 6 2 0 . 5 3 ( f ) 4 1 . 3 2 3 8 . 6 4 (a) 1 2 . 3 1 8 . 5 2 (b) 9 . 8 2 7 . 3 1 (c) 4 . 1 1 4 . 2 3 Second S t y l e 1 F o l d The two measurements f o r each bed i n d i c a t e w i t h i n sample v a r i a t i o n from c l o s e samples f o r a given bed. 90. E. WATER QUALITY ANALYSIS Rampton (personal communication, 1973) p r o v i d e d the r e s u l t s of water q u a l i t y t o g e t h e r with those f o r i c e from ot h e r bodies i n the Tuktoyaktuk area. TABLE 3 A n a l y s i s ( M i l l i g r a m s per L i t r e ) Ice C e l l a r Nearby Pingo Slump Face i n I n v o l u t e d H i l l near 1 2 3 1 2 .Tuktoyaktuk C0 2 5-7 4.4 2.7 1.2 12.3 A l k a l i n i t y (CaC0 3) 117 143 75-3 111 10.0 0.0 Spec. 268 463 157 269 44.1 40.5 Conductance Hardness 132 247 83.8 135 17.1 18.0 ( T o t a l ) As CaCC>3 15.0 104 24.0 7.1 2.1 (non- carbonate ) Ca 48.7 93.8 8.1 49.6 5-7 5-4 Mg 2.5 3.1 2.7 0.7 1.1 Na 3-4 4.4 0.3 1-7 0.7 0.4 K 2.8 2.9 0.6 1.7 0.6 0.1 HC0 3 143 174 135.0 12.2 19-4 S 0 4 12.4 96.2 23.3 2.7 2.3 C l 5-4 5.5 0.8 2.3 1.0 0.8 N 3-1 4.2 0.07 1.5 0.29 S i 0 o 1.7 3.2 1.5 2.4 0.4 0.00 91. Thus t h e r e e x i s t s wide v a r i a t i o n among the three samples from the c e l l a r . The two most s i m i l a r samples are C e l l a r sample 1 and the Pingo sample 1. In comparison with t a b u l a t e d values f o r samples from present-day g l a c i e r s and i c e - s h e e t s (Langway 1970) a l l the Tuktoyaktuk samples d i f f e r i n having a very much h i g h e r chemical content. Thus i t may be concluded t h a t the p l a c e o f o r i g i n o f the deformed beds was not the upper p a r t o f a g l a c i e r . C o n s i d e r i n g i c e o r i g i n at the base of an i c e - s h e e t terminus, water sources would be l o c a l ground water, p r e c i p i t a t i o n and i c e meltwater. The s i m i l a r i t y between i c e c e l l a r water q u a l i t y and t h a t of pingo i c e r e c e n t l y f r o z e n i n d i c a t e s t hat i f the c e l l a r i c e i s of g l a c i e r o r i g i n , d i l u t i o n of ground water by meltwater and p r e c i p i t a t i o n was s m a l l . CHAPTER VI CONCLUSION The d i s c u s s i o n i n t h i s paper shows that the f o l d e d underground i c e i n Tuktoyaktuk, N.W.T. has been s u b j e c t to p r o g r e s s i v e deformation. S e v e r a l stages of f o l d i n g have been d i s t i n g u i s h e d , the mi c r o s c o p i c and mesoscopic f e a t u r e s b e i n g r e l a t e d by t h e i r symmetry. A change i n d i r e c t i o n o f the major s t r e s s a x i s has been i n f e r r e d . Such are the i n f e r - ences from study of the l i m i t e d a v a i l a b l e exposure. There remain the problems o f : (a) determining the o r i g i n o f the i c e - i c y sediment sequence; (b) determining whether deformation o c c u r r e d as p a r t o f an i c e sheet or by o v e r r i d i n g o f ground i c e by an i c e sheet. (a) O r i g i n o f the bedding sequence S e v e r a l p o s s i b l e mechanisms e x i s t : ( i ) F r e e z i n g , from above, of f l u v i a l sands with sedimentary s t r u c t u r e s . ( i i ) the unfrozen sediment was i n c o r p o r a t e d i n t o the bottom of an i c e sheet: (a) sediment was p a r t o f the i c e sheet bed, at some d i s t a n c e from the snout, and was f r o z e n on to the i c e sheet, the water being l o c a l ground- water, or s u b g l a c i a l meltwater from up g l a c i e r , (b) sediment was t r a n s p o r t e d to the base o f the i c e sheet by s u b g l a c i a l water near the i c e sheet margin. The water and sediment would be of s e v e r a l o r i g i n s ; water from p r e c i p i t a t i o n , melt at the i c e snout, melt from u p g l a c i e r , each type s u p p l y i n g sediment. ( i i i ) wind- or water-deposited sediment h i g h e r on the i c e sheet or g l a c i e r , ( i v ) r i v e r , lake or sea i c e with a p e r i o d i c supply o f wind blown sand. Examination of mechanisms Mechanism ( i i i ) i s r e j e c t e d , on the grounds that (a) water q u a l i t y a n a l y s i s shows chemical content of water from the Tuktoyaktuk i c e to be s i g n i f i c a n t l y d i f f e r e n t from those f o r g l a c i e r i c e r e p o r t e d by Langway ( 1 9 7 0 ) , and t h a t (b) Ice o f such an o r i g i n c o u l d not s u f f e r the deformation d i s p l a y e d . Mechanism ( i v ) i s r e j e c t e d on the grounds t h a t (a) wind blown sand i s not o f s u f f i c i e n t q u a n t i t y under the c o n d i t i o n s of i c e cover a c t i v e today to give the rhythmic bedding shown, (b) the mechanism r e q u i r e s f r e e z i n g upwards; water supply would be i n s u f f i c i e n t t o give the i c e t h i c k n e s s shown, and (c) water q u a l i t y i s a t y p i c a l of such i c e . There remain mechanisms ( i ) , ( i i a ) , ( i i b ) . C o n s i d e r i n g mechanism ( i ) , water q u a l i t y a n a l y s i s of the f o l d e d i c e shows 94. more s i m i l a r i t y to t h a t of nearby pingos, which are thought to have grown by s e g r e g a t i o n of ground i c e , than to upper p a r t s o f present day i c e sheets. T h i s a p p l i e s a l s o i n the case of s u b g l a c i a l l y e n t r a i n e d sediment, where some o f the water i s of subterranean o r i g i n . But a d i s t i n c t i o n i s made i n mechanism ( i i ) , based on d i s t a n c e from the i c e sheet margin. Because of overburden p r e s s u r e s , sediment below an i c e sheet cannot have i c e i n i t s pores unless there i s a mechanism o f p r e s s u r e r e l e a s e . Such r e l e a s e cannot occur at great d i s t a n c e s from the snout, thus mechanism ( i i a ) i s r e j e c t e d . Mechanism ( l i b ) i s r e t a i n e d , as near the snout s u b g l a c i a l channels occur, a l s o pressure may be r e l e a s e d through the bed. T h i s mechanism r e q u i r e s b u r i a l of the deformed i c e by sand and g r a v e l , without t o t a l m e l t i n g . The narrow g r a i n s i z e range must be e x p l a i n e d . The p r e g l a c i a t i o n h i s t o r y of the area i s p o o r l y understood, but the d i s t r i b u t i o n o f v a r i o u s sediment types i s being mapped, sands u n d e r l y i n g much o f the area as f a r east as N i c h o l s o n P e n i n s u l a . The g r a i n s i z e can be e x p l a i n e d by both mechanism ( i ) and ( i i b ) . I f the p r e - f r e e z i n g sediment i s of wind or water t r a n s p o r t a t i o n , by analogy with present f r e e z i n g p r o- cesses the g r a i n s i z e d i s t r i b u t i o n would not be a l t e r e d as a f r e e z i n g f r o n t p e n e t r a t e d as i n mechanism ( i ) . S i m i l a r l y i n " f r e e z i n g - o n " c a l l e d f o r by ( i i b ) . A f u r t h e r p o s s i b i l i t y e x i s t s i n case ( i i b ) , where the g l a c i e r bed would be of a wide range of sediment s i z e , but a g r a i n s i z e s e l e c t i v e 95. i n c o r p o r a t i o n o c c u r s , as d e s c r i b e d by Souchez (1967). The presence of some pebbles complicates the i s s u e . Also present are s m a l l wood fragments which are c h a r a c t e r i s t i c of the surrounding sands. Thus, r e s t r i c t i n g the argument t o the p r e - d e f o r m a t i o n a l o r i g i n of the bedding, no c o n c l u s i v e d i s t i n c t i o n can be made between mechanisms ( i ) and ( i i b ) . Thus c o n s i d e r a t i o n i s given to the mode of deformation. (b) Mode of deformation A c c e p t i n g that two a l t e r n a t i v e o r i g i n s of the p r e d e f o r m a t i o n a l bedding e x i s t , an attempt i s made t o d i s - t i n g u i s h them by c r i t e r i a of mesoscopic and m i c r o s c o p i c d e f o r m a t i o n a l form. The two p o s s i b i l i t i e s are (a) normally segregated ground i c e l a t e r deformed by o v e r r i d i n g g l a c i e r i c e , (b) the i c e i s an i c e - s h e e t remnant, i n which case the deformation was i n t e r n a l . The mesoscopic f o l d s show axes t r e n d i n g approximately 130°; o f the two p o s s i b l e d i r e c t i o n s o f major t r a n s p o r t , f o l d form i n d i c a t e s movement from approximately 220°. These d i r e c t i o n s are r e l a t i v e t o magnetic North; a f t e r c o r r e c t i o n t o geographic r e f e r e n c e p o i n t s , deformation i s seen t o be from a s o u t h e r l y d i r e c t i o n . T h i s would apply i n both case (a) and case ( b ) . T h i s d i r e c t i o n i s i n agreement with d i r e c t i o n s of i c e movement i n f e r r e d from other f e a t u r e s i n the area. Separate examination o f the two mechanisms i s made. Suggested Deformation Mechanism (a) The s t r e s s system o p e r a t i v e d u r i n g o v e r r i d i n g o f ground i c e by an a c t i v e i c e - s h e e t i s c o n s i d e r e d . Mackay and Stager (1966) d e s c r i b e d t i l t e d beds of segregated i c e i n the Mackenzie D e l t a r e g i o n . The s t r e s s system r e s p o n s i b l e was an advancing i c e - s h e e t . The g l a c i a l geology l i t e r a t u r e c o n t a i n s many d e s c r i p t i o n s o f f o l d e d sediments, the deformation being a t t r i b u t e d t o i c e (de S i t t e r 1964, p. 329). The s t r e s s system depends on the topographic form encountered by the advancing i c e - s h e e t . At p r e s e n t , massive i c e bodies form topographic u p l i f t s , which would be s u b j e c t to l a t e r a l compression and buckle f o l d i n g . Such e a r l y formed f o l d s would s u f f e r o v e r t u r n i n g and ex t e n s i o n i n the flow d i r e c t i o n as the o b s t r u c t i o n was o v e r - r i d d e n , with d i f f e r e n t i a l flow i n the d i f f e r e n t beds. Both open and t i g h t f o l d s occur i n an ice-sediment sequence a p p a r e n t l y continuous with undeformed m a t e r i a l , on P e l l y I s l a n d (Mackay 1973, p e r s o n a l communication). Suggested Mechanism (b) In t h i s case, sediment accumulates i n l a y e r s of v a r y i n g c o n c e n t r a t i o n at the base of an i c e sheet. These o r i g i n a l l y s u b - p a r a l l e l l a y e r s are then s u b j e c t t o f o l d i n g w i t h i n an a c t i v e l y deforming body, namely the t e r m i n a l r e g i o n o f an i c e sheet. 97. The s t r e s s system i n such a body v a r i e s from p l a c e to pl a c e w i t h i n the body, and over time. Shears occur, but between shears, a c t i v e f o l d i n g o c c u r s , thus there i s a com- p r e s s i v e s t r e s s system. But above, both v e r t i c a l l y and u p - g l a c i e r , a zone of t e n s i o n w i l l e x i s t , p r o d u c t i v e of cr e v a s s e s . In the b a s a l compressive zone, f i r s t - f o r m e d f o l d s are c o n c e n t r i c , but become p r o g r e s s i v e l y more t i g h t l y appressed. Shears occur o b l i q u e to f o l d a x i a l s u r f a c e s . Compression of beds with d i f f e r e n t r h e o l o g i c a l p r o p e r t i e s g i v e s r i s e t o boudinage-type s t r u c t u r e s . E x t e n s i o n of beds may l e a d to r o o t l e s s f o l d s . I f the i c e at Tuktoyaktuk i s of such an o r i g i n i t w i l l have come from a p o s i t i o n some d i s t a n c e up from the g l a c i e r bed, i n order to e x p l a i n the t i g h t n e s s of f o l d s . For i c e o f such an o r i g i n to have s u r v i v e d , two c o n d i t i o n s must be s a t i s f i e d (a) b u r i a l of the i c e ; (b) continued temperatures below the m e l t i n g p o i n t o f the i c e . C o n d i t i o n (a) co u l d be s a t i s f i e d by the p r o d u c t i o n of a veneer of f l u v i o - g l a c i a l sand. C o n d i t i o n (b) i s known to have been the case, as r a d i o c a r b o n dates i n the r e g i o n i n d i c a t e i c e bodies t o be of ages g r e a t e r than p r e - C l a s s i c a l Wisconsin. 98. M i c r o s c o p i c S t r u c t u r e Deformation mechanism (a) P e t r o f a b r i c s o f i c e from such a body have not been d i s c u s s e d i n the l i t e r a t u r e . I t i s suggested t h a t e a r l y - formed f o l d s would be f l a t t e n e d and extended, g i v i n g s t r o n g o p t i c a x i s maxima orthogonal to a x i a l s u r f a c e s , a l s o p r e - f e r r e d dimensional o r i e n t a t i o n p a r a l l e l to the flow. Deformation mechanism (b) Intense i n t e r n a l m o d i f i c a t i o n i s expected under the c o n d i t i o n s suggested. Reports of f i e l d s t u d i e s o f present-day g l a c i e r and i c e - s h e e t margins show s t r o n g c r y s t a l o p t i c a x i s o r i e n t a t i o n s t o occur, a l s o bending o f c r y s t a l s , and a s s o c i a t e d o p t i c anomalies. G r a i n shape s t u d i e s o f a c t i v e i c e show some p r e f e r r e d dimensional o r i e n t a t i o n . I n v e s t i g a t i o n s of p o s t - d e f o r m a t i o n a l r e c r y s t a l l i z a t i o n o f s t r o n g l y f o l d e d i c e have not been r e p o r t e d . Summary Due to the l a c k of p u b l i s h e d r e s u l t s of f i e l d s t u d i e s on the s e v e r a l i c e types under c o n d i t i o n s o f a c t i v e deformation, and before and a f t e r p o s t - d e f o r m a t i o n a l r e c r y s t a l l i z a t i o n , no d e c i s i o n can be made concerning the deformation of the i c e at Tuktoyaktuk. There i s a great s i m i l a r i t y between the i c e at Tuktoyaktuk and f o l d e d i c e i n i c e sheet margins. 99. A l s o the r e c r y s t a l l i z a t i o n t e x t u r e s can be e x p l a i n e d on t h e o r e t i c a l grounds. However, due to the l a c k o f knowledge of p r o p e r t i e s of ground i c e known t o have been f o l d e d by an e x t e r n a l l y Impressed s t r e s s system, t h i s a l t e r n a t i v e remains. The o r i g i n of the sand-ice system i s thus unknown, although the p o s s i b i l i t i e s are reduced to two. (c) D i a g n o s t i c p e t r o g r a p h i c f e a t u r e s of the Tuktoyaktuk i c e One of the o b j e c t i v e s of t h i s study was to l i s t d i a g n o s t i c p e t r o g r a p h i c f e a t u r e s of the i c e f o r f u t u r e f i e l d r e c o g n i t i o n from l i m i t e d samples. Owing to the i n c o n c l u s i v e knowledge o f o r i g i n a l i c e growth and subsequent deformation the c h a r a c t e r i s t i c s l i s t e d below w i l l not be u s e f u l i n attempts to d i s t i n g u i s h the two types o f deformation. I t i s hoped t h a t the p r o p e r t i e s w i l l be v a l u a b l e i n determining the a r e a l extent and depth of the Tuktoyaktuk i c e . I t i s u n l i k e l y t h a t core samples would y i e l d f o l d c l o s u r e s , thus the summary concentrates on m i c r o s c o p i c f e a t u r e s . R e l a t i v e l y pure i c e i s c o n s i d e r e d s e p a r a t e l y from s e d i m e n t - r i c h i c e . O r i e n t a t i o n of the f o l i a t i o n r e l a t i v e to the cover must be known. (I) Pure i c e ( i ) Ice G r a i n shape Grains have a dimensional p r e f e r r e d o r i e n t a t i o n i n an approximately h o r i z o n t a l plane. G r a i n boundaries may be s u t u r e d , or be s t r a i g h t 100. with t r i p l e p o i n t angles t e n d i n g to 120°, e s p e c i a l l y where r e l i c t s t r a i n e d g r a i n s are embayed, ( i i ) Ice Gr a i n s i z e S i z e ranges vary with g r a i n shape type. Sutured g r a i n s are approximately 1.0 cm by 1.0 cm by 0.7 cm, although much l a r g e r g r a i n s occur. R e l i c t s t r a i n e d g r a i n s are approximately 1.5 cm by 2.0 cm and are surrounded by s m a l l e r u n s t r a i n e d g r a i n s 0.7 cm by 0.5 cm. ( I I ) Ice with sediment bands ( i ) Ice Gr a i n shape Grains are elongated p a r a l l e l t o the bedding f o l i a t i o n , g r a i n boundaries meeting the sediment band at approximately 90°. Away from the sediment bands, shape i s s i m i l a r t o t h a t i n category ( a ) , ( i i ) Ice g r a i n s i z e W i t hin sediment bands, i c e c r y s t a l s are l i m i t e d t o in t e r - s e d i m e n t g r a i n space s i z e , many being l e s s than 1 mm. Elsewhere, s i z e c o r r e - sponds t o t h a t i n category ( a ) , although few r e l i c t g r a i n s occur c l o s e to sediment bands. ( I l l ) O p t i c a x i s o r i e n t a t i o n i n i c e and i c y sediment Optic axes show s t r o n g c o n c e n t r a t i o n s , of up t o 20$ per 1% a r e a , i n a v e r t i c a l d i r e c t i o n . 101. Minor v a r i a t i o n s occur, dependent on degree of r e c r y s t a l l i z a t i o n . G i r d l e p a t t e r n s occur i n a v e r t i c a l plane f o r Ice from a r e l i c t open f o l d . (d) Suggestions f o r f u r t h e r work The extent of the Tuktoyaktuk i c e body i s unknown, both a r e a l l y and to depth. 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G l a c , v. 7, no. 50, pp. 155-159. WHITTEN, E.H.T. (1966) S t r u c t u r a l Geology o f Folded Rocks. Rand McNally and Co., Chicago, 663 p. WILLIAMS, P.J. (1964) Unfrozen water content of Frozen S o i l s and s o i l moisture s u c t i o n . Geotechnique, v. 14, no. 3, PP. 231-246. , (1967) The nature of F r e e z i n g S o i l and i t s F i e l d Behaviour. Norwegian Geotech. I n s t i t . Publ. No. 72, pp. 91-119. Figure 1. Location Map F i g u r e 2. Maximum and l a t e Wisconsin l i m i t s of g l a c i a t i o n F i g u r e 3a. Kink bank i n a deformed c r y s t a l SP.= S l i p plane / / / / F i g u r e 3b. Bending has produced a change i n l a t t i c e and o p t i c a l d i r e c t i o n s a c r o s s the c r y s t a l . Undulatory e x t i n c t i o n r e s u l t s . 114 0.01 0.02 0.03 0.04 0.05 A x i a l s t r a i n ( i n / i n ) Figure 4. S t r e s s - s t r a i n curves f o r pure i c e and i c e w i t h v a r y i n g sediment ; contents. : ( a f t e r Goughnour and Andersland 1968). Kinematic View Dynamic View DEFORMATION MOVEMENT PLAN OR PICTURE INITIAL FABRIC STRESS FIELD DURING DEFORMATION V SYMMETRY ARGUMENT OBSERVED FABRIC DEFORMATION MECHANISMS R e c r y s t a l l i z a t i o n F i g u r e 5. Dynamic and Kinematic viewpoints o f Deformation R e l a t i o n s h i p between S - s u r f a c e s S Q = o r i g i n a l bedding S, = a x i a l s u r f a c e o f F o l d 1 1 7 STYLE 2 1 ! 2.5 cm **<ZZ2>» |n AP/ SYTLE 3 j 50 cm j • O ^ - ^ ^ s j : •* i V.' •.*•/ \ * *S. Y • * 1 1 .*•/ " / AP ^ * • • • • •X 1 _ . J 1 • T # f/ 1/ ™ * • F i g u r e 7 - F o l d S t y l e s AP = A x i a l Plane 118 F i g u r e 8. "Rootless f o l d s " o f S t y l e 1. Figure 9. Style 3 Fold passing l a t e r a l l y and v e r t i c a l l y into Style 1 Folds F i g u r e 10. Sampling S t a t i o n s f o r F i r s t S t y l e 1 F o l d . 1, 2, 3, 4, 5 are p o s i t i o n s . o f b l o c k s f o r t h i n s e c t i o n s a n a l y s i s . 121 F i g u r e 11. The Three Th i n s e c t i o n O r i e n t a t i o n s 122 F i g u r e 12 a, b. Boudinage of sandy i c e w i t h i n i c e . Both boudins are rounded, (b) has S-shape. F i g u r e 1 3 . T r a n s p o s i t i o n s t r u c t u r e s . Bedding f o l i a t i o n l a r g e l y o b l i t e r a t e d . F i g u r e 14. Shear i n d i c a t e d by j u x t a p o s i t i o n o f two s y n c l i n e s . Minor S-shaped s t r u c t u r e s occur w i t h i n sediment band. 12 4 F i g u r e 15. E f f e c t o f sediment on g r a i n boundary shape. F i g u r e 16. Mimetic p o s t - d e f o r m a t i o n a l c r y s t a l growth i n S t y l e 3 f o l d .  Figure 18. Grain boundary shapes. 5 cm Figure 1 9 . Grain boundary shapes on c e l l a r w a l l . Redrawn from p e n c i l r u b b i n g . Arrow shows approximate flow d i r e c t i o n . r o 12 8 F i g u r e 20. R e l i c t c r y s t a l shows deformation bands. Note tendency to 120° angles at boundary t r i p l e p o i n t s . r - n i i i i i i i n - , 90 120 150 Figure 21. Frequency d i s t r i b u t i o n of boundary angles of small s t r a i n - f r e e c r y s t a l s surrounding strained r e l i c t c r y s t a l s . 129 F i g u r e 22. Texture-type I l a . S e r r a t e d boundaries.  131 5.0 1 0 0.5 0.1 0.05 Figure 24. Sediment-size curves DIAGRAM 1 HORIZONTAL MAX. 19% 100 CRYSTALS DIAGRAM 2 VERTICAL MAX. 16% 100 CRYSTALS DIAGRAM 3 VERTICAL MAX. 15% 100 CRYSTALS 135 DIAGRAM 4 HORIZONTAL MAX. 16% 100 CRYSTALS DIAGRAM 5 HORIZONTAL MAX. 19% 150 CRYSTALS DIAGRAM 6 VERTICAL MAX. 12% 175 CRYSTALS DIAGRAM 7 VERTICAL MAX. 13% 100 CRYSTALS DIAGRAM 8 VERTICAL MAX. , « ,00 CRYSTALS DIAGRAM 9 HORIZONTAL MAX. 11% 75 SMALL CRYSTALS  0 DIAGRAM 11 VERTICAL MAX. 13% 100 CRYSTALS DIAGRAM 12 HORIZONTAL MAX. 11% 250 CRYSTALS DIAGRAM 13 H O R I Z O N T A L M A X . 8% 50 C R Y S T A L S 145 DIAGRAM 14 HORIZONTAL MAX. 6% 50 CRYSTALS 146 DIAGRAM 15 HORIZONTAL MAX. 8% 50 CRYSTALS 147 DIAGRAM 16 HORIZONTAL MAX 9% 100 CRYSTALS 148 DIAGRAM 17 HORIZONTAL MAX. 13% 100 LARGE CRYSTALS DIAGRAM 18 VERTICAL MAX. 16% 100 CRYSTALS 150 DIAGRAM 19 VERTICAL MAX. 12% 125 CRYSTALS DIAGRAM 20 HORIZONTAL MAX. 18% 200 CRYSTALS DIAGRAM 21 HORIZONTAL MAX. 11% 110 CRYSTALS 153 DIAGRAM 22 HORIZONTAL MAX. 8% 47 CRYSTALS DIAGRAM 23 HORIZONTAL MAX. 8% 43 CRYSTALS 155 DIAGRAM 24 HORIZONTAL MAX. 18% 175 CRYSTALS DIAGRAM 25 HORIZONTAL MAX. 19% 100 CRYSTALS DIAGRAM 26 HORIZONTAL MAX. 6% 40 CRYSTALS DIAGRAM 27 HORIZONTAL MAX. 4% 30 CRYSTALS DIAGRAM 28 HORIZONTAL MAX. 16% 250 CRYSTALS DIAGRAM 29 HORIZONTAL MAX. 12% 130 CRYSTALS 161 DIAGRAM 30 HORIZONTAL MAX. 14% 120 CRYSTALS 162 DIAGRAM 31 HORIZONTAL MAX. 9% CRYSTALS IN SEDIM DIAGRAM 32 VERTICAL MAX. 6% 90 CRYSTALS 164 P l a t e 1. S t y l e 1 F o l d morphology d i s p l a y e d on c o r r i d o r w a l l . Wall height i s approximately 2 m. Dark bands are i c e ; l i g h t bands are sediment. P l a t e 2. Boudin of i c y sand i n i c e . L i g h t e r m a t e r i a l i s sediment. Knife i s 15 cm long. 166: P l a t e 3- S t y l e 1 Fold. O f f s e t t i n g of sediment i n f o l d c l o s u r e . G r i d s i z e i s 1 cm , P l a t e h. S t y l e 2 F o l d . A x i a l surface i s oblique to l o c a l f o l i a t i o n . P l a t e 5« Etched c r y s t a l boundaries showing up as a network of f i n e l i n e s on c e l l a r w a l l .

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