I This dissertation has been microfilmed exactly as received 69-11,663

LINDSAY, John Francis, 1941- STRATIGRAPHY AND SEDIMENTATION OF TOE LOWER BEACON ROCKS OF TOE QUEEN ALEXANDRA, QUEEN ELIZABETH, AND HOLLAND RANGES, ANTARCTICA, WITH EMPHASIS ON PALEOZOIC GLACIATION.

The Ohio State University, Ph.D., 1968 Geology University Microfilms, Inc., Ann Arbor, Michigan STRATIGRAPHY AND SEDIMENTATION OF THE LOWER BEACON ROCKS OF THE QUEEN ALEXANDRA, QUEEN ELIZABETH, AND HOLLAND RANGES,

ANTARCTICA, WITH EMPHASIS ON PALEOZOIC GLACIATION

DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By John Francis Lindsay, B.Sc.(Hons.), M.Sc,

*******

The Ohio State University 1958

Approved by

a Adviser Department of Geology ACKNOWLEDGMENTS

The writer wishes to acknowledge R. J. Baillie, P. J.

Barrett, D. H. Elliot, J. D. Gunner and D. H. Johnston for their assistance and companionship in the field. Particular thanks are due to D. K. King whose patient assistance in the field made much of the fabric study in Chapter II possible. Field support was provided by U. S. Navy Task Force 43.

The study was funded through National Science Foundation grant numbers GA-534 and GA-1159. Research on the Casement Glacier, Alaska was supported by the U. 5. Atomic Energy Commission, Contract No. AT(11-1)-1473.

Dr. C. H. Summerson supervised the dissertation. The manuscript was critically read by C. B. B. Bull, C. H. Corbatt, A. G. Everett and J. F. Splettstoesser. Extensive and invaluable assistance with regards to the fabric studies was given by J. F. Bridge and C. H. Corbatti. The writer is also grateful to the many members of the Institute of Polar

Studies who willingly gave advice and assistance.

ii VITA

January 22, 1941 Born - Gosford, New South Wales, A ustralia.

1961 ...... 8 .Sc., University of New England, Armidale, Australia.

1962 ...... B.Sc. Honours, University of New England, Armidale, Australia. 1964 ...... M.Sc,, University of New England, Armidale, Australia. 1964 ...... Research Officer, Commonwealth Scientif­ ic and Industrial Research Organization, Melbourne, Australia. 1964-65 ...... Teaching Assistant, Department of Geology, The Ohio State University, Columbus, Ohio, 1965-66 ...... Graduate Student, Department of Geology, The Ohio State University, Columbus, Ohio.

1966-68 ...... Graduate Research Associate, Institute of Polar Studies, The Ohio State University, Columbus, Ohio.

PUBLICATIONS

"Magnetic Anisotropy and Fabric of some Foliated Rocks from S. E. Australia." Geofisica Pura e Applies ta. Vol. 47 (1960/lll), pp. 30-40, (with, F. D. Stacey and Germain Joplin). "The Stratigraphy, Sedimentation and Palaeontology of a Permian and Carboniferous Sequence at Willi Willi near Kempsey, N. S. W." Unpublished honors thesis, Univ. of New England, Australia, 1961.

iii "Permian and Carboniferous Sedimentation of the (Klacleav D istrict, W. S. W." Unpublished Masters thesis, Univ. of New England, Australia, 1964, "Observations on the Level of a Self-draining Lake on the Casement Glacier, Alaska." J. of Glaciology, Vol. 6, p p . 443-445, 1966,

"Carboniferous Subaqueous Mass-movement in the lïlanning- lïlacleay Basin, Kempsey, Mem South Wales." J. Sed. Petrol., Vol. 36, pp. 719-732, 1965. "A Blastoid from the Lower Permian of the IKlanning-Macleay Basin, New South Wales." Austr. J. Sci., Vol. 29, pp. 223, 1967.

"The Development of Clast Fabric in Mudflows.; J. Sed. Petrol., in press, December, 1958.

IV CONTENTS Page

LIST OF TABLES...... vii

LIST OF ILLUSTRATIONS...... vii FIELD WORK...... 1 Treatment of Orientation D a t a , . . , . . . . . , ...... 2

CHAPTER I. STRATIGRAPHY OF LOWER BEACON ROCKS IN THE QUEEN ALEXANDRA, QUEEN ELIZABETH AND HOLLAND RANGES...... 5 Previous Investigations ...... 5 Stratigraphy ...... 11 Devonian( ? ) ...... 11 Alexandra Formation...... 11 Distribution ...... 12 Lithology ...... 14 Thickness...... IS Relation to Older Formations...... 19 Current Structures...... 24 Age and Correlation ...... 34 Environment of Deposition...... 38 Permian ...... 40 Pagoda Formation ...... 40 Distribution ...... 42 Lithology...... 43 Thickness I...... 45 Relation to Older Formations..,...... 45 Paleocurrent and Paleoslope Indicators. 47 Paleoice Direction ...... 48 Age and Correlation ...... 49 Environment of Deposition ...... 54 lYlackellar Formation...... 55 Distribution and Thickness ...... 55 Lithology...... 57 Relation to Older Formations.... 69 Paleocurrent and Paleoslope Indicators. 70 Age and Correlation ...... T4 Environment of Deposition ...... 29 Page

CHAPTER II. CLAST FABRIC OF TILL AND ITS DEVELOPMENT...... 82 Alignment of Clasts in Glacier Ic e ...... 82 • Optic Axis Fabrics of Glacier Ice ...... 84 Orientation of Clasts in Poly crystalline Glacier Ice...... 87 Observed Englacial Clast Fabrics...... 89 Effects of Deposition on Clast Fabric ...... 94 Clast Fabric Field Observations ...... 103 Sample Size and F a b r ic ...... 103 Description of Fabric, ...... 106 Variations of Clast Fabric within a Till Sheet...... 119 Horizontal Variation of Fabric ...... 119 Vertical Variation of Fabric ...... 123 Summary and Discussion ...... 132 CHAPTER III. DEPOSITIONAL ENVIRONMENT OF THE PERMIAN PAGODA FORMATION, ANTARCTICA...... 136 Geologic Setting and Previous Work ...... 136 Description of the Pagoda Formation ...... 137 Thickness...... 137 Lithology ...... '...... 138 Shale...... 138 Limestone ...... 141 Sandstone ...... 141 Conglomerate...... 189 Glacial Lithologies ...... 164 Sedimentary Structures and Directional Features...... 191 Paleocurrent Structures ...... 191 Paleoslope Indicators ...... 200 Paleoice Directional Structures...... 200 Clast Fabric...... 217 Tillite Clast Fabrics...... 217 Conglomerate Clast F a b r ic s ...... 232 The Regional Distribution of Permian Glacial and Postglacial Sediments in Antarctica ...... 235 A Model for Permian Glacial and Postglacial Sedimentation in Antarctica ...... 241

SUMMARY...... 253

APPENDIX I ...... 257

BIBLIOGRAPHY...... 292 vi LIST OF TABLES Table Page

1. Location and Fisher’s (1953) Statistics for Clast Fabrics Figured in Chapter I I ...... 109 2. Modal Analyses of T illite from the Pagoda Formation ...... 167

3. Lithology of Clasts from T illite Units in the A Section of the Pagoda Formation., 172 4. Lithology of Clast Samples from T illite Units in the K Section of the Pagoda Formation.. 173 5. Lithology of Clasts from T illite Units in the U Section of the Pagoda Formation ...... 174

6. Lithology of Clasts Collected from Six Sections of the Pagoda Formation ...... 176

LIST OF ILLUSTRATIONS Figure Page

1. Aerial view of the northern end of the Queen Alexandra Range ...... 6

2. Locality map ...... 8 3. Columnar sections measured in the Queen Alexandra, Queen Elizabeth and Holland Ranges ...... 10 4. Exposures of well-bedded, quartzose sandstone of the Alexandra Formation ...... 13 5. Conglomeratic sandstone channel in the Alexandra F o rm a tio n ..f...... 15 6. K Section on the southeastern face of Mount M iller ...... 15 7. Map and cross-section through a pre-Pagoda cave f i l l ...... • 21 vii Figure Page B. Angular blocks of limestone and rounded quartzite clasts forming the pre-Pagoda cave f i ll at Mount Counts ...... 22 9. Angular blocks of limestone and quartzite clasts from the lower part of the pre- Pagoda cave f i l l ...... 22 10. Summary map of paleocurrent directions for the Alexandra Formation ...... 25

11. Paleocurrent directions at various levels within the Alexandra Formation*., ...... 25

12. Synoptic diagrams of cross-bedding in the Alexandra Form ation...... 28

13. Long-axis fabric of 27 clasts from a conglomerate channel in the Alexandra F ormation ...... 32 14. Long-axis clast fabrics and cross-bedding from three units in A Section of the Alexandra Formation ...... 33 15. Tentative correlation of lower Beacon rocks in the Transantarctic, Pensacola and Ellsworth Mountains ...... 36 16. The head of the T illite Glacier showing the location of A, B, C, and D Sections ...... 41 17. Typical sandy tillite" from A Section of the Pagoda Formation...... 44

IB. Thinly bedded sandstone and shale units from the Mackellar Formation...... 58 19. Typical interbedded sandstone and shale of the Mackellar Formation ...... 58

20. Sinuous animal tra il on the upper surface of a sandstone bed in T Section of the Mackellar Formation ...... 62 21. Symmetrical ripple marks with abundant superimposed animal tra ils from T Section of the Mackellar Formation ...... 62 viii Figure Page 22. Q Section of the Mackellar Formation in the Moore Mountains ...... 64 23. Large contorted blocks of sandstone contained in the mudflow unit in Q Section ...... 64 24. An angular granitic clast contained in a mudflow unit at Q Section...... 67 25. Contours of the sand/(sand+shale) ratio of the Mackellar Formation ...... 68 26. Summary map of paleocurrent directions from the Mackellar Formation ...... 72 27. Paleocurrent and paleoslope orientation throughout the Mackellar Formation...... 73

28. Orientation of 25 ripple mark foreset slopes from the upper part of T Section of the Mackellar Formation...... ,'...... ,...... 75 29. Englacial clast fabrics ...... 50 30. Idealized long axis englacial clast fabric... 95

31. Controlling obstacle size as a function of roughness ...... 101 32. Variation of the radius of 95 percent circle of confidence of a tillite long-axis clast fabric with sample s i z e ...... 105 33. Tillite long-axis clast fabrics with well- developed modes paralleling the ice-flow direction and plunging upstream ...... 108 34. Tillite long-axis clast fabric diagrams with subhorizontal modes paralleling the ice-flow direction ...... Ill 35. Long-axis clast fabrics with features ex­ pected of fabrics partly reorganized subglacially at the depositional interface 112

36. T illite long-axis clast fabric with a strong transverse moçle and a girdle dipping in an upstream direction ...... 114 ix Figure Page 37. Tillite long-axis clast fabrics with well- developed modes transverse to the ice- flow direction ...... 116 38. Tillite long-axis clast fabric with a mode transverse to the ice-flow direction ...... 118 39. Tillite long-axis clast fabrics from three separate localities ...... 122 40. Five long-axis clast fabrics measured from different levels within a single unit of t i l l i t e ...... 124

41. Four long-axis clast fabrics from a single unit of tillite ...... 127

42. Evidence of mass movement in the form of distorted bedding at the top of a tillite unit...... 129 43. Two long-axis clast fabrics from a single tillite unit...... 131 44. Massive beds of t i l l i t e separated by a sandstone unit ...... 139 45. Massive siltstone with interbeds of sandstone in the upper part of the Pagoda Formation ...... 140

46. Small sandstone channel between two beds of tillite in the-lower part of the Pagoda Formation ...... 143 47. The extremely large sandstone channel as it appears in D Section...... 143

48. Thickness of sandstone and tillite in large channels exposed in C, D, G, and H Sections, of the Pagoda Formation ...... 145 49. Planar cross-bedding in a tabular sandstone body near the top of A Section of the Pagoda Form ation...... 146 50. Cross-section sketch of the esker-]ike sandstone body exposed in P Section of the Pagoda Formation...... » 149 X Figure Page 51. Esker-like sandstone body exposed in massive tillite of the Pagoda Formation ...... 151

52. Poles to sandstone wedge structures in" t i l l i t e of the Pagoda Formation ...... 154 53. Thin crumpled bed of sandstone within t i l l i t e in the lower Pagoda Formation 158 54. A small conglomeratic channel in A Section of the Pagoda Formation ...... 160 55. Thin interbedded units of conglomerate, sandstone and diamictite exposed in a channel in L Section of the Pagoda Formation ...... 163

55. Poorly cross-bedded tabular conglomeratic unit exposed in R Section of the Pagoda Formation...... 163 57. Typical poorly sorted tillite with a sandy m atrix...... 165 58. Graph showing variations in the percentage of quartz in the fine fraction of the t i l l i t e ...... i ...'...... 169 59. Grain size distribution of clast samples taken from t i l l i t e u n its ...... 178 50. Cumulative grain size distribution of large clasts.....; ...... 179

51. 8oulder concentration between two tillite units...... 180 52. Cumulative frequency curves for roundness of clasts...... 182 53. Cumulative frequency curves for sphericity of c la s ts ...... 184 54. Water-washed t i l l i t e ...... 186 55. Thickness of laminae in rhythmically laminated fine sandstone ...... 192

XI Figure Page

55. Fabric diagrams of cross-bedding in channel sandstones ...... 193

67. Paleocurrent and paleoslope map for the Pagoda Formation ...... 195 58. Plot showing general decrease in slope of foresets as thickness increases in sets of planar cross-beds ...... 197 59. Small complex slump f o l d . . . , ...... 201

70. Grooved pavement beneath the Pagoda Formation at Mount M iller ...... 203 71. Finely grooved soft sediment pavement ...... 203

72. Deep grooves exposed in a soft sediment pavement ...... 205

73. Close-up view of the same grooves as in Figure 72 ...... 205 74. Small granite pebble at the head of a groove in a soft sediment pavement...... 206 75. Grooves exposed on the same pavement as in Figure 74 ...... 206 75. Boulder pavement exposed in cross section.... 209

77. Soft sediment tail formed on the downstream side of a very small clast on a boulder pavement...... 212 78. roicro-roche moutonnes on the surface of a clast exposed on the same boulder pavement as Figure 77 ...... 213

79. (ïlicro-roche moutonnes on the surface of a clast from the same boulder pavement as Figure 78 ...... 213 80. Line of clasts emphasized by a groove on either side...... 214 81. Paleoice flow map ...... 215

X ll Figure Page

82. A Section ;'rom the northeastern end of the Queen Alexandra Range...... 218

83. B Section, Queen Alexandra Range ...... 220

84. C Section, Queen Alexandra Range ...... 222 85. D Section, Queen Alexandra Range...... 223 86. I Section, Queen Alexandra Range ...... 225 87 . K Section from Mount M iller ...... 226

88 . N Section at the head of the Lowery Glacier.. 228 89 . P Section in the Moore Mountains...... 229 90. Paleoice directions throughout K Section ...... 231

91. Long-axis clast fabrics from conglomerate bodies in the Pagoda Formation ...... 233 92. Thickness of a postglacial shales and Paleozoic tillite s along the Trans­ antarctic, Pensacola and Ellsworth [mountains ...... 236 93. Paleoice directions in the Transantarctic and Pensacola Mountains ...... 238 94. Profile of two ice sheets with radii of (l) 950 km and (2} 2250 km...... 243 95. Position of the postglacial strandline in relation to the retreat of the Paleozoic ice sheet ...... 247 96. Calculated rates of sedimentation for the postglacial shales ...... 249 97. Thickness of rhythmite units in parts of A and K Sections of the Mackellar Formation ...... ,...... ■...... 250

xiii FIELD WORK

The Queen Alexandra, Queen Elizabeth and Holland Ranges are centered at about 83°30'S, 164°Q0'E in the central Transantarctic Mountains of Antarctica. The mountains are rugged, extensively glaciated and in places exceed 4000 m in elevation. They are bounded on the southwest by the Polar Plateau and on the northeast by the Ross Ice Shelf. The present study is based on field work carried out during the 1965-57 and 1957-68 austral summers. On November 16, 1966 the writer as a member of a four- man party was landed by Hercules LC130F aircraft on the Polar Plateau at the southern end of the Queen Alexandra Range. Access from this point to the field areas was by way of the Lennox-King Glacier which transects the range. Approximately one month was.spent on the T illite Glacier in the Queen Alexandra Range studying in detail the Pagoda

Formation and revisiting the type localities of the Alexandra, Pagoda and Mackellar Formations (Grindley, 1953).

In late December and early January a three-week sledge journey was made to the southern end of the Holland Range and the eastern side of the Queen Elizabeth Range. A shorter trip was made to the southern end of the Queen 2

Alexandra Range prior to being airlifte d from the field on

February 7, 1967, On November 11, 1967 the writer as a member of a five- man party was landed on the Marsh Glacier beside the Moore

Mountains which form the western side of the Queen Elizabeth

Range, The Marsh Glacier provided access to the mountains enabling the study of the Pagrr' and Mackellar Formations

to be extended as far north jnt Counts. The party was

a irlifte d from the field on ^d..--...per 11, 1967 . The present study is treated in three parts. Chapter I deals with the regional aspects of the stratigraphy of the lower Beacon rocks of the Queen Alexandra, Queen Elizabeth

and Holland Ranges. In Chapter II special attention is given to the development of t i l l clast fabric to allow its use as a tool in Chapter III which deals with the deposi­ tional environment of the Pagoda Formation. A further

study (Lindsay, 1968) was carried out on the development of clast fabric in mudflows^ to allow a more complete

understanding of the fabrics measured in the Pagoda

Formation but is not included in the dissertation.

Treatment of Orientation Data

Extensive use is made of fabric diagrams for clast fabric and cross-bedding information. In all cases fabric diagrams are based on an equal area projection and are contoured by a method developed by Kamb (1959), Kamb’s 3 method uses a counting circle of variable size depending on the number of points plotted and the level of significance desired. The resulting densities are then contoured in

terms of the standard deviation for points with a uniform distribution. Thus, observed densities that differ from

the expected density by a predetermined number of standard deviations are likely to be significant. All diagrams presented are contoured on the basis of the density being larger than three standard deviations. The contour interval for all diagrams is, unless otherwise stated, one standard deviation (d). The diagrams were contoured and plotted on an I.B.iyi. 7094 computer, using a Fortran IV subroutine developed by Dr. C. E. Corbat'b of the Department of Geology

of The Ohio State University. Fabric statistics are calculated using Fisher's (1953) distribution on a sphere. Cross-bedding information is in all cases plotted as the direction and angle of dip of the foreset as it provides a fabric diagram which is more readily

visualized in terms of paleocurrent direction. Because cross-bedding can be regarded as a vector, Fisher's method may be applied directly to the data. However, clast axes are not vectors and it is necessary to rotate the resultant point of the data to a vertical orientation to allow an estimation of the value of the various parameters. In all

cases the radius of the circle of confidence is given for the 95 percent level even though it is not stated in the text. It must be kept in mind that, while this treatment 4

of fabric diagrams is probably reasonable for comparing

diagrams, Fisher's method is only completely valid for fabrics with a spherical normal distribution* It is readily apparent that the method cannot reasonably be applied to a

. fabric diagram with more than one principal mode. A considerable portion of the paleocurrent and paleo-

slope information can be treated only in two dimensions. Where five or more readings are available, the vector mean

and standard deviation is calculated and the results appear in the text in the form 250^11° where the direction of the

vector mean is taken in a clockwise direction from true north. Where the plus-or-minus figure (the standard deviation) is not given, less than five measurements are » available. The vector mean and standard deviation were calculated using a Scatran program written by P. J. Barrett of the Institute of Polar Studies of The Ohio State University. CHAPTER I

STRATIGRAPHY OF LOWER BEACON ROCKS IN THE QUEEN ALEXANDRA, QUEEN ELIZABETH, AND HOLLAND RANGES

Previous Investigations

Shackleton and his party of 1908-09 discovered the Beardmore Glacier and were the firs t to sight the Queen Alexandra Range (Fig. 1). David and Priestley (1914) discussed the geological findings of Shackleton's party and established a sim ilarity between the geology of the Queen

Alexandra Range and that of the better-known area in Victoria Land. Taylor ( ij} David and Priestley, 1914, p. 235-240) described Archaeocyathids from morainal erratics and specimens taken from Mount Buckley at the head of the Beardmore Glacier. Debenham (1921) and Smith (1924, p. 219-237) discussed the geological findings of Scott's (1911-12) parties and Seward (1914) described Glossooteris collected by Scott's polar party. This was one of the most significant geological discoveries made during the expedition for it provided the basis for a Permian age of the Beacon rocks and suggested their relationship to the Glossopteris-bearinq rocks of other southern continents. (The name Beacon earlier applied 5 ■ ' v i - ' '@#W ,

4#*% ' .40:

M

Figure 1. Aerial view of the northern end of the Queen Alexandra Range, the southern end of the Holland Range and the Bowden Neve. This is the main area investigated during the 1966-67 field season. Figure 2. Locality map. The cross-hatched area indicates the location of the Queen Alexandra, Queen Elizabeth and Holland Ranges. Figure 2

é >

ROSS IC SHELF

SO

ROSS in the sense of a series or a system is no longer appropriate in formal stratigraphie nomenclature but continues to be used in an informal sense as Beacon rocks or Beacon sequence for those rocks overlying the Lower

Paleozoic and Precambrian basement and underlying the lavas of the Ferrar Group.) Gunn and Walcott (1962) published the results of the geology of the Commonwealth Trans-Antarctic Expedition and the 1959-60 New Zealand Geological Survey Expedition, Additional Permian plant remains were collected by the Trans-Antarctic Expedition at Cranfield Peak in the Queen Elizabeth Range and by the Geological Survey at the northern end of the Bowden Neve. Most important in terms of the present study were the sections measured by Gunn and Walcott (1962) in Bunker Cwm (L Section, Fig. 3). The sections included part of what is now called the Pagoda Formation as well as the lYlackellar, Fairchild, and Buckley Formations. Unfortunately, Gunn and Walcott failed to recognize the t i l l i t e , probably because the highly weathered rock looks like fissile shale. Grindley (1963), while a member of the 1951-52 New Zealand Geological and Survey Antarctic Expedition, pro­ vided the first detailed stratigraphy of the area and divided the stratigraphie sequence into six units.

Recognition of the tillite and discovery of further Permian plant fossils, along with the detailed stratigraphy provided 10

Figure 3, Columnar sections measured in the Queen Alexandra, Queen Elizabeth, and Holland Ranges. Sections are lettered from A to V and their locations are marked on the inset map. (In pocket at back.) 11 a very good basis for correlation with sections outside the area and with other southern continents. Young and Ryburn (1956) showed that Grindley's (1963) stratigraphy could be extended to the Buckley and Darwin Islands (nunataks) at the head of the Beardmore Glacier.

Stratigraphy

The lower Beacon sequence is divided into the Alexandra

Formation of probable Devonian age and the disconformably overlying Pagoda and Mackellar Formations of Permian age. The sequence is for the most part horizontally bedded and rests unconformably on the highly deformed Precambrian and Lower Paleozoic basement complex (Goldie Formation and Shackleton Limestone).

Devonian(?)

Alexandra Formation The Alexandra Formation was named by Grindley (1963).

The name is derived from the Queen Alexandra Range where it was f ir s t described. The formation consists of well-bedded, quartzose sandstones which unconformably overlie the base­ ment complex and are disconformably overlain by the Pagoda

Formation. The type section, as defined by Grindley (1963), exposed on Hampton Ridge beside the Montgomery Glacier at

83°55.4'S, 167°03»E ( SU 56-50/15, Mt. Elizabeth Sheet) is incomplete and only about half the formation is represented. 12

A supplementary section (F Section, Fig. 3) was measured by the present writer 2 km southwest along Hampton Ridge from the type section 5.4 km northeast of the summit of Pagoda

Peak at 83°55.0'S, 156°59'E ( SU 56-60/15, lYlt. Elizabeth Sheet). This section is relatively complete, some 311 m thick, although the contacts of the formation are not exposed.

Distribution Exposures of the Alexandra Formation are very limited but widely distributed. At the northeastern end of the Queen Alexandra Range the top of the formation is exposed in the ridge between the T illite and Montgomery Glaciers. The most complete sections, including the type and supple­ mentary sections, are present along the ridge between the

Montgomery and Bell Glaciers. A well-exposed, apparently complete section is exposed at the base of the Mount

Elizabeth Massif, although i t was not visited. In the Holland Range exposures were visited at the southern end of the range beneath Mount Miller ( K Section) and at Bunker Cwm (L Section) on the Robb Glacier. On the eastern side of the Queen Elizabeth Range a section was visited at Turnabout Ridge (M Section) and exposures of the formation can be seen in the vicinity of the Helm Glacier. At the head of the Helm Glacier near Solitary Peak (V Section) and on the western side of the range at Mount Counts (U Section) the formation is absent. 13

ïiiffîasïMi

Figure 4. Exposures of well-bedded, quartzose sandstone of the Alexandra Formation in F Section. 14

Lithology In the vicinity of the type section the Alexandra Formation consists largely of thick beds of coarse- to medium-grained, cross-bedded, well-sorted sandstone with local channels of pebbly sandstone and conglomerate. A few of the sandstones are massive and have a sugary texture resulting from recrystallization. Near the base of the type section numerous calcareous concretions up to 5 cm in diameter are found in a poorly cross-bedded, medium- grained sandstone. Directly above is a thin sandstone bed containing small algal "biscuits" up to 3 cm in diameter. The conglomerates all occur as local channel deposits (Fig. 5), The clasts are of well-rounded, black and gray chert and white vein quartz, and have a maximum grain size of 17 cm. At Mount Miller ( K Section), where the upper 100 m of the formation is exposed (Fig. 6), a slightly different facies is represented. Well-sorted and well cross-bedded, quartzose sandstones are still the dominant lithology but they are interbedded with a small amount of shale (5 percent) end lesser amounts of limestone and poorly sorted sandstones.

Most of the sandstones (80 percent) are medium-grained, well-sorted and well cross-bedded but the beds have a much greater range in thickness than the sandstone beds exposed in the type area. Where the sandstone is interbedded with shale and limestone the beds range from 3 to 15 cm. Toward 15

Figure 5. Conglomeratic sandstone channel in F Section of the Alexandra Formation.

Figure 6. The K Section on the southeastern face of Mount Miller. This is one of the most completely exposed sections in the area studied. 15 the top of the formation, above the shale and limestone, bedding thickness increases to as much as 1.5 m although it is more generally 40 cm to 1 m thick. Thin beds frequently display symmetric ripples, whereas the thicker beds are cross-bedded. Toward the top of the formation, particularly the upper 40 m, cross-bedding becomes less frequent and the beds become thicker and are recrystallized.

Poorly sorted sandstones comprise almost 15 percent of the exposed portion of the formation at Mount Miller. It is medium- to fine-grained and olive-green in color, and generally finer grained than the associated well-sorted sandstones. Ripple-drift cross-bedding occurs more frequently than larger scale cross-bedding. One bed of poorly sorted, fine-grained sandstone, 3,1 m thick and lying 43 m below the top of the formation, is orange-brown in color and lies directly over an apparent erosion surface.

The surface is marked by red iron staining which penetrates 20 cm into the underlying sandstone bed which is massive and fine-grained. The shales are black, somewhat calcareous, and general­ ly interbedded with thin limestone beds or thin beds of quartzose sandstone. Borings are common in some shales and mudcracks outlined by sand occur on the top of some, shale layers directly below limestone beds. The limestone is gray or black in color and always occurs in beds 5 to 15 cm thick interbedded with units of shale from 50 to 100 cm thick. 17

The few poorly exposed portions of the Alexandra Formation present in Bunker Cwm (L Section) are all cross­ bedded, well-sorted, quartzose sandstones that weather to a tan color on the surface. Too l i t t l e of the formation

is exposed to be of value in any environmental interpreta­ tion. At the head of the Lowery Glacier on Turnabout Ridge

the Alexandra Formation has a somewhat different character again. With the exception of two thin shale beds which form less than one percent of the thickness, the formation is entirely sandstone. However, unlike the type locality, only 14 percent is the typical light-colored, well-sorted sandstone. The remaining 85 percent is olive-green to

gray in color and poorly sorted. The well-sorted sandstones occur mainly in the lower 50 m with some thin beds occurring throughout. The beds are flaggy or poorly cross-bedded and average about 60 cm

in thickness. The less well-sorted sandstones, commonly bright green, are much more variable in color. The grain

size ranges from fine to coarse. Many of the beds, particularly the coarse-grained units, contain a high proportion of coarse, red, highly angular garnet which is plainly visible in hand specimen. Channel structures and festoon cross-beds are common, particularly in the middle portions of the section. Some of the channel sandstones contain scattered, well-rounded pebbles of yellow and 18 white quartz and red and black chert, whereas others contain angular fragments of bright red shale derived from contem­ poraneous sediments. Two bright red beds of shale, each about 1 m thick and separated from each other by 4 m of gray-green sandstone, occur about 70 m above the base of the section. They are probably similar to the beds which supplied the red shale fragments found in many of the channel sandstones.

Thickness The only complete section measured of the Alexandra Formation is that along Turnabout Ridge (IKI Section) at the head of the Lowery Glacier where the formation is 333 m thick. The supplementary type section is incomplete but judging from nearby exposures of both the upper and lower contacts the total thickness of the formation in the type area is very similar to that at Turnabout Ridge. In contrast at Solitary Peak (V Section) and again at Mount Counts (U Section), the formation is completely absent.

Accepting the assumptions about the age of the karst topography at Mount Counts, which is discussed in a follow­ ing section, the absence of the formation represents non­ deposition rather than erosion. If so, the change in thickness from zero near Solitary Peak to 333 m at Turnabout Ridge, 6,6 km away, represents a very marked change in conditions. Similar changes in thickness, however, have been recorded only a short distance away to the north on 19 the opposite side of the Nimrod Glacier (Laird and others, in preparation).

Relation to older formations The Alexandra Formation unconformably overlies the basement complex. In the vicinity of the type section and at Turnabout Ridge, the basement rocks are metagraywackes of the Goldie Formation (Grindley, 1963, p. 321; Gunn and

Walcott, 1962). The contact is not exposed in the vicinity of the supplementary type section, Grindley (1963, p. 321),

however, notes that a "pebbly quartz arenite rests sharply on the planed and smoothed surface cut in the basement greywacke" beneath the type section. Grindley (p. 322) also notes that "the surface below the Beacon sediments in the Beardmore region is iron stained but little weathered," At Turnabout Ridge the contact itse lf is concealed by rubble, but basement rocks exposed nearby show no signs

of iron staining or weathering. The exposures of sediment nearest the contact are all" medium-grained, white to pale

yellow, quartzose sandstone. In the vicinity of Solitary Peak the Pagoda Formation rests on Goldie Formation. The

surface of the la tter is deeply grooved and clearly has been modified considerably since the time of deposition of the Alexandra Formation in the nearby areas. At Mount Counts the Pagoda Formation rests directly on Shackleton Limestone, This locality is of particular interest as a filled cave is exposed in the cliffs of t.TO

Shackleton Limestone directly beneath the Pagoda Formation

(Fig, 7), The surface upon which the Pagoda Formation rests is gently undulating and has a relief of 12,3 m. The hollows on the limestone surface are filled with sandy t i l l i t e but the surface its e lf is not grooved and does not show any signs of glacial erosion. The tillite appears to have been deposited directly over the preglacial surface.

A large amphitheater-shaped depression leads from the limestone surface down to the cave and is thought to be part of a sinkhole. Green sandy breccia containing large, rounded, quartzite clasts occurs thinly distributed over the surface of the depression, and filling fissures which cut across the steeply dipping Shackleton Limestone. The fissures range from a few centimeters to 1.6 m in width and could often be traced from up to 10 m across the surface and across the slopes of the sinkhole. The former cave is a tubular structure 9.5 m below the erosion surface and is 5.2 m wide and 5,5 m high at section AA' in Figure 7 but at 38* is reduced to 4 m in width and

2 m high. The cave is completely filled with sediment, the

deposition of which appears to have taken place in two stages. The lower 3.5 m of the fill at AA' section is a cave breccia consisting of blocks of limestone up to 1.5 m in diameter which were presumably derived by collapse of the cave roof and large well-rounded quartzite and white quartz clasts up to 23 cm in diameter (Figs. 8 and 9). Figure 7. lïlap and cross-section through a pre-Pagoda cave f i l l in Shackleton Limestone at U Section beneath Mount Counts. Note large debris-filled fissure.

. QUARTZITE CLASTS + CALCITE RHOMBS LIMESTONE BLOCKS

. "^WEAK STRATIFICATION

' DEBRIS COVER

METERS

CONTOUR INTERVAL I METER i 'O c J t • • • ^ ^ — (METERS BELOW EROSION SURFACE) SECTION AA' 0 1 2 LIMESTONE CAVE METERS MT. COUNTS 22

Figure 8. Angular blocks of limestone and rounded quartzite clasts forming the pre-Pagoda cave f ill at Mount Counts. The limestone visible in the upper le ft of the photograph is the cave wall.

Figure 9. Angular blocks of limestone and quartzite clasts from the lower part of the pre-Pagoda cave f i ll . 23

The clasts are set in a coarse green sand which was presumably carried in by stream action. The quartz and quartzite clasts are completely unsorted and about 60 per­ cent are broken rounds. The sandy matrix is highly

calcareous and stained brown near the walls of the cave but grades to a bright green toward the interior. For the most part, the matrix is massive and shows no sign of bedding except near the walls where a vague layering is visible. The cave breccia also contains rhombs of crystal­ line calcite which appear to have been derived from vug-like pockets within the limestone. Some of the pockets contain well terminated calcite crystals up to 8 cm in width. The second phase of f ill consists of a coarse green sandstone with a few scattered small clasts of quartzite. To determine whether the sediment was deposited by stream action through the cave or simply by dumping of sediment down a sinkhole, a clast fabric was measured. The fabric

(Fig. 7) is similar to those of stream gravels (Schiemenz, 1960) with two modes, one paralleling the orientation of the cave -- that is, the stream flow direction — and the other lying transverse to it. The second phase suggests a change in conditions resulting in rapid and complete filling of the cave. Two possibilities are apparent: (1) i t may have resulted from a purely local change in the surface drainage pattern which allowed large volumes of sediment to be transported into the cave, or (2) it may 24 represent a general change in conditions on the surface, perhaps the onset of a fluvial period represented elsewhere by the Alexandra Formation. The second hypothesis is supported by the marked similarity between the green sandstone and the clasts in the cave f ill, particularly the lighter green sandstones in the upper portion of the f ill and the green sandstones and quartz clasts contained in some sandstone beds exposed on Turnabout Ridge a few kilometers away at the head of the Lowery Glacier. The sediments of the second phase,notably the clasts, are not comparable with the Pagoda Formation. Current structures in the Alexandra Formation at Turnabout Ridge suggest a source area in the direction of Mount Counts. The karst topography at Mount Counts may have been dry land during

Alexandra time.

Current structures Paleocurrent information based on measurements of planar cross-beds, channel "structures, ripple-drift cross­ beds (205 measurements) and long-axis fabric of conglomer­ ate pebbles, presents an inconsistent picture (Fig. 10). Cross-bedding. Vector means of planar cross-bedding measured at various levels within the supplementary type section (F Section, Fig. 11) show current directions varying through 229° in a clockwise direction from 071° to 300°. The variations follow no regular pattern and it can only be concluded that the structures represent deposition 25

IWE3 \ > iar;

M 1. RA301 A COUNT

MT MILLER PEAK

160®EA

ALEXANDRA FOR^/iATION PALEOCURRENT DIRECTIONS

£ 0 p- -> CROSS-BEDDING - PARTING LINEATIONS -5 CHANNEL ORIENTATIONS MACKELLAR^

RIPPLE DRIFT CROSS-BEDS I65°E

Figure 10. Summary map of paleocurrent directions for the Alexandra Formation. Each symbol represents the vector mean of all measurements for the current structure indicated at that one locality. METERS ? ? ? ? ? ? g g ? ? ? I ? ? M 8 ? ? ^ P ? I ^ I ^ 8 ? ^ ^ 8 H / / / \ X /

I I I I I I I I J 1 I \ oi-

Ul-j i-c n

J 1 L J I I I L J I I L J L J I I ro / i rv OJ- -Of A- I Figure 11» Paleocurrent direction at various levels within the Alexandra Formation at F, K and !K1 Sections, (l) cross-bedding, (2) parting linea- tions, (3) channel structures, (4) ripple-drift cross-bedding, (5; ripple ro marks. o\ 27 in very shallow water close to or possibly at wave base and the current structures probably represent local fluctuations associated with the shifting of sand bars and channels. The well-sorted and well-rounded nature of the sandstones supports this concept by suggesting recycled sands or a relatively high energy environment. There is, however, no evidence that the conditions were

subaerial. A synoptic diagram for all cross-bedding measurements made (N=3l) from this section is presented in Figure 12A. The resultant direction is 159° with a circle of confidence of 5.00° and a k value of 19.53 (Fisher, 1953). Despite the variations from bed to bed,

the k value and the radius of confidence indicate a strong overall trend in the main transport direction. A total of 76 Cross-bedding orientations were determined from very limited exposures on the east side of

the T illite Glacier beneath Pagoda Peak. Within any one bed the cross-bedding orientation is quite consistent but from bed to bed the vector mean varies from 069° to 132°. A synoptic diagram using all points measured is presented in Figure 128. The resultant direction is 103° with a circle of confidence of 2.5° and a k value of 43.13. The

high k value and the small radius of confidence probably reflect the small area of the exposures studied. Planar cross-bedding measurements from the upper part of the Alexandra Formation at Mount Miller vary to some extent but not as markedly as they do in the vicinity of o o

- > z

Figure 12« Synoptic diagrams of cross-bedding in the Alexandra Formation (a; F Section, N=31, (b) A Section, N=76, (c) K Section, N=20, (d) fil Section, N=38.

K) cn 29 the type section. Vector means of cross-bedding orientation from individual units fluctuate from 146° to 358°. The synoptic diagram (Fig. 12C) for all cross-bedding measure­ ments (N=20) has a resultant direction of 223° with a circle of confidence of 6.51° and a k value of 25.33, The orientation of a single channel structure is 258°. Planar cross-bed orientations measured on Turnabout Ridge are more consistent than in most other sections and suggest that the directions given are more meaningful on a regional scale. The consistency probably reflects a response to the nearby strandline. The orientation of the vector means at seven levels within the formation varies from 099° to 341°. The general direction of transport indicated by the synoptic diagram (Fig. 12D) is 098° with a circle of confidence of 5.8° and a k value of 17.43 (iM= 38). Channel orientations were measured at four levels lower in the formation and give a vector mean of 049*26°, which is in reasonable agreement with the cross-bedding determination. Exposures of the Alexandra Formation in Bunker Cwm are very restricted and it was possible to measure the orienta­ tion (309°) of only one planar cross-bed. The variation in directions found at other localities indicates the very limited value of this observation. 30

Ripple marks. Ripple marks are not common in the

Alexandra Formation except in K Section. At this locality the crests of the ripple marks have a mean orientation of

107*4°, They occur on the tops of thin (2-5 cm) units of medium- to coarse-grained, well-sorted, quartzose sand­ stone, The ripple marks from ten beds within the formation have a mean wave length of 4.27 cm (ranging from 3,5 to 6,4 cm) and a mean wave height of 0,55 cm (ranging from

0,4 to 1,4 cm). The mean ripple index is 5,5 with a range from 6,2 to 9,0, The ripples are remarkably symmetrical and have a mean ripple symmetry index of 1,05, Following Tanner (1957), the combination of ripple index (less than 15) and ripple symmetry index (less than 1,5) indicates a wave origin for the ripple marks which is in agreement with other features suggesting shallow water at this locality.

Clast fab ric. The orientation of the long axes of

27 clasts was measured from a coarse channel deposit 113 m above the base of the supplementary type section (F Section) The channel deposit is 32 m thick and consists of a very coarse sandstone with a high proportion of large well-

rounded clasts of white quartz and gray or black chert (Fig, 5), The largest clast measured was 17 cm in diameter. The unit was. both horizontally laminated and poorly cross­ bedded in festoon structures. The sediment is poorly sorted and suggests rapid sedimentation. 31

The fabric (Fig. 13) has two relatively strong modes at a high angle to each other; consequently, Fisher’s sta tistic s were not applied. Both modes are of roughly equal strength, one oriented at 123° and the other at 242°.

Patterns of this general form are recorded frequently in stream gravels (Schiemenz, I960), with one mode parallel to the current and one transverse to it; however, the modes are not quite normal to each other. The vector mean of the cross-beds is 141*8°, suggesting that the mode oriented at 123° parallels the stream direction. At A Section on the Tillite Glacier, clasts were measured from three sequential beds. The upper and lower beds are well cross-bedded in planar units, whereas the middle unit is massive. Consequently, the cross-bed orientations were measured from the upper and lower beds as were the clast fabrics (Fig. 14). Cross-bedding from

the lower unit gives a current direction of 137° with a radium of confidence of 3.4° and a k value of 58.58 (N=3l). The upper bed has a current direction of 74° with a radius of confidence of 3.5° and a k value of 46.50 (N=36). The long-axis clast fabrics for the upper and lower beds correlate well with their respective cross-bed orientations, i.e ., the long axes of the clasts lie in the plane of the cross-beds and are oriented parallel to the slope. They

indicate currents strong enough to roll the larger clasts and align them parallel to the current direction in the 32

i

Figure 13, Long-axis fabric of 27 clasts from a conglomerate channel deposit 113 m above the base of the F Section of the Alexandra Formation, 33

Figure 14, Long-axis clast fabrics and cross-bedding measurements from three units in A Section of the Alexandra Formation. (A) Cross-bedding from the uppermost unit, N=30, (B) Long-axis clast fabric from the uppermost unit, N=23, (C) Long-axis clast fabric from the massive middle unit, N=34, (D) Cross-bedding from the lowermost unit, l\I=31, (E) Long-axis clast fabric from the lowermost unit, N=33. 34 plane of the cross-bed. In contrast to this, thé clast fabric of the middle unit is concentrated in the plane of the bed and in that plane it has five apparently randomly distributed modes. One mode with a north-south orientation

is somewhat stronger than the others and may represent the current direction. If the clasts have any real orientation, it is clearly weak and a considerably larger number of clasts would be necessary to define it adequately.

The cross-bedded units appear to represent currents of moderate strength, capable of at least rolling, orienting

clasts up to 5.8 cm in diameter, and stable for the time period necessary to deposit the unit. The fabric of the middle unit and the absence of cross-bedding suggest rapid

deposition from a highly turbulent stream. The horizontal nature of the fabric indicates that the unit was not deposited as a single unit in a highly turbulent slurry, but was built up over an interval of time, and as the clasts were deposited from the current they came to rest under gravity in a horizontal plane. They must have been

buried rapidly, however, to prevent alignment by the current once they came to rest.

Age and correlation The only fossils known to come from the Alexandra Formation are a few small algal ' b iscu its,' up to 3 cm in diameter, which were found in well-washed sandstone 35 with a calcareous cement near the base of the supplementary type section (F Section). Trace fossils in the form of burrows and tra ils were found at two levels in the Turn­ about Ridge section (lYI Section) and also at Mount Miller

(K Section), Fossils allowing correlation within the range were not found, therefore, the age is based on stratigraphie position and similarity of lithology. Datable fossils from the base of the Beacon rocks are known from two regions within the Transantarctic Mountains:

McMurdo Sound and the Horlick Mountains (Fig. 15). Woodward (1921) described fish remains from erratics on the Mackay Glacier and assigned them to the Upper Devonian. Gunn and Warren (1962) have collected fish remains from three localities and at two levels at a stratigraphie position identified by Grindley (1953, p. 322) and Harrington (1965, p. 30) as the. Aztec Siltstone. Gunn and

Warren report that the fish remains have been assigned to Upper or Middle Devonian or possibly both. Plant remains, collected from the Pyramid Sandstone by Harrington and

Speden (1962), and described by Plumstead (1952), were identified as forms restricted to the Lower and Middle

Devonian. Boucot and others (1963) described a terebratuloid fauna from the Horlick Formation, the lowermost formation

in the Horlick Mountains, and assigned it to the Lower Devonian. AXEL- WISCONSIN HEIBERG GL QUEEN CENTRAL SOUTHERN ELLSWORTH PENSACOLA OHIO RANGE TO AMUNDSEN TO SHACKLETON ALEXANDRA NIMROD DARWIN VICTORIA SHACKLETON GL GL RANGE SCOTT GL GL RANGE GL LAND MINS MTNS GL CHAPPELL CRADDOCK SCHMIDT LONG MINSHEW LONG BARRETT WADE THIS ^ D OTHERS HASKELL ALLEN AND OTHERS AND OTHERS (1965) (1966) (IN PREP­ (1966) AND OTHERS PAPER (IN PREP­ AND OTHERS (1962) (1965)_ (1965) ARATION) (1965) ARATION) (1965) MAC­ DISCOVERY WEAVER FM ROARING UNIT A MACKELLAR MACKELLAR POLARSTAR SHALE FM KELLAR RIDGE FM MIDDLE AND FM 9 8 - FM 9 0 0 + M LOWER MBRS LOWER UNIT FM FM 168-195 M 18-49 M 116 M 60-121 M 305 M 137 M O-IOM WHITEOUT BUCKEYE BUCK­ SCOTT SCOTT BASAL BUTTERS PAGODA DARWIN GALE MST EYE PAGODA CGL TILLITE FM80- GL FM GL FM CGL FM FM TILLITE lOOO^M 3 0 0 + M 256-313 M 140 M 0 -20 M 3 -3 4 M 0-15 M 6 9 M 136-395 M FM 27 M DOVER % ÀLixÂi^ HATHERTON HEISER % HOR­ FORTRESS LICK DRA FM SS CRASHSITE ELBOW FM 0-311* SS QUARTZITE FM 450 M ELLIOT S3 M BROWN O-M WEBB RIDGE^ CGL BROWN RAGS SS 2600+ M HILLS CGL

Figure 15, Tentative correlation of lower Beacon rocks in the Transantarctic, Pensacola and Ellsworth Mountains. Cross-hatched areas represent erosion intervals or non-deposition. 37

In both regions Devonian ages have been established for sandstone formations on the basement. Similarly, in both regions the upper contact of the Devonian sediments is marked by an unconformity. It is not unreasonable to suggest, as Grindley (1953, p, 322) has, that the Alexandra Formation, primarily a sandstone unit, which rests on the basement and has its upper lim it marked by an unconformity, occupies a similar position to the Devonian sandstone formations in the iïlclïlurdo Sound region and the Horlick Mountains, Recently Laird and others (in press) described the stratigraphy of the central Nimrod Glacier area and correlated well-sorted quartzose sandstones near the base of the Beacon rocks with the Alexandra Formation, Wade and others (1965) correlated the Butters Formation of the Queen Maud Mountains with the Alexandra

Formation, However, as discussed in detail under the Pagoda Formation, the equivalence of this later correlation seems unlikely because the lithology of the Butters

Formation is more similar to the Pagoda Formation. The Hatherton Sandstone and the Brown Hills Conglomer­ ate in the Darwin Glacier region were described by Haskell

and others (1964, 1955) and correlated with the Alexandra Formation on the basis of stratigraphie position and

lithologie similarity. 38

Environment of deposition The discontinuous distribution of the Alexandra Formation, the inconsistent paleocurrent directions, and the limited exposures make an environmental interpretation of this formation difficult. The current directions recorded From the vicinity of the type section indicate a general transport direction to the southeast. At Mount Miller ( K Section) and Turnabout Ridge (M Section), the current directions oppose each other and may represent transport into a trough-like structure from opposite sides.

Available evidence suggests deposition in shallow water. As discussed previously, the sediments at Turnabout Ridge were probably derived from land nearby in the direction of Mount Counts; deposition in shallow water is indicated by the abundance of channel structures with festoon cross- beds and mud-chip breccias. At Mount Miller (K Section), periods of subaerial deposition are indicated by an iron- stained erosion surface and a persistent occurrence of . mudcracks. The mudcracks are always filled with sand and directly overlain by thin, fine-grained limestone units, which suggest chemical precipitates in very shallow water. Shallow deposition is also suggested by the occurrence of a small number of channels in the sandstone and ripple marks of wave origin. At the type section, evidence of subaerial conditions is lacking and the sediments consist of well-bedded quartzose sandstone. However, a few coarse 39. conglomeratic channels suggest fluvial conditions for short periods of time. The presence of algal material in a bed near the base of the section indicates light penetration and hence shallow water. Overall, the environment, for the most part, was high energy because, with the exception of some of the Turnabout Ridge sediments, the sandstones are well sorted, mature, and consist in many cases of well- rounded quartz grains. In some beds, notably at Mount Miller, the sandstones are almost perfectly sorted and the grains of quartz are almost spheres. It is apparent from this ttiat some of the sediment has been recycled, perhaps more than once. However, the less well-sorted green sand­ stones at Turnabout Ridge indicate the introduction of considerable amounts of unworked sediment. The abundance of highly angular garnet throughout M Section suggest a relatively local source, possibly from the garnet-rich metamorphic rocks exposed in the Miller Range. Such a source fits the paleocurrent data well. The lack of fossil material, along with the very shallow water nature of much of the sequence, supports a non-marine rather than a marine environment. The discontinuous distribution of the forma­ tion also suggests relatively local deposition, but it could also indicate considerable erosion. Sr^^/Sr^^ ratios on the algal material have high values, which also suggest a non-marine origin (Barrett, Faure, and Lindsay, 1968). 40

It is most likely that the Alexandra Formation was deposited in a shallow high energy non-marine environment. Deposition appears to have taken place in a narrow trough­ like structure with sediments being introduced from both sides of the basin. Land appears to have been exposed to the west of the basin, but information is lacking for the source of sediment to the east. The overall picture suggests that the sediment was transported along the length of the basin in a southeasterly direction.

Permian Pagoda Formation Grindley (1953, p. 322) introduced the name Pagoda

T illite from exposures on nearby Pagoda Peak (83°46.5'S, 166°45'E, SU 56-60/15, Mount Elizabeth Sheet)(Fig. 16). The formation consists of massive t i l l i t e with interbedded sandstones and shales. It overlies the Alexandra Formation disconformably and is overlain by the lYlackellar Formation conformably. As the unit over much of its extent consists of a large proportion of sediments other than tillite, it is proposed here that the more general term of "formation” be applied rather than " tillite " as proposed by Grindley,

Grindley defined the type locality as "below the cliffs of Pagoda Peak and Mount Mackellar." The section at this locality is incomplete because at least 30 m of the formation lie beneath the ice. Consequently., a supplementary 41

Figure 16. The head of the T illite Glacier showing A, B, C, and D Sections. The peak in the background is Mount Bell, and in front of it is Pagoda Peak. 42 section mas measured on a nearby spur of the same ridge.

The section is located on the ridge between the Tillite and Montgomery Glaciers 9.4 km north of Mount Mackellar at 166°33.0'E, 83°54.3‘S (SU 56-60/l5, Mount Elizabeth Sheet), The supplementary section is 174 m thick.

Distribution Exposures of the Pagoda Formation are quite restricted.

Northward from the base of Pagoda Peak, the formation is exposed for about 10 km in spurs along the ridge between the T illite and Montgomery Glaciers in the Queen Alexandra Range, An isolated section was measured at Portal Rock at the mouth of the T illite Glacier. At the southern end of the Holland Range, the formation is exposed on the southeastern and southern faces of Mount

Miller and at the base of Clarkson Peak in Bunker Cwm, In the eastern end of the Queen Elizabeth Range, at the head of the Lowery Glacier, the Pagoda Formation is exposed on Turnabout Ridge. The Pagoda Formation is exposed at a number of localities in and around the Moore Mountains. A limited exposure of the upper few meters of the formation occurs on the northern face of Mount Weeks, just south of the Moore Mountains. Several exposures of the upper 100 m of the formation are exposed in the Moore Mountains them­ selves, notably at the head of an unnamed glacier below Mount Angler, North of the Moore Mountains, a well- exposed complete section of the formation occurs on the 43 northern ridge and face of Mount Counts. Barrett (personal communication, 1967) reports a well-exposed section on the eastern ridge of Solitary Peak near Mount Rabot, Laird and others (in press) have recently found a series of limited exposures of the Pagoda Formation north of the area studied by the present writer on the opposite side of the Nimrod Glacier.

Lithology

The lower half of the type section consists largely of massive beds of olive-green t i l l i t e (Fig. 17), 0.5 to 18 m thick, locally interbedded with cross-bedded channel sandstones, 1 to 8 m thick, which pinch out laterally in a few meters. The upper half of the formation consists of dark-green to gray shale with dropped clasts (in a few beds) interbedded in planar cross-bedded sandstone and some t i l l i t e .

In contrast to the Tillite Glacier area, the Pagoda

Formation at Mount Miller and Bunker Cwm in the Holland Range consists almost entirely of olive-green to dark-gray t i l l i t e with a few interbedded channel sandstones. At the head of the Lowery Glacier at Turnabout Ridge (M Section), the Pagoda Formation consists of about 56 percent sandstone. The gray-green to olive-green tillite units are 8 to 24 m thick and occur more frequently toward the top of the section. About 6 percent of the formation consists of gray to black shale. 44

Figure 17. Typical sandy tillite from A Section of the Pagoda Formation. Note the large clast. 45 There are no complete sections of the Pagoda Formation exposed in the Moore Mountains. However, to the north at Mount Counts there is a single well-exposed section (U Section). The section there is exceptionally thick and contains a greater thickness of sediment than any other section in the area studied. Much of the extra thickness is made up of poorly sorted sandy sediments containing large numbers of scattered clasts. These sediments are interpreted as being deposited from floating ice, probably in a proglacial lake. Barrett (personal communication, 1967) also measured a complete section near Solitary Peak (V Section), which is also exceptionally thick. In this case, however, the extra thickness appears to be made up by an increase in the total thickness of tillite. The lithology of the Pagoda Formation is discussed in considerable detail in a following section (Chapter III).

Thickness The thickness of the Pagoda Formation in the area studied is relatively consistent and the slight variations encountered are mainly the result of changes in the thick­ ness of shale and sandstone rather than tillite. In the vicinity of the type section, the formation averages 175 m (total thickness), with tillite forming about 56 percent of the thickness. At Mount Miller the 45 thickness decreases to 125 m, mainly as a result of a decrease in the thickness of water-deposited sediments. Consequently, t i l l i t e forms 89 percent of the section. At Bunker Cwm the formation is 160 m thick, of which 70 percent is tillite , and at the head of the Lowery Glacier the formation is 135 m thick, with 51 percent tillite. The section measured at Mount Counts is 395 m thick, of which 45 percent is tillite. At Solitary Peak, Barrett (personal communication, 196?) reports 303 m with 91 percent of the thickness being t i l l i t e . The increase in thickness at these two locations appears to represent deposition in a pre-glacial depression or valley. Elsewhere in the vicinity of the Moore Mountains, the measured sections are all incomplete.

Relation to older formation Where the Alexandra Formation was observed, i t is directly and disconformably overlain by the Pagoda Forma­ tion. On the ridge between the T illite and Montgomery Glaciers in the vicinity of the type section, the contact is generally poorly exposed. Where exposed at G Section, massive medium-grained, pale-green sandstone with scattered clasts rests on a slightly iron-stained surface of white quartzose sandstone of the Alexandra Formation. The surface of the Alexandra Formation has no visible relief and the iron staining penetrates only a few centimeters. 47

The contact at Turnabout Ridge (lYl Section) is similar, but without iron staining and tillite lies directly on the surface. The contact at Bunker Cwm is poorly exposed, but, like that in the vicinity of the type section, has very low relief and is somewhat iron stained. At Mount Miller, the Pagoda Formation rests on a deeply grooved and striated surface cut in sandstones of the Alexandra Promotion. The grooves are up to 2 m deep and three striation directions cross the surface. The surface shows no signs of weathering or staining. The deep grooves in the surface are filled with a very pale-green, almost white, medium- to coarse-grained, very sandy tillite , which is derived almost entirely from the underlying quartzose sandstones.

Paleocurrent and paleoslope indicators Paleocurrent and paleoslope indicators were measured at all sections visited and present a relatively consistent picture. A more detailed account is presented in Chapter III. With few exceptions, the currents flowed to the south or southeast across a southeasterly dipping paleoslope. In the Moore Mountains, paleocurrents are generally oriented in a more easterly direction and suggest a local topographic high to the west, perhaps in or beyond the region of the present Miller Range. 48

Evidence of paleoslope orientation was obtained from the orientation of the axes of relatively small slump folds (5 to 60 cm amplitude) and the dip of their axial planes. Fold orientation is more consistent than that of the current structures and they indicate a paleoslope dipping to the southeast.

Paleo-ice direction Grooved and striated soft sediment pavements and boulder pavements are present in most of the sections studied and are discussed in detail in Chapter III. Striae orientations measured on the pavements range from 114° to 184° with an overall mean direction of 149*21°. In the Moore Mountains,

the grooves have more easterly orientations. This appears to be the result of the ice being deflected slightly by

the same topographic high reflected in the current structures although the degree of response to the changing paleoslope

is considerably smaller. Direction sense can be readily determined from an excellent pavement exposed in the supplementary type section (A Section), and the pavement exposed near Mount Angier. (P Section). The pavement exposed

in the former locality has small-scale stoss and lee effects

on the boulders and crag-and-tail both on the surface

of the boulders and as soft sediment tails streaming behind pebbles, a ll of which give an unambiguous direction to the southeast. Similarly, the soft sediment pavement 49 exposed at Mount Angier has very well-preserved grooves with the clasts that formed them lying at their head. Again the directional sense is unambiguous and to the southeast. Similar but less well-preserved features were seen on most of the pavements encountered.

Age and correlation Unidentifiable plant fragments occurring in the upper part of the formation are the only fossils known from the

Pagoda. Plant fragments were encountered in A, C, and D Sections at Mount Mackellar, from I Section at Portal Rock, K Section at Mount Miller and P Section near Mount Angier.

The best preserved specimens were obtained from a single clast-poor t i l l i t e at Portal Rock. Preliminary examination by Schopf (personal communication, 1968) suggests that an alliance with the Glossopteris flora is not precluded. Beneath Mount Angier (R Section), Barrett (personal communication, 1967) has recorded the presence of Ganqamopteris in the Fairchild Formation 120 m above the top of the Pagoda Formation in what appears to be a continuous sequence. Since Long's (1959) original discovery of t il l it e in the Ohio Range, rocks of similar nature have been found over much of the Transantarctic Mountains. In the Sentinel Range of the Ellsworth Mountains, the UJhiteout Conglomerate, which is regarded by Craddock and others (1965) and Matthews and others (1967) to be glacial 50 sediment deposited subaqueously, is overlain in apparent conformity by Glossopteris-bearing sediments. The Gale Mudstone, which is regarded as t i l l i t e (Schmidt and others, 1965; Frakes and others, 1956), is exposed in the Neptune Range of the Pensacola Mountains. Strata containing the Glossop teris flora probably overlie the Gale Mudstone (Frakes and others, 1966, p. 1). It is directly underlain by sandstones which are lithologically similar to sedimentary rocks which elsewhere in the range contain Devonian plant material.

Long (1962, 1965) and Minshew (1966) found that the Buckeye Formation in the Horlick Mountains rests unconform­ ably on an erosion surface either directly on the basement complex or on sandstones of the Horlick Formation which contain a Devonian invertebrate fauna (Boucot and others, 1963). The tillite s are conformably overlain by beds containing Glossopteris. Spores from the upper portion of the Buckeye Formation were reported by Schopf (i_n Long, 1965, p. 95) to be similar to Permian spores. More recently, Schopf (1967) has found a spore assemblage of Permian age in the middle of the Buckeye Formation, leaving l it t le doubt that the entire formation is Permian in age.

Minshew (1967) has described a tillite , the Scott Glacier F ormation, exposed on most of the mountains border­ ing the Scott Glacier and the Queen Maud Mountains. More recently, work by Long (in preparation) has shown that the 51 Scott Glacier Formation extends to the Nilsen Plateau in the Amundsen Glacier area. The formation overlies directly an undulating surface of basement rocks. At most lo calities, the Scott Glacier Formation is conformably overlain by a sequence which higher up contains the

Glossop teris flora. Locally the top of the formation is marked by a disconformity. In the vicinity of the Axel Heiberg and Shackleton

Glaciers in the Queen Maud Mountains, Barrett (1965) reports a thin tillite unit restricted to depressions in the basement erosion surface. The tillite is overlain conformably by a sequence containing Glossopteris. Minshew

(1967) comments on the lithologie similarity between the Scott Glacier Formation and the unit described by Barrett. Wade and others (1965) described a conglomeratic unit at the base of the section at the head of the Shackleton

Glacier and called it the Butters Formation. They regard the unit as a possible equivalent of the Alexandra Forma­ tion in the Queen Alexandra Range. The unit rests unconformably on an irregular erosion surface on the basement complex and is overlain in apparent conformity by sedimentary rocks regarded by Wade and others (1955) as the Mackellar Formation. Wade and others (1965, p. 14) described the upper contact as "a sharp lithologie discon­ tinuity." They note the sim ilarity between this unit and the basal unit described by Barrett (1965). If the Butters 52

Formation is equivalent to the Alexandra Formation, the occurrence of clasts of granite, quartzite, quartz, and metasediemnts mentioned by Wade and others as being up to 1 m in diameter is unusual, for in the type area of the

Alexandra Formation clasts are not common and are generally of chert and quartz and less than 17 cm in diameter. The matrix of poorly sorted but rounded quartz grains apparently suggested to Wade and others that the unit was related to the quartzites of the Alexandra Formation. However, at Mount Miller ( K Section) in the Holland Range, the basal t i l l i t e of the Pagoda Formation which directly overlies the Alexandra Formation consists almost entirely of well-rounded medium- to coarse-grained quartz with a few scattered clasts of a variety of lithologies. It is quite possible that the Butters Formation is a sandy tillite similar to that at Mount Miller and derived largely from the Alexandra Formation which was locally completely eroded. The assortment of lithologies present in the clasts in the Butters Formation were derived from the basement and transported some distance in the ice to be mixed with the more locally derived quartz sand. This suggests it is reasonable to correlate the Butters Forma­ tion with the basal unit described by Barrett (1955), particularly when it is realized that the type section of the Butters Formation is only 30 km from the section described by Barrett. 53

The t i l l i t e s forming the Darwin Formation were

described by Haskell and others (1954) from the Darwin mountains. The formation rests unconformably on sandstone

of possible Devonian age and is disconformably overlain by

coal measures containing Glossooteris. Mirsky (1964) and Harrington (1965) concluded that the section in Victoria Land was divided by a major unconform­ ity, below which the sedimentary rocks contain fish remains of Devonian age, whereas above the unconformity the sedimentary rocks contain the Permian Glossop teris flora. Recently, lYlatz and Hayes (1967) have shown that this

disconformity is real and widespread. The significance and magnitude of this hiatus are discussed in more detail in a following section. Watz (written communication, 1967) has also discovered pebbly mudstones in Victoria Land which

may be the equivalent of the t i l l i t e .

The stratigraphie position, particularly with regard to the presence of Glossopteris and, locally, the occurrence of Devonian fossils, suggests that the tillite s throughout the Transantarctic Mountains are correlatives. This is supported further by the lithologie similarity of the

formations throughout the range. In Victoria Land, the time interval representing the t i l l i t e is marked

by a hiatus. The occurrence of the Glossooteris flora in beds conformably overlying the t i l l i t e and Permian spores 54 within the til l it e s of the Horlick Mountains leaves l i t t l e doubt that the t il l it e s are Permian in age.

Environment of Deposition The occurrence of extensive deposits of tillite at the same stratigraphie level along approximately 2000 km of the Transantarctic, Ellsworth and Pensacola Mountains show that the sediments were deposited by an ice sheet of continental proportions. Evidence from the region studied by the writer suggests that the ice sheet advanced across the area more than once. At Mount Miller 13 beds are present, although undoubtedly not all represent major ice advances. In the type area, the formation is divided into two by a very massive channel deposit clearly representing a period of erosion by water. The section at Mount Counts provides perhaps the best evidence for more than one ice advance by the presence of lake sediments. There are two thick units of lake sediments which would suggest at least three advances of the ice sheet. There is, however, no strong evidence to suggest the extend of the various advances. The presence of plant fragments, some of them quite large, in some t i l l i t e beds, particularly toward the top of the formation, indicates that the ice advanced across a region where the climate was not too severe. At the time of deposition, there was free water at the base of 55 the ice as is evidenced by the water-sorted diamictites and the sandstone lenses within the tillites. These structures have been interpreted (Chapter III) as evidence of open cavities beneath the ice, which suggests thinning ic e . mackellar Formation The mackellar Formation was firs t defined by Grindley (1963, p. 329). The name is derived from Mount Mackellar

(4297 m). The formation consists of alternating units of laminated shale and fine sandstone. It conformably over­ lie s the Pagoda Formation and is conformably overlain by the Fairchild Formation. Grindley (1963, p. 329) defined the type section as being "below the cliffs of Pagoda Peak and Mount Mackellar"(166°33 .0 'E, 83°54.5'S, SU 56-60/15, Mount Elizabeth sheet). The type section is complete and is 73 m thick (C Section).

Distribution and Thickness , The Mackellar Formation is exposed along both walls of the valley of the T illite Glacier and at the head of the Montgomery Glacier. In this area, the formation ranges in thickness from 93 m at A Section near the type section to 61 m at Portal Rock at the mouth of the T illite Glacier (I Section). Well exposed sections occur on the south­ eastern face of Mount Miller (K Section), where it is 71 m thick, and on the valley walls beneath Clarkson Peak 56 at Bunker Cwm (L Section). At Mount Miller it is 71 m thick and at Bunker Cwm it is 51 m thick. Other well exposed sections occur at the head of the Lowery Glacier, notably along Turnabout Ridge ( i\l Section), where it is 60 m thick. The Mackellar Formation is exposed at several lo calities in and around the Moore Mountains. At Mount Weeks, south of the Moore Mountains (T Section), the formation is well exposed and 87 m thick. Beneath Mount Angier in the Moore Mountains (R Section), the formation is very sandy and 90 m thick. Farther north along the western side of the Moore Mountains (Q Section), the formation is 54 m thick. North of the Moore Mountains at Mount Counts a well exposed section was found to be 121 m thick. A lithologie equivalent of the Mackellar Formation was recognized by Wade and others (1965) in the region of the Shackleton Glacier, where it was found to be 304 m thick. However, they divide the unit into upper and lower parts. The lower part is described as being "dark grey to black hard silty shale" and the upper part "thick-bedded, greenish arkose" (Wade and others, 1965, p. 14-15). The upper part does not comply with Grindley's

(1963) description of the type Mackellar but is probably equivalent to the Fairchild Formation (Barrett, in preparation). Only the lower part, which is 137 m thick, appears to be the equivalent of the Mackellar Formation. 57

lïlore recently, Laird and others (in preparation) described a lithologie equivalent of the mackellar Formation on the central Nimrod Glacier. Here, the formation ranges from 107 m thick in the Chappell Nunataks to 12 m thick at Mount Hunt.

Lithology The Mackellar Formation consists of interbedded units of rhythmically laminated shale and sandstone, black shale, thinly bedded sandstone, and massive lensoidal sandstone bodies (Fig.18). Most sections contain a small number of beds of limestone. The units of rhythmically bedded shale and sandstone are perhaps the most striking and distinctive feature of the formation (Fig. 18). Laminae thickness in these units is generally relatively regular but can vary from 0,2 to almost 40 cm (Fig. 19). The overall thickness of the interbedded sandstone and shale units varies from 1 to 29 m. Laterally, sandstone beds grade over 50 cm to 2 m into shale and vice versa - single beds of either lithology seldom persist more than 6 to 8 m. In the vertical direction either lithology may decrease in relative proportion such that a laminated shale and sandstone unit in the space of

30 cm to 1 m may change to shale or well-bedded fine­ grained sandstone. The sandstones are light gray to dark gray or , less frequently, green in color and weather either to tan or 58

Figure 18, Thinly bedded sandstone and shale from the Mackellar Formation at the top of A Section in the Queen Alexandra Range,

a

Figure 19, Typical interbedded sandstone and shale of the Mackellar Formation, showing poorly developed ripple- drift cross-bedding. 59 orange. Ripple-drift cross-bedding is common, particularly

in the thinner beds. At some localities, particularly near the top of the formation and in units where shale is the dominant lithology, sandstone beds are deformed into slump . folds. At a few lo calities small sole markings, possibly due to current scour, were found at the base of some sandstone beds. Where sandstone becomes massive from a distance, it may have the appearance of a channel, however,

as mentioned previously, massive sandstones interfinger

with laminated sandstones and shales. Generally the only

current structures in these thick sandstone units are parting lineations. The shales range from hard gray-green and calcareous

where interbedded in laminated shale and sandstones, to thick, soft, extremely fissile black or gray beds 3 to 21 m thick. At a few localities the thick units show thin laminations approximately 0.5 mm to 1 cm thick. Mudstone pellets occur at the base of some beds. In most sections a few beds of fine-grained, black or gray limestone occur, some of which are 10 cm to 1 m thick. Laterally the beds are not very persistent and

they grade over a 5 to 10 m interval to fine sandstone.

Locally these units show signs of concretionary structures. Vague cross-bedding is present in some of the limestone

beds. In a very general way, the limestones are found about once in every 10 m of section. 60

In the vicinity of the type section (C Section), the formation contains a thick, very atypical, member near the top. It is a massive featureless olive-green fine- to medium-grained sandstone. It commonly contains large white ellipsoidal concretions in the lower part. The concretions average 1 m in length and 50 to 70 cm in cross-sectional diameter. Higher in the sandstone, instead of the larger concretions, small spherical iron- stained concretions with an average diameter of 20 cm occur. At all localities visited, columnar jointing is well developed in the sandstone as a result of the intrusion of a dolerite sill in the section directly above. The columnar jointing cuts across the concretions which indicates that the intrusion of the dolerites post-dates the formation of the concretions. The concretionary sandstone member is quite local and is known only from the four sections measured along the ridge between the T illite and Montgomery Glaciers (Sections A, B, C, E). The member thins both north and south from A Section (Fig. 3). At A Section, the member is 29 m thick, whereas 0.9 km north at B Section it is 19 m thick and 0.6 km farther north at E Section it is 9 m thick. In C Section, 1.5 km to the south, it thins to 17 m. The size and number of concretions decreases as the member thins. 61

At Mount Weeks numerous beds of medium sandstone are found in the section. Sandstone occurs infrequently at the base of the section where thin white sandstone and gray silty shale alternate. Upward, the sandstone beds increase in thickness and frequency until the formation is dominantly massive sandstone. Locally, toward the top of the section, a festoon cross-bedded channel, which has a mudchip breccia at its base, cuts into the massive sand­ stone. The sandstones are remarkable for the abundance of structures preserved on their bedding surfaces, including abundant animal tra ils (Figs, 20 and 21), possible rain prints on one bed, and mudcracks were found at two levels preserved on the upper surface of silty sandstone beds in the upper part of the formation. Ripple marks are common on the surface of many of the sandstone beds (Fig, 21), They have wavelengths ranging from 7,5 to 9.5 cm with a mean of 8,2 and ripple heights of 0,3 to 0,6 cm with a mean of 0,5 cm. The mean ripple index is 18,7, The ripples are quite symmetrical with a mean ripple symmetry index of 1,1, There is a slight tendency for cross lamination to develop on the south side of the ripple crest. Measurement of the dip and orientation of the slope of the ripple foresets indicates a mean dip of 11° after correction for local tilting. According to Tanner (1967), the combination of the ripple index (greater 62

ILm aa

Figure 20. Sinuous animal trail on the upper surface of a sandstone bed in T Section of the Mackellar Formation,

Figure 21. Symmetrical ripple marks with abundant super­ imposed animal tra ils from T Section of the Mackellar Formation. 63

.than 15) and the ripple symmetry index (less than 1.5) indicates that the ripples formed in the swash zone. Ripple marks observed from elsewhere in the iïlackellar Formation possess different dimensions. At K Section, the mean ripple index is 10.0; ripple symmetry was not measured. At N Section the mean ripple index of a set of ripples is 11.3 and the ripple symmetry index is 2.0. At R Section, the ripple index is 8.3 and the ripple symmetry index is

2.3, whereas at S Section they are 13.3 and 3.7. In contrast to the T Section,in all cases the ripple symmetry index is greater than 1.5 and the ripple index is always less than 15 which indicates a water current origin. The most reasonable interpretation is that the sand­ stone with ripples at I Section represents a transgressing beach facies. This f its well with the well-washed nature of the sandstone, the abundance of animal tra ils and the presence of rainprints and mudcracks. In contrast, at l\l,

R, and S Sections, the thinly bedded alternating sandstone and shale probably represent deposition in a completely subaqueous environment. In the Moore Mountains, beneath Mount Angier, Q Section

contains an unsorted mudflow unit 5.5 m thick (Fig. 22). The unit consists of 2.9 percent by volume of clasts larger than 1 cm set in a matrix. The clasts range from angular to well-rounded, although most show a moderate degree of rounding. The clasts, some of which are 64

Figure 22. The Q Section of the îïlackellar Formation in the Moore Mountains showing the mudflow deposit. The lower rubble-covered slope is the Pagoda Formation.

Figure 23. Contorted blocks of sandstone in the mudflow unit in Q Section. 65 striated, have the same range of composition as those of the t il l it e in the Pagoda Formation. Clast size ranges up to 1 m in diameter. The unit also contains numerous highly contorted blocks of sandstone and conglomerate

(Fig. 23). Boulder clusters and nebulous sandy patches are also common, suggesting poor mixing. The matrix is gray-green in color, moderately fissile and sandy. The fissility generally lies in the plane of the bedding, but was found to curve around boulders and contorted sediment blocks, suggesting that it is similar in nature to the fissility described by Lindsay (1956) and the grain flow deposits described by Stauffer (1957), and possibly relates to grain alignment during flow. Clast fabric and paleo- current data suggest that the mudflow came from the north (Lindsay, 1958). The.composition of the clasts and matrix and the occurrence of deep grooves on the clasts suggest that the mudflow may have resulted from the slumping of

Pagoda sediments from a local high. Laterally, the mud­ flow extends for over a kilometer, but there is no sign of the unit in R and 5 Sections farther south or in U Section to the north. The top of the mudflow unit is clearly marked by a calcareous quartzose sandstone bed which is 20 to 40 cm thick. As interesting as the main mudflow itself is a similar 1-m-thick flow directly overlying the sandstone at the top of the main mudflow. The unit is a poorly laminated, weakly 66 fissile dark-gray shale containing scattered angular clasts

(Fig. 24) of granitic composition ranging up to 15 cm in diameter. The laminae which curve smoothly round the clasts are 2 to 5 mm thick and result from concentrations of carbonaceous material. The bed appears to have been deposited by a mudflow traveling in a laminar fashion as

discussed by Lindsay (1956) and Stauffer (1967). The layering is probably due to inhomogeneities in the original material, which have been drawn out in a linear fashion much as a smoke stream in a wind tunnel. The mudflow probably originated in a manner similar to the larger mudflow but because of either its small mass of sediment or higher viscosity it did not become turbulent.

Apart from anomalies such as the mudflow units the ITIackellar Formation is surprisingly consistent in general appearance over the extent of the area investigated. The general characteristics of bedding thickness, current structures and the composition and grain size range of the sediments changes very l i t t l e . The main lithologie variable is the relative proportion of sandstone and shale. Figure 25 presents an interpretation of all of the avail­ able data as contours of the sand/ (sand+shale) ratio. A typical ratio for the formation appears to be approximately 0.3 to 0.4. The most striking feature of the diagram is the anomalously high ratios in the vicinity of the Moore Mountains at Q, R, S, and V Sections, which have ratios of 0,66, 0.93, 0,53, and 0.66, respectively. The consistency 67

Figure 24. An angular granitic clast contained in a mudflow unit at Q Section. The fine carbonaceous laminae appear to be the result of inhomogeneities in the original sediment being drawn out in a linear fashion during flow. 58

U©/

/ PS, 0.4

0.3

MACKELLAR FORMATION

SAND / SAND -h SHALE © 0,34

CONTOUR INTERVAL 0.1 0.65

Figure 25. Contours of the sand/ (sand+shale) ratio of the lYIackellar Formation. 69 of current structures and bedding thickness in the formation suggests that the energy of the environment changed little , either aerially or in a temporal sense. The high values in the Moore Mountains probably reflect a slight change in the source of sediment rather than energy. The beach deposits at Mount Weeks suggest a strand line to the west. It is interesting to note that parting lineations from N and Q Sections, which came from the more massive sandstone lenses, project back to an area to the north of the high sand/(sand+shal4 ratios, whereas the ripple-drift cross- bedding directions taken from finer, less massive sediments point in a more southerly direction. This suggests that the coarser sediments were being transported by long shore currents which paralleled the strand line to the west. It is also interesting to note that the high sand/ (sand+ shale) ratios occur in the region where the Pagoda Formation thickens over a pre-glacial depression.

Relation to older formations The Mackellar Formation conformably overlies the Pagoda Formation at all localities visited. Grindley (1963, p. 330) mapped the contact "at the uppermost level of the fluvio- glacial sandstone typical of the underlying" Pagoda Forma­ tion. Fluvioglacial sandstone as used by Grindley, appears to refer to the sandy tillite s found in the upper portion of the formation. There is little question that these 70 units are t i l l i t e as they are massive and, in D Section, rest directly on a grooved pavement. The top of the highest tillite .would, in most cases, be an adequate definition for the Pagoda - Mackellar boundary except in the vicinity of the type section where the upper t il l it e units thicken and thin markedly. For example, the upper­ most t i l l i t e in the type section was deposited in a channel and is 40 m thick, whereas 2,2 km north, in B Section, this

bed is represented by a layer of boulders. However, in all other sections visited the uppermost t i l l i t e was quite obvious. The rhythmites and the extremely fissile black shales are the most characteristic lithologies of the Mackellar Formation, and if any doubt exists about the presence of the uppermost t il l it e , the boundary is probably best placed as close as possible to the base of the lowest rhythmite unit or the lowest very fissile black shale unit above the highest tillite or unit of till-like lithology.

At most sections visited, away from the type section, the uppermost t i l l i t e is directly overlain by a highly fissile

black shale. In general, the boundary is obvious but there is a potential for complication, notably and unfortunately in the vicinity of the type section.

Paleocurrent and Paleoslope Indicators

Paleocurrent directions are based largely on 98 measure­ ments of ripple-drift cross-laminations. Ripple axes and parting lineations were also measured (106 in all). In 71 general, sediment ujas transported from north to south, although ripple-drift orientations from individual lo ca litie s range from 093° to 234° in a clockwise sense

(Fig. 26). In the vicinity of the type section, the paleocurrent direction is 093±74°, which is considerably more easterly than elsewhere in the area studied (Fig. 27A). Ripple orientations measured in the same area give a more southerly orientation (113±4°). On the opposite side of the Lennox-

King Glacier, at K Section on Mount Miller, the ripple- drift cross-beds give a direction of 185^59° and ripple marks give a similar direction (177-9°)(Fig. 27K) . In Bunker Cwm, at L Section, there is also good agreement between rip p le-d rift cross-beds (234*72°) and ripple marks (228^23°), although the direction is a little more westerly (Fig. 27L). At Turnabout Ridge ( N Section), ripple-drift cross-beds have a southerly orientation (185*14°), but the ripple marks still maintain a more westerly trend (226*65°)

(Fig. 2 7 iM). Parting lineations from some massive sandstone

units gave a much more easterly orientation (136*7°). Parting lineation and ripple-drift cross-bed measurements were taken only a few meters apart at this locality from beds that are lateral equivalents. The divergence suggests that the sandstone lenses result from the introduction of

coarser materials from a slightly different source, rather than a change in the energy of the environment. In the 72

83°S -

RAEQ COUNTS^

MT; MILLER CLARKSON K9 PEAK

WEEK

MACKELLAR FORMATION PALEOCURRENT DIRECTIONS

PARTING LINEATIONS RIPPLE DRIFT CROSS-BEDS MACKEL U RIPPLE MARKS

“ FOLDS

Figure 26. Summary map of paleocurrent directions from the mackellar Formation. Each symbol represents a vector mean direction for all observations of the particular structure at that locality. METERS METERS ro w Ü1 |\) W 4^ Ül m 03 o o O s O O O 0 o O L _ î . JL 1

ro - "1/r

OJ I-OJ

l ro - y f\3 ro- t -ro z OJ- -OJ o i- ■OJ

—A ^ / y Figure 27. Paleocurrent and paleoslope orientation throughput the Mackellar Formation at A, K, L, and M localities. The columns represent paleocurrent and paleoslope directions derived from (l) ripple-drift cross-badding, (2) ripple marks, (3) slump folds, and (4) parting lineations. 74

Moore Mountains at Q, R, and S Sections, ripple-drift cross-beds are oriented at 162*36°, 150*24°, and 130*31°, respectively. Parting lineations are oriented at 220*24°, 182-12°, and 158*13°, respectively. South of the Moore

Mountains at Mount Weeks (T Section), ripple-drift cross- beds are oriented at 228*24°, whereas the foreset slopes of 25 ripple marks give a paleocurrent direction of 138° with a radius of confidence of 24° and a precision para­ meter of 159.19 (Fig. 28), North of the Moore Mountains at Mount Counts, ripple-drift cross-beds again indicate a more southerly transport direction (185*25°), In the

central Nimrod Glacier region, Laird and others (in preparation) report that the paleocurrents flowed to the south away from what appears to be a strandline.

The orientation of the axial planes of a limited number of slump folds was determined at Sections A, L, and I, At A and T, where the paleoslope directions are 195*87° and 112*15°, respectively, the paleocurrents did not flow directly down the paleoslope but across it at quite a high angle. At L Section in Bunker Cwm, the paleoslope direc­ tion is 218*52° and both ripples and ripple-drift cross­ beds indicate that the paleocurrents flowed down slope.

Age and Correlation The only fossils known from the Mackellar Formation are tracks, trails, and borings. Generally they are not common and are found only at one or two levels within any 75

Figure 28. Orientation of 25 ripple mark foreset slopes from the upper part of T Section of the îïlackellar Formation. 76

one section. However, at Mount Weeks, in T Section, they

occur in great abundance throughout the formation. They occur frequently in and on the upper surfaces of sandstones

and less commonly in the shales. The absence of other . fossil remains, along with the abundance of the tra ils and the high proportion of sandstone at this locality, suggest that the environment was probably much better oxygenated than was general for the Mackellar Formation. Unfortunate­

ly, the tracks, trails and borings do not provide an age

for the formation. As mentioned in discussing the age of the Pagoda Formation, Ganqamopteris occurs in the Fairchild Formation

which directly and conformably overlies the Mackellar

Formation. If the plant remains from I Section at Portal Rock.do in fact have glossopterid affinities, there can be l i t t l e doubt of a Permian age. Sequences of well-bedded shales and sandstones occupying a similar stratigraphie position to the Mackellar Formation are known from several localities in the Trans- antarctic Mountains (Fig. 15). In the Ohio Range of the Horlick Mountains, Long (1964, 1965) described the Discovery

Ridge Formation, which consists of a succession of dark- gray and black shales. These overlie the Buckeye T illite and are overlain by the Mount Glossopteris Formation, a

sequence of coal measures containing the Glossopteris

flo ra . 77

Doumani and fflinsheu/ (1965) and Minshew (1966) have

described a 430-m-sequence of interbedded siltstones and shales, the U/eaver Formation, from the Wisconsin Range and from the region of the Scott Glacier. The formation

is informally divided into upper, middle, and lower members. The lower member is 85 m thick and consists of well-bedded fissile shales with small amounts of interbedded sandstone.

The middle member is 220 m thick and consists of rhythmic­ ally bedded siltstone and shale. The upper member is about 125 m thick and consists of fine- to medium-grained, well- sorted sandstone. On a lithologie basis, it is probably most reasonable to suggest that the lower and middle members of the Weaver Formation are correlatives of the

Iïlackellar Formation. The upper member is probably equival­ ent to the Fairchild Formation (Barrett, personal communi­

cation, 1967). Plant remains similar to the Glossopteris flora were recorded by iïlinshew (1967) from the lower member and a well-developed Glossopteris flora occurs in the uppermost shales of the upper member.

Long (in preparation) calls a thin shaly unit over- lying the Scott Glacier Formation on the Nilsen Plateau the Roaring Formation. The Roaring Formation is overlain by the Amundsen Formation of fine- to coarse-grained sandstone . and the sandstones of the Queen iïiaud Formation which contain

the Glossopteris flora 78

Barrett’s (1965) informally defined unit A at Mount

Fridtjof Nansen and Mount Wade in the area of the Axel Heiberg Glacier consists of up to 100 m of dark shale or sandy shale with some ripple-drift cross-bedded fine sand­ stone. The unit directly overlies a basal conglomerate thought to be glacial in origin and is itself overlain by a sandstone (unit B) and coal measures (unit C) which contain Glossopteris. Locally, at Cape Surprise, unit A is absent and unit B rests directly on the basal conglomerate. Barrett suggests that on a lithologie basis, unit A is probably a correlative of the Mackellar Formation.

As previously mentioned, direct lithologie correla­ tives of the Mackellar Formation have been described by Wade and others (1965) in the Shackleton Glacier area and by Laird and others (in preparation) in the central Nimrod

Glacier area. North along the Transantarctic Mountains from the Nimrod Glacier, equivalents of the Mackellar Formation are absent from the section. In the Darwin Glacier area coal

measure sedimentary rocks of the Misthound Formation rest directly and unconformably on the t il l it e s of the Darwin

Formation (Haskell and others, 1954). In the McMurdo

Sound region Glossopteris-bearinq coal measures rest directly and unconformably on Devonian sediments (Mirsky,

1964; Harrington, 1955; Matz and Hayes, 1957). 79

Along the Transantarctic Mountains from the Horlick

Mountains to the Nimrod Glacier, there is a consistency in the stratigraphie sequence. Black fissile shales or rhythmically interbedded fine sandstones and shales occur with t i l l i t e underlying them, and coal measures containing Glossopteris overlying them. It seems reasonable, on this basis, to suggest that all of these units are probably correlatives of the Mackellar Formation.

Environment of Deposition In the area studied, the sediments are remarkably consistent throughout. The persistence of thin bedding, ripple-drift cross-bedding, the fine-grained sediments, and the lack of evidence of extensive reworking all suggest a low energy environment. Further support for a low energy environment is presented by the preservation of very delicate tracks and trails at many localities, notably

Mount Weeks. The general paucity of fossil material throughout the formation with the exception of the tracks and tra ils and the abundance of carbonaceous material in much of the sediment suggest a poorly oxygenated environ­ ment which is in keeping with the other indications of low energy. The T Section at Mount Weeks appears to be the only exception to this interpretation. The exceptional abundance of tracks and trails on the,surface of ripple- marked, fine-grained, well-sorted and well-washed sand­ stones suggest a well-oxygenated shallow water environment. 80 This interpretation is supported by the ripple marks themselves, which have a comparatively high ripple index (greater than 15) and a low ripple symmetry index (less than 1 .5), which suggests that they developed in the swash zone (Tanner, 1957), The presence of possible rain prints and the occurrence of a channel structure in a sandstone unit suggest that the sediments were exposed above water for at least short periods. The presence of beach deposits in T Section suggests a strand line to the west. This being the case, the parting lineation measured from the massive sandstone units in the Moore Mountains possibly represents transport of the coarse fraction by long shore currents. The presence of a shoreline to the west, evidence of a topographic high in the vicinity of the Miller Range during Pagoda time, and the evidence suggesting a narrow basin of deposition for the Alexandra Formation, suggest that the Mackellar Formation may also have been deposited in a relatively narrow basin. Thinly bedded, fine-grained sandstone and shale are known from the Ellsworth Mountains to the Nimrod Glacier, a distance of approximately 1500 km. The nature of these sedimentary rocks suggests a quiet lacustrine environment. Recent studies (Barrett, Faure, and Lindsay, 1968) of strontium isotope ratios suggest a non-marine environment. However, the thickness and enormous extent of the post­ glacial unit make a lacustrine environment unlikely. 81

Probably the most plausible explanation involves a trans­ gressing sea following the retreat of the last of the Permian ice prior to isostatic readjustment. The return to fluvial conditions represented by the Fairchild and

Buckley Formations reflects the regressive phase as isostatic readjustment takes effect. If the Mackellar Formation was deposited into a relatively narrow basin, as may have been the case for the Alexandra Formation, the large masses of fresh water and the fine-grained sediment provided by the retreating ice sheet would result in a situation much like the Baltic Sea during the retreat of the Pleistocene ice sheet and up to the present time. The resulting brackish water conditions, along with a high proportion of fine sediment from a continental source, would readily explain the high Sr^^/Sr^^ ratios. Other aspects of this hypothesis are examined in some detail in

Chapter III. CHAPTER II

CLAST FABRIC OF TILL AND ITS DEVELOPMENT

The value of till clast fabrics as an indicator of paleoice direction has been known for some time (Miller,

1884; Bell, 1888). However, questions remain as to how till clast fabrics develop and what parameters control them. The following discussion is an attempt to define some of

the processes more clearly, based on information now available in the literature, and on studies of Permian

tillites in Antarctica.

Alignment of Clasts in Glacier Ice

The clast fabric of a till is the result of a large

number of processes. Of these, the one most likely to affect the fabric is the icre flow mechanism, although, as discussed later, depositional and postdepositional conditions

can also have considerable effect. Glen and others (1957) were among the first to examine the mechanism by which clasts are aligned in ice. By using methods developed by Jeffery (1922) for motion of a particle in a fluid in laminar flow, they were able to explain many of the features of t i l l fabrics. However, ice is not a fluid but a polycrystalline monomineralic- tectonite. 82 83

A tectonite body can be divided into smaller domains of statistically homogeneous deformation called shear domains. After deformation, shear domains may be repre­ sented as fabric domains and the deformational discontin­ uities often survive as fabric elements. The relationship between the movements in deformation and the resultant tectonite fabric is what Sander (1948) called the movement picture. The movement picture is then a complex vector field corresponding only in its broad features to the simple vector field of a strictly homogeneous strain (Patterson and Weiss, 1961). An infinite variety of movement pictures is then possible depending on the ordering of local discontinuities and shear domains. The movement picture has a space symmetry of the array of the rotations of the local strain ellipsoids. Four common symmetry classes are recorded in tectonite fabrics; axial, orthorhombic, monoclinic, and triclinic. The last three classes can often be related to the symmetry of the mean strain. Movement on discontinuities may be periodic, and then the movement picture may have the space symmetry of a crystal lattice. If spatial periodicity is present, the highest permissible symfhetry is tetragonal. 84

Optic Axis Fabrics of Glacier Ice The flow of ice involves both adjustments on a molecular scale and differential movement across grain boundaries. Experimental work by Glen and Perutz (1954), Griggs and Cole (1954), Steineman (1954), and Nakaya (1958) has shown that ice can deform by movement on a single basal glide plane (OOOl). lYluguruma and Higashi (1953) suggest that other glide planes may exist but basal glide appears to be the main means of direct movement in glacier ice, Flinn (1965) stated that mechanical equilibrium of crystals under deformation cannot be attained by crystals with a single glide system. Thus, for ice to develop optic-axis fabrics of any strength, basal glide must be complemented by recrystallization. Shumskii (1964) refers to this combined process of basal glide and migratory recrystallization as "paratectonic perecrystallization" (p. 247), and believes it to be the.main process active in glacier ice deformation. Many optic-axis fabric patterns have been recorded in glacier ice. Fabrics may be axial with a single mode or a small circle girdle (Allen and others, 1960; Kamb, 1959; Taylor, 1963; Stanley, 1965), orthorhombic with either two or four maxima (Bader, 1951; Rigsby, 1951, 1955, 1960; Kamb, 1959; Kamb and Shreve, 1963) and at times a three-maximum fabric is found which may be a variant of the four-maximum pattern (Vallon, 1962; Taylor, 1963), mono- clinic with a single girdle and maximum, and triclin ic 85

(Rigsby, 1955; Schwarzacher and Utersteiner, 1953;

Shumskii, 1964) . Where ice is actively deforming a relationship often exists between fabric symmetry and stress (as interpreted from strain). Generally, the fabrics are symmetrically disposed about the normal to the plane of maximum shearing stress (Anderton, 1967; Rigsby, 1960; Goldthwait, 1960;

Kamb, 1959). To the present time,the majority of ice petrofabrics have been measured on the upper surface of glaciers. A knowledge of ice fabrics close to the base of a glacier is important in understanding the development of clast fabric for if the shear domains reflect the planes of maximum shear stress, one set should be tangential to the bed of the glacier. Kamb and Shreve (1963) measured three- and four- maximum ice fabrics at the base of the Blue Glacier in

Washington and found that the fabrics deviated 30° from the expected orientation, based on the inferred stress. It is possible that at the base of a glacier the shear domains are not related directly to the planes of maximum shear stress. The orthorhombic fabrics occurring in glacier ice are of particular interest as they suggest the possibility of spatial periodicity associated with the deformation. Turner and Weiss (1963) made this suggestion after seeing the four-maximum fabrics of Rigsby (1951). Similar fabrics 86 have been recorded From quartzites and have been shown by

Ramsauer (1941) to be the result of the periodic develop­ ment of shear domains. It appears possible that ice fabrics may result from periodicity associated with up to four separate spatial groups related through their symmetry to the stress field. Since ice deforms mainly by glide on the (OOOl) plane, the fabric maxima may represent four separate symmetrically disposed sets of shear domains. Schwarzacher and Untersteiner (1953) and Taylor (1963) all felt that the maxima were associated with planes of shear; however, shear domains are not necessarily expressed as discontinuities. There is also no reason why any of the four possible shear domains could

not be suppressed locally so that fabrics bearing less than four maxima could develop. Ramsauer (1941) suggests that periodic development of shear domains appeared at least reasonable as a

mechanism for rock deformation, but it would be necessary to carry out detailed ice pétrographie studies before the

reality of the mechanism could be ascertained for the deformation of glacier ice. However, if periodicity is present in actively deforming glacier ice, the strain

ellipsoid may be resolved into as many as four components related to the separate shear domains, and each related

to the overall strain by the fabric symmetry. 87

Orientation of Clasts in Polycrystalline

Glacier Ice Because glacier ice is not a homogeneous medium, knowledge of the scale of deformation relative to the grain size of the clasts is required to understand the development of clast fabric. Motion of a clast embedded in polycrystalline ice depends on the amount of deformation of the individual ice crystals surrounding the clast. The extent of slip in a single crystal depends on the magnitude of the shearing stress and the orientation of the glide planes to the shearing stress. Assuming that ice deforms as a plastic material, motion on a slip plane begins when the shearing stress on the slip plane in the slip direction reaches a threshold called the critical resolved shear stress, the value of which depends largely on temperature and ourity of the ice crystals. For a single cylindrical crystal of cross-sectional area Ar, the critical resolved shear stress Tr is related to a tensile load E;

Tr - E: sin ■ 2Ar where ^ is the angle between the pole to the glide plane

(the optic axis) and the axis of tensile stress. Consider the situation of a single clast contained in polycrystalline ice where the glide planes of the crystals are randomly oriented. The greater the number of crystals 88 in contact with the surface of the clast the more nearly the stress distribution over the surface approaches that for a homogeneous deformation. The degree to which the orientation of the clast approaches that expected for a homogeneous deformation depends on the ratio of the surface area of the clast to the mean size of the ice crystals. In general, as we have already seen, the orientation of ice crystals is not random but bears a relationship to the stress field. Consequently, the effect of clast and ice- crystal size depends on the optic-axis fabric strength of the ice crystals. If a strong optic-axis fabric forms, the clast most probably rotates to a stable orientation such that a minimum cross-sectional area lies normal to the direction of transport in the shear plane, and the least dimension of the clast lies normal to the shear plane, so that the torque on the clast is reduced to a minimum. The presence of the clasts themselves in the basal portion of the glacier affects the local stress environ­ ment and hence the clast fabric. If clasts are densely packed, they interfere with each other, and disrupt ideal fabric formation. 'J/eertman (1958) discusses in some detail the dispersion of clasts in deforming ice as a result of clast interaction.

Thus, several variables can affect the orientation of clasts in glacier ice. However, the effect of most of them 89 will be simply to increase or decrease the rate of clast alignment or to cause weakening of the fabric strength. Most important in terms of t il l fabrics is the symmetry of the optic-axis fabrics for if the optic-axis fabrics of glacier ice reflect the spatial distribution of shear domains, the clast fabrics similarly reflect the d is tri­ bution of the shear domains.

Observed Enqlacial Clast Fabrics

Current literature presents little data on englacial clast fabrics. Harrison (1955, 1957) presents several fabrics of clasts taken from shear planes in the Greenland ice cap. Glen and others (1957) present a single two- dimensional englacial clast fabric measured in Spitsbergen, During the summer of 19 65 the writer measured the orientation of 15 clasts encountered in an ice tunnel within the Casement Glacier in southeastern Alaska. The clasts were 2 to 10 cm in maximum dimension and all were within 1.5 m of the bed of the glacier. The long-axis fabric (Fig. 29A) presents a single maximum with an upstream plunge of 20° to the horizontal plane. The estimate of the precision parameter, k, of the fabric is 3.70 and the radius of the 95 percent circle of confidence

is 23.2°. The plunge of the mode reflects the,dip of nearby shear planes although the clasts appeared to be in massive ice. The short-axis fabric (Fig. 298)has a 4 -> Z

Figure 29. Englacial clast fabrics. (A) long-axis clast fabric from the Casement Glacier, Alaska. I\l=15. (B) Short-axis clast fabric for the same clasts as in diagram (A). (C) Long-axis clast fabric of blade and rod­ shaped particles from the Greenland ice cap (Harrison, 1956), l\l=37. Note that the mode is transverse to the ice flow. (D) Short-axis clast fabric of blade and disc-shaped particles from the Greenland ice cap (Harrison, 1956), N=1Q7. (Contour interval for (D) is 2 sigma). Tick marks for all diagrams indicate the ice-floiu direction. All fabrics are measured in relation to the horizontal plane. VD CD 91 single maximum, whose orientation shows that the planes of maximum projection of the clasts lie parallel to the nearby shear planes. The maximum plunges downglacier at 77°. Harrison (1956) fe lt that only one of his diagrams, that for sample 3, represented a fabric developed englacially. The clast sample was collected from a shear plane and consists primarily of shale particles with an average roundness of 0.45. The fabrics for sample 3 of Harrison (1955) have been replotted and contoured using Kamb's method to make them more readily comparable with other diagrams presented (Fig. 29C). The long-axis fabric diagram of rod- and blade-shaped particles presents a single maximum with k equal to 2.95 and a circle of confidence of 18.7° radius. The maximum lies transverse to the flow direction and horizontal. However, a broad girdle is present with an upstream dip of 20°. The short-axis fabric diagram of blade- and disk-shaped particles has a precision parameter equal to 4.45 and a circle of confi­ dence of 7.3° radius. The fabric has two maxima, one several times stronger than the other. The strongest maximum plunges downglacier at 64° and the weak maximum plunges upglacier at 15°. The maxima lie in a plane

containing the flow vector and are separated from each other by an angle of 79°. The strongest maximum is almost

coincident with the pole to the shear plane, which plunges upstream at 37°. 92

It is suggested that the two modes present on the short-axis fabric diagram represent orientations on two separate shear domains. The shear plane described by Harrison (1955) containing the greatest number of clasts represents one shear domain, SI, which has been accentuated by becoming a discontinuity. The second shear domain, 52, has been expressed only through discontinuities on a smaller scale and would probably appear as a mode in an optic-axis fabric. Assuming that the two maxima of the short-axis fabric represent the poles to two separate shear domains, 51 dipping upglacier at 26° and 52 dipping downglacier at 75°, the lineation formed by the intersection of 51 and 52 parallels the maximum of the long-axis fabric. It is thus apparent why the mode of the long-axis fabric is transverse to the ice flow direction rather than plunging downglacier in 51. When only a single shear domain is active, the clast is oriented in the plane of the shear domain and rotated until parallel to the transport direction. However, when two shear domains are active, the clast is unable to take a stable orientation in either shear domain as the other shear domain interferes.

Consequently, the only orientation the clast can take is parallel to the intersection of 51 and 52 (Ll). This is obviously an unstable position, for if one shear domain becomes better developed than the other, the clast 93 will immediately rotate until i t is parallel with the transport direction in the plane of the more active shear domain. The weak girdle appearing on the long-axis clast fabric of Harrison (1956) (Fig. 29C) indicates that SI, which also appears as a shear plane, is more active than 32. The two-dimensional long-axis fabric diagram presented

by Glen and others (1957) is of little value in ascertaining orienting mechanisms because of the absence of the third

dimension. However, the bimodal distribution indicates that it is possible for both parallel and transverse

long-axis maxima to develop englacially at the same time. Although limited, the data on the development of

englacial clast fabrics lead to several important conclu­ sions. Englacial clast fabric development is probably controlled by periodic development of shear domains in ice.

At least two, and perhaps up to four, shear domains can develop. The most common situation is for one shear domain, SI, to develop with a shallow upglacier dip and less frequently for a second less strongly developed shear

domain, S2, to develop dipping steeply downstream (Fig. 30).

The two shear domains are probably symmetrically disposed about the major axis of the strain ellipsoid so that they intersect in a lineation, Ll, parallel to the intermediate

axis of the strain ellipsoid. 94

In general, the plane of maximum projection (the plain containing the long and intermediate axes) of the clasts is probably contained in the plane of the shear domain so that individual short-axis clast fabric modes develop for each shear domain. The modes of the short-axis clast fabrics are centered around the poles of the shear domains. If only a single shear domain is active (Sl), a single long-axis mode develops, plunging upstream in SI and parallel to the transport direction. The mode developed approaches a point maximum. If both 51 and 52 are active, the long-axis clast fabric is controlled by the intersection of 51 and 52 and by the relative activity in each shear domain. Greater activity on 51 leads to the development of a girdle (Fig. 30), In general, 51 is the dominant shear domain and is often expressed as shear planes; however, i t is possible that 52 could become the more strongly developed in some situations. The fabric is quite strong when only 51 is present, because the fabric develops under a single orienting mechanism. The fabric is weaker when 51 and 52 occur together as more than one orienting mechanism comes into effect.

Effects of Deposition on Clast Fabric

Clasts can become preferen tially.aligned in deforming ice and their orientation is modified to some extent during deposition from the ice. 95

Figure 30. Idealized long-axis englacial clast fabric showing the possible distribution of modes and girdle in relation to shear domains. Arrow at bottom indicates ice flow direction. 96

It can be assumed that the deposition of till often

takes place during a retreat phase or when the ice mass becomes locally stagnant. This depositional environment was f irs t suggested by Goodchild (1875) and has been echoed by many later writers. Under these conditions, the fabric developed during flow is preserved almost in its entirety.

The concept of "plastering" of t il l onto the

depositional interface beneath a moving glacier has been

discussed by many authors since Fairchild (1907) first proposed it. As pointed out by Holmes (1941) and Glen and others (1957), interaction between clasts in moving ice and the depositional interface is probably a powerful

orienting mechanism and tends to align the longer edges of the clasts rather than the long axes. The presence of

striae paralleling the long edges of the clasts demonstrates well the existence of the orienting mechanism. Inter­ action between the ice and, the depositional surface has been suggested as a mechanism for developing both parallel

and transverse long-axis fabric maxima. Any long-axis

clast fabric developed at the depositional interface develops in a horizontal girdle, and according to Holmes

(I94l) two possible modes are expected, one parallel and the other transverse to the ice direction. However, while

striae are commonly found paralleling the long edges of clasts, very few striae are found that suggest either 97 rolling or dragging of the clasts in a transverse orienta­ tion. Parallel modes developed at the depositional in ter­ face could be expected to have a slight upglacier plunge as a result of weak imbrication, developed in much the manner as stream gravel imbrication with clasts coming to rest one upon another. Both the depositional mechanisms mentioned are extreme conditions, either requiring stagnant ice and preserving the englacial fabric in its entirety or requiring active ice and having the fabric develop entirely at the

depositional interface. Clearly a range of conditions is possible between the two extremes. The next steps are to determine the conditions that limit the preservation of

an englacial fabric and the lim its within which the englacial clast fabric is destroyed or to what degree it is preserved. It may be possible to resolve some of these conditions in part by referring to the studies of tl/eertman (1957, 1954) on sliding at the base of a temperate ice mass. The rate at which a glacier slides over its base depends, among

other factors, upon the bottom surface roughness r, which is a function of the mean grain size of obstacles on the

bed of a glacier and the distance between the obstacles (llleertman, 1964, p. 292). Initially, before deposition

of the t i l l begins, the value of r depends on the nature of the bedrock surface over which the ice is moving. 98

However, once deposition begins the surface roughness also depends on the size distribution of clasts in the deposited sediment. Generally, when a clast fabric study is made,

the clasts measured are selected from within a certain size range, the upper limit of which is d. At a fixed roughness factor, r, the controlling obstacle size, A , can be determined from the following equation (llleertman, 1964, p. 293):

where all except the shear stress t and the roughness r

can be regarded as constants. ( p is the density of ice, 0.9 g.cm”• " 3 ; D is the thermal conductivity of the rock forming the obstacle, ~ 0.005 cal °C”^sec~^; a is a constant equal to 1 if heat flow is confined to the obstacle

but is larger than 1 if heat also flows through the surrounding ice; H is the heat of fusion of ice, 80 cal

gm~^; 3 is a constant equal to 1 or 2 and 8A is the value of 3 for the controlling obstacles; y is a constant independent of obstacle size, % 1; C is a constant, 7.4

X 10 cm^dyne"^; n is the constant from Glen's (1955)

creep law, % 3 ; 8 is a constant, 0.017 bar'^yr"^; k is a constant equal to 2.3 or 3.4.) Once the controlling obstacle size and the bottom roughness have been established

the sliding velocity, S, can be calculated from the following equation (Ueertman, 1964, p. 293); 99

S = 2(ctCDbBY^"^/H g where the symbols are the same as before. As the roughness increases, the sliding velocity decreases. UJeertman shows that the effective shear stress acting on the controlling obstacles is one-half to one-third of the shear stress and that the additional resistance is supplied for the most part by obstacles larger than the controlling obstacle size (A)« Clearly, the first condi­ tion for the preservation of the clast fabric is that A is larger than d, the maximum clast size measured, because, as noted previously, the surface roughness depends on the grain size distribution of the clasts in the deposited sediment.

If the size distribution of clasts in a fixed volume of sediment is known, i t is then possible to estimate the value of r at a fixed value of A assuming that only clasts larger than A are effective in absorbing the shear stress at the base of the glacier. In the field, the value of r is estimated by drawing a series of straight lines across the surface of an exposure and measuring the lengths of intercepts, L, crossing clasts which have mean diameters larger than A and the intercepts crossing the intervening matrix, L'» The estimate of the roughness, r',o f the subglacial surface during deposition of the till is: 100 IM-l N " t l 4 L'l . Ll) r' = ^ (N-1) i=i Li where N is the total number of clasts larger than A that were intersected by the line. Figure 31 is a plot of data from a t i l l i t e unit of the Pagoda Formation, together with the curve calculated from îl/eertman's relationship (values used for the constants are the same as those used by Uieertman, 1964, with gA = 2 and k = 2.31). The two lines intersect at a controlling obstacle size of about 0.4 cm. This means that above a clast size of 0.4 cm, the englacial fabric is probably destroyed because the clast size being measured is larger than the controlling obstacle size at the same bottom roughness. For example, to measure the orientation of clasts 1 cm in diameter, requires a roughness of 30, but at this bottom roughness the controlling obstacle size determined from llleertman's plot is considerably smaller — about 0.2 cm. This indicates that the clasts protruding 0.2 cm or more above the depositional interface absorb a large proportion of the shear stress and are probably reoriented. Conversely, clasts smaller than 0.4 cm are more likely to retain their englacial fabric because they will be smaller than the controlling obstacle size. The other variable to be considered is the rate of deposition, which depends on the rate of melting and the quantity of sediment contained in the basal ice. Uieertman 101

50-1 4 0 - 3 0 -

20 -

1 10- j :: N 4_ CO

LU

E 00 o o z 0.8 - o a: h~ 0.6- Zo 0.5- ^ 0.4-

0 .3 -

0 .2 -

O.H I 2 3 4 5 6 8 10 20 30 40 5060 80 100 ROUGHNESS

Figure 31. Controlling obstacle size as a function of roughness (Weertman, 1964) compared with the roughness calculated from the distribution of clast sizes in a t i l l i t e . 102

(1961, p. 975) has shown that the amount of ice A(x) being melted from or frozen to the base of an ice sheet has the following relationship;

_ 1 - (Qg+Qs) where K is a coefficient of thermal conductivity (1.7 x 10^ cal cm ^yr ^ AT is the temperature difference between the top of the glacier and the base, h is a compensated ice thickness, Qg is the geothermal heat flow

(about 39 cal cm ^yr”^), and Qs is the heat produced by sliding. Since the base of the ice mass is melting, AT is either zero or slightly positive, that is, if any thing,heat is being lost from the base of the ice mass,

A(x ) is dependent almost entirely on Qg and Qs. It is evident here thatconditions are severely restricted. By limiting A to values greater than d, we limit r and hence S, the sliding velocity. If 5 is small, Qs becomes small and the function depends largely on the geothermal heat flow. If A = d (10 cm), the sliding velocity is approximately 27 cm yr~^ and, therefore, Qs is about

0.7 cm'^yr"^. Thus, the rate of basal melting is of the order of 0.5 cm yr”^. Even by accounting for the heat produced by the surface velocity, which is unlikely to be more than ten times the sliding velocity, the rate of basal melting is not significantly large. 103

The best conditions for the preservation of englacial clast fabric are encountered where the sliding velocity is relatively small. The conditions are con­ trolled largely by the size distribution of the larger clasts in the sediment being deposited.

Clast Fabric Field Observations During the austral summers of 1966-57 and 1967-63, 48 long-axis clast fabrics were measured from tillite s of the Permian Pagoda Formation in and near the Queen Alexandra, Queen Elizabeth and Holland Ranges, Antarctica (Barrett and others, 1967). Where possible, at least 50 clasts were measured for each diagram. F or all diagrams, clasts were selected with long axes between 1.5 and 10,0 cm. Only clasts for which the long axis could be determined without question were used. The section and unit number from which each fabric was measured are given in Table 1.

Sample Size and Fabric The question that inevitably arises in any fabric study is the number of clasts necessary to obtain a meaningful result. The question is of even greater importance when dealing with tillite s because of the difficulties encountered in removing clasts from indurated sediments. All clasts measured in this study were removed completely from the matrix to determine the position of 104 the long axis and then replaced in the depression to measure the orientation. The strength of the fabric depends on the effective­ ness of the orienting forces and consequently the number of clasts necessary to determine a fabric is different for different depositional media. The difficulties of treating multiple maxima diagrams in a quantitative may has been mentioned previously. To allow at least a semi- quantitative treatment of the problem, two tillite lo calities mere selected which mere known to have single maximum fabrics -- one transverse and the other parallel to the ice-flom direction. At each locality, the orientation of 150 clasts was measured. The radius of the circle of confidence at the 95 percent level mas determined for varying numbers of clasts, beginning with 10 and incrementing by 10 to 150. For each increment of the sample size, 10 clasts mere selected at random and added to those used in the previous determination. The results of the calculations are plotted in Figure 32. The curves become parallel to the N axis, as expected, and suggest that 50 clasts are probably adequate to determine a long-axis clast fabric of a t i l l i t e . 105

40n 5? UNIT 7 lO TRANSVERSE FABRIC cntn ^30- V UNIT 12 rr IL u '' PARALLEL FABRIC o ui Û y 204 LU o o s Ll. Q O c 104 v> z 2 o 8 < oc - 1 ------1 1--- 1------1 1 1 1 1------1 1 1 1 1 1 10 20 30 40 50 60 70 80 9 0 100 110 120 130 140 150 NUMBER' OF CLASTS

Figure 32. Variation of the radius of 95 percent circle of confidence of tillite long-axis clast fabrics with sample size. 105 Description of Fabric

Almost all long-axis fabric diagrams have tiro features in common; a horizontal girdle and an area of loir concen­ tration in the central region of the diagram. In general, the girdle contains a single, well-developed mode, although four of the 48 diagrams present two modes normal to each other and quite similar to fabrics described by Holmes (1941). Of the remaining diagrams, 25 have well-developed maxima paralleling the ice movement direction and 11 have well-developed maxima transverse to the ice transport direction. The other eight fabric diagrams show the effects of secondary orienting mechanisms -- four have been modified by water sorting and the ice maxima are very d ifficu lt to identify and four have superimposed mass- movement fabrics (Lindsay, 1968).

In the following discussion, ice-movement directions are mentioned frequently, in all cases these directions have been determined independently from grooved pavements within the section.

Fabrics with Modes Paralleling Ice Transport Maxima paralleling the ice-movement direction can form either englacially or at the depositional interface, during deposition. If developed englacially, the maxima should, as previously discussed, plunge upglacier at about 20°, be relatively strong, and the fabric is symmetrical about the 107 maximum. The fabric may be modified during deposition, particularly by compaction. Several of the 25 fabrics with maxima paralleling the ice-movement direction have some of the expected features. Three of the diagrams, however, stand out by having strong maxima with upglacier plunges of A. 20°, B. 14°, and C. 9° (Fig. 33). The maxima are relatively symmetrically distributed about their resultant points (Fisher, 1953), although a weak horizontal girdle is present and the maxima are somewhat elongated in the horizontal plane, presumably due to compaction. As expected, the k values are larger than those of most other fabrics with parallel maxima (Table 1). Similarly, the radii of the circles of confidence are smaller than those presented by other parallel maxima with 50 clasts. The three diagrams of Figure 33 represent englacial fabrics. The plunge of the modes of all three diagrams suggests that the shear domains present in the basal glacier ice prior to deposition of the t i l l may not relate directly to the planes of maximum shear stress which at least theoretically should be tangential to the bed of the glacier. This problem cannot be resolved, however, until petrofabric information is available for basal ice. If the clast fabric is completely reorganized at the depositional interface, the final fabric will be contained almost entirely within the plane of the depositional o

Figure 33, Tillite long-axis clast fabrics with well-developed modes paralleling the ice-flow direction and plunging upglacier. These fabrics may have developed englacially.

o CD 109

Table 1. Location and Fisher’s (1953) Statistics for Clast Fabrics Figured in Chapter II.

Fisher's Statistics Figure Location Section Unit k Radius l\J 33A I 3 4.58 10.6 50 338 K 5 3.33 13.2 50 33C K 12 3.69 12.3 50 34A 8 3 2.94 14.4 50 348 P 3 2.87 14.7 50 34C A 13 2.92 14.2 51 340 C 3 3.20 13.4 51 35A K 8 3.08 14.0 50 358 K 3 2.36 17.2 50 36 P 8 2.40 16.9 50 37A K 4 4.41 10.9 50 378 A 23 4.32 14.9 50 37C A 10 3.35 13.1 50 38 A 4 2.65 15.0 54 39A A 12 2.23 17.9 51 398 8 4 2.79 15.0 50 39C A 12 2.60 15.7 51 390 C 1 2.50 15.9 50 39E A 12 2.94 14.4 50 39F A 12 3.22 13.5 50 40A A -7 2.22 17.8 52 408 A 7 3.08 19.2 29 40C A 7 3.18 13.1 50 400 A 7 1.75 30.6 50 40E A 7 2.35 16.4 55 41A A 10 2.57 15.3 51 418 A 10 3.63 12.2 52 41C A 10 2.96 14.2 51 410 A 10 2.65 15.6 50 43A K 1 3.27 19.1 25 438 K 1 2.77 21.7 25 110 interface. Consequently, a nearly horizontal girdle and maximum are expected. The strength should be weaker than its englacial counterpart as the orientation is affected by local irregularities in the depositional surface. Five fabrics (Fig. 34 and Fig. 390) show these characteristics well. The fabrics are all less regular than their englacial counterparts and the horizontal girdles are broader. The k values are less than the minimum values encountered in the englacial fabrics indicating greater dispersion (Table 1). Further, the radius of the circle of confidence is larger than in the englacial fabrics (Table l). It is surprising, however, that the values of k and the radii of confidence are so close to those of the englacial fabric values. The most noticeable feature of the diagrams is the irregular shape of the main maximum and the presence of small subsidiary modes which appear irregularly. Seventeen fabrics with parallel modes fall between the two extremes. If a fabric is modified at the depositional interface, the plunge of the mode is affected most. Because the orienting mechanism operated in the plane of the depositional interface, the final plunge of the mode is controlled by the local slope, lïlost of the 17 fabric modes plunge to some extent (up to 12°). Many

of the diagrams, particularly those with a downglacier plunge (Fig. 35) probably represent fabrics that have been largely altered along a dipping depositional interface. Figure 34* T illite clast long-axis fabric diagrams with subhorizontal modes paralleling the ice-flow directions. These fabrics may have developed sub- glaci.ally at the depositional interface. Note the irregular nature of the modes compared to those in Figure 33. Figure 35. Clast long-axis fabrics with features expected of fabrics partly reorganized subglacially at the depositional interface. The main mode of each diagram plunges downstream. Diagram 8 has a remnant of a transverse mode. 113

Both fabrics in Figure 35 have modes with a slight down-

glacier plunge; diagram 8 has a weak remnant of a trans­ verse mode. Several of the fabrics also have moderately

strong maxima plunging upglacier (Fig. 39), which are not

quite as intense as those figured for englacial fabrics but probably represent englacial fabrics that have been partly reoriented at the depositional interface. Four of

the diagrams in Figure 39 (B, C, E, and F) all appear to be englacial fabrics partly reoriented at the depositional interface. They have fairly symmetrical maxima which plunge upglacier, but they are not as well defined nor as strong as the englacial fabrics in Figure 33.

Transverse Clast Fabrics Several features can establish the englacial origin

of a transverse fabric. The most striking feature is the presence of a well-developed, relatively broad transverse

maximum on a girdle dipping upglacierat about 20° and reflecting SI. The girdle "may also contain a mode parallel to the ice-flow direction. Only one of the 11 diagrams with transverse maxima shows all of these features (Fig.

36). As would be expected with a bimodal distribution resulting from two interacting orienting mechanisms, Fisher's (1953) sta tistic s are weaker than those for the parallel englacial fabrics (Table 1), and the values calculated are not as meaningful. The girdle is broad but well developed and contains a broad but weak mode, plunging upstream at 26°. 114

N

Figure 35. Long-axis clast fabric with a strong trans­ verse mode and a girdle dipping in an upstream direction, Note the weak mode contained in the girdle paralleling the. ice-flow direction. This tillite fabric has all the features expected of.an englacial clast fabric in which both SI and S2 were active (compare with Figure 30). 115

In the extreme case where SI and 82 are equally well expressed and are both active, the transverse mode is quite strong as there is only one effective orienting mechanism. The mode is symmetrically disposed about the resultant point. Three diagrams which have this form are displayed in Figure 37. These fabrics are as strong as, or slightly stronger than, their parallel englacial counterparts (Table 1). As previously mentioned, the presence of striae on clasts is a good indication that the orienting mechanism at the depositional interface is strong. However, for the most part, the striae on clasts within the t ills parallel to within 10° the long edges or the long axis of the clast.

The clasts in boulder pavements can be grooved in any direction. To examine the effect of the depositional interface on clast orientation, a search was made for striated clasts in three tillite units, in order to find evidence that clasts were dragged or rolled in a trans­ verse orientation and to see how effective the orienting mechanism is in the direction parallel to the ice flow. The lowermost quarter of one unit which has a transverse fabric (Fig. 41D) produced five grooved clasts ^ si tu ; all were grooved parallel to the long axis and so gave no evidence of a transverse orienting mechanism. The vector mean of the long-axis orientations of the five clasts is 147±11°, almost at right angles to the transverse mode Figure 37. Tillite clast long-axis fabrics with well-developed modes transverse to the ice-flow direction. These fabrics probably developed englacially.

o> 117 with an azimuth of 062°. Thus, the striated clasts parallel the ice-flow direction in contrast to the trans­ verse fabric. A second unit lower in the same section also has a transverse clast fabric and produced a single striated clast. The clast long-axis was oriented at 125°, whereas the transverse fabric mode has an orientation of 049° (Fig. 38). Again, the striated clast long-axis parallels the ice-flow direction. As a check on the relationship between clast striae and the parallel orientation of the long axis, measurements were made on four randomly chosen clasts without grooves and of similar dimensions found within one meter of the grooved clast. The clast long axes have a mean orientation of 035±26°, which is very close (within the circle of confidence, radius of 15.00°) to the orientation of the fabric mode. A detailed search on a unit with a single parallel fabric maximum, higher in the same section than the units described previously, also^produced a single clast with grooves parallel to its long axis. The clast long axis is oriented at 158° compared with 140° (radius of confi­ dence 13.5°) for the fabric mode (Fig. 39F) and is thus almost parallel to the ice-flow direction. The data are limited but the writer believes that the evidence is strong enough to suggest that, in general, transverse maxima form englacially rather than by rolling or dragging at the depositional interface. 118

Figure 38. Tillite clast long-axis fabric with a mode transverse to the ice-flow direction. Tick marks show the orientation of the long axes of, striated clasts (125° parallel to ice flow; and non-striated (035±25° parallel to the fabric mode). 119

Variations of Clast Fabrics

Within a T ill Sheet Conditions change, in both a horizontal and vertical sense, at the depositional interface during formation of a till. The effects of these changes in conditions can be detected in fabric diagrams.

Horizontal Variation of Fabric

Near the type section of the Pagoda Formation in the

Queen Alexandra Range, it is possible to trace a single bed of 14 m thickness over a distance of 2.5 km and to obtain fabrics at three localities in this distance (Fig. 39). The bed luas divided vertically into quarters and fabrics were measured from all four quarters at locality II but only from the third quarter from the bottom at the II and III localities. The third quarter was selected to avoid the effects of mass movement which appeared in the upper quarter at all three localities. Fifty clasts were measured at that level for each diagram. It is reasonable to assume that the tillite at all three lo calities was deposited nearly contemporaneously and that because of their proximity, the rate of basal

melting was about the same during deposition. Any variation in the fabric should then be related to the nature of the depositional interface and in particular to the bottom roughness. The values of k for the three fabrics taken at the third quarter level are roughly the same (2.79, 120

2.60 and 2.60, respectively) and the radius of the 95 percent circle of confidence increases only slightly from A to C (15.0°, 15,7°, and 15.9°, respectively). The fabrics are of about the same strength and orientation

(152°, 144°, and 150°, respectively). A noticeable feature is that the fabric measured at locality III has a horizontal mode, as expected for a fabric formed completely at the depositional interface (compare with Figure 34). In contrast, the fabric modes of the I and

II lo calities plung upstream and both show slight develop­ ment of transverse modes, which suggest that the origin of the fabrics is in part englacial. This is particularly true for the locality B diagram where the mode is symmetrical. Assuming that boulders are uniformly distributed throughout the till, a general idea of the relative bottom roughness can be gained from the largest clasts at each locality. The mean of the five largest clasts was determined by measuring the diameter of the largest clasts exposed within 10 m of the fabric locality.

The means are 34.5, 54.G, and 16.3cm, respectively. Clearly the nature of the fabric is related to the boulder size. At I and II localities, where the englacial fabric seems to be preserved to some extent, the boulder size is much larger than the clast measured for the fabric (up to 10 cm) but at locality III, where the fabric appears to have developed at the depositional interface, i t is only slightly larger than the fabric clasts. 121

Figure 39. Tillite clast long-axis fabrics from three separate lo calities. Diagrams A, C, E, and F are from the top third, second, and lowest quarters of a single unit at one locality, respectively, whereas diagrams B, C, and D come from the same third quarter level of the unit at three separate localities. The double tick mark on diagram F indicates the orientation of a long axis of a striated clast. Figure 39 122 123

Fabric diagrams were also measured at localities II and III from a thin tillite (2.7 m thick) directly overlying that previously described (see Fig. 34C, D). The two tillite units are separated by a small erosional surface associated with channel sandstones and the upper bed is underlain by a very distinct boulder pavement. The similarity of the two diagrams shows that conditions at the two localities 1.2 km apart were relatively consistent. The mean boulder sizes are small (4.9 and 15.2 cm) and close to the size of the fabric clasts (10 cm). As previously discussed, the fabrics were probably developed at the depositional interface which is supported by the small boulder size observed. The mean boulder size appears to give a reasonable estimate of the relative magnitudes of the bottom roughness and the controlling obstacle size.

Vertical Variation of Fabric Variations of fabric in the vertical sense reflect changes in the nature of th'e material being deposited, the controlling obstacle size, and the rate of bottom melting. Fabrics were measured from three separate units in the type section of the Pagoda Formation. The lowermost unit (Fig. 40) was divided vertically into five parts. The upper portion of the unit shows very distinct signs of water sorting in the form of poorly defined bedding and lines of pebbles, and therefore is considered as a separate unit for the fabric study (Fig. 40E). However, m o CD

Figure 40, Five clast long-axis fabrics measured from different levels within a single unit of tillite. Diagrams A and B show considerable evidence of water sorting, whereas the remaining diagrams have typical till fabrics, with well-developed modes transverse to the ice-flow direction,

ro 125 the water-sorted material grades imperceptibly into unaltered t i l l i t e . The remaining portion of the bed was divided into four parts of equal thickness (2.8 m). Clast fabrics were measured from each division of the bed (Fig. 40). The three lowest divisions present weak although regular transverse fabrics which increase in strength higher in the unit (Table 1). The small number of clasts (N=29) measured in diagram B (Fig. 40) makes a quantitative comparison of the fabric strengths difficult. However, the strength increases significantly from diagrams A to C (Table 1). The presence of transverse modes indicates preservation of englacial fabric and hence the controlling obstacle size was large which should be reflected in a larger boulder size. Measurement of the five largest clasts 10 m on either side of each fabric site give means of 50.4, 44.0, and 44.0 cm, respectively. In contrast to the lower three diagrams, diagram D (Fig.

40) is dominated by a strong mode plunging east. When compared to diagram E (Fig. 40), it is clear that the mode

is the result of water sorting. However, a much weaker mode is present with an azimuth of 166°, which is almost certainly a parallel ice-derived mode. The two orienting media must have worked in a very close association, suggesting that deposition took place during a retreat

phase and that water sorting became dominant as the ice stagnated and melted. The presence of the weak parallel 126 mode is of interest as it suggests a change in conditions at the depositional interface. The mean of the five largest clasts (Fig. 400) is 4.5 cm which leaves little doubt that the sudden decrease in the controlling obstacle size allowed the transverse englacial fabric to be destroyed and the parallel mode to develop before water sorting became the dominant orienting mechanism.

Directly overlying the unit just described is another til l it e unit 17.5 m thick. The unit is massive and shows no signs of depositional breaks. Consequently, it was split into four equal divisions and clast fabrics were measured from each (Fig. 41). The firs t and third divisions from the bottom (diagrams D and B) have typically weak but readily apparent transverse maxima (Table 1). The other two fabric diagrams have been completely reorganized by water sorting such that horizontal modes, both oriented . at 194°, have developed parallel to the paleocurrent direction. The ice direction is 158°. The tillite offers no apparent evidence of water sorting and again the indication is that there is a close relationship between the two orienting mechanisms, which again suggests deposition during a retreat phase. The third unit to be examined directly overlies the other two and has been discussed previously (locality II,

Fig. 39) relative to horizontal variation. The upper few meters of this unit show signs of mass movement (Fig. 39) Figure 41, Four clast long-axis fabrics from a single unit of tillite, Diagrams A and C show signs of water sorting, whereas diagrams B and D have well-developed modes transverse to the ice-flow direction. The tick marks on diagram D show the orientation of the long axes of grooved clasts.

NÎ 128 but by dividing the unit into four equal parts the effects of the mass movement are all contained in the upper quarter. Again, clast fabrics were measured from each quarter. The lower three diagrams (Fig. 39), C, E, and F, are all typical parallel fabrics with single modes plunging upstream. Diagram F (Fig. 39) was also figured previously in relation to partial modification of englacial fabrics during deposi­ tion. The means of the five largest boulders are 27.0, 19.3, and 53.0, respectively. The boulder size does not reflect the fabric strength as clearly in this case as in previous examples, which probably indicates that the rate of basal melting was changing with time (Table 1). The mode of diagram F (Fig. 39) is the most symmetrical of the three diagrams and the fabric strength as reflected by k and the radius of confidence (Table 1) may be weakened by the weak transverse mode present. However, all three fabrics are probably largely englacial in origin and presumably the controlling obstacle size was large enough in all three cases to allow its preservation. The fourth diagram (Fig

39A) shows very clearly the effects of mass movement with the horizontal girdle rotated until it dips at 60° in a direction of 027°. The mass movement is clearly displayed in folded sandstone units overlying the tillite and by thin sandstone lenses within the t i l l i t e (Fig. 42). It probably represents slumping into a local depression, possibly due 129

Figure 42. Evidence of mass movement in distorted bedding at the top of a tillite (A Section, Unit 12). The fabric from the top of this unit is shown in Figure 39A. 130 to melting of buried ice, as the fabric suggests movement at a high angle across the regional paleoslope.

Interesting, but limited, data are available for a tillite unit exposed in the section beneath Mount Miller (K Section), approximately 50 km north of the type section. At this locality, two 25-clast fabrics were measured from a unit 11 m thick. Twenty-five clasts were taken from the base of the unit, up to the 3 m level, and another 25 were taken from the 4 to 7 m level. Although there are no visible breaks within the unit, the two fabrics are entirely different. The lower fabric (Fig. 438) has a parallel mode, whereas the upper diagram (Fig. 43A) has a transverse mode. The small number of clasts makes the determination of

the origin of the parallel fabric difficult. However, the plunge of the mode is small, suggesting that the fabric was probably formed at the depositional interface. If so, the change to a transverse fabric higher in the unit may

reflect an increase in the. rate of basal melting. The mean size of the five largest clasts, however, changes from 25.4 cm for the lower locality to 34.6 cm for the upper locality, which indicates that the controlling obstacle size was slightly larger for the deposition of the upper portion of the unit, possibly allowing the englacial clast fabric to be preserved. If, on the other hand, both fabrics are englacial in origin, the change could reflect a change from activity on a single shear domain within the ice to activity on two shear domains. Figure 43, Tu/o clast long-axis fabric diagrams from a single t i l l i t e unit. Note that the fabric from the upper part of the bed (A) has a transverse mode, whereas the fabric from the lower part ( b) has a mode parallel to the ice-flow direction. In both cases N=25, 132

Summary and Discussion

Limited observations on the orientation of clasts in ice by Harrison (1956) and by the writer show that strong clast fabrics develop englacially. The fabric diagrams, along with information gained from ice petrofabric studies

(Rigsby, 1951, 1955, 1960; Kamb, 1959; Taylor, 1950; Anderton, 1957), indicate that the orientation of clasts is controlled generally by one or two shear domains in the deforming ice, although up to four shear domains appear to be possible. When a single shear domain (Sl) is active, long-axis clast fabrics develop a single mode, plunging upglacier in the plane of the shear domain and parallel to the ice transport direction. When two shear domains are active, the long axes of the clasts take up an orientation parallel to the intersection of the two shear domains (Ll). Thus, a mode develops transverse to the direction of ice flow and in a horizontal plane. If SI is more strongly developed than 52, which is frequently the case, a girdle may develop in the plane of 51, and a weak mode may develop in the girdle parallel to the transport direction. The girdle without the mode is present in Harrison's diagram. Because the orientation of the clasts is controlled by two mechanisms, the transverse fabric is frequently weaker than its counter­ part with a single mode parallel to the direction of ice motion. 133

The short-axis fabrics indicate that the plane of maximum projection of the clasts is contained in the plane of the shear domains. When two shear domains are present, short-axis clast modes develop in association with each shear domain. The mode associated with SI, the most active shear domain, should be several times stronger than that associated with 52. It is clear that any fabric formed englacially is modified to some extent during deposition. One of the main factors modifying an englacial clast fabric during deposition is the sliding at the base of the ice mass. The rate of basal sliding depends on the size and number of projections on the glacier bed, or in UJeertman's

(1957, 1964) terms, the controlling obstacle size and the bottom roughness. Once the deposition of sediment begins, the ice rides over its own debris so that the controlling obstacle size depends mainly on the distri­

bution of the larger clasts in the sediment being deposited. The controlling obstacle size bears most of

the shear stress and, consequently, if the clasts normally measured in a fabric study are smaller than the control­ ling obstacle size, the englacial clast fabric may be

preserved. If the clasts are larger than the controlling size, they are reoriented by shearing at the interface.

A second factor that appears to be of importance is the rate of basal melting at the time of deposition. The 134 optimum rate of malting for the preservation of the fabric probably is when it equals the sliding velocity of the glacier or ice sheet. However, melting rates will generally be considerably smaller than the sliding velocity. Forty-eight long-axis clast fabrics from the Permian

Pagoda Formation in Antarctica show many of the expected features. Three of the fabrics with modes paralleling the ice direction and plunging upglacier have strong and very symmetrical maxima. These features indicate that they are undisturbed englacial fabrics. Four fabrics with modes transverse to the ice direction are similarly thought to be englacial in origin. One of these fabrics is particulery significant, because it has a weak girdle and mode plunging upstream in a plane which probably reflects SI. Five fabric diagrams have strong, asymmetric modes in a horizontal plane and paralleling the ice direction. All appear to have been reoriented at the depositional interface. Twenty-eight of the remaining fabrics lie in intermediate positions between these two extremes. Eight of the fabrics showed signs of the effects of water sorting and mass movement. Limited data on the orientation of striated clasts, in relation to clasts without striae, suggest that the orienting mechanism active at the depositional interface tends to align clasts parallel to the ice direction. The results are particularly significant for, in two beds 135 with transverse fabric maxima, grooved clasts were found paralleling the ice direction and ungrooved clasts of similar dimensions lay transverse to the ice direction. It is contended here that transverse modes probably do not

develop at the depositional interface. By measuring a series of fabrics from the same bed at different localities, it is possible to show that

conditions at the depositional interface change both horizontally and vertically. In one example studied, a horizontal change from an englacial fabric to one formed

at the depositional interface was found to be related to the size and number of the larger clasts and hence the controlling obstacle size. Similarly, in a vertical

profile, the size of the largest clasts seems to be the

main controlling factor. However, the fabrics were found to increase in strength upward in some cases, even though

the boulder size changes l i t t l e . This, along with evidence of water sorting in some beds, suggests an increased rate of melting, probably during a retreat phase. CHAPTER III

DEPOSITIONAL ENVIRONMENT OF THE PAGODA FORMATION

Late Paleozoic glacial sediments were first described from India by Blandford and others (1856). Selwyn (1859) first recorded the presence of Paleozoic glacial rocks in

Australia. Boulder conglomerates had been known for some time in South Africa before Sutherland (1370) realized their glacial origin. The first report of Paleozoic glacial rocks in South American was made by Derby (1888).

Until 1957, Antarctica remained the only Gondwana continent from which Upper Paleozoic glacial rocks had not been reported (Long, 1959, 1962). Following the Inter­ national Geophysical Year, til l it e s were identified by other workers in several areas of the Transantarctic Mountains, as well as in the Ellsworth and Pensacola

Mountains.

Geologic Setting and Previous Work

Although earlier parties briefly described the geology in the vicinity of the Beardmore Glacier, Grindley (1963) was the f irs t to describe the stratigraphie sequence and

136 137 recognize that part of it, the Pagoda Formation, was glacial in origin. The Pagoda Formation disconformably overlies massive, quartzose sandstones of the Alexandra

Formation, which Grindley believed were probably Devonian in age. The glacial rocks pass conformably upward into thinly bedded shales and sandstones of the filackellar Formation, which are in turn conformably overlain by

G1ossopteris-bearing sediments which Grindley referred to as the Buckley Coal Measures. More recent work by Barrett

(in preparation) has shown that this unit can be divided into two formations -- the Fairchild and Buckley Formations, The Buckley Formation is overlain by a sequence of sand­ stones and tuffs which contain the Triassic Dicroidium flora. These sediments are divided into the Fremouw, Falla, and Prebble Formations (Barrett, in preparation). The sequence is capped by the Jurassic Kirkpatrick Basalts (Grindley, 1963; E lliot and Tasch, 1967).

Description of the Pagoda Formation

Thickness In the area studied the Pagoda Formation ranges in thickness from 395 m to 126 m. In the northwestern portion of the area at Mount Counts (U Section) and on the south­ eastern ridge of Mount Rabot (V Section) the formation is 395 m and 308 m thick, respectively (Fig. 3). A short distance to the east, at Turnabout Ridge (M Section) and 138

Bunker Cwm (L Section), it thins to 135 m and 160 m, respectively. The smallest known thickness occurs on the southeastern face of Mount Miller (K Section) where i t is 126 m thick. Near the type section, the T illite

Glacier beneath Mount Mackellar (A Section), the formation is 179 m thick.

Lithology The Pagoda Formation consists predominantly of t i l l i t e and interbedded sandstone (Fig. 44); shale is locally important and conglomerate and limestone occur in thin units at some localities.

Shale

Near the type section at Mount Mackellar (A to I Sections), shale is locally abundant, forming 30 percent of the formation; elsewhere it forms less than 10 percent. Shale becomes more abundant toward the top of the formation

In many units sandstone and shale alternate in thin beds (Fig. 45). Where bedding is present, a number of large- scale slump folds involving up to 8 m of sediment occur. The shales are black or gray and are generally highly fissile. At some localities, a strong fracture cleavage cuts the fissility at a low angle. Sorting is poor and many beds have micaceous silt scattered uniformly through­ out. A few units contain scattered clasts, some of which are striated. 139

Figure 44. Massive beds of t i l l i t e separated by a sandstone unit in the upper part of A Section of the Pagoda Formation. 140

Figure 45. Siltstone with interbeds of sandstone in the upper part of B Section of the Pagoda Formation. 141

Limestone Limestone occurs in the Pagoda Formation in very small amounts as thin beds. The beds average 20 cm in thickness and are very persistent; one bed near Mount Mackellar, ranging from 17 to 23 cm thick, can be traced continuously for almost 2 km without a break. The limestone generally occurs interbedded within shale units or at the base of shale units. Locally, it is found interbedded with tillite or underlying channel sandstones. The limestones are dark gray or black and weather to a light gray. They are very- fine-grained and, except for a few fine, pebble-sized clasts scattered throughout, relatively homogeneous. Recent studies (Barrett, Faure and Lindsay, 1958) have shown that the Sr^^/Sr^^ ratio of the limestone is relatively high (0.7228), which is interpreted to mean that the sediments probably originated in .fresh water. This interpretation is consistent with the sedimentary associations.

Sandstone Apart from the tillite , sandstone is the most abundant rock, forming from 6 to 70 percent of the lithology. The

total thickness of the tillite is relatively constant so that changes in thickness of the formation are generally the result of the presence or absence of sandstone. The sandstone occurs in five distinct types of sedimentary bodies. 142 Sandstone Channels

Sandstone channel deposits range from a small local channel deposit 2 m thick and 5 to 6 m wide, separating

beds of t il l i t e , up to one (Fig. 47) 75 m thick and 275 m

• wide which cuts through half the thickness of the forma­ tion. The smaller sandstone channels (Fig. 46) are frequently laminated but seldom cross-bedded. At a very

few lo calities, conglomerate occurs in the bottom of the channel deposit and a few channels are largely of conglom­ erate, The deposits are most numerous along prominent levels in the formation separating tillite units. They are more common in the lower half of the formation around Mount Mackellar but occur throughout the formation else­ where .

The larger channels cause much greater disruption by

cutting through considerable thicknesses of the formation.

The largest channel is exposed in C and D Sections near Mount Mackellar. In forming the channel, the stream cut through several t i l l i t e units and caused slumping of the

unconsolidated sediment (Fig. 85). The effects of the slumping are discussed in a following section. The channel was later partially filled with well-washed medium-grained quartzose sandstone, most of which is cross-bedded. No conglomerate is present in the channel. The remainder of

the channel was filled with till deposited by a following ice advance. Fabric studies indicate that the ice was 143

Figure 46. Small sandstone channel between two beds of t i l l i t e in the lower part of the Pagoda Formation, A Section.

Figure 47. The extremely large sandstone channel as i t appears in D Section. 144 deflected 65° as it passed over the channel, depositing the till. At the same stratigraphie level, a smaller channel is exposed in G and H Sections and probably represents a tributary of the larger channel. Again, the channel is partly filled by sandstone and overlain by t i l l i t e deposited during an ice advance. It is possible using the thickness of the sandstone and t il l it e deposited in the channel to estimate a minimum value for the gradient of the stream ('Fig, 48). Prior to the sand f ill, when the channel was at maximum depth, the gradient was 1:370, After partial fillin g with sand, the gradient was reduced to 1:1930,

Tabular Sandstone Bodies The tabular sandstone bodies are distinguished from channel structures by their greater lateral extent which in some is as much as 2 km without a break. The beds range in thickness from 1,5 m to 22 m and generally contain either planar or festoon cross-bedding, although festoons appear to be most common (Fig, 49). Most tabular sandstone bodies separate beds of tillite and are probably left by shifting braided streams of low gradient. At some localities, particularly in the upper part of the formation in the Mount Mackellar area, the tabular bodies are in ter­

bedded with shale. Planar cross-bedding dominates in the sandstone which has a higher proportion of matrix. Sub­ aqueous deposition is suggested by units of thin (3 to 145

r-U) \

- l O

\ 2 : \ LÜ \ ■ rO O \ g (fi

-CM

1 - 0 nr I O o 7 "o' o 00 J g ro OJ m NO SS3NM0IH1

Figure 48. Thickness of sandstone and t il l it e in large channel structures exposed in C, D, G, and H Sections of the Pagoda Formation. 146

Figure 49. Planar cross-bedding in a tabular sandstone body near the top of A Section of the Pagoda Formation, 147

15 cm) alternating beds of sandstone and shale which occur interbedded with larger tabular sandstone bodies. These interbedded units often have small slump folds.

Sandstone Bodies of Probable Deltaic Origin Near the top of the section at Mount Counts (U Section) a local lensoidal sandstone body was found with a single 3-m-thick bed of planar cross-bedded, medium- to coarse­ grained sandstone. The bed is quite local and only about

50 m wide normal to the paleocurrent direction. The sandstone bed is underlain by a 2.5-m-thick bed of ripple-

drift cross-bedded, and laminated shale containing scat­ tered clasts. The latter is in turn underlain by a 1-m- thick unit of black, highly fissile shale. The main sandstone unit is overlain by thinly bedded (20 to 50 cm),

medium-grained quartzose sandstone with well-developed festoon cross-bedding. This extends laterally much

farther than the main thick sandstone unit, and in turn grades upward to medium-grained, ripple-drift cross-bedded sandstone.

The succession appears to have formed in a low energy environment where shale and mudstone with dropped clasts

were deposited and which was invaded for a short period of time by a small stream building a series of delta foresets into the body of water. The stream its e lf shifting over the deltaic deposit in small channels of 148 low gradient formed a series of festoon cross-bedded units.

Gradually this passed into a quieter environment which resulted in the ripple-drift cross-bedded unit at the top of the succession. The presence of glacial lake sediments throughout U Section supports the delta interpretation for the sandstone body. Other similar units occur in the section but are not well exposed.

Esker-like Sandstone Bodies

Beneath Mount Angier (P Section) a sandstone channel occurs within a tillite bed 11 m thick. The sandstone is triangular in cross section and is 2.5 m wide and 2.0 m high (Fig. 50). It is a poorly sorted, pale orange-yellow sandstone, ranging in grain size from medium sand to small pebbles. Bedding is weak and is parallel to the wall of the body (Fig. 50), Well-rounded pebbles are found toward the center and top of the body. There is no

sign of a depositional break in the t i l l i t e and the weak fissility which is very typical of the tillite is deflected around the body such that it parallels the contacts with the sandstone. It appears that the sandstone body was

deposited synchronously with tillite. Enough of the length of the channel is exposed to indicate that it is oriented at 090°, Parting lineations measured from tabular sandstone bodies higher in the same section indicate a paleocurrent direction of 087±9° and plant fragments of 085±2°. The orientation of the sandstone 149

BEDDING TRACES

T ILLIT E X WITH FISSILITY

0 I METERS

Figure 50, Cross section of the esker-like sandstone body exposed in P Section of the Pagoda Formation, 150 body clearly parallels the local paleocurrent trend which suggests that the sandstone body was not disarranged by the ice during deposition of the t i l l around it. An indication of the mode of preservation of the sandstone body is given by the clast fabric of the t i l l i t e which is interpreted as being entirely englacial in origin and indicating that the tillite was deposited by rapid basal melting of stagnant or near-stagnant ice (further discussion is given in Chapter II). A large number of smaller sandstone lenses occur throughout the unit along with sandstone wedges. The smaller lenses probably represent small stream channels flowing beneath the ice, possibly at the time of deposition of the t i l l i t e . A similar, but considerably larger, sandstone body occurs in C Section beneath Pagoda Peak. The body is also triangular in cross section and is 9,4 m wide and 6,2 m high. It occurs in the massive 43-m-thick t il l it e unit directly overlying the large channel structure described previously. The sandstone is light yellow, moderately well-sorted, and coarse-grained. Well-defined bedding occurs at the base of the structure and parallels the two sides (Fig, 51), Unlike the sandstone body in P Section, it lacks clasts but apparently was deposited synchronously with the tillite. Similar sandstone bodies have recently been described by Frakes and Crowell (1967) from the Falkland Islands and by Frakes and others (1968) from 151

sa

Figure 51. Esker-like sandstone body exposed in massive t i l l i t e in the upper part of C Section of the Pagoda F ormation. 152

Parana Basin in Brazil, which they interpret as eskers.

Because.of their similar features, the sandstone bodies at P and C Sections are also interpreted as eskers. The triangular cross-section tapering upward and the apparent synchronous deposition of the sandstone and tillite are supporting evidence for an origin as eskers (Flint, 1928; Goldthwait, 1939). The traces of bedding found in the sandstone bodies may represent the anticlinal dips which characterize eskers. The lack of larger clasts at the top of the structures is not surprising as conglomeratic material is uncommon throughout the Pagoda Formation. The size of the sand bodies lie within the limits for an esker, but the body at the P locality, like those described by Frakes and others (1963), borders on the lower size lim it. The close agreement between the orientation of the sandstone body and the current structures in the underlying beds and the information obtained from the tillite clast fabric at the P locality suggest that the sediment was deposited intact, most probably from a stagnant ice mass. The conformity of the fis s ility in the t il l it e with the walls of the esker suggests synchronous deposition rather than deposition in an erosional channel. As the evidence suggests that the tillite was deposited from a stagnant ice mass, the sandstone most probably formed in a sub­ glacial tube. 153

Wedge-shaped Sandstone Bodies

Wedge-shaped bodies of medium- to coarse-grained, pale-yellow sandstone occur at three localities (A, C, and P). The wedges project downward from beds of sandstone into the underlying t i l l i t e and at a high angle to the bedding planes. At A locality, the sandstone overlying the t i l l i t e varies in thickness up to 3,5 m;at C locality, it is quite thin but reaches up to 40 cm; and at the P locality it is up to 1 m thick. At all localities there is evidence of erosion of the upper surface of the t i l l i t e prior to deposition of the sandstone. At A and P localities there is 3 m of relief on the surface. At A locality the topographic lows are filled by typical channel sandstone with a thin veneer of pebbles in the bottom overlain by cross-bedded sandstone. The wedges are as small as 5 mm wide and range up to

70 cm wide without evidence of bedding. Generally, however, they are less than 6 cm in^ width. The majority seldom project more than 1 m into the t il l it e , but a few at P locality extend downward as much as 9 m. The fissility of the t il l it e surrounding the sandstone wedges is not deformed by the wedges but, instead, curves to conform with the surface of the wedges. It was possible at P locality to measure the orienta­ tion of a small number of the structures which are shown as poles to the planes of the wedges in Figure 52. There 154

N

Figure 52. Poles to sandstone wedge structures in tillite of the Pagoda Formation, P Section. 155 are two modes present; one horizontal and oriented at

138°, and the other plunges at 07° and is oriented at 258°. The ice direction determined from the tillite clast fabric is 129°. The horizontal mode represents a series of vertical wedges with their strike oriented within 9° of the normal to the paleo-ice direction. The second mode represents a series of wedges with strikes of 158° plunging east at 83°, that is, 39° away from the ice direction. At all three localities, a line of boulders occurs pressed into the upper surface of the sandstone bed over- lying the tillite. At one locality (A), the boulders are grooved and overlain by t i l l i t e . At C locality, the sandstone is overlain by thin beds of alternating cross­ bedded sandstone and a till-lik e lithology in a sequence suggesting deposition in a proglacial lake. At P locality, interbedded till- lik e lithology and sandstone overlie the sandstone, but the units of till- lik e lithology are quite thick and it is uncertain whether they represent glacial lake deposits or simply thin ice-contact deposits. The structures are very similar in almost all respects to sandstone wedges described by Frakes and others (1968) from the Paranâ Basin in Brazil. They interpret the structures to be sand fillings of open fissures in frozen t i l l .

The regular orientation of the sandstone wedges and their apparent relationship to the ice direction suggest 156 that they are most probably related to a joint pattern in the original till. Richter (1933) describes joints in till that appear to be related to the ice movement. The evidence of erosion at the top of the t i l l i t e units suggests that there was a period of time between deposition of the tillite and the deposition of the overlying sandstone beds, includ­ ing the sandstone forming the wedges. Although there are no signs of sedimentary structures in the wedges themselves, they are continuous with the overlying sandstone beds which probably indicates synchronous deposition by water. The only logical solution appears to be a mechanism involving the reopening of joint-controlled structural breaks in the till by perhaps freezing of the unconsolidated till or even more likely by contraction of the t i l l due to dessication. The absence of soil, which was regarded by Frakes and others (1968) as evidence ruling out patterned ground, is not necessarily valid as it depends on the time available for the development of the soil and to a large extent on the climate in relation to plant growth. However, if the sandstone wedges were formed by normal ice wedges, some evidence in the form of sedimentary structures could be expected as a result of intermittent deposition of sediment into the wedge in response to freezing and thawing. The only other readily apparent explanation for the origin of the regularly oriented wedges is that they are 157 crevasse fillin g s . However, as pointed out by Frakes and others (1958), the contact between the sandstone and t i l l i t e is much too sharp to have resulted from a normal crevasse filling. Further, if they were normal crevasse fillings they could be expected to be less well sorted as they would undoubtedly be derived by erosion of local morainal m aterial.

Sandstone Laminae Within the T illite

Contained within many beds of t il l it e are thin laminae of sandstone, averaging 0.5 cm thick with a maximum thick­ ness of 7 cm and generally extending less than 2 m laterally. The sandstone is medium- to coarse-grained, moderately well-sorted and well-washed. It is white to yellow and weathers tan. The laminae occur in slightly more than 40 percent of the t il l it e beds examined, and frequently occur at several levels within a bed. Approxi­ mately half the sandstone laminae are grooved or notice­ ably stretched in the direction of paleo-ice flow. A few are crumpled or complexly deformed as in Figure 53. Laterally the sandstone laminae wedge out and the t i l l i t e

shows no signs of a depositional break nor is there any change in its clast fabric that might suggest that it had

been water sorted; As far as can be seen, the sandstone laminae were deposited by small streams flowing in cavities beneath the ice synchronously with t i l l deposition. The streams 158

Figure 53. Thin, crumpled bed of sandstone within the t i l l i t e in the lower Pagoda Formation, A Section. 159 were active for very short periods and in some cases may have been disrupted by basal sliding which resulted in the grooving and stretching of the lenses. The presence of open cavities and free water beneath the ice during deposition of the till suggest relatively thin ice, possibly retreating during deposition of at least 40 percent of the till beds. The observation that basal sliding took place during deposition of at least 20 percent of the beds is also important from the point of view of the modifica­ tion of the clast fabrics. This point is discussed at length in Chapter II.

Conglomerate A very minor proportion of the sedimentary rock of the Pagoda F ormation is conglomerate, occurring in channels and as small tabular bodies.

Conglomerate Channels Channels consisting entirely of conglomerate are uncommon and generally small. A typical example in A Section is about 1.1 m thick and approximately 3 m wide (Fig. 54). The conglomerate lies in a trough eroded 1.0 m into the underlying t i l l i t e . Clasts are moderately well sorted, with some in te rs titia l sand, although the framework is continuous. The clasts consist of a variety of lithologies. A random sample of clasts contained the following; graywacke (44 percent), mudstone (6), chert 160

Figure 54, A small conglomeratic channel in A Section of the Pagoda Formation. 161

(6), quartz (16), granite (18), gneiss (2), and schist (2)» Generally, if conglomerate is present in a section, i t occurs locally in small amounts with cross-bedded sandstone at the bottom of a channel. Perhaps the best exposed and most interesting of these deposits occurs in L Section at Bunker Cwm, where a 4-m-thick massive conglomerate interbedded with cross-bedded sandstone rests in the bottom of the channel and is overlain by 14 m of cross-bedded, well-sorted, medium-grained sandstone in beds 0.5 to 1.0 m thick. This conglomerate is not as well sorted as those of the smaller channels and contains clasts up to 29 cm in diameter. The mean of the five largest clasts is 24.8 cm. The clasts consist of several lithologies: graywacke (26.9 percent), mudstone (20.9), limestone (1.5), chert (3.0), quartz (10.4), granite (25.4), gneiss (3.0), and schist (9.0). The most interesting feature presented by the conglomerate at this locality is the lateral gradation from water-sorted conglomerate to till-like sediment over a distance of generally less than 1 m. The unit passes from interbedded water-sorted conglomerate and well-sorted, cross-bedded sandstone to interbedded till- lik e sediment and cross-bedded sandstone without change in the bedding thickness (Fig. 55). One bed of conglomerate contained a 27-cm ball of till-like sediment, presumably derived quite locally from 162 unconsolidated till. This is, however, an atypical locality and at all other localities visited, conglomerate, if present at the base of the channel, pinches out laterally

in a short distance.

Tabular Conglomerate Bodies At R locality, a single unit of conglomerate and sandstone was found to persist laterally for at least 100 m.

The lower 1.5 m of the unit consists of poorly cross-bedded,

very poorly sorted conglomerate (Fig. 56). Grain size in the conglomerate ranges from medium sand to boulders 105 cm in diameter. The mean of the five largest clasts is 72 cm. The clasts have a full range of lithologie types; graywacke (27.2 percent), mudstone (3.3), limestone

(10.9), chert (2.2), quartz (2.2), granite (41.2), and gneiss (13.0). That the bed is a single depositional unit is shown by the weak cross-beds that cut across its full thickness. The conglomerate is overlain by a 4-m-thick unit of fine, ripple-drift"cross-bedded gray-green sand­

stone which is poorly sorted, which is in turn overlain by a further 4 m of massive fine- to medium-grained green sandstone. The absence of conglomerate from the Pagoda Formation

at most localities visited is most perplexing as moderately

large volumes of outwash material could be expected. The number of rounded clasts contained in the t il l it e s suggests that at least some outwash materials were reworked by 163

Figure 55. Thin interbedded units of conglomerate, sandstone, and diamictite exposed in a channel in L Section of the Pagoda Formation. The diamictite is thought to be ablation moraine.

Figure 56. Poorly cross-bedded tabular conglomerate exposed in R Section of the Pagoda Formation. The conglomerate is probably outwash material. 164 successive advances of the ice. The composition of the conglomerate clasts indicates that they were probably derived quite locally by erosion of the underlying tillite.

Glacial Litholoqies T illite T illite forms from 33 to 89 percent of the sediments of the Pagoda Formation. The beds range in thickness from a lit t le less than 2 m to 12 m. Some poorly exposed beds in U Section at Mount Counts may be as much as 66 m thick, but poor exposure leaves some uncertainty. It is difficult to determine the maximum number of beds present in many sections. However, at Mount Miller (K Section) an exceptionally well-exposed section contains at least 13 distinct beds of tillite and possibly 21 if some of the thin sandstone beds represent depositional breaks. In contrast, only six beds could be identified at Mount Counts

(U Section). The small number is probably partly connected with the poor quality of the exposures, but nevertheless there is a real decrease in the number of beds. The upper and lower contacts of the til l it e beds are quite sharp and at several localities they rest directly on either a boulder pavement or a grooved pavement. In most cases, the erosion is relatively minor and very little tillite has been removed, but at some localities, such as the type locality, channels cut through a considerable portion of the formation. 165

The tillite consists of clasts of large size and varied composition in a gray-green to dark-gray matrix (Fig. 5 7), which generally forms more than 90 percent of the rock. It consists mostly of quartz grains set in a submicroscopic matrix with smaller amounts of feldspar, calcite, sericite, biotite, garnet, zircon, and lithic fragments (Table 2). The quartz grains which form from 27 to 85 percent of the fine fraction are generally medium- to coarse-grained. A high proportion of the grains are well rounded, many as much as 0.9. Many of the remain­ ing grains are broken rounds. Quite clearly, most of the quartz is reworked water-sorted and rounded material. Both plagioclase and K-feldspar are present in small quantities (generally less than 3 percent) and in sizes of about 0.1 mm. The feldspars are fresh for the most part, although a few of the plagioclase grains show signs of weathering in the form of calcite patches. A smallportion of the K-feldspar grains have well-developed microcline twinning. The lithic fragments are almost entirely of chert and are as well rounded and sorted as the associated quartz grains. Next to the quartz, the unidentified ground- mass forms the highest proportion of the rock (up to 71.5 percent). For the most part, the groundmass is too fine for microscopic identification, and in plain light appears olive green with scattered fine mineral grains visible. It appears to be largely a green chloritic material with 166

Figure 57, Typical poorly sorted tillite with a sandy matrix. 167

Table 2. Modal Analyses of T illite from the Pagoda Formation (Mount Miller, K Section),

Sample Quartz Feld. Points Access. Lithic Matrix Counted 190 . 29.6 2.5 0.7 0.4 66.8 423 191 38.0 0.5 - - 61.5 222 192 27 .0 0.5 0.5 - 72.0 212 186 31.0 2.5 - - 65.5 200 184 33.5 1.0 - 0.5 65.0 235 182 28.5 - 0.5 - 71.0 200 188 36.5 1.5 0.5 - 61.5 200 180 39.5 5.5 1.0 1.0 53.0 200 178 40.0 4.0 0.5 — 55.5 209 176 39.5 0.5 0.5 1.0 58.5 205 174 45.0 1.5 0.5 - 53.0 216 172 33.5 1.5 - - 65.0 204 169 30.0 2.5 — « 67.5 200 167 29.5 3.0 - 0.5 67.0 200 168 32.5 1.0 0.5 0.5 65.5 200 165 37.0 1.5 1.0 0.5 60.0 224 163 41.5 - - - 58.5 200 160 49.5 5.0 - 0.5 45.0 200 156 30.5 0.5 0.5 0.5 68.0 220 157 49.0 5.5 - 0.5 44.5 200 158 60.5 1.0 - 1.0 37.5 226 146 . 85.0 0.5 - - 14.5 265 168 a small proportion of unaltered silicate mineral grains.

Well-rounded zircon, angular red garnet, and biotite flakes are the only accessory minerals identifiable. Vertical or temporal changes in the composition of the t il l it e are best shown by the fluctuation in the percentage

of quartz (Fig. 58). At least three quartz peaks are present at 0, 11, and 30 m above the base of the formation,

each peak weaker than the one before. Between the firs t two peaks there are only two beds of tillite ; a lower unit 0 to 2 m thick and an upper unit 10 m thick. Between the

second and third quartz peaks there are five separate units of tillite. The quartz content of the tillite affects its appearance such that with increasing quartz content the

fissility decreases, the color changes from dark gray to olive green, and the mean grain size of the fine fraction increases. One possible explanation for the origin of the quartz peaks is that they are the^result of a more major recession of the ice front than is represented by the individual

beds of tillite. After deposition of the first tillite unit, the local source of quartz, the underlying Alexandra Formation, was no longer available. Consequently, the

percentage of quartz contained in successive tillite units gradually decreases as a result of dilution by other materials. For the most part, the thin units of t il l it e probably resulted from local fluctuations in the ice THICKNESS (M) oi m00

© o m Oi

Figure 58, Graph showing variations in the percent of quartz in the fine fraction of the t i l l i t e in the Pagoda Formation, K Section, Note the I-' cn prominent modes. Cross-hatching emphasizes suggested alternate glaciations, VO 170 margin, the ice retreated a short distance, the basal layer was deposited, and the ice readvanced with further debris at its base. However, the debris at the base of the ice is not too different from that already deposited,

as basically the new debris layer has come from the same source and suffered the same processes of dilution as the previous debris layer. If, on the other hand, the ice

margin goes into a more major recession, the whole debris

mass contained at the base of the glacier would be deposited. Thus, upon readvance of the ice margin, the

new debris layer consists of a proportion of material derived at a considerable distance from the point at which we are looking. If this initial material was derived from

exposures of the Alexandra Formation or its equivalent, it could result in a debris layer of quite different character by the time the ice advanced to the point at which we are looking such that the quartz content was considerably higher despite dilution by other materials during advance. The result would be a series of quartz

peaks successively decreasing in magnitude as the source

of the quartz sand was either buried or eroded away. Clasts form less than 10 percent of the t il l it e in most beds. For the most part, they are distributed relatively uniformly through the matrix but concentrations occur at some levels. The composition of the clasts ranges considerably at most of the rock types exposed in 171 the basement complex are represented. Pebble counts for clasts 1 to 10 cm in diameter for most of the beds exposed in A, K, and U Sections are presented in Tables 3, 4, and 5. The most common lithology is dark gray-green graywacke derived almost certainly from the Goldie Formation, the most common basement rock exposed locally. Next to the graywacke, granite and gneiss are the most common lithologies. Granite stocks are exposed relatively frequently and the gneiss and small amounts of schist are probably derived from exposures of the Nimrod Group. The proportion of limestone varies considerably. It is probably derived mainly from small exposures of the Shackleton Limestone which occurs throughout the area. A small proportion of the limestone clasts are sandy and coarse grained and were possibly derived from the Starshot Formation farther to the north. In addition, much of the mudstone probably comes from the Goldie Formation. The quartz and chert probably Represent a stable residuum as most of the clasts are very well rounded. However, some quartz is less well rounded and occasionally has graywacke attached, suggesting that it originated as vein quartz in the Goldie Formation. Most of the remain­ ing lithologies are of minor importance. Perhaps the most unusual feature of the clast compo­ sition is the apparent inconsistency within a single bed. Initially, it had been hoped that rough correlations could Table 3. Lithology of Clast Samples from T illite Units in the A Section of the Pagoda Formation.®

No. Unit 1 2 3 4 5 5 7 8 9 Clasts

23 4.6 5.4 - 5.4 3.6 - 79.2 — 1.8 82 21 39.3 25.0 3.6 7.1 - 10.7 7.1 3.6 3.6 28 13 : 39.4 12.1 - 6.1 6.1 9.1 18 .2 3 .0 6.0 33 12 24.6 11.6 12.8 9.6 4.8 14.7 15.6 1.5 4.8 264 10 40.0 5.6 Ï0.2 3.5 9.3 13.4 11.2 1.8 5.0 291 9 41.1 3.3 12.0 3.3 2.2 25.1 8.7 - 3 .3 92 7 27.8 12.4 13.7 11.2 2.8 19.9 6.7 1.7 3.8 228 4 31.2 4.7 6.2 21.9 18.7 9.4 4.7 1.6 1.6 64 TOTAL 1082

^1-grayuiacke, 2-mudstone, 3- limestone, 4- chert, 5-quartz, 6-granite, 7-gneiss, 8- schist, 9-other lithologies. Table 4. Lithology of Clast Samples from T illite Units in the K Section of the Pagoda Formation,®

No. Unit 1 2 3 4 5 6 7 8 9 Clasts

18 35.1 8.3 - 5.6 5.6 44.4 - - - 36 17 48.0 16.0 12.0 8.0 8.0 8.0 - - - 25 12 47.9 29.2 - 4.2 6.2 12.5 - - - 48 9 44.8 14.9 4.5 1.5 11.9 20.9 1.5 — — 67 9 45.5 9 .1 3.0 3.0 6.1 30.3 3.0 — — 33 8 44.5 8.5 3.7 4.9 7.4 24.7 6.2 — — 81 ? 52.3 10.8 '1.5 6.2 - 18.5 9.2 1.5 65 5 61.8 11.1 6.2 3.7 1.2 14.8 1.2 - - 81 5 48.6 18.9 1.4 1.4 - 27.0 2.7 - - 74 4 69.1 7.4 1.5 4.4 2.9 14.7 - - - 68 3 59.3 5.6 5.6 4.2 5.6 19.7 - — — 71 2 35.4 12.7 10.9 1.8 9.1 21.8 7.3 — — 55 1 42.3 5.8 1.9 5.8 11.5 28.9 1.9 1.9 — 52 TOTAL 756

^l-grayu/acke, 2-mudstone, 3- limestone, 4- chert, 5-quartz, 6-granite, 7-gneiss, 8- schist, 9-other lithologies.

-o Table 5. Lithology of Clast Samples from T illite Units in the U Section of the Pagoda Formation.3

IMo. Jnit 1 2 3 4 5 6 7 a 9 Clasts

a 18.4 3.1 8.5 2.3 5.4 40.7 12.3 7.7 1.5 130 5 27.2 1.4 7.2 5.7 10.0 28.6 15.7 2.8 1.4 70 4 20.4 3.7 6.5 14.8 8.3 37 .0 7.4 1.9 - 108 2 38.2 7.3 4.2 6.7 6.7 27.2 8.5 - 1.2 165 » 2 51.4 3.4 0.4 7.7 3.8 25.4 5.9 0.4 1.6 236 . 1 33.7 2.0 3.0 - 9.2 42.9 8.2 1.0 - 98 0 18.6 — 14.3 41.5 2.8 7.1 5.7 5.7 4.3 70 TOTAL 877 ^1-grayu/acke, 2-mudstone, 3- limestone, 4- chert. 5-quartz, 6-granite, 7-gneiss, 8- schist, 9-other lithologies.

-0 4i- 175 be made between sections by comparing the lithologies by a chi-square test. However, initial tests on control data indicate that samples from the same bed are signifi­ cantly different, in most cases, at the 95 percent level. The significant difference probably reflects the extremely varied nature of the basement complex or inadequate sampling and more meaningful results could probably be obtained by lumping several lithologies under a single category. For example, porphyry is not a common lithology and is probably related to local occurrences in granitic intrusions.

Similarly, the mudstone encountered is probably derived mostly from the Goldie Formation. By grouping the lithologies according to their associations in the basement complex, a more re a listic picture may be obtained. On a broader scale, however, when the total sample from A, B, C, and D Sections are compared with each other, it is found that they are quite similar, which is readily apparent from Table 6. This is to be expected as the four sections are quite close together. They also compare quite favorably with the total sample from U Section 110 km to the northwest. In contrast, the total sample from K Section, which is only 50 km to the north, does not compare well with the other sections. This latter difference in composition probably relates to the ice direction. The pavement directions from the vicinity of A Section project back toward the Moore Mountains rather than toward K Section. Table 6. Lithology of all Clasts Collected From Six Sections of the Pagoda Formation.®

No. Section 1 2 3 4 5 6 7 8 9 Clasts

A 29.4 9.7 9.4 8.2 5.6 13.8 13.4 1.5 4.0 1084 B 29 .8 9.2 8.6 6.2 11.0 22.8 8.6 1.6 2.2 370 C 35.8 4.1 4.1 7.1 11.2 23.5 10.2 2.0 2.0 98 30.4 4.5 25.8 9.5 1.8 8.0 336 D 3.6 \ 4.2 12.2 K 48.9 12.2 4.0 4.2 5.8 22.1 2.6 0.2 - 756 U 29.9 3.0 5.3 11.3 6.3 29.8 9.1 2.8 1.5 877 TOTAL 3521 ^l-grayiuacke, 2-mudstone, 3- limestone, 4-chert, E i-quartz , 6-granite, 7-gneiss, 8- schist, 9-other lithologies.

-> 3 cn 177

In general, the difference is an increase in the graywacke and mudstone in the sample from K Section along with a corresponding decrease in the other lithologies, suggesting larger exposures of the Goldie Formation upglacier from K Section. The clasts range up to a maximum of 2.8 m in diameter, although the maximum clast size in any one bed is generally less than 1 m. Size distribution was deter­ mined for clasts in the range of -2 to -7 phi. The samples used are the same as those used for the composition studies.

The weights of the individual clasts were summed in half phi intervals, using the b axis of the clast as a measure of grain size. The resulting cumulative curves for A Section are presented in Figure 59. There is very lit t le variation in grain size or sorting from bed to bed, despite varia­ tions in clast composition. A few of the curves diverge slightly in the -5 to -7 phi range, which probably indicates inadequate sampling at those lo calities rather than a true difference. For the most part, it is difficult to gain an insight into the grain size distribution of the larger boulders. However, at A Section pronounced boulder concentrations (Fig. 51) occur at the top of four beds, and i t was possible to measure the size of enough clasts from two of these beds to plot a size distribution between

-7 and - 11 phi (Fig. 50). The slope of the two curves and, hence, the sorting of the samples, is almost identical to that of the smaller clasts in Figure 59. The boulder 178

CVJ I

rO

LU N CO

10 £: ' < cc e>

(0 I

r~ N- m G) O O o O o l o I Q Gi en 00 LD \j- CVJ — m en (% NI) 1H9I3M Figure 59. Grain size distribution of clast samples taken from t i l l i t e units of the Pagoda Formation, A Section, Note the consistency in the slope of the curves. 179 in ric;

-N

X CL

LU N -CO CO

z < c n CD

_ o

OT (%NI) 1H0I3M

Figure 50. Cumulative size distribution of large clasts exposed in (A) boulder concentrations at the top of tillite units in A Section (dashed line) and (S) boulder pavements at several localities (solid line). 180

Figure 61. Boulder concentration between two til l it e units (units 11 and 12) in the Pagoda Formation, A Section. 181 concentrations were deposited in continuity with the tillite and appear to represent a modified tillite. As there is no evidence of water sorting, i t is suggested that they may represent ablation moraines from which the fine fraction of the sediment was removed prior to deposition. The indication is that from -2 to -11 phi the slope of the grain size curves is uniform, which suggests minimum recycling of outwash material by readvancing ice. The consistency of slope of the curves, despite the variation in clast composition, is also good evidence that outwash materials have not been recycled. The clasts range in roundness from 0.1 to 0.9, although the mean roundness of all samples ranged only from 0.45 to 0.55. The mean roundness of 1082 clasts grouped together from A Section is 0.49. Not only is the mean roundness consistent, but the cumulative round­ ness frequency curves for all the samples from A Section are very consistent (Fig. 52) and form straight-line distributions on log normal paper. Again, as with the grain size distribution, the roundness appears independent of the clast composition which also suggests minimum recycling of outwash materials. Like the roundness, the sphericity of the clasts is very consistent from sample to sample. The mean value of all samples collected ranges from 0.85 to 0.89. For the 1082 clasts from A Section, the mean is 0.37. Cumulative 182

99-1

98-

90-

80 -

60 - uj 40-

10-

0.5 0 2 ,3 4 5 6 ,7 .8 ROUNDNESS

Figure 62. Cumulative frequency curves for roundness of samples .of clasts from A Section of the Pagoda Formation. 183 number frequency curves of sphericity for all samples from A Section are plotted in Figure 63 and, regardless of composition, the sphericity distribution is remarkably consistent. A high proportion of the clasts are equant and thus cause the sphericity to be high. Counts made in the field of all clasts larger than 1 cm indicate that, in general, less than 5 percent of the clasts are striated. However, when 1600 clasts from 1 to 10 cm in diameter were collected from 25 separate beds at several localities, only 0.8 percent were found to be striated. A sample of striated clasts has the following composition; sandstone (52 percent), mudstone (35), and limestone (13). Mo other lithologies were found bearing striae. The mean roundness of the clasts is 0.50 which falls in the lower part of the t i l l i t e clast range for a random sample, but the difference is only slight. The mean sphericity is 0.33 which is slightly lower than the

typical t i l l i t e sample. The mean flatness ratio (A+B/2 x C) for the striated clasts is 2.29 which is slightly higher than the average t i l l i t e clast sample. For example, the

1082 clasts from the A Section have a mean flatness of 1,91, This is in agreement with the lower sphericity. In general, the striated clasts are fine-grained lithologies which could be readily striated, and they are slightly more angular and slightly flatter than the non- striated clasts. 0QUS^^

V-*CO

Figure 63. Cumulative frequency distribution curves of sphericity for samples of clasts from A S e c t i o n of t h e

Pagoda Formation. 185

Water-washed T illite At most localities visited some of the tillites show signs of water sorting (Fig. 54), The evidence usually takes the form of weak layering of the sediment and concentrations of clasts along some of these layers. In most cases, where evidence of sorting is found, it occurs in the upper portion of a relatively thick t il l it e unit.

The contact between the t i l l i t e and the water-sorted material is gradational and, as discussed in the fabric section (Chapter II), water sorting can alter the clast fabric of the tillite without leaving any outward sign. The matrix, for the most part, shows little effect of the water sorting, mainly because of the predominance of quartz sand in the t i l l i t e . The clasts, however, are modified, the most noticeable feature being the reduction in the maximum clast size. The clasts in one bed of t i l l i t e in A Section often exceed 50,cm, whereas the largest clast observed in the 2.1 m of water-sorted material at the top of the same bed is 9.1 cm. The mean roundness of the clasts in the same unit changes from 0.52 in the underlying t i l l i t e to 0.57 in the water-

sorted material, while at the same locality the sphericity changes from 0.36 to 0.38. The changes are not large but significant. The clasts have the following composition: graywacke (29.7 percent), mudstone (2.7), limestone (5.4), quartz (10.3), granite (21.5), and gneiss (10.8). The 186

Figure 64. 'J/ater-u/ashed t il l it e at the top of unit 7 in A Section of the Pagoda Formation. The water-washed material grades downward into unaltered tillite. 187 composition of the clasts does not differ significantly from that of the underlying t il l it e . Some attention is given to the origin of the water- washed t i l l i t e in another section where it is concluded from fabric studies that the water sorting took place in close association with the deposition of the t i l l i t e . The reduction in clast size and the increase in roundness and sphericity suggest that the water-sorted material represents the bed load of a highly turbulent stream which left the larger boulders as a lag concentrate upstream from the deposits examined.

Glaciolacustrine Deposits Sediments of probably glaciolacustrine derivation are present in C, U, and V Sections and possibly in P Section. At C locality, beneath Pagoda Peak a 7-m-thick unit of alternating lensoidal beds of a till-like lithology and sandstone are found directly overlying a thick bed

of t il l it e . The beds of both lithologies range in thick­ ness from 10 to 50 cm with an average of 25 cm. The sandstone beds are somewhat more continuous than the till-like lithology and in some cases they are cross-bedded.

Occasional lenses of conglomerate are found in association with the sandstone. The unit of till-like lithology and sandstone appears to be relatively local in nature as it is not present in A, B, or D Sections which are all within a short distance. 188

The beds of till- lik e lithology are much too thin and discontinuous to be ice-contact deposits. This, along with the local nature of the unit, suggests that they may have formed in a proglacial lake. In this case, the alternation between a till-lik e lithology and sandstone possibly reflects changes in the number of icebers released into the lake. Presumably, early in the melt season a larger number of icebergs would be released into the lake and consequently a layer of till- lik e sediment would be deposited as they melted. However, later in the melt sea­ son, with fewer icebergs and increased melting, a layer of sandstone would be deposited as currents reworked the existing sediments and by introduction of material from subglacial streams. Assuming that the alternations are seasonal, the lake existed about 30 years. Similar sediments exposed in the Moore Mountains at U, V, and P Sections may all be closely related. In U Section at Mount Counts are. two massive units of a t i l l ­ like lithology. The units are 129 m and 24 m thick. The sediments consist of a variety of clasts ranging in size up to 90 cm set in a poorly sorted olive-green matrix. The unit varies both vertically and laterally from massive to well bedded. In part, the sediment is sorted and poorly cross-bedded and could almost be regarded as a poorly sorted sandstone. Locally, some conglomeratic material is present. Evidence of slumping in the form of deformed bedding is 189 abundant throughout. The clasts which are randomly distributed throughout the unit have a similar composition to the interbedded tillites. In fact, apart from the matrix being sandier and lighter in color and the presence of the discontinuous and chaotic bedding, these sediments are quite similar to tillite. The upper portion of both units of till-like lithology pass into festoon cross­ bedded channel structures of medium- to coarse-grained, poorly sorted, gray-green sandstone. Laterally, these units are persistent and show no signs of slumping.

The sediments described appear to be the result of dumping of glacial sediments from floating ice into a proglacial lake. The size, composition and uniform distribution of the clasts leaves little doubt that the sediments are glacially derived. The presence of irregular bedding and sorting indicates some feeble currant action; however, the rate at which the sediment was being dumped far exceeded the ability of the currents to sort it. Rapid deposition is also suggested by the abundance of slump features. The extreme thickness, particularly that of the lower unit, indicates that the lake was of considerable depth. As noted by Flint (1957, p. 144), abundant ice-rafted material implies deep water, as ice ending in shallow water can only discharge small icebergs. The sediments probably resulted when ice dammed a pre­ glacial valley or depression during a retreat phase in 190 much the way proglacial lakes formed at the terminus of the retreating Pleistocene ice sheets in North America and Europe. The lakes were terminated either by filling with sediment or further retreat of the ice and lake sedimentation was supplanted by fluvial sedimentation. At the top of U Section, the delta structure described previously indicates the presence of another lake for a short existence prior to the onset of the deposition of the

Mackellar Formation. Near the top of P section are comparatively thick interbeds (50 cm to 1 m) of a very sandy gray-green till-like lithology and yellow or gray-green sandstone. The beds of till-like lithology are laterally persistent and contain boulders up to 1 m in diameter. The sandstone beds are frequently discontinuous and some are deformed by slumping. The whole unit is 24 m thick.

The origin of these sediments is uncertain. The persistence of units of tijl-lika lithology suggests ice contact, but their large number and thinness make this interpretation difficult to accept. The only other apparent interpretation is that they are ice-rafted lake sediments which probably relate to the large lakes postulated for the Mount Counts material a short distance to the north. A thin (29 cm) bed of light gray, very-fine-grained sandstone in the middle portion of V Section is probably a lake deposit. The bed is rhythmically laminated in 191 units 4,6 to 17.8 mm thick with an average thickness of

10.4 mm (Fig. 65). The bed is the only unit encountered in the area studied that could possibly be interpreted as a varve sequence. This interpretation is reasonable when it is realized that U Section, with its massive units of ice-rafted material, is only a short distance to the northwest. The thickness of the laminae rises to

a prominent three-peaked mode and then declines again. Possibly the in itia l rise represents the formation of the lake with a gradual increase in the supply of sediment and then a gradual decrease in supply as the ice front

recedes.

Sedimentary Structures and Directional Features

Paleocurrent Structures Large-scale cross-bedding is by far the most common

sedimentary structure in the Pagoda Formation, and generally occurs in the large-scale channel sandstones. An example is the exceptionally large channel exposed in

C and D Sections. At these localities, the cross-beds 0.1 to 1.0 m thick occur in well-sorted, quartzose sand­ stones. Orientations of 41 cross-beds were measured across the width of the channel (Fig. 56A), giving a resultant azimuth of 180° with a radius of confidence of 8.0° and a precision parameter of 3,86. The resultant 192

20-1

15-

20 30

Figure 65. Thickness of laminae in a rhythmically laminated fine sandstone in the middle part of V S action. o -V

\

Figure 66. Fabric diagrams of cross-bedding in channel sandstones of the Pagoda Formation.

V£) w 194 azimuth is within 9° of the orientation of the channel. Note the well-defined girdle indicating that smaller numbers of cross-beds dip in from the sides of the channel (Fig. 56A). A total of 20 cross-beds taken from a much smaller channel structure in B Section has a resultant azimuth of 183° with a radius of confidence of 8.8° and a precision parameter of 14.6 (Fig. 66B). These figures are very similar to the large channel nearby.

Ten cross-bedding measurements were made on a channel at I Section which give a resultant azimuth of 211° with a radius of confidence of 13.7° and a precision parameter of 13.32. Similarly, at the Bunker Cwm section (L Section) 10 cross-beds have a resultant azimuth of 037° with a radius of confidence of 10.81° and a precision parameter of 20.93. At sandstone localities overlying the lake sediments in U Section and in sections L and fil festoon cross-bedding becomes important (Fig. 67%. At L Section the festoon cross-bedded channels are oriented at 156*20° which is quite close to that of the large-scale channels. At 1Ï1 and U Sections, they are oriented at 122*03° and 174*33°, respectively (Fig. 67).

Planar cross-bedding is not common and is found mainly in poorly sorted tabular sandstone layers interbedded with shales in the vicinity of the type section. The cross­ beds range from 10 cm to over 60 cm in thickness. The dip 195

/O ^83®S

MT. MT. RABOT COUNT 0 MT A MILLER LA'RKSO R m PEAK

X M T . g WEEK < ^ 160° I PAGODA FORMATION PALEOCURRENT DIRECTIONS

-> CROSS-BEDDING - PARTING LINEATIONS -5 CHANNEL ORIENTATIONS RIPPLE DRIFT CROSS-BEDS -H RIPPLE MARKS 4 SLUMPFOLDS

Figure 67. Paleocurrent and paleoslope map For the Pagoda Formation. Each symbol represents the vector mean For all measurements oF that structure at that locality. 196 of the foresets ranges from 6° to 31° and appears to be closely related to the thickness. This relationship is emphasized in Figure 63 and is probably controlled by the velocity of the currents as the grain size of the clastic material is relatively constant (Jopling, 1955). A sample of 25 cross-bed orientations from a unit in A Section shows in Figure 65C a consistency of orientation and lack of a girdle. The resultant azimuth is 157° with a radius of confidence of 5.7° and a precision parameter of 27.06. The high value of the precision parameter emphasizes the unimodal nature of the distribution. Small-scale ripple-drift cross-lamination is not common in the Pagoda Formation but is present in L, 1Ï1, R, and V Sections. Generally, they occur either overlying festoon cross-beds or at the top of channel sandstones, sometimes

overlying laminated sandstone with parting lineations. The vector means of the ripple-drift cross-laminations are given in the summary map in Figure 67. Standard deviations range from 11° to 73°. For the most part, the ripple-drift

cross-laminations agree reasonably with other current structures, with the exception of L Section, where they are oriented at right angles to large cross-beds in the channel lower in the section.

Parting lineations occur in L, P, and U Sections, generally at the top of channels or overlying festoon cross-bedding. They are oriented at 310±11°, .087*5°, and Figure 68, Plot showing general decrease in slope of foreset as thickness increases in sets of planar cross-beds from tabular sandstone bodies at the 40-, top of the Pagoda Formation, A Section.

(/) w 30- » CO LU # CC £ u. 2 0 o

CL O

10-

0 - r ~ 1 . 0 1 0 20 30 40 50 60 70

THICKNESS (IN CM) -0 198

145*4°, respectively. The vector means of the parting lineations are shown in Figure 57. The direction of the symbol is the implied current direction based on whatever other information may have been available, such as cross­ bedding. In general, if all three sedimentary structures are present, large-scale cross-beds occur in the lower portion of the sand body overlain by laminated sandstone with parting lineation, and then by ripple-drift cross­ lamination at the top. Presumably this represents a regular change in the flow regimen. This change is also reflected in a change in standard deviation from 4° to 11° for parting lineation, to 8° to 11° for festoon cross­ bedded channels, and to 11° to 73° for the ripple-drift cross-lamination. The summary map in Figure 67 presents an unsystematic picture. The generalization that can be made is that the sediment is being transported overall to the south or southeast. However, exceptions are present at L Section, where ripple-drift cross-lamination indicates a north­ westerly flow, with the large channel cross-beds flowing at right angles to this direction. In the Moore Mountains, the current directions are even more variable. An unusual feature of the channel sandstone in L Section is the direct evidence of being active during a retreat phase. If we assume that the ripple-drift cross- lamination and the parting lineation represent true local 199 paleoslope orientation, that is, northwest, the orientation of the stream channel is readily explained. During retreat of the ice, meltwater would be unable to flow downslope in this situation because the ice mass lies in the down­ slope direction. Consequently, either a proglacial lake would form or meltwater would have to flow along the ice margin, more or less at right angles to the regional paleoslope. Hence, the orientation of the channel and the intimate association of conglomerate and ablation moraine complement each other.

The absence of shale and the small proportion of sand­ stone in t< Section strongly suggest a local high which also fits well with the reverse slope in L Section; presumably, the drainage divide lay close to K Section. At Mount Counts (U Section) a similar situation prevailed except that a large depression was present and the retreating ice formed a proglacial lake which upon being filled with sediment.allowed the streams to flow to the south and southeast. The flow pattern to the south of Mount Counts probably reflects the flow of water down the sides of the depression, perhaps along the ice margin. The present relief of Miller Range may coincide with a topographic high which existed in Pagoda time. The deflection of the ice locally by the topographic high from the regional mean of 149° to the local mean of 114°, the orientation of the esker in P Section, and other 200 current structures trending in an easterly direction all point to the Miller Range being a local high. Evidence from other sources indicates a low relief on the pre-Pagoda surface; however, some undulations existed on the surface and a few may have had considerable r e lie f .

Paleoslope Indicators

Slump folds are common in the Pagoda Formation in the vicinity of the type section, but elsewhere occur in small numbers (Fig. 69). Axial plane orientations from 55 localities in A, B, C, and D Sections give a paleoslope orientation of 147^53°. Slumping, for the most part, is associated with interbedded sandstone and shale near the top of the section. Slump folds were measured at four levels within A Section at 81 m, 103 m, 128 m, and 154 m above the base. The vector means at the four levels are 135±39°, 126*27°, 162±31°, and 106±33°, respectively.

Paleoice Directional Structures

Grooved surfaces in the Pagoda Formation are grouped into three types; rock-pavements, soft sediment pavements,

and boulder pavements.

Rock Pavements The Pagoda Formation was observed resting on rock pavements at two lo calities, K and V Sections. At most other localities, with the exception of U Section, the 201

Figure 59. Small complex slump Fold in an alternating sandstone and shale unit at the top of A Section of the Pagoda Formation. 202 surface beneath the formation u/as not visible. At U

Section the contact is well exposed, but the tillite rests directly on a rough ungrooved limestone surface.

At K Section the surface contains grooves 2 m in depth cut into sandstones of the Alexandra Formation (Fig. 70). Two sets of striae cut across the grooves at an angle. Both sets of striae are on top of a discontinuous basal

t i l l i t e which f ills the older grooves. The sharpness of detail preserved in the older grooves leaves little

doubt that the sandstones of the Alexandra Formation were well lith ifie d at the time of the grooving. At V Section t i l l i t e rests directly on graywacke and phyllite of the Goldie Formation. Here the surface, which is unweathered

and has a relief of 30 m, is polished, striated, and grooved. At K locality the oldest set of grooves has an orientation of 132^5° and the other two have orienta­

tions of 148*4° and 123*6°. At V Section the striae are

oriented at 184*2°. In alJL cases, the standard deviations are remarkably small.

Soft Sediment Pavements

At six localities soft sediment pavements were found beneath or within tillite units. The surfaces beneath t i l l i t e units take two forms: they are either finely striated (Fig. 71) or grooved by individual boulders (Fig. 72). The finely striated surfaces generally have 203

Figure 70. Grooved pavement beneath the Pagoda Formation at Mount Miller (K Section). The grooves arn cut into sandstones of the Alexandra Formation. Note the second less well preserved set of grooves parallel to the ice axe.

Figure 71. Finely grooved soft sediment pavement exposed beneath unit 9 in K Section at Mount Miller. 204 of the order of six striae in 10 cm. Figures 72 and 73 show a typical grooved soft sediment pavement which occurs at B locality. One gr.oove at this locality is 26 cm wide and 2.3 cm deep and could be traced for 15 m. The grooves were probably made by individual boulders being dragged at the depositional interface. At P locality, the grooves vary from 1 to over 14 cm wide and up to 3 cm deep.

Several of the smaller grooves at this locality s till have clasts ij2 situ at the head of the grooves, giving an unambiguous ice direction to the southeast (114° for this pavement). The groove in Figure 74 is 12 cm long and has a single clast 3.5 cm in diameter at its head. The sand must have been quite soft at the time of the grooving as the sediment is piled up in front of the pebble. The effect is shown to advantage in Figure 75, where the clast has been removed from the head of the groove. The form of the groove suggests that the sand was not frozen, at least at the surface, at the time the grooves were formed. In all cases, the soft sediment pavements are cut into moderately well-sorted sandstone. In contrast to what would be expected, the grooves are never directly overlain by tillite. At all localities examined a thin unit of sorted sediment intervenes. The deep grooves at B locality are fille d with very fine silt which is over- lain by a sandstone unit. The siltstone is pale gray- green or black and in fine laminations with an average 205

Figure 72, Deep grooves exposed in a soft sediment pavement at 8 Section. The groove is 26 cm wide, 2.3 cm deep, and could be traced for 15 m

Figure 73. Close-up view of the same groove as in Figure 72. Note the sharpness of the detail, the groove is □reserved beneath a thin unit of siltstone. 206

— ;------

Figure 74. Small granite pebble at the head of a groove in a soft sediment pavement in P Section (beneath unit 5)

Figure 75. Grooves exposed on the same pavement as in Figure 74, but with the clasts removed to show the sediment piled in front of the clast. 207 thickness of 0,2 m. The siltstone averages 3.0 cm in thickness and is cut off at the top by a sharp erosional surface. Medium-grained, light-gray to tan sandstone rests sharply on the erosion surface. The average size of the largest sand grains in the sediment is 0.6 mm. The sandstone is bedded in two microcross-bedded units, the lower one being 2.0 cm thick and the upper one 1.0 cm thick. The current direction is 172° which is quite close to the current direction determined from large-scale cross-bedding higher in the section. The sandstone is quite poorly sorted and has a large matrix content, as well as large fragments (up to 2 cm in length) of dark- gray to black sandy material identical in composition to the overlying tillite. The fragments show no sign of rounding to suggest that they may have been moved by the current. The upper cross-bed is incomplete and appears to have been interrupted by the deposition of the tillite. The low angle of the cross^bed and the irregular nature of its upper surface suggest that the tillite itself confined the upper surface of the cross-bed during its formation. Similarly, at K and P localities, the finely grooved pavements are overlain by a very fine black shale which is in turn overlain by a few millimeters of medium- grained sandstone.

Laterally, the soft sediment pavements at B and K localities disappear if the fine sediment layer is not 208 present directly above them. Where the soft sediment pavements disappear, they are replaced by boulder pave­ ments. Measurement of the orientation of grooves on the soft sediment pavements gives standard deviations of 4° to 5°, indicating that they are of the same order of reliab ility as the hard rock pavements for determining paleoice direction. Soft sediment pavements occur within the tillite s on the upper surface of thin sandstone laminae. Orienta­ tion of grooves on the surfaces of the sandstone laminae indicate standard deviations ranging from 4° to 7° which is similar to basal soft sediment pavements.

Boulder Pavements In general, boulder pavements occur more frequently than soft sediment pavements because of resistance to erosion (Fig. 76). With one possible exception, the boulder pavements mark disconformable surfaces between tillites. Generally, the boulders do not protrude above the surface of the sandstone bed, although laterally the sandstone beds often wedge out. The boulders on the surface were pressed into the surface rather than being planed off to a uniform height by abrasion. In all cases, the original rounding of the boulders could be seen suggesting minimum abrasion of the clasts once they had been impressed into the surface. The pavement clasts are generally well rounded in con­ trast to those in the tillite, although of the same 209

Figure 76. Boulder pavement exposed in cross-section between units 11 and 12 in K Section. This pavement could be traced laterally for some distance and contained rounded clasts derived from a small channel deoosit. 210

general composition. A cumulative frequency plot of boulders measured on several pavements is presented in Figure 50. The slope of the line suggests sorting similar

to the t i l l i t e but in general the clasts are smaller. At

K Section it ujas found that the density of the boulders on the surface increased and could be traced in an upglacier direction to a small conglomerate-filled stream channel. Beyond the channel the boulder pavement ceased.

Clearly, the clasts were derived from the small channel deposit rather than from the basal load of the ice sheet. The orientations of striae measured on the surface of boulders imbebbed in boulder pavements are remarkably consistent with standard deviations, ranging from 1° to

6°. Near the type locality it is possible to measure striae on a pavement at two points separated by approxi­ mately 1.5 km. The directions are 151-4° and 152^5°.

This points out two things; first, it indicates the value of boulder pavements for determining ice-flow directions because of their consistently small standard deviations,

and second, it indicates just how subdued the local topography must have been over the 1.5 km at the time of

deposition. Lumping together 49 readings gives a standard deviation of only 4°. From the experience gained in the area studied, it

seems that if there is any doubt about a particular boulder pavement, it probably should be disregarded if the standard deviation is greater than about 10°. 211

In determining the direction sense of paleoice flow probably the most distinctive structure is the stoss and lee effect produced by the formation of soft sediment ta ils behind small clasts projecting above the surface (Fig. 77). Two types of stoss and lee effect are also produced on the grooved surface of the clast its e lf. The f ir s t involves the polishing and grooving of the upstream side of projections on the clast to produce micro-drumlin effects which ta il off downstream or shows signs of small- scale plucking (Figs. 78 and 79). The second type is only rarely seen and generally involves quartz phenocrysts in porphyry. As the quartz grains are harder than the matrix, they are left projecting above the surface of the clast with a raised ta il of matrix remaining on the downstream side. An attempt was made initially to use lines of boulders

that are often seen on the pavement surface as in Figure 30. Generally, three, sometimes four, boulders occur one behind the other, decreasing in size in one direction. The line of boulders is often emphasized by deep grooves cut into

the sediment on either side. It was originally thought that the boulders decrease in size in the downstream

direction; however, repeated observation of these features showed that they are oriented in both directions on the

same surface. 212

Figura 77. Soft sediment ta il formed on the downstream side of a very small clast on a boulder pavement between units 12 and 13 in A Section. The ice moved from right to le ft. This is the same oavement as in Figures 72 and 73. 213

Figure 78 « Micro-roche moutonnée on the surface of a clast exposed on the same boulder pavement as Figure 77 The ice moved from right to le ft.

Figure 79. Micro-roche moutonnée on the surface of a clast from the same boulder pavement as Figure 78. The ice moved from rioht to left. 214

Figure 30. Line of clasts emphasized by a groove on either side. The ice moved from right to left. In this case, the clasts increase in the downstream direction, but at other localities the reverse is true. 215

All directional features show that the ice flowed consistently to the southeast with a mean direction of 148-21° and a range from 114° to 132° (a total of 17 pavements were measured). Directional information deter­ mined from the pavements is summarized in Figure 81. The direction determined at P Section diverges the most from the average direction, apparently in connection with a change in the paleoslope. The change in paleoslope

is also reflected in the paleocurrent data and in the orientation of the esker in P Section. The pavement also provides information about the environment at the bottom of the ice mass prior to deposition. For a pavement to have formed, the base of

the ice mass must have been sliding, which suggests that the ice at its base may have been at or near its melting point. However, we have already seen that the clasts

forming the boulder pavements come not from the basal debris load of the ice mass but from stream gravels exposed on the surface over which the ice was riding.

Thus, in itially , deposition was unable to take place, suggesting that there was no basal melting to this point. At this stage, large clasts were being dragged across

the subglacial surface, forming grooves in the soft sediment which are preserved only under special circum­

stances. The sediments directly overlying the pavements must have been deposited in subglacial cavities or depressions in the subglacial surface. The extremely 215

1 / 165® E P AI^RAM

MX RABŒF

MX MILLER 6

MX WEEK

PAGODA FORMATION PALEO-ICE DIRECTIONS DETERMINED FROM PAVEMENTS N

ABODE

MX J ^ C ^ L A R a ORIENXAXION OEM STRIAE ON A SINGLE PAVEMENT MEAN

Figure 31. Paleoice flow map showing the orientation of the vector means of all grooved surfaces found in the, area studied. 217 sharp detail preserved on the pavements along with the very fine laminae preserved in the, mudstone suggest a very quiet depositional environment, which allowed the sediments to be deposited directly on the unmodified pavement. The only other alternative to deposition in a subglacial cavity is to suggest that the ice retreated without depositing any till and without disturbing the grooves on the surface, and then, after deposition of the finely laminated mudstone, it readvanced without disturbing the fine laminae in the mudstone. This mechanism may be possible but seems highly unlikely. It is probably more realistic to suggest deposition in a subglacial cavity that was kept open by local topographic irregularities.

Clast Fabric Tillite Clast Fabrics

Long-axis clast fabrics were measured from eight beds in A Section. Unfortunately, the lower 30 m of the forma­ tion was covered with debris and fabrics could not be measured. Transverse modes are present in fabrics from

units 4, 7, and ID (Fig. 32), whereas unit 9 has both transverse and parallel modes. Units 4, 7, and 9 all

contain sandstone^laminae within the tillite, indicating the presence of open cavities beneath the ice during

deposition of the till and suggesting deposition from thin ice. However, grooves on the upper surface of the laminae in unit 9 and the lower part of unit 7 indicate Figure 82. A Section from the northeastern end of the Queen Alexandra Range. This and the following diagrams (Figures 32 and 89) provide a summary of the main features observed and measured from the Pagoda Formation. Numbers to the le ft of the columns are unit numbers which correspond with numbers to the le ft and beneath each fabric diagram. Numbers to the right and beneath each fabric diagram are the number of clasts measured. / wen \ ro rvj-t^cn OOlD / üi CO to— O ro iliiIÏ I ii| & Ik. iHisail

m

N) t-" m 219 that the ice was not stagnant during deposition of at least these two units, for basal sliding was active. Other factors, most probably the rate of basal melting combined with the controlling obstacle size, allowed the preserva­ tion of fabrics that were most likely developed englacially. The mean of the five largest clasts in the lower part of unit 7 is 50 cm (Fig. 82), which suggests that the control­ ling obstacle size may have been quite large (see Chapter II). Parallel fabrics were recorded from units 12, 13, 22, and 23. The fabric from unit 12 appears to be the only one with a relatively strong mode, plunging upstream to suggest that it may in part be englacial. The remaining three diagrams indicate that they were reoriented fairly completely at the depositional interface. At B locality, 0.9 km to the north of A Section, fabrics were measured from four beds (Fig. 33). Those from units 1, 3, and 4 have parallel fabrics, whereas unit 2 has a well-developed transverse fabric. The abundance of sand­ stone laminae within the t i l l i t e in unit 2 indicates that deposition occurred beneath thin ice. The laminae are not grooved which suggests little basal sliding and perhaps stagnant ice, which would explain preservation of a possible englacial fabric. Units 1 and 3 have likely been completely reorganized at the depositional interface as the modes are subhorizontal and somewhat irregular, suggesting deposition from fairly active ice. The fabric of unit 4 has been Figure 83. B Section of the Pagoda Formation at the northeastern end of the Queen Alexandra Range. Symbols as in Figure 82.

— ro OJ CJi CD (S> rooj

1 1 1 ml I, i. 11 ! 11

CO ^ ~n Qt*

tsJ NJ O . 221 has been reorganized to some extent, but still has a relatively strong mode plunging upstream, suggesting that it is englacial in part. Two fabrics with weak subhorizontal modes were measured from the lower part of C Section (Fig. 84). Both fabrics have parallel modes and were probably reorganized at the depositional interface. The mean of the five largest clasts is 16.3 and 16.2 cm, which suggests that the controlling obstacle size may have been small. Five fabrics were measured from D Section (Fig. 85). Unit 1 has a well-developed transverse fabric, suggesting that it had an englacial origin. The overlying unit, in contrast, has a poorly developed parallel fabric which was probably reorganized at the depositional interface. The fabric from unit 3 has the characteristic dipping girdle associated with mass movement. The distribution of the modes suggests that they are the remnants of the t i l l fabric on which the mass movement fabric was superimposed. The large channel structure described previously cuts this unit quite close to the point where the fabric was measured, suggesting that the slumping was probably in response to the relief caused by the erosion of the channel (Fig. 85). Unit 5 is extremely thick (63 m) at the point where it directly overlies the channel. A fabric of 25 clasts taken near the base of unit 5 directly above the channel sandstone indicates a paleoice direction of 188° which is close to the channel 222 9

^ A

8

D METERS

7

6

5

4

3 A 2

/ ^ W A Oo

50 0 10 20 30 Figure 34, C Section at the northeastern CM end of the Queen Alexandra Range. Note the large sandstone channel structure and MEAN OF 5 compare with Figure 70, Symbols as in LARGEST Figure 82, CLASTS 223

wwiChg

^ METERS HORIZONTAL SCALE

6

Figure 35, D Section of the Pagoda Formation at the north­ eastern end of the Queen Alexandra Range, Note the large sandstone channel and the exceptional thickness of the t i l l i t e overlying the channel. Symbols as in Figure 82, 224 paleocurrent direction. A second fabric taken 30 m above the base of the unit gives an ice direction of 123°, which is close to the regional ice direction. It appears that in itia lly the ice flow was redirected locally along the channel but later as the channel filled with debris the ice direction reverted to the regional flow pattern. A single fabric measured from unit 3 in I Section

(Fig. 86) has a single well-developed mode parallel to the ice direction and plunging upglacier. It is an almost ideal example of what could be expected from an englacial fabric. Grooved laminae at the top of the unit suggest thin ice and basal sliding The K Section is the most completely exposed section visited by the writer and, consequently, it was possible to measure fabrics from 13 beds (Fig. 37). Six of the diagrams have parallel modes, three have transverse modes, two have both, and two diagrams show modification by mass movement. Two of the diagrams.with parallel modes, those from units 5 and 12, are exceptionally strong and probably reflect an englacial origin. Both diagrams have well- defined maxima plunging upstream. The remaining four diagrams with parallel modes have relatively poorly defined subhorizontal modes which probably result from clast reorganization during deposition. Five of the remaining diagrams have either single transverse modes or both parallel and transverse modes which are, for the most part, englacial in origin as available evidence suggests that transverse A A & 225 t A 14 A A A A A 13 A A A 12 A A AAA A A A 10 METERS A A A A A

1 0 Ï»;

8 50 AAA 6 7 A A A 5 A A 4 A gtpAoa A effiSsAcCCOBC A A A A A A A

2 I 0 10 20 30 Figure 86. I Section of the Pagoda Formation at the mouth of the T illite CM Glacier in the Queen Alexandra Range. MEAN OF 5 Symbols as in Figure 32. LARGEST CLASTS CO — — —— ^5 — rooJ-^ üi o> CO O 3 r o o i ( J \ O ) ooco o ► ► 1,1: o s » s m » »» 0».■ i

o (/>cr>$ Qo - Hm C/>COq 8

Figure 87. K Section from Mount Miller at the southern end of the Holland K) Range. Note the large number of pavements in this section. Symbols as in r\) Fiqure 02. cn 227 maxima develop, for the most part, englacially. Thus,

7 of the 13 beds have fabrics which are largely englacial. Units 6 and 9a both have abundant evidence of mass move­ ment in the form of soft sediment folds. Both reflect the slumping in their fabrics by having girdles dipping at low angles to the west and by having their fabric symmetry reorganized about an east-west plane of symmetry, suggesting a paleoslope oriented in an east-west direction

(Lindsay, 1958). The fact that this does not coincide with the paleoice direction suggests that slumping was in response to local relief, perhaps caused by stream erosion or possibly the melting of buried ice. A single fabric was measured from the upper part of unit 6 in N Section (Fig. 38). The fabric mode has some residual upstream plunge which probably results from reorganization, to a large extent, at the depositional interface. The ice direction determined from the fabric is 127°. The underlying boulder pavement has, by compari­ son, a direction of 152°. This provides one of the very few examples where the ice direction changes significantly during deposition of a bed. A single fabric was taken from unit 3 in P Section (Fig. 89). It is significant in that it has all the features that could be expected in a transverse englacial clast fabric. The presence of this fabric, along with an esker deposit described previously, indicates deposition from near-stagnant ice. The size of the largest clasts 228

9

8

6

5

4

10 METERS 2

0 10 20 30 40 50 60 Figure 33. N Section at the head of the Lowery Glacier in r\r- c the Queen Elizabeth Range. MtlAN Ur O Symbols as for Figura 82. LARGEST CLASTS 229

X A X X X 10 XXX

° . . . / 9- . -°.g-»z. . ■ 0 0 10 METERS o 0 o o O 0 O O c 0 N r v » r a m 8 iii

4 '.ixiQCfiCKlfiS

1 A ^ A I AAA

Figure 39. P Section in the Moore Mountains. Note the sandstone wedges and the esker-like sandstone body in unit 8. The symbols are the same as For Figure 32. 230 in the unit seldom exceeds 20 cm, which suggests that even if rapid basal melting was possible, the controlling obstacle size would have been too small to prevent basal sliding from reorganizing the fabric at the depositional interface. Consequently, it is thought that the ice must have been nearly stagnant during deposition of the till. The fact that the esker and the joint pattern controlling the sandstone wedges at this locality are preserved leaves little doubt that the till was deposited from stagnant ice.

inhere it was possible to measure several fabrics from a single section, it was found that the ice direction fluctuated considerably. However, in general, the changes within a single bed are small (Chapter II), and most of the variation occurs between beds. No consistent changes in ice direction are apparent and the ice-flow direction appears to have varied randomly within its range in relation to time (Fig. 90). The overall vector mean of the ice direction determined from clast fabrics is 143^13° which is in good agreement with the overall vector mean for pavement directions (143-21°).

Following the interpretations established i-n Chapter II, about 17.5 percent of the beds have clast fabrics which are englacial in origin. About 12.5 percent of the fabrics have features indicating that they were completely reworked at the depositional interface, whereas the remaining 70.0 percent reflect both modes of development to varying degrees. In a few beds it was possible to DEPTH (M) ü» o

m

r o

Figure 90» Paleoice directions throughout K Section. The ice directions are based on ail available pavements and clast fabrics. Note that there is no apparent consistency in the.- fluctuations in ice direction. ro 0 3 232 establish that the ice was stagnant during deposition of the t i l l . For the most part, there is strong evidence of basal slide either from the fabrics themselves or from the grooved sandstone lenses within the tillite. However, the abundance of the sandstone lenses leads to the con­ clusion that the ice was relatively thin at the time of deposition, and the general impression gained is that the ice was retreating as it deposited the till. 'JJhere englacial clast fabrics are present, their preservation is related to the presence of larger clasts, which suggests that the controlling obstacle size was large. In all beds where soft sediment deformation in the form of slump folds could be identified, the fabrics produced had the characteristic girdle described by Lindsay

(1966, 1963). In general, the slumping appears to have been in response to local relief caused by stream erosion. This is to be expected since, for the most part, the regional paleoslope appears to have bean quite small and it would have been difficult for terrestrial mudflows to take place. Subaqueous mass movement was, however, closely controlled by the regional paleoslope,as indicated by the orientations of slump folds in the upper part of A Section.

Conglomerate Clast Fabrics

A small number of long-axis clast fabrics were measured from various conglomeratic bodies (Fig. 91). On all diagrams, the current direction as determined from Figure 91. Long-axis clast fabrics from conglomerate bodies in the Pagoda Formation. Tick marks indicate the paleocurrent direction determined from cross-bedding. (A) Small conglomeratic channel, A Section, i\I=50. ( b) Conglomerate lens at the base of a large sandstone channel, B Section, l\l=25. (C) Conglomerate interbedded with probable ablation moraine,. L Section, rj=30. (D) Tabular conglomerate body, R Section, 1\)=50.

CJ C/I 234

associated cross-bedding is shown. Diagram A of Figure 91

was measured from the small conglomeratic channel described previously from A Section. The mode which is transverse is quite strong for a clast fabric (radius of confidence

10.78°, precision parameter 4.48, N=50). Fabric B (Fig. 91) was measured from conglomeratic lenses in the base of a moderately large channel in the B Section. The mode is not

as well defined as the A diagram, which is to be expected as l\l=25. The radius of the circle of confidence is 20.39°

with a precision parameter of 2.92. Unlike the A diagram, the mode is parallel to the stream-flow direction (Krumbein, 1940). The C diagram (Fig. 91) comes from the poorly sorted conglomerates at the base of the sandstone channel at Bunker

Cwm (L Section). The mode, of the fabric is diffuse and bears no apparent relationship to the cross-bedding data

taken from the associated sandstones. The radius of confidence is 18.9° with a precision parameter of 2.93 (|\I=3Q). The fabric is equivalent to the 8 diagram, but both are weaker than the A Diagram. In addition to the

main diffuse mode, there is a smaller weak horizontal mode more or less normal to i t . The presence of the second mode suggests that the fabric may be due to water sorting, but

other processes related to the retreating ice have dis­ rupted it to some extent. The fabric represented by diagram D (Fig. 91) was taken from a thin horizontal bed of conglomerate directly overlying the foresets of the tabular conglomerate body in 235

R Section (N=50). The fabric exhibits two subhorizontal modes at right angles to each other, and similar to fabrics described by Schiemenz (1960). The current direction determined from ripple-drift cross-bedding from overlying beds coincides exactly with the smaller of the two modes. The clarity of the modes indicates a very consistent current direction during deposition of the bed from which the fabric was measured.

The Regional Distribution of Permian Glacial and Postglacial Sediments in Antarctica

Sediments believed to be correlatives of the Pagoda and Mackellar Formations are found along much of the length of the Transantarctic, Ellsworth, and Pensacola Mountains. The thickness of the Permian t il l it e in these areas is shown diagrammatically in Figure 92, and their directional properties are presented in Figure 93, The thickness expresses two well-defined maxima: one in the Queen Alexandra Range and the other in the Ellsworth Mountains (Fig. 92). Beginning with isolated pockets of what may be t i l l i t e in the vicinity of Mcuurdo Sound

(Matz, personal communication, 1967), the thickness of the tillite increases gradually to a maximum of over 100 m in the Queen Alexandra Range (Orindley, 1963; Haskell and others, 1964; Laird and others, in prepara­ tion) and then decreases in a very short distance to less 235

T— I— I— I— I— I— I— I— I— I— I— r ^ T ~ r 24 22 20 18 16 14 12 i6 8 DISTANCE FROM CENTER OF ICE SHEET x 100 KM S 10 1 1 13 2

Figure 92. Thickness of postglacial shales (upper graph) and Paleozoic tillite s (lower graph) along the Trans­ antarctic, Pensacola, and Ellsworth Mountains, Antarctica. Numbers beneath the lower graph give the number of beds of tillite at each locality. 237

Figure 93. Paleoice directions in the Transantarctic and Pensacola fountains (derived from many sources). Note the relatively consistent orientation of the directions. Figure 93. 238

PALEO-ICE DIRECTIONS

WITH DIRECTION SENSE

DIRECTION SENSE UNKNOWN

90® W

m

j UJ

ROSS ICE SHELF

8 0

ROSS I S .^ W 180* E 239 than 15 m in the Axel Heiberg Glacier area (Barrett, 1965;

Wade and others, 1965). The thickness of the til l it e then increases gradually to a maximum of near 1000 m in the Ellsworth fountains (Craddock and others, 1955; Matthews and others, 1967). With the possible exception of the sediments in the Ellsworth Mountains, the number of beds of t i l l i t e correspondingly increases as the total thickness of t i l l i t e increases (Fig. 92), with the average thickness of the individual beds decreasing. For example, from the Darwin to Beardmore Glacier, the formation shows a fourfold increase in thickness from 27 m to a little over 100 m, and the number of beds increases from 2 to 13 and possibly 21, or from 6 to 10 times in number. The paleoice flow data are summarized in Figure 93, Despite disagreements as to the ice-flow direction at two localities (iKlinshew, 1967 ; Frakes and others, 1966), the orientation of the striae over their known extent is remarkably con­ sistent. Over much of its known extent, the t il l it e is conform­ ably overlain by thinly bedded and laminated gray shales, sandstone and, in places, thick units of black shale. The thickness of the postglacial shales is shown in Figure 92.

From Mcfilurdo Sound along the Transantarctic Mountains to the Nimrod Glacier, the shales are absent. At the Nimrod Glacier, Laird and others (in preparation) found that the Mackellar Formation varied in thickness and changed laterally to the north and northeast into carbonaceous 240 sandstone. This, combined with current structures which indicate that current flowed to the south, suggests a strandline to the north of the Nimrod Glacier. South from the Nimrod Glacier, the formation thickens gradually to Mount Butters, where Wade and others (1965) report the thickness of the lower shale unit as being approximately 137 m. From Mount Butters to the Nilsen Plateau on the Amundsen Glacier, the shales thin to 49 m (Long, in preparation), and then increase to the Wisconsin Range where Minshew (1966) reports the correlative lower Weaver

Formation to be 300 m thick. The thinning of the shales appears to indicate a large topographic high on the pre­ shale surface in the vicinity of the Amundsen Glacier. This possibility is supported by the presence of an erosion surface reported by Long (in preparation) between the t i l l i t e (Scott Glacier Formation) and the shale (Roar­ ing Formation). In the Ohio Range, Long (1965) reports 170 to 190 m of shale (Discovery Ridge Formation) overlying the t i l l i t e (Buckeye Formation). Schopf (1967) reports 900 m of shale overlying the t i l l i t e (Whiteout Conglomer­ ate) in the Ellsworth Mountains which may be equivalent to the Mackellar Formation, The extreme thickness of shale at this locality is a result of deposition in a subsiding basin. 241 A Model for Permian Glacial and Postglacial

Sedimentation in Antarctica

Glacial Paleogeography The problem with any paleogeographical reconstruction for the Paleozoic tillites in Antarctica is, as pointed out by Schmidt and Williams (in press), that the glacial deposits are only exposed in an elongate strip. Restricted as the information is, it is possible to suggest a simple model.

The abundance of grooved pavements within and beneath the t i l l i t e show that over most of its extent the t il l it e is an ice-contact deposit. Despite the uncertainties in direction of ice flow at two localities, the orientation of the striae are nearly parallel over the known extent of the glacial deposits. These features, along with the extent and apparent continuity of the deposits (over about 2000 km), suggest the presence of an ice sheet of continental proportions in Antarctica during the Permian, Late Paleozoic sedimentation from the Horlick Mountains to Victoria Land in Antarctica probably occurred on a stable continental block, whereas sedimentation in the Ellsworth and Pensacola Mountains occurred in a subsiding basin which accumulated a considerable thickness of sediment. This interpretation of the continental framework of Antarctica suggests a regional paleoslope toward West Antarctica during the Upper Paleozoic (Schmidt and Williams, in preparation). 242

The extreme thickness of t i l l i t e in the Ellsworth and Pensacola Mountains is the result of tectonic sub­ sidence along with an abundant supply of sediment at the edge of the ice sheet. However, there is no evidence to suggest that the thickening of the tillite in the vicinity of the Beardmore Glacier is a result of tectonic subsidence. Further, the gradual nature of the thickening and its broad extent probably precludes it being a valley f i l l .

The most reasonable hypothesis for the origin of the thickening is that at some point in time, probably during

the final retreat, the ice margin remains relatively stable for a considerable length of time in the area of the Beardmore Glacier at a distance of about 950 km from its

center of dispersal. A section of the ice sheet is shown in relation to the full extent of the ice sheet in Figure 94. The model does, however, tend to exaggerate the thickness of the ice sheet at the center. The increase in

the total number of beds in the vicinity of the Beardmore Glacier area suggests that the ice margin was not completely

stable during this time period, but like the Pleistocene ice sheet of North America i t flucturated backwards and

forwards for short distances across the area, each time

depositing a thin unit of tillite. The increase in the number of beds in the vicinity of the Ohio Range can

probably be explained in a like manner. 243

THICKNESS OF ICE SHEET ( Mx 1000)

œ o~

CD-

Figur'e 94. Profile of two ice sheets with radii of (l.) 950 km and (2) 2250 km. 244

Time Requirements for the Paleozoic Glaciation It is possible to make some estimate of the order of magnitude of time necessary for the glaciation. Taking U/eertman's (1964) simple model with uniform accumulation over the whole ice sheet at 50 cm yr"^, an ice sheet of 2250 km radius requires 3.5 x 10^ yr to build. On the other hand, in a retreat phase with overall ablation of 100 cm —1 3 yr” , the ice sheet would require at least 8.7 x 10 yr to melt completely. Thus, the glaciation requires no more than 10^ yr for completion, which is two orders of magnitude smaller than the time available for Permian sedimentation.

Postglacial Paleogeography

The Permian postglacial shales in Antarctica pose a problem in that they form a relatively thin, very persis­ tent unit, lying in sequence above terrestrial glacial deposits and beneath fluvial sandstones, while they them­ selves are clearly of subaqueous origin. It is proposed here tha the deposition of the postglacial shales is tied directly to the final retreat of the Permian ice sheet.

At its greatest extent (R = 2250 km), the Permian ice sheet appears to have reached to sea level at a point just short of the Ellsworth Mountains. If at this stage the ice mass was more or less in isostatic equilibrium, it is possible that the land surface was depressed such that 245 upon retreat of the ice sheet the sea mas able to follow the retreating ice to a point just north of the Nimrod Glacier where it formed a shore line. This would require that the in itia l land surface had an average slope of about 1:900 which is quite reasonable as the preglacial surface appears to have had a relatively low relief. The problem then is to obtain some estimate of the time available for deposition of the postglacial shales. This is controlled by two opposing variables which can be estimated and two lesser variables for which we have no information. The estimated variables are the rate at which ice front retreats and the rate at which land surface rebounds following removal of ice. The unknown variables are the rate of tectonic subsidence in the region of the

Ellsworth and Pensacola Mountains and the rise in sea level resulting from the melting of the ice sheet. There is no way of estimating the rise in sea level, as there is really no knowledge as -to whether the Late Paleozoic ice sheets were synchronous over their known extent on

other continents. Bearing in mind the lim itations, i t is possible to calculate the time required for the ice sheet to retreat (b’eertman, 1964, p. 150), The time (t) required for an ice sheet of initial radius R (= 2250 km) to reach a radius of R^ is:

t = -(1/a) (3x/pg)2 (R-R’)^ 246 where t is the shear stress at the base of the ice sheet (= 1.0 bars), p is the density of glacier ice ( p= 0.9 g cm" ), and g is acceleration due to gravity. As the ice retreats, the crust is unloaded and begins to rebound as a negative exponential function of time,

p = l-e-t/Tr where p is the proportion of the ultimate recovery occurring at time (t) since removal of the load, Tr is the relaxa­ tion time (Heiskanen and Vening Meinesz, 1958, p. 361) which is the time in years required for the depressed surface to recover to l/e of its initial depression. Heiskanen and Vening Meinesz (1958, p. 369) found that, for the Fennoscandian ice sheet, Tr % 5 x 10 yr which is a reasonable value to assume for the present analysis. With the above information and assuming an overall ablation rate of 100 cm yr~^ (A % it is possible to graph the change in the position of the postglacial shore line with time, firs t as the ice retreats and the shore line moves inland, and later as isostatic uplift dominates and pushes the shore line out. The results are summarized in Figure 95. This provides a means of estimating the order of magnitude of time available for deposition of the postglacial shales at any point along their extent. Beyond the Horlick Mountains, tectonic subsidence makes any meaningful estimate out of the question, but the values are probably of reasonable magnitude on the continental Figure 95. Position of the postglacial strandline in relation to the retreat of the Paleozoic ice sheet.

10- FLUVIAL

WATER’ COVERED LJ 5- H 4- ICE COVERED

23 22 21 20 19 18 17 16 15 14 13 12 II (0 9 8 7 6 5 4 3 DISTANCE FROM CENTER OF ICE SHEET x 100 KM N3 ->3 248 block, With a knowledge of the time available for deposi­ tion of the shales at any point, it is possible, using the known shale thicknesses, to determine the sedimentation rate. The rates of sedimentation calculated by this means are shown in Figure.96 and range from 4.7 cm yr~^ on the Nilsen Plateau to 17,6 cm yr”^ in the Wisconsin Range, The problem is to find an independent method of estimating the sedimentation rate against which the above figures may be compared. The niackellar Formation is well bedded in thin rhythmic units which alternate from ripple-drift cross-bedded sandstone to black or gray shale. The rhythrnites are so prominent that Grindley (1963) was prompted to associate them with glacial lake sediments. This suggestion is not entirely unreasonable for if, as postulated, the deposition of the shales was in close association with the retreating ice, the rhythmite may have been in part controlled by seasonal changes in sedi­ ment supply. With this in mind, the thicknesses of the rhythmite pairs were sampled at A Section in the Queen

Alexandra Range and K Section in the Holland Range (Fig, 97). From these samples a mean rhythmite thickness was calculated. For A Section, the mean rhythmite thickness is 11,6 cm, whereas the calculated sedimentation rate is 10.0 cm yr” , and for K Section the mean rhythmite thick­ ness is 3.6 cm, whereas the calculated sedimentation rate is 10,9 cm yr”^. The figures are remarkably close considering the approximations involved and the 249

S ZLÜ 25 LU O z LU «s 8| 20H < c r I luû: COLU S I5H o /\ g o g

0 “T " T" T" I ~ r —I 16 15 14 13 12 11 10 9 8 7 6 5 DISTANCE FROM CENTER OF ICE SHEET x 100 KM

Figure 95. Calculated rates of sedimentation for the postglacial shales based on the measured thickness of the shales and the time available for sedimentation from the .model proposed in Figure 95. 250

30-1 30- SANDSTONE SHALE A SECTION K SECTION ÏZZ1 20-

10- I 0- 1 \ < i r SEDIMENTATION UNITS

Figure 97. Thickness of rhythmite units in parts of A and K Sections of the [Klackellar Formation. 251 assumptions made. The unusual feature of the sedimentation rates is that, contrary to what would be expected, they do not decrease with distance from the readily apparent source of supply, namely the melting ice mass. This suggests that the supply of sediment was not controlled entirely by the retreating ice front but that sediments were being introduced from elsewhere, perhaps from either side of a relatively narrow depositional basin. Evidence is available from several other sources in the Beardmore Glacier area to suggest that this was the case. First, the presence of beach deposits in the niackellar Formation at Mount iJieeks (T Section) suggest a strand line to the west (Chapter l). Current structures from the Alexandra

Formation suggest that sediment was introduced from either side of a narrow basin. Evidence of land to the west was found but there is a lack of information on the source to the east. In the Pagoda Formation, both paleocurrent and paleoice indicators suggest a topographic high to the west in the vicinity of the Miller Range, Barrett (in prepara­ tion) reports similar indications from the formations overlying the ülackellar Formation. Overall, there is a strong indication that deposition of the postglacial shales may have taken place in a basin that is much longer than it is wide. This being the case, the basin is probably quite closely comparable to the postglacial to the present Baltic Sea. Du Toit (1954) came to a similar conclusion for sediments directly overlying the Dwyka 252

T illite in South Africa; "the sediments composing the ilhite

Band were apparently in the nature of black, organic highly sulphuretted muds like those formed in the Black Sea or Gulf of Bothnia at the present day" (p. 278-279).

The confined nature of the basin may have resulted in brackish to fresh water conditions. Thus, the Sr^^/Sr^^ ratio could be expected to have continental affinities as the waters of the confined basin were unable to mix freely with the ocean (Barrett, Taure, and Lindsay, 1963). By comparison with postglacial sedimentation rates in the

Baltic Sea (Ignatius, 1958), the rates calculated for the

Paleozoic postglacial shales in Antarctica are high. However, some of the sections contain thick sandstone units which may have increased the overall sedimentation ra te . SUMMARY

The sedimentary rocks of the lower Beacon succession in the Queen Alexandra, Queen Elizabeth and Holland Ranges in Antarctica consist of the Alexandra, Pagoda and Mackellar Formations. The Deuonian(?) Alexandra Formation rests unconformably on the basement complex, and consists largely of massive, well-sorted, cross-bedded, quartzose sandstone. The formation is absent in the Moore Mountains but elsewhere is up to 300 m thick. The sediments appear to have been deposited in a narrow, shallow, non-marine basin. The Permian Pagoda Formation consists predominantly of t i l l i t e and sandstone and is from 125 to 395 m thick.

The formation rests disconformably on the underlying Alexandra Formation and is^conformably overlain by the Permian Mackellar Formation. The Mackellar Formation consists of thinly bedded shales and fine-grained, ripple- drift cross-bedded sandstones which range from 61 to 121 m thick. The origins of the Mackellar and Pagoda Formations are closely linked. The Mackellar Formation is conformably overlain by the Fairchild Formation. The Pagoda Formation was studied in considerable detail and particular emphasis was placed on the 253 254 measurement of tillite clast fabric. The clast fabrics result from two possible mechanisms; they may form englacially, or at the base of the ice mass at the time of deposition. The main factor determining the final form of the fabric appears to be the controlling obstacle size at the base of the ice mass. The larger the control­ ling obstacle size the greater the chance that the englacial fabric will survive. If the controlling

obstacle size is smaller than the clasts measured for the fabric the clasts will have been modified by the shear

stress at the base of the ice mass during deposition. A knowledge of clast fabric provides, as well as the ice-flow direction, information on the depositional environment of the t i l l i t e . For example, fabrics formed englacially have either a single well-developed mode parallel to the ice direction and plunging at about 10°

to 20° upglacier or a subhorizontal mode transverse to the ice-flow direction, or.less frequently, both modes are present. Fabrics formed at the depositional interface have a single subhorizontal mode lying parallel to the

ice-flow direction. The mode is generally weaker and less regular than its englacial counterpart. The considerable extent and apparent continuity of the Paleozoic glacial sediments in Antarctica, along with the consistency in the orientation of interpreted ice directions, indicates that the sediments were deposited by an ice sheet of continental dimensions centered 255 on southern Victoria Land. On one or more occasions, the

ice sheet extended to a point beyond the Pensacola Mountains and at some stage, probably during final retreat, the ice margin remains relatively stationary in the vicinity of the Beardmore Glacier for a length of time. In general, the regimen of the Paleozoic ice sheet was very similar to that of the Pleistocene of North America. The glacial sediments were deposited from active temperate ice, although evidence from a few beds suggests that the ice may locally have been stagnant. During fluctuations

of the ice margin, large streams with gradients of the order of 1:400 to 1:2000 flowed across the surface. Local topography caused diversion of some of the streams along

the ice margin and at some localities proglacial lakes

formed. The distribution, thickness and lithology of the postglacial shales appears to be related closely to the final retreat of the ice sheet. Most likely, as the ice sheet retreated, the sea was able to follow the ice front inland as a result of depression of the land surface by the ice mass and probably to some extent a rise in sea

level. This allowed a limited period of time for

deposition of sediments until isostatic rebound forced the strandline seaward again. Approximations based on this model suggest sedimentation rates of the order of 4.7 to 17.6 cm yr”^ which f it well with the observed thickness of sedimentation units in the area studied 255 if it is assumed that the units are seasonal. The basin into which the postglacial shales were deposited was long and probably relatively narrow. Evidence from the sediments themselves suggests a very low energy environment which locally was stagnant. Thus, the large masses of water provided by the melting ice sheet and surrounding land masses probably resulted in a situation much like that of the Baltic Sea following the Pleistocene ice sheet. The resulting brackish to fresh water conditions would readily explain the high Sr^'^/Sr^® ratio observed in the post­ glacial shales by Barrett, Faure and Lindsay (1968). . APPENDIX I

Twenty stratigraphie sections were measured through lower Beacon rocks. Large thicknesses were measured by altimetry and hand leveling, whereas thin units were measured with a tape. Lithologie units are described and numbered in ascending order. Column A contains the unit number, column B the thickness of the unit in meters, and column C the cumulative thickness from the base of the measured section. Each section has an alphabetic designation (A to U). The location of the sections is given in Figure 3. Rock sample numbers are given follow­ ing the description of each lithologie unit. The numbers consist of six characters, three letters followed by three digits. The first letter designates one of three broad areas; T, the Tillite Glacier area; lYl, Mount Miller and Lowery Glacier area; and A, the Moore Mountains area. The second letter signifies the formation; A, Alexandra;

P, Pagoda; and M, Mackellar. The third letter signifies the section. The three digit numbers were given as the samples were collected in the field and do not necessarily relate to stratigraphie order. The numbers range from

001 to 456.

257 258

Rock properties are described in the following order:

..ithology, color of unweathered surface, weathered color ("w/" equals "weathers"), grain size and other prominent properties. The nature of the contact, where relevant, is described in the line between unit descriptions. Except where otherwise stated, the sections were measured by the writer. 259

A B : TILLITE GLACIER AREA

A Section. Alexandra Formation

SNOW 1 Sandstone, light-orange-yellom (vu/same), coarse-grained, massive, quartzose, cross-bedded in units 60 cm thick. Samples, TAA023, TAA024, TAA025...... 2.5 2.5 2 Sandstone, light-orange-yellow (w/same), coarse-grained, scattered pebbles of quartz and chert. Samples, TAA026, TAA027, TAAÜ23 ...... 6.0 8.5

3 Sandstone, light-orange-yellow, coarse­ grained, festoon cross-bedding, scattered oebbles of quartz and chert. Samples, TAA038, TAA039 ...... 14.7 Pagoda F ormation

- sharp contact - 1 RUBBLE covered, probably t i l l i t e . Isolated exoosure of t i l l i t e . Samples, TPA04Q, TPA041 ...... 28.4 43.1

2 Shale, black, highly f is s ile ...... 1.0 44.1

3 Tillite, gray-green, sandy ...... 0.6 44.7 4 T illite, gray-green, sandy, massive. Samples, TPA042, TPA043, TPA044...... 1.45 45.2 5 Shale, black, highly f i s s i l e ...... 1.2 47.4

6 T illite, gray-oreen, sandy, massive. Samples, TPA084, TPA0B5, TPA.Ü97 1 .3 48.7 7 T illite, gray-green, sandy, massive. Samples, TPAD45, TPA045, TPA047, TPA043, TPA049, TPA050, TPA051, TPA052, TPA053, TPA054...... 11.1 59.8 8 Diamictite, gray-oreen, stratified. Samples, TPA055, TPA056, TPA057...... 2.1 61.9 250

A B C 9 Tillite,. gray-green, sandy, massive. Samples, TPA058, TPA059, TPA050 2.0 63.9 - sharp contact - 10 T illite, oray-green, sandy, massive. Samples, fPAOOl, TPA061, TPA052, TPA063, TPA064, TPA065, TPA066, TPAD67, TPA058, TPA059, TPA070, TPA071 ...... 17.5 81.4 - sharp contact - 11 Sandstone, tan (w/light-orange), coarse­ grained, quartzose, lensoidal. Sample, TPA096...... '...... 0.9 82.3 12 T illite , gray-green, sandy, massive. Samples, TPA072, TPA073, TPA074, TPA075, TPA077, TPA07B, TPA079, TPA080, TPA081, TPA082, TPA083, TPA095 ...... 13.8 96.1 13 Sandstone, tan, medium-grained, lensoidal. Samples, TPA093, TPA094, TPA099, TPAIGO... 3.0 99.1

- boulder pavement, sharp contact - 14 T illite , black, sandy, micaceous, fissile . Samples, TPA004, TPA0Q5...... 5.5 104.6 15 Shale, black, micaceous, contains some scattered clasts. Sample, TPA006.... 14.7 119.3 16 Sandstone, brown, quartzose, minor cross- bedding, interbedded jy'ith shale, gray- green, slump folds common. Samples, TPA007, TPAOOa, TPA092...... 7.4 126.7 17 Shale, black (w/gray), thin sandstone beds highly contorted as slump folds ...... 7.4 134.1 18 Shale, black, highly fissile, thin interbeds of fine gray limestone. Sample, TPA009 11.0 145.1 19 Sandstone, gray-green, medium-grained, contains stringers of gray and white sandstone...... 1.2 146.3 20 Sandstone, brown-gray, medium-grained, planar cross-bedding. Samoles, TPAOll, TPA012, TPAQ13, TPA091....' 6.2 ,152.5 251

A B C 21 Shale, gray-green, fissile, becomes sandy and contains scattered clasts toward the top. Samples, TPA014, TPA015, TPA016, T P A O i a...... 14.7 167.2

22 Sandstone, tan, medium-grained, quartzose, well cross-bedded, thin interbeds of conglomerate and shale. Samples, TPAQ17, TPA090 ...... 1.6 168.8 23 Tillite, gray-green, fine-grained matrix, clasts small by comparison to t i l l i t e lower in section. Samples, TPA0B6, TPA0B7, TPAOaa, TPAOag 6.7 175.5

24 Shale, black, highly fissile, contains interbeds of fine-grained sandstone, slump folds common. Samoles, TPA019, TPA020...... '...... 13.8 189.3 25 Sandstone, gray-green, medium-grained, massive. Sample, TPA021 ...... 4.6 193.9 Mackellar Formation - sharp contact -

1 Shale, black, massive for all but top meter which contains interbeds of ripple- drift cross-bedded sandstone and two thin beds of light-gray fine-grained limestone. Sample, TMA022 2.8 196.7

2 Shale, black, highly fissile, interbedded with sandstone, gray, fine-grained, riople-drift cross-bedded, calcareous. Samples, TMA029, TMA030 ...... 7.4 204.1 3 Sandstone, gray, fine-grained, calcareous, ripple-drift, cross-bedded, interbedded with shale, black, highly fis s ile . Unit capped by bed of green-gray fine-grained limestone ...... 11.0 215.1 4 Shale, black, highly fissile, interbedded with sandstone, gray-green, fine-grained. Sandstone gradually becomes more promin­ ent toward the top of the unit. Two thin beds of gray, fine-grained limestone occur in the middle of the unit. Samoles, TMA031, TMA032, TMA033...... ' 25.1 240.2 252 A a C 5 Sandstone, gray, fine-grained, calcareous, ripple-drift cross-bedded. Large cal­ careous concretions up to 1 m occur throughout the unit ...... B.3 248.5

- gradational contact -

6 Sandstone, olive-green, medium-grained. Contains large calcareous concretions up to 1 m in diameter. Samples, T1Y1A034, TIÏ1A035, TiYlAD36, TmA037 ...... 29.2 277 .7

7 Shale, olive-green, finely laminated, abundant animal t r a i l s ...... 3.0 280.7

DOLERITE SILL, 202 m thick. 8 Shale, drab-olive-green, highly fissile... 3.0 283.7

********

B Section Pagoda Formation RUBBLE covered slope probably t i l l i t e 8.3 8,3

1 Tillite, gray-green, sandy, massive. Samples, TPB105, TPB127...... 6.4 14.7 - sharp contact -

2 T illite , gray-green, sandy, massive except for a feiu thin sandstone lenses. Samples, TPB106, TPB128 ...... 6.0 20.7 - sharp contact -

3 T illite , gray-green, sandy, massive except for weak stratification toward the top. Samples, TP8107, TPB129 ...... 6.0 26.7

4 Tillite, gray-green, sandy, massive. Top of the unit marked by a thin sandstone about 10 cm thick. At 2 m a line of boulders possibly a pavement. Samples, TPBlOl, TPB108, TPB130, TPB131 ...... 18.4 45.1 boulder pavement, sharp contact - 263

A B C 5 T illite , black, fine-grained matrix, smaller and fewer clasts, a few sandstone lenses at 3 m. Toward the top the unit becomes sandy and green in color. The top of the unit marked by a 17-cm-bed of limestone. Sample, TPB1Q2...... 6.4 51.5 6 Shale, black, highly fissile, scattered clasts some weakly striated. At 5.5 m a 15-cm-bed of fine-grained, gray lime­ stone. Top 2 m of unit contains a few thin beds of sandstone ...... 12.9 64.4

7 Sandstone, tan, coarse-grained, quartzose, channel structure...... 6.0 70.4

8 Shale, gray-green, thin beds, interbedded with sandstone, gray-green, medium- to fine-grained. Soft sediment folds occur frequently ...... 10.7 81.1

9 Sandstone, tan, massive weathering, cross-bedded ...... 3.5 84.6 10 Sandstone, gray-green, fine-grained, soft, thinly bedded, interbedded with sandstone, white, medium-grained, quartzose, beds thicker. Some slump folds ...... 15.6 100.2 11 Siltstone, gray-green, coarse-grained, contains some sandstone lenses, top 3 to 5 m has numerous slump folds ...... 13.6 113.8

12 Sandstone: tan, coarse- to medium-grained, channel structure with some lenses of conglomerate. Sample, TPB103...... 2.0 115.8

13 Sandstone, olive-green, fine-grained, soft. Contains sparsely distributed pebbles 4.5 120.4 - sharp contact-

14 Shale, black, highly fissile. Top of unit marked by a thin bed of green fine-grained sandstone ...... 17 .5 137 .9 264

A B C

lYlackellar Formation - sharp contact - 1 Shale, gray-green, laminated, interbedded with sandstone, gray-green (w/red), fine­ grained, ripple-drift cross-bedded. Gray- green fine-grained limestone beds occur in the unit but are not common ...... 55.1 194.0 - sharp contact -

2 Sandstone, gray-green, medium-grained, massive. Contains large concretions up to 1 m in diameter 19.3 213.3

3 Shale, gray-green or olive-green, with some thin interbeds of gray-green, fine­ grained, ripple-drift cross-bedded sandstone ...... 17 .5 230.3

DOLERITE SILL, 200+ m thick.

C Section Paooda Formation

S WO'JJ 1 Tillite, gray-green, sandy, massive. Contains a few thin sapdstone lenses. Samples, TPC114, TPC115 14.6 14.6 2 Diamictite, gray-green, poorly stra tifie d . 1.0 15.6 3 Tillite, gray-green, sandy, massive. The upper contact of this unit is irregular and may be an erosion surface. Samples, TPC116, TPC117 ...... 11 .0 26.6 - sharp contact - 4 Diamictite, gray-green, interbedded with sandstone, gray-green 6.4 33.0 5 Sandstone, gray-green, medium-grained, alternating with diamictite, gray-green... 8.3 41.3 265

A B C 5 Shale, black, sandy, highly fissile . Contains a few scattered pebbles. Thin sandstone lenses at 3 ...... 15 .5 56.9

7 Sandstone, gray, medium-grained, alterna­ ting with shale, gray. Beds average 1 m thick 6.4 63.3

8 Tillite, gray-green, cliff-forming, fewer and smaller clasts. Contains calcareous concretions up to 1 m in diameter and scattered plant fragments. Samole, TPC104...... ■ 39.6 102.9

9 Shale, black (w/sarne), highly f is s ile 5.1 103.0

Mackellar Formation - sharp contact -

1 Shale, gray-green, calcareous, inter­ bedded with sandstone, gray-green (w/red), fine-grained, ripple-drift cross-bedded... 56.1 164.1 2 Sandstone, gray-green, medium-grained, columnar jointed. Contains some small limonitic calcareous concretions up to 20 cm in diameter 16.5 180,7

3 Shale, black and olive-green, laminated, highly fissile . Unit becomes sandy toward the top and some ripple-drift cross-bedding occurs.."...... 7 .4 133.1

DOLERITE SILL, 200+ m

D Section Alexandra Formation 1 Sandstone, light-orange-yellow, coarse­ grained, festoon cross-bedded, scattered chert and quartz clasts. Beds average 50 cm to 1 m thick. Sample, TAD109., 15.0 15.0 266

A B C Pagoda Formation

1 RUBBLE covered slope probably mainly t i l l i t e 25.8 40.8

2 T illite , gray-green, sandy, massive. Top of unit marked by thin bed of quartzose sandstone. Samples, TPD119, TPD120 4.6 45.4 - sharp contact -

3 Tillite, gray-green, sandy, massive. Top of unit crudely laminated. Samples, TPD124, TPD125 25.0 70.4

- sharp contact -

4 T illite, gray-green, sandy, massive. Samples, TPD121, TPD122 10.0 80.4

- sharp contact - 5 Sandstone, tan, medium-grained. A large sandstone channel up to 75 m thick but pinching out laterally . Sample, TPDllO... 0.0 80.4

6 Tillite, black, massive. Numerous large concretions up to 1 m in diameter. Above 34 m plant fragments are common. Samples, TPDlll, TPD123 63.3 143.7 7 Sandstone, gray-blue, medium-grained, poorly sorted.. 2.0 145.7 a Sandstone, black, fine-grained, flaggy. Clasts occur scattered throughout the unit such that it may be a t i l l i t e . Samples, TPD112, TPD114 14.7 160.4

9 Sandstone, gray-green, massive but thinly bedded toward the top. A few scattered clasts. Sample, TPD113 5.5 165.9 - boulder pavement, sharp contact - 10 Shale, black, highly fissile. A few thin sandstone beds toward the top of the unit. 17.6 183.5 11 Sandstone, dark-gray-blue, medium-grained. 0.3 184.3

******** 267

A B C

E Section Mackellar Formation

SNOUl 1 Shale, black, highly fissile, laminated... 13.7 13.7 2 Shale, dark-gray, interbedded with sand­ stone, gray-green, fine-grained, cal­ careous, ripple-drift cross-bedded. Thin limestone beds occur at 8.0 m, 11.9 m and 23.2 m...... 26.5 40.2

3 Sandstone, green, medium-grained. Con­ tains large concretions...... 9 .4 49 .6

********

F Section Alexandra Formation SNOW 1 Sandstone, white to light-gray, medium- grained, cross-bedded. Numerous cal­ careous concretions and nodules up to 6 cm diameter. Sample, TAF133...... 16.6 15.6

2 Sandstone same as unit 1 but no concretions. Samples, TAF132, TAF146 IB.4 35.0 3 Sandstone, similar to tinits 1 and 2 but poorly exposed. Sample, TAF134 ...... 7.0 42.0 4 Sandstone, dirty white, very-coarse­ grained, cross-bedded. Contains scattered quartz and chert pebbles...... 7.7 49.7 5 Sandstone, white, medium-grained, quartzose, massive. Recrystallized with quartz cement. Samples, TAF135, TAF136...... 51.5 101.2 6 Sandstone, white, medium-grained, cross- bedded. Contains scattered clasts of chert and quartz. Sample, TAF137 ...... 3.0 104.2 7 Sandstone, coarse-grained, poorly cross- bedded. Contains numerous scattered quartz and chert clasts..... 32.2 136.4 268

A B C 8 Sandstone, medium-grained, well-developed cross-bedding. Recrystallized quartz cement. Sample, TAF138 ...... 11.0 147.4

9 Sandstone, white, medium-grained. Alter­ nating beds of flaggy sandstone and more massive well cross-bedded sandstone. Sample, TAF139 ...... 40.5 187.9

10 Sandstone, similar to unit 9 but more flaggy sandstone. Sample TAF140 ...... 3.7 191.6

11 Sandstone, coarse-grained, quartzose, massive, low angle cross-bedded. Sample, TAF141...... 4.6 196.2

12 Sandstone, similar to units 9 and 10 but slightly coarser. Samples, TAF142, TAF143...... 70.3 267 .0 13 Sandstone, coarse-grained, quartzose, massive. Consists of thick cross-bedded units with scattered clasts of chert and quartz. Sample, TAF144...... 34.0301.0 14 Sandstone, coarse-grained, massive, quartzose. Large number of quartz and chert clasts. Sample, TAF145 ...... 10.2 311 .2

********

G Section Pagoda Formation - contact with Alexandra Formation sharp - 1 Sandstone, gray-green, medium-grained, thinly bedded, minor cross-bedding ...... 3.0 3.0

2 RUBBLE covered slope probably mainly t i l l i t e ...... 3.4 6.4

3 T illite , gray-green, sandy, massive. Poor exposure...... 11.0 17.4

4 Sandstone, tan, medium. Irregular lensoidal bodies ...... 0.0 17.4 5 Tillite, gray-green, sandy, massive...... 21.5 39.0 269

A B C 6 Sandstone, tan, mediun rained ...... 3,0 42.0 7 Tillite, gray-green, : massive.. 27.6 69.6 8 Sandstone, tan, mediur. .o coarse-grained, quartzose 1.0 70.6

9 Tillite, gray-green, s.mdy, massive. Contains calcareous concrétions up to 70 cm in diameter...... 27.3 97.9 10 Sandstone, tan, medium-grained, quartzose, cross-bedded...... 4.6 102.5

11 T illite , dark-green, sandy. Contains large calcareous concretions...... 9.0 111.5 12 Sandstone, tan, medium- to coarse-grained. 2.0 113.5

- top of section removed by erosion -

********

H Section Pagoda Formation

FAULT 1 T illite , gray-green, sandy. Lower 4 m contains sandstone lenses ...... 8.3 8.3 FAULT, 10 m wide crush^zone. 2 Tillite, gray-green, sandy, massive ...... 9.2 17.5 3 Sandstone, tan, coarse- to medium-grained. 12.0 29.5 4 Tillite, black, massive. Fewer and smaller clasts than units 1 and 2. Sample, TPH147 ...... 7 .1 36.6

5 Limestone, black, fine-grained...... 0.1 36.7 6 Shale, black. Contains some scattered c la sts...... 2.0 38.7

7 Shale, black, interbedded with sandstone, bray, fine-grained ...... 3.0+ 41.7+

******** 270

A B C

I Section Pagoda Formation

SNOW 1 T illite, gray-green, sandy, massive, F i s s i l e ...... 2.8 2.8

2 Conglomerate, medium-grained. Consists mainly of quartz and chert clasts...... 1.9 4.7

3 T illite, gray-green, sandy. Lower 3 m of unit has concentrations of larger boulders mainly granite and gneiss. At 13 m a 40-cm lens of fine-grained sand­ stone 15.9 20.6

4 Sandstone, tan, m edium -grained...... 0.2 20.8 5 T illite, gray-green, sandy. At 3 m and 3.8 m lenses of medium sandstone 4.7 25.5 6 Sandstone, gray-green, medium-grained..... 0.6 26.1 7 Tillite, black, highly fissile. Contains fewer and smaller clasts than units 1, 3 and 5 1.8 27.9 8 Sandstone, gray-green, medium-grained, flaggy, cross-bedded. Contains some scattered clasts...... ; 4.0 31.9 9 Shale, black, laminated, highly fissile . Contains plant fragments and scattered c la s ts . 1.0 32.9 SNOW, unknown thickness missing.

10 Sandstone, gray-green, medium-grained, cross-bedded, massive 10.1 43.0

II T illite , gray, sandy. Poorly exposed clasts sparse 8.3 51.3

12 Tillite, black, sandy, massive. Weak laminations near top of bed ...... 6.4 57.7 13 Sandstone, gray-green, fine-grained, ripple-drift cross-bedded...... 1.8 59.5 271

A B C 14. Tillite, gray-green, sandy, highly fissile. Contains plant fragments ...... 8 .3 67 .8

Mackellar Formation - sharp contact - 1 Shale, black, finely laminated, highly fissile . At 5 m a 20-cm bed of medium- grained sandstone 12.9 80.7

2 Shale, gray-green, sandy, well laminated.. 6.5 87.2 3 Shale, gray-green, interbedded with sand­ stone, gray-green, fine-grained, ripple- drift cross-bedded. Contains calcareous concretions up to 40 cm diameter 26.7 113.9 4 Sandstone, black, fine-grained. At2 m a 10-cm bed of fine-grained gray limestone.. 12.0 125.9

DOLERITE SILL, 50+ m thick.

********

K Section Alexandra Formation

SNOW 1 Shale, black, calcareous, interbedded with limestone, gray, fine-grained. Lime­ stone units 5 to 15 cm thick. A few thin quartzose sandstone beds 1.5 cm thick with symmetrical ripples. Well preserved mud cracks occur on the surface of some beds. Samples, MAK134, IÏ1AK135 6.2 6.2

2 Sandstone, white, medium-grained, quartzose, thin beds. Beds thicken toward the top of the unit and a few thicker units (10 cm) are well cross­ bedded. Sample, iyiAR136.... 9.2 15.4

3 Sandstone, bright-green, medium-grained. Deeply w eathered...... 3.1 18.5 4 Sandstone, tan, quartzose, well cross­ bedded in 70 cm beds. Sample, IÏ1AK137.. . . . 6.2 24.7 272

A B C 5 Sandstone, white, medium-grained, inter­ bedded with sandstone, green, fine­ grained, vagus ripple-drift cross-beds..., 3.1 27.8

6 Sandstone, white, medium-grained, massive, well cross-bedded units 10 to 80 cm thick. Sample, MAK13 8 . 3.1 30.9

7 Sandstone, green, medium-grained, cross­ bedded. Occasional interbeds of white sandstone. Sample, [Y1AK139... 7.7 38.6

8 Sandstone, white, medium-grained, cross­ bedded in units up to 1 m thick. Sample, IÏ1AK140...... 1 4.5 53.2

9 Sandstone, tan, medium-grained, massive except for upper 3 m which is thinly bedded. Samples, MAK141, 1Y1AK142 8.1 61.3 10 Sandstone, red and iron stained. In reality, a thin weathered zone at the top of unit 9 0.2 61.5

- sharp contact - 11 Sandstone, orange-brown, fine-grained. Badly weathered. Sample, IÏ1AK143 3.1 64.6 12 Sandstone, white, medium-grained, massive, few cross-beds. Beds range from 50 cm to 1 m t h i c k . . . . . 40.0 104.6

Pagoda Formation - deeply grooved surface, sharp contact - Tillite, pale-green, very sandy, clasts sparse. Occurs filling the deep grooves on the surface. Sample, IY1PK145...... 2 . 0 1 0 6 . 6 - sharp contact - Tillite, greenish-gray, sandy, massive. Matrix becomes slightly finer toward the top. Top marked by a sandy calcareous zone. Samples, IÏ1PK155, MPK156, MPK157, l Y l P K l S e ...... 9.1 115.7 273

- sharp contact - 2 Tillite, gray-green, sandy,massive. Top marked by a brown sandy zone. Samples, IÏ1PK159, IY1PK150, MPK161 ...... 2.6 118.3 3 Tillite, gray-green, sandy, massive. Top marked by sandy iron-stained zone. Samples, 1Y1PK162, MPK163...... 2.6 120.9 " sharp contact - 4 Tillite, gray-green, sandy, massive. Matrix slightly more sandy than unit 3 but becomes finer toward the top. Top marked by a poorly defined iron-stained zone with some discontinuous sandstone and conglomerate lenses. Samples, IÏ1PK164, [Ï1PK165...... 1 .9 122.8 5 Tillite, gray-green, sandy, massive. Top marked by a stained sandy surface which has 1 m of re lie f. Samples, MPK166, HflPK167, MPK16B...... 6.5 129.3 - sharp contact -

6 Tillite, gray-green, sandy, massive. Slightly less fissile than lower units and contains a few sandstone lenses. Unit becomes slightly less fissile and more sandy up to 2 m then finer and more fissile to 4,5 m then becomes sandy again. The lower 30 cm of the unit is weakly laminated. Samples, MPK169, IYIPK170, mPK171, MPK172...... 5. 6 134.9

- sharp contact - 7 T illite , gray-green, sandy, massive. Bottom meter contains lenses of sandstone. Top marked by a stained sandy zone which laterally becomes a boulder concentration. Samples, 1Y1PK173, IY1PK174, [Ï1PK175, MPK176... 5.8 141.7 - sharp contact - 8 Tillite, gray-green, sandy, massive. Matrix slightly finer than lower units. At 5 m a very thin sandstone lens. Top marked by a thin but very persistent 274

A B C

sandstone bed which is slightly deformed and has a well-developed soft sediment pavement on its upper surface. Samples, IÏ1PK177, [Ï1PK17B, IÏ1PK179, IKIPKIBO, 1Ï1PK193.... 11 .3 153.0 - soft sediment pavement, sharp contact -

9 T illite , gray-green, sandy. Thin sand­ stone beds occur at 2 m (3 cm thick), 4 m (S cm thick). 6 m (3 cm thick), 7.5 m (10 cm thick), and 11 m (7 cm thick). Samples, (Ï1PK181, MPKIBZ, IYIPK183, (Ï1PK184, mPK187, ...... iïlPKlSB...... 20.0 173.0

- sharp contact -

10 Sandstone, tan, medium- to coarse-grained. Contains a few interbeds of conglomerate. The unit is a channel structure. Sample, mPK147 2.0 175.0

11 T illite , gray-green, sandy. Contains several interbeds of medium sandstone from 10 to 80 cm thick. Top of unit marked by a boulder pavement...... 7.9 182,9 - boulder pavement, sharp contact - 12 T illite, gray-green to dark-green, sandy. At 0.7 m a thin sandstone with a boulder pavement on its upper surface and at 4.3 m a thin sandy limestone 15 cm thick. Samples, mPK148, [Y1PK185, IÏ1PK185 7.3 190.2 13 Sandstone, tan, medium-grained, cross­ bedded. Lensoidal channel deposit. Sample, IÏ1PK149 4.0 194.2

14 Shale, black, very fissile . Contains scattered clasts. At 4 m clasts stop but reappear again at 8 m in reduced numbers.. 21.8 216.0

15 Sandstone, tan, medium-grained. Channel deposit. Samples, (Ï1PK150, MPKlSl 2.3 218.3

16 Shale, black, highly fissile . Contains scattered clasts. Sandstone beds occur at 1 m (50 cm thick) and several occur above 2 m. Top marked by a green-gray sandstone unit with a boulder pavement on its upper surface. Samples, IÏ1PK152, MPK153 3.9 222.2 275

A B C - boulder pavement, sharp contact -

17 Tillite, dark-green, fissile. Clasts well rounded, lower meter contains a few conglomerate lenses. Top of unit marked by a stained zone with a possible boulder pavement. Samples, MPK191, IÏ1PK192 ...... l.S 224.0 - sharp contact - 18 T illite, gray-green, sandy, massive. Clasts are sparse. At 1 m a thin sandstone...... 3.6 227.6

19 Sandstone, tan, medium-grained. Variable in thickness up to 2 m. Samples, MPK154, MPK189, IYIPK190 ...... 0.5 228.1

20 Shale, gray-green, very fissile. Con­ tains a very small number of c la sts ...... 5.9 254.0

ITlackellar Formation (Measured by P. J. Barrett and J. F. Lindsay) - sharp contact - 1 Shale, dark-gray (w/black), highly fissile, finely laminated. Mudstone fragments in lower 20 cm...... 5.0 239 .0

2 Sandstone, gray (w/brown), fine-grained, ripple-drift cross-bedded, calcareous, interbedded with shale, gray-green, very fissile, sandy. Bedding thickness 1 to 20 cm. Sample, (yiMK194 ...... 1.0 240.0

3 Shale, gray (w/greenish gray or black), very fissile, interbedded with sandstone, gray, fine-grained. At 0.7 m an 8-cm bed of limestone. Sample, IÏ1IY1K195 .. 4.0 244.0

4 Sandstone interbedded with shale, very similar to unit 2. Bedding thickness and the proportion of sandstone increases toward the top of the unit 11.0 255.0 5 Shale, black, very fissile. Sample, IKliyiKl96...... 10.0 265.0 276

A B C 6 Sandstone, gray-green (w/red), medium- to fine-grained, ripple-drift cross­ bedded. Few interbeds of gray weakly fissile shale. Bedding thickness ranges from 30 to 50 cm. Samples, MMK197, IY1(Ï1K198 19.0 284.0

7 Shale, gray-green and black. A few thin beds of fine-grained sandstone. Above 15 m the shales become a little sandier and ripple-drift cross-bedding and asymétrie ripples appear. A few animal t r a i l s . 21.0 305.0

- contact with Fairchild Formation sharp -

********

L Section - contact with Alexandra Formation obscure - 1 SNOW, probably mainly t i l l i t e ...... 32.4 32.4

2 RUBBLE covered slope probably mainly t i l l i t e . . . . 14.8 47.2

3 Tillite, black. Poorly exposed and badly weathered...... 1.1 48.3 4 Sandstone, tan, medium-grained, quartzose. The unit is a lensoidal channel. Sample, (Ï1PL215 2.6 50.9 5 Tillite, gray, sandy. Badly weathered.... 0.6 51.5 6 RUBBLE covered slope probably mainly t i l l i t e 4.8 56.3

7 Tillite, gray, sandy. Badly weathered.... 0.6 56.9 a RUBBLE covered slope probably mainly t i l l i t e 28.6 85.5 9 Sandstone, tan, fine-grained, thinly bedded in 8 cm units and interbedded with occasional 2 cm units of mudstone...... 3.2 88.7 10 Tillite, gray-green, sandy, massive 3.5 92.2 277

A B C 11 Shale, black, very fissile.,,, ...... 1,9 94,1 - traverse across slope to complete section - 12 Conglomerate, coarse-grained, alternating with sandstone, tan, medium-grained, cross­ bedded, A large channel structure bedded in 50 cm units. Samples, MPL199, MPL200, mPL201, [Ï1PL202...... 4.0 98,1

13 Sandstone, tan, medium-grained, massive, well cross-bedded. Samples, IÏ1PL203, iYlPL204...... 12,8 110,9

14 Sandstone, tan, medium- to fine-grained, flaggy and/or fis s ile . Pebble horizons at 0,5 m and 2 m. Sample, HflPL205...... 3,5 114,5

15 Tillite, black, massive. Poorly exposed but becomes more sandy toward the top. Sample, [YIPL207 4,7 119,2 15 Sandstone, gray, medium-grained, fissile . Some ripple marks. Sample, IYIPL206 4,7 123,9 17 Tillite, black, fissile. Badly weathered. Sample, [Ï1PL2Ü8 , , , , 0,9 124,8 18 Sandstone and conglomerate, interbedded. Poorly exposed ...... 1,0 125,8 19 Sandstone, tan, coarse-grained. Some ripple-drift cross-bedding and a few scattered clasts. Samples 1Ï1PL209, MPL210, 5,5 131.4 20 Tillite, black, fissile ...... 1,0 132,4 21 Sandstone, tan, coarse-grained. Scattered clasts and contorted bedding 0,7 133,1 22 Tillite, black, fissile 2,0 135,1

23 Sandstone, gray, coarse-grained, calcare­ ous, poorly cross-bedded. Scattered c la sts...... 0,5 135,5

24 Tillite, black, fissile. Badly weathered, 10,1 145,7 25 Sandstone, coarse-grained, ...... , , , 1.0 145,7 26 Tillite, black. Contains thin sandstone lenses...... 4,1 150,8 278

A B C

27 Sandstone, gray-green, fine-grained, fis s ile . Sample, MPL211 0.5 151.4

28 Tillite, black, fissile, grades into sandy shale above 1.5 m. Sample, !Ï1PL212...... 4.5 155.9

29 T illite, gray, sandy, fissile . Sparse c la sts 0.9 156.8 30 Sandstone, gray, calcareous 0.9 157.7

31 Shale, black, highly fissile . Unit capped by a 50-cm bed of fine-grained gray limestone ...... 1.9 159 .6

lYlackellar Formation

- sharp contact - 1 Shale, black, papery, finely lam inated.... 4.0 153.6 2 Shale, black, laminated (90 percent), interbedded with sandstone, gray, fine­ grained, ripple-drift cross-bedded, thinly bedded. Animal tra ils common at some levels. Ripple-drift cross-bedding more common in sandstones at the 10 m and 14 m levels...... 15.7 179 e J 3 Shale, black, very fissile ...... 21.2 200.5 4 Mudstone, gray, (70 percent), interbedded with sandstone, gray, fine-grained. Bedding up to 50 cm thick. Ripple-drift cross-beds occur in some sandstone beds. Sample, MIY1L213...... 14.0 214.5

5 Shale, black, well-laminated, fissile. Occasional thin beds of fine sandstone up to 1 cm thick. Slump folds and some animal t r a i l s 5 .5 221.0 “ sharp contact with Fairchild Formation -

******** 279

A B C

LOWERY GLACIER AREA lYl Section Alexandra Formation

Sharp unconformably contact with the graywacke of the Goldie Formation 1 RUBBLE covered e lo p e ...... 8.5 8.5

2 Sandstone, white, medium-grained, quartzose. A few interbeds of gray- green sandstone in 60 cm beds. Sample, lïlAiyi215...... 22.6 31.1

3 RUB8LE covered slope 11 .3 42.4

4 Sandstone, white, medium-grained. Poorly exposed. Sample, IYlAni217 6.6 49.0

5 Sandstone, pale-green-gray, medium- grained, well cross-bedded. Bedding units 60 cm thick. Sample, MAM218 12.2 61.2 6 Sandstone, very-pale-green, medium- to coarse-grained, some cross-bedding. Numerous channel structures with quartz pebbles and red mudstone chips in their troughs. Samples, MAM219, (ï!Afil220...... 12.2 73.4 7 Shale, bright red, sandy ...... 0.9 74.3

8 Sandstone, gray-green," fine- to medium- grained, Sample, MAM221 ...... 4.0 78.3

9 Shale, bright red, sandy. Sample, IÏ1AIÏ1222. 1.0 79.3 10 Sandstone, gray-green, fine- to medium- g r a in e d ...... 4.0 83.3 11 Sandstone, gray-green, flaggy, thinly bedded. Some animal t r a i l s 4.0 87.3 12 RÜB8LE covered s l o p e ...... 8.2 95,5

13 Sandstone, gray-green. Poorly exposed. Sample, IYlAiïl223 4.7 100.2 280

A B C

14 Sandstone, gray-green, fine-grained, some cross-bedding, flaggy almost fissile, thinly bedded in units 1 to 10 cm thick... 8.5 108.7

15 Sandstone, gray-green. Poorly exposed.... 12.2 120.9 16 Sandstone, gray-green, medium-grained, well cross-bedded. Sample, MAM224 ...... 10.0 130.9 17 RUBBLE covered s lo p e ... 28.5 159,4

18 Sandstone, gray-green, medium-grained, some cross-bedding ...... 9.4 168.8

19 Sandstone, gray-green, medium-grained, massive, cliff-forming, some cross- bedding, Sample, [Ï1AIÏ1225 ...... 25.4 194.2

20 Sandstone, gray-green, fine- to medium- grained, some ripple-drift cross-bedding. Some animal tra ils . Sample, (Ï!A(Ï1226...... 18.8 213.0 21 Sandstone, similar to unit 20 but cross­ bedded. Sample, MAM227 31.0 244.0

Pagoda Formation - sharp contact -

1 T illite, gray-green, sandy. Contorted sandstone beds within the unit suggest slumping. Samples, 1ÏIPJÏ1228, MPM229...... 15.0 259.0

2 Sandstone, medium-grained. Discontinuous. 0.5 259.5

3 T illite, gray-green, sandy. At 5 m a thin sandstone bed. Sample, MPM230 ...... 9.8 269.3

4 Sandstone, gray-green, medium-grained. Sample, MPM231 ...... 32.7 302.0

5 Conglomerate. Sample, MPM232 ...... 0.1 302.1 6 Sandstone, gray-green, coarse-grained, well-bedded...... 13.0 315.1 7 Sandstone, gray-green, very-coarse-grained, cross-bedded. Sample, IYlPf(1233...... 14.0 329.1 281

A B C

8 Shale, soft, green with lenses of lime­ stone and sandstone ...... 2.4 331.5

9 Tillite. Poorly exposed...... B.7 340.2 10 Sandstone, gray, quartzose. Sample, MPm234...... 2.0 342.2

11 T illite , gray-green (w/black), sandy. Contains some sandstone len ses..o ...... 9.4 351.6 12 Sandstone, gray-green, medium-grained. Contains scattered clasts. Sample, IÏ1PIÏ1235...... 14.0 365.6

13 T illite . Poorly exposed. A few sand­ stone lenses at 2 m...... 6 .0 373.6

14 Shale, gray, calcareous. Unit capped by a bed of gray concretionary limestone 6.6 380.2 - contact with lYlackellar Formation sharp -

********

N Section Pagoda Formation

1 SNOW 2 Tillite, black, massive. Very poor exposure, boulder concentration at base... 20.5 20,5

3 Sandstone, white to pale-green. Lensoidal bed with some conglomerate 2.0 22.5

4 T illite, gray-green, sandy. Contains small lenses of gray-green sandstone 22.0 44.5

5 Sandstone, gray-green, fine-grained. Capped by a boulder pavement ...... 1 .0 45.5 - boulder pavement, sharp contact - 6 T illite , gray-green (w/black), sandy. Sample, IY1PN240...... 24:4 69.9 7 Mudstone, gray, alternating with sand­ stone, gray-green, fissile . Sandstone becomes more massive higher in the unit. Sample, MPN236...... 16.7 86.6 282

B C

lïlackellar Formation

V - S h a r p contact -

1 Shale, black, papery. 7.4 94.0

2 Shale, black, highly fissile, interbedded with sandstone, gray, fine-grained. Sand­ stone beds 0.5 cm thick occur about every 5 cm. At 4 m a decrease in the sandstone at 7 m a 20-cm limestone u n it...... 9.3 103.3

3 Shale, gray-green. Occasional 50-cm thick interbeds of gray sandstone. Sample, miïlN237 ...... 4.7 108.0

4 Sandstone, gray, fine- to medium-grained, massive except for two thin shale units at the base. Sample, ri1iïllV238 ...... 7.4 115.4 5 Shale, gray-green, fissile, sandy. Gradually becomes finer upward and contains a few interbeds of sandstone near the middle of the u n it ...... 8.4 123.8

6 Sandstone, gray, fine- to medium-grained. Calcareous toward the top. Sample, IÏ11Y1I\I239...... 10.2 134.0

7 Shale, dark-gray-green. Contains a few thin interbeds of sandstone 12,1 146.1 - contact with Fairchild Formation sharp -

********

MOORE MOUNTAINS AREA

P Section Pagoda Formation

SNOW 1 Tillite, dark-gray-green almost black (w/ light-gray-green), sandy, fissile. Samples, APP401, APP402...... 4.7 4.7 2 Shale, black, papery... 1.0 5.7 283

A B 3 Sandstone, light-gray-green, fine-grained, ripp le-drift cross-bedded.. 2.0 7.7

4 Conglomerate, coarse-grained, interbedded with sandstone, tan, medium-grained. Channel deposit. Samples, APP403, APP404, APP429 ...... 5.6 13.3

- boulder pavement, sharp contact - 5 T illite , gray-green, sandy. Poorly exposed...... 5.7 19.0

6 Shale, gray-green, sandy, ripple-drift cross-bedded..... 9A.fl 4?.h

Q Section Pagoda Formation

SNOW 1 Tillite, purpole (w/gray-green), very sandy, massive. Contains concretions up to 35 cm in diameter. Samples, APQ407, APQ40B...... 13.5 13.5 2 Tillite, black (w/green), very fissile. Samples, APQ409, APQ410 ...... 2_^ 16.4

lYlackellar Formation - sharp contact -

1 Shale, black, papery, finely laminated.... 6.8 23.2 284

A B C

2 Shale, black, papery, (80 percent), interbedded with sandstone, drab-olive- green, medium-grained.. 2.5 25.7

3 Sandstone, olive-green (w/pink), medium- grained, massive. One thin shale unit with animal tra ils. Sample, Af!lQ411...... 3,5 29.2 4 Shale, olive-green (w/green), sandy, interbedded with minor sandstone, gray- green, fine- to medium-grained, ripple- drift cross-bedded 20.3 49.5

5 Diamictite, dark-gray-green. Contains clasts up to 1 m in diameter, probably a mudflow unit. Samples, A[Ï1Q412, AMQ413, AmQ414, Ar/1Q415, AMQ416, AmQ417, AmQ418, A(Ï1Q419, AmQ420, AfflQ421 9.7 59.2 6 Shale, black, poorly laminated. Contains large angular c la sts 1.9 61.1

7 Sandstone, pale-olive-green, well-bedded in units 30 cm to 2 m thick ...... 30.0 91.1 DOLERITE SILL, 200± m thick

********

R Section Pagoda Formation

SNOW 0 T illite, gray-green, sandy. Contains a clast 2.8 m in diameter. Sample APR42B... 8.0 8.0 1 Sandstone, fine- to medium-grained. Poor e x p o s u re ...... 5.9 13.9

2 RUBBLE covered slope probably t i l l i t e 9,0 22.9 3 Sandstone, gray-green, medium- to coarse­ grained ...... 12.0 34.9 4 T illite, gray-green, sandy. Poorly exposed. Samples APR426, APR427 25.0 59.9 285

A B C

5 Conglomerate, coarse-grained, very poorly sorted, low angle cross-bedded. Conglomerate overlain by 4 m of gray- green, fine-grained sandstone. Samples, APR422, APR424, APR425...... 16.0 75.9

6 T illite, gray-green, sandy. Contains lenses of sandstone up to 3 m thick...... 33.3 109.2 7 T illite, gray-green, sandy. Thin veneer of sediment on the pre-Mackellar surface.. 0.5 109.7

lYlackellar Formation

- sharp contact -

1 Shale, black, papery... 6.1 115.8 2 Sandstone, greenish-gray (w/red), medium- grained, massive. Bedded in units 30 cm to 1.5 m thick ...... 13.3 129.1 3 Sandstone, similar to unit 2, but bedding thickness reduced to 10 to 50 cm. Sample, APR423 14.3 143.4

4 Sandstone, gray (w/red), medium-grained, ripple-drift cross-bedded. Bedding thickness ranges from 3 to 10 cm ...... 56.3 199.7

- contact with Fairchild Formation sharp -

********

S Section lYlackellar Formation

DOLERITE SILL, 30+ m thick. 1 Shale, gray-green, silty, (60 percent), interbedded with sandstone, gray-green. Sandstone beds 80 cm thick...... 5.9 5.9

2 Sandstone, gray, fine-grained, fissile, thinly bedded...... 8.9 14.8 3 Sandstone, gray, fine-grained, massive.... 2.0 16.8 286

A B C

4 Shale, gray-green, ( 9O percent), inter­ bedded with sandstone, olive-green, fine­ grained, ripple-drift cross-bedded. Bedding thickness 10 to 30 cm ...... 13.8 30.5 5 Shale, black (w/gray), fissile ...... 5.9 35.5 5 Shale interbedded with sandstone, similar to unit 4 ...... «...... 11 .8 48.3

7 Sandstone, gray, medium-grained, flaggy, weathers massive...... 3.051.3

8 Shale interbedded with sandstone, similar to unit 4 but only 70 percent shale. A few animal t r a i l s ...... 17 .8 59 .1

DOLERITE SILL, 50+ m thick,

********

I Section Pagoda Formation

DOLERITE SILL, 40+ m thick. 1 T illite , gray-green, massive, baked by sill...... 8.9 8.9 2 Sandstone, white, coarse-grained, laminated...... 2.5 11.4

3 Tillite, gray-green, sandy,massive ...... 1.9 13.3

lYlackellar Formation (Measured by P. J. Barrett and J. F. Lindsay) - sharp contact -

1 Shale, black (w/same), highly fissile. Unit capped by 50-cm unit of fine- to medium-grained sandstone ...... 5.0 19.3 T sharp contact - 2 Shale, gray-green (w/same), silty, highly fissile, weakly laminated...... 12.1 31.4 287

A B C - sharp contact - 3 Sandstone, gray ( ir/red-brou/n), laminated, flaggy. Some concretionary structures.... 12.1 43.5

4 Shale, gray-green, silty, poorly f i s s i l e ...... 4.0 47.5

5 DOLERITE SILL, 4 m thick. 6 Shale, dark-gray (ui/gray-green) . Becomes silty upwards. Sandstone beds occur in the upper 5 m. Animal tra ils near to p .... 15.1 52.6 7 Sandstone, alternating gray-green and white, medium-grained, laminated. Some cross-bedding in the upper part of the u n i t ...... 13.1 75.7

8 Sandstone, white (w/red-brown), medium- grained, (90 percent), interbedded with shale, gray-green. Animal trails 9.1 84.8 9 Shale, dark-gray (w/light-gray), laminated...... 11.1 95.9 - contact with Fairchild Formation sharp -

********

U Section Pagoda Formation - unconformable contact with Shackleton Limestone -

1 Tillite, olive-green (w/purple), very sandy. F ills depressions on pre-Pagoda surface. Samples, APU455, APU456 15.1 15.1

2 Sandstone, white, quartzose ...... 3.0 18.1

3 RUBBLE covered slope 4.0 22.1 4 Tillite, (w/purple), sandy. Poore exposure ...... 2.0 24.1

5 Sandstone, white, medium-grained ...... 4.0 23.1 5 RUBBLE covered slope, probably sandstone.. 7.0 35.1 288

A B C

7 Sandstone, white, medium-grained, poorly bedded ...... 8.1 43.2 8 SNOW 2.4 45.5

9 T illite , gray-green, sandy, weak fis s ility . Samples, APU431, APU432 ...... 17 .0 62.6

10 T illite, gray-green, sandy. Separated from unit 9 by a 3-m laminated zone at the base. Samples, APU433, APU434, APU435, APU435...... 38.2 100.8

11 Sandstone, tan, coarse-grained 48.7 149.5

12 Diamictite, gray-green, sandy, weakly cross-bedded. Interpreted as proglacial lake d e p o s it...... 79.7 229.2

13 Tillite, gray-green, sandy, massive. Top marked by a discontinuous sandstone unit. Samples, APU438, APU439 ...... 17.4 245.5

14 Tillite, gray-green, sandy, massive. Contains a few small concretions. Samples, APU440, APU441 55.1 312.7

15 Sandstone, green, medium-grained, poorly sorted. Sample, APU442 5.0 318.7

15 Diamictite, gray-green, sandy, weakly cross-bedded, poor bedding.... 18.1 335.8 17 Tillite, gray-green, sandy, sparse clasts. Poor exposure. Samples APU443, APU444.... 37.7 374.5

18 Shale, black, papery 1.0 375.5 19 Mudstone, gray, laminated and ripple-drift cross-bedded ...... 2.5 377.0 20 Sandstone, tan, medium-grained, large- scale cross-beddino (3 m thick). Sample, APU445...... Z ...... 15.5 392.5

DOLERITE SILL, 2 m thick. 289

A B C

lïlackellar Formation 1 Shale, black (ui/green), papery ...... 31,5 424.1

2 Sandstone, gray-green (uj/red), medium- grained, massive 13.2 437.3 3 Shale, gray-green, silty, interbedded with sandstone, gray-green, fine-grained, f i s s i l e ...... 8.0 445.3

4 Sandstone, gray, fine-grained, (60 percent), ripple-drift cross-bedded, interbedded with shale, gray, s ilty ...... 68 .1 513.4

- contact with Fairchild Formation sharp -

********

V Section Pagoda Formation (Measured by P. J. Barrett) - angular unconformity with Goldie Formation - 1 Sandstone ( t il l it e ) , light-gray (w/same), fine- to medium-grained. A few water- sorted sand and fine conglomerate lenses up to 1 m thick...... 41.0 41.0

2 Shale, gray-green (w/same or chocolate- brown), papery ...... 17 .0 58.0

3 Tillite, dark-gray-green (w/light-gray- green). Exposed only in a few patches. Surround scree contains a large proportion of well-rounded white and yellow stained quartz and quartzite clasts up to 30 cm across. Lenses of fine conglomerate with the occasional cobble in the upper m 73.0 131.0 - sharp contact -

4 Sandstone, light-gray (w/red-brown), fine­ grained, massive, festoon bedding in lower part. Lower surface has at least 1 m of local relief...... 8.0 139.0 290

C

- grooved pavement, sharp contact -

5 Tillite, dark-gray-green (lu/light-gray- green), very-fine-grained. Boulder horizon at 12 m, mainly of coarse-grained granite, granitic gneiss and quartzite. Boulders commonly up to 1 m across. Rare sandstone and fine conglomerate lenses up to 1.5 m th ick . 28.0 167.0

Note; Traversed west along ridge for about 1000 m to foot of spur leading to summit of Solitary Peak. 6 - contact in scree 6 Shale, dark-gray (w/gray-green), papery... 3,0 170.0

7 SCREE. T illite fragments and erratic clasts common 37.0 207.0

8 Tillite, dark-gray-green (w/light-gray- green), very-fine-grained, massive, cliff- forming. Clasts generally less than 1 cm long and quite scarce. A few slumped lenses of sandstone and fine conglomerate up to 1 m thick in upper part of u n i t..... 21.0 228.0 9 Sandstone, light-gray (w/same), very-fine­ grained, varvoid lamination 1 to 2 cm thick and gently wavy.. 2.0 230.0

10 Tillite, dark-gray-green (w/light-gray- green). Poorly exposed 5.0 235.0

11 Sandstone, light-gray (w/same or light- red brown), fine-grained, massive...... 12.0 247.0 12 Tillite, similar to unit 10. A few thin sandy l e n s e s ...... 13.0 260.0

13 Sandstone, similar to unit 11. A few thin pebble stringers 7.0 267 .0 14 T illite, similar to unit 10. The lower meter well-exposed in bluff 12.0 279.0 15 Sandstone, similar to unit 11 4.0 283.0 16 Tillite, similar to unit 10. Generally massive but shaly to papery in places. Several thin sand lenses 15.0 298.0 291

A B C

17 Sandstone, light-gray-green (w/same or brown), fine-grained, flaggy to massive, parallel lamination. Oval depressions about 0.5 m deep, 3 m wide and at least 7 m long with patches of t i l l in the bottom found on the upper surface of this sandstone about 500 m to the south of the ridge ...... 5.0 303 .0

lYlackellar Formation - sharp contact -

1 Shale, dark-gray (w/black), papery ...... 12.0 315.0 2 Shale, medium- to dark-gray (w/light- gray). Subordinate beds of sandy silt- stone about 10 cm thick every 20 to 30 cm...... 22.0 337 .0

- gradational contact - 3 Siltstone, light- to medium-gray (w/ light-gray-green and light-red-brown), sandy, locally shaly, laminated and microcrosslaminated. Crescentic ripple marks common associated with thin beds and laminae of very fine sandstone. Unit weathers to a series of ledges 1 or 2 m apart ...... 44.0 361 .0

. - contact with Fairchild Formation sharp -

******** BIBLIOGRAPHY

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