JOHN H. MERCER Institute of Polar Studies, the Ohio State University, Columbus, Ohio Glacial Geology of the Reedy Glacier Area

JOHN H. MERCER Institute of Polar Studies, The Ohio State University, Columbus, Ohio

Glacial Geology of the Reedy Glacier Area, Antarctica

Abstract: The Rccdy Glacier is an outlet from the East Antarctic Ice Sheet and flows through the Transantarctic Mountains to the Ross Ice Shelf. The higher parts of the mountains consist of plateau remnants at about 3000 to 3500 m elevation. A shallow depression in this surface is rilled with 40 m of till underlain by mass-wasted sandstone bedrock. The basal till consists of granite fragments, probably derived from a hill nearby. The remainder has a clay-rich matrix and contains fragments of igneous, metamorphic and sedimentary rocks that were probably derived from the plateau surface. All the till except the superficial layer was apparently deposited by temperate, wet-based ice. In an ice-free area at 1400 m elevation alongside the Reedy Glacier, about halfway between the East Antarctic Ice Sheet and the Ross Ice Shelf, stranded lateral moraines indicate former ice levels 750 m, 400 m, and 260 m above the present glacier surface. Granitic boulders on the surface at 750 m are highly weathered, those at 400 m are moderately weathered, and those at 260 m are virtually unweathered. Toward the head of the glacier these three sets of stranded moraines progressively approach each other and are also closer to the present ice surface. There is no evidence that the ice of the Polar Plateau has varied much since its establishment. Alongside the Reedy Glacier at about 1500 m elevation, 90 m of ice-marginal lake sediments are exposed. At present virtually no meltwater is present. Inactive solifluction flows occur further up the glacier at about 2000 m elevation. The till sequence on the high plateau is believed to indicate progressive refrigeration and the replacement oi a small, local glacier by a temperate, local ice cap that later became polar and dry- based. The temperate ice cap must have antedated the Antarctic Ice Sheet and probably existed during the Pliocene. The variations in thickness of the Reedy Glacier after it had become an outlet of the East Antarctic Ice Sheet are thought to have been determined mainly by the position of the grounding line of the Ross Ice Shelf, which was controlled by eustatic changes in sea level, so that the glacier thickened during northern hemisphere glaciations. The lake sediments and solifluction flows indicate "interglacial" conditions 6° to 10° C warmer than at present.

CONTENTS

Introduction 472 Age of the Horlick Glaciation ...... 482 Geographic and physiographic setting . 472 Variations of independent glaciers ...... 482 Climate 472 Variations of the Reedy Glacier ...... 482 Ice cover 472 Causes of the variations of the Reedy Glacier 483 Acknowledgments 474 Summary and conclusions ...... 484 Bedrock geology 474 References cited ...... 485 Glacial geology 475 Quartz Hills 475 Former ice levels 475 Figure Stratified drift . 475 1. Map of Reedy Glacier area, Antarctica, includ- Independent glacier 476 ing location map ...... 473 Caloplaca Hills 476 2. Mapof Quartz Hills, Reedy Glacier, Antarctica, Former ice levels 476 showing glacial geology ...... 476 Independent glaciers 477 3. Map of Caloplaca Hills, Reedy Glacier, Antarc- Camp Reedy-Olentangy Glacier aica 477 tica, showing glacial geology ...... 477 Queen Maud erosion surface .... 477 4. Map of Camp Reedy-Olentangy Glacier area, Variations of the ice cover 478 Antarctica, showing glacial geology . . . 477 Blue ice field and independent glaciers 480 5. Diagrammatic sketch showing the effect of a Metavolcanic Mountain area 481 rise and a fall in sea level on the thickness Discussion 481 of the Reedy Glacier ...... 484

Geological Society of America Bulletin, v. 79, p. 471-486, 5 figs., 6 pis., April 1968 471

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Plate Following Following 1. Reedy Glacier and Quartz Hills, Antarctica . ] Glacier, Antarclica 2. I'.nd moraines and glaciolacnstrinc deposits, 6. Glacial deposits, Reedy Glacier, Antarctica . j Ouarlz Hills, Antarctica .•>. Hncl moraines and glaciolacustrinc deposits, ! ., Tablc Ouartz Hills, Antarclica | 1. Section of Horlick drift on edge of Wisconsin •I. Glacial and penglacial deposils. Reedy Glacier, Plateau 478 Antarclica 2. I leight in meters of Reedy end moraines above 5. Glacial dcposns and group ol nunataks, Reedy j present glacier surface 483

INTRODUCTION Glacier. Because of the dryness and compara- tive warmth of the descending winds, extensive Glacial deposits indicate pasl changes in the areas of blue ice he in front of the west- and extent ol both the local ice on the mountains, north-facing escarpments. Annual accumula- and also ol the outlet glaciers from the Kast tion is 10 g/cm2 both at lat 85° S. a short dis- Antarctic Ice Sheet. Other deposits are evi- tance nortb of the range (Rubin and Giovinet- dence ol higher temperatures than prevail to, 1962, pp. 5165-5167), and also 125 km south today, and abandoned cirques and other fea- of the range (Taylor, 1965, Table 1). tures resulting from glacial erosion also appear The firn temperature at 10m depth is -45° C to indicate changed conditions. After a descrip- at 3000 m south of the Scott Glacier, which is tion ol the geographic setting of the area, ac- 150 km west of the Reedy, -41° C at 2645 m counts are given ol the glacial geology oi the south of the Reedy (Taylor, 1965, Table 1), and several ice-irec areas. Finally, the interred -19° C on the Scott at 640 m (Swithinbauk, glacial history ol this part of Antarctica is dis- 1964, p. 44), indicating that average annual cussed in the light ol. the held evidence. temperatures increase downglacier at the dry adiabatic lapse rate of about 1° C per 100 m. (Icographif and Physiographic Sctfmif Temperatures on the lower halves of these I he Rccdy Glacier is the most easterly of the glaciers are thus anomalously high; in the- great outlet glaciers flowing through the Trans- center of the Ross Ice Shelf at 80 m elevation antarctic Mountains from the Kast Antarctic and away from the influence of descending Ice Sheet to the Ross Ice Shelf, ft flows in a winds, the 10 m lirn temperature is about northwesterly direction from about lat 86°30' -28.5° C (Crary and others, 1962, p. 125), the S. to lat 85°30' S.. cutting through the moun- same as at 1500 m elevation on the Rccdy tains where they ate closest to the Pole, and Glacier, calculated from the lapse rate. joins the Ross Ice Shell near its grounding line (IHig. 1). Block-laultcd tabular mountains lie on Ice Cover both sides ol the glacier, the Queen Maud The Reedy Glacier itself consists mainly of Mountains on the west and the Wisconsin ice from the East Antarctic Ice Sheet, but Range ol the I lorlick Mountains on the east. plateau ice caps and their outlet glaciers, and These, mountains rise about 3600 m above sea small independent glaciers, are all of local level, 1000 m above the level of the adjacent origin. I'.ast Antarctic Ice Sheet. The Wisconsin Range South of the Wisconsin Range the surface- appears to consist of two principal fault blocks: elevation of the East Antarctic Ice Sheet is the Wisconsin Plateau in the northwest and a 2900 m at lat 88°30' S. and 2650 m at lat lo\\er plateau in the southeast, separated by an 87°1()' S. (Robinson, 1964, Fig. 26). At lat ice-covered escarpment at about 2900 m. North 86°20' S. the surface is at about 2400 m near the ol the Queen Maud Mountains a lower, dis- upper margin of the cone of intake of Reedy sected landscape extends 50 km to the Ross Ice (ilacier. Before the Reedy Glacier joins the Shelf, but north ol the Wisconsin Range similar Ross Ice Shelf, it becomes the westernmost ice- terrain is partly submerged by the West stream in a wide body of grounded ice, part of Antarctic Ice Sheet whose surface rises 1000 m the West Antarctic Ice Sheet (PI. 1, fig. 1). above sea level at the eastern end of the range. Plateau ice caps entirely cover the tabular summits ol the easternmost Queen Maud Climate Mountains, and are drained by ice flowing Snow-surface features show that easterly down the escarpments. This ice partially buries winds prevail on the Wisconsin Plateau and the dissected terrain of aretes and cirques be- southeasterly downglacier winds on the Reedy tween the escarpment and the Reedy Glacier

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I35°W 86° 30'S -|-

EDGE OF QUEEN MAUD SURFACE p 'ICE-ROCK CONTACT MILES -:SS-:- RIDGE 9_ KILOMETERS <^t^ ICEFALL GROUNDING UNE OF ICE SHELF FIELD OF VIEW PL.5, FIG.2 ROSS AREA CONSISTING PARTLY OR ICE SHELF (\•••'.•;\~^) ENTIRELY OF EXPOSED ROCK |/ iMgurc 1. Map of Reedy Glacier area, Antarctica, including location map.

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(PI. 1, fig. 1). Plateau ice caps also occupy most supply in the field. Helicopters of the U. S. of the Wisconsin Plateau, and iccfalls descend Army provided invaluable support during part the northwest-facing escarpment which rises of the field season; without it many of the ob- 1500 m to 2200 m above the West Antarctic servations could not have been made. The Ice Sheet. In iront of this escarpment a blue manuscript has been critically reviewed by Dr. icefield extends 30 km to 40 km, an area of net Colin Bull, Dr. Richard Cameron, and Dr. ablation where some inset glaciers terminate. Arthur Mirsky of the Institute of Polar Studies, The northwest part of the escarpment over- the Ohio State University. Velon Minshew, also looking the Reedy Glacier is heavily ice- of the Institute, has contributed the section on covered, but southeast of the Olentangy bedrock geology. Glacier, rock ridges rising above the general level of the plateau effectively keep the ice BEDROCK GEOLOGY away from the edge of the escarpment. Inde- The bedrock geology of the Wisconsin Range pendent glaciers, defined as those that flow and easternmost Queen Maud Mountains con- neither from nor into other glaciers and have sists of a complex suite of metamorphic and distinct termini, lie on the escarpment face be- igneous rocks, ranging in age from Precambrian low, some inset into the blue ice ol the Reedy to Ordovieian, nonconformably overlain by Glacier. The position of the ice-covered south- several hundred meters of Late Paleozoic sedi- east-facing escarpment is marked by a break in mentary rocks. The oldest rocks in the area slope about 2900 m above sea level. Ice flows consist of several thousand meters of steeply over it onto the lower plateau, but the bound- dipping schist, slate, and phyllite of the La- ary between this local ice and the ice of the Gorce Formation which, except for small Polar Plateau is not known. isolated patches, are restricted to the foothills 'The Reedy Glacier receives increments of along the lower part of the Reedy Glacier and local ice from the Wisconsin Range and the strike parallel to the front of the mountain Queen Maud Mountains (Fig. f). North and range. These rocks generally form subdued un- south of Metavolcanic Mountain, local ice flows dulating ridges. in a wide front from the lower plateau, but flow Metavolcanic rocks of Late Precambrian age lines show that comparatively little ice is con- crop out m Metavolcanic Mountain, along the tributed; some of this ice enters an area of net west side of the upper part of the Reedy Glacier ablation and tongues of blue ice flow northeast- and on the Wisconsin Plateau to the east of the ward toward the escarpment and terminate Olentangy Glacier; these strata, the Wyatt For- against it. mation, overlie the LaGorce Formation. In ice-free areas bordering the Reedy Glacier, A few hundred meters of gently dipping a few small independent glaciers end on land. sandstone and shale crop out in the Wisconsin Benson's concept of glacier facies (Benson, Range at one nunatak south of Metavolcanic 1962, p. 14), developed in Greenland, must be Mountain. Similar rocks near the Leverett modified to apply to such independent glaciers Glacier in the Queen Maud Mountains contain in Antarctica: the dry snow facies is present, a Middle Cambrian trilobite fauna (Minshew, the percolation and soaked facies are absent, and 1966). The remainder of the basement consists the ablation facies is of a different type, for of a suite of granitic and gneissic rocks. only sublimation and perhaps some mechanical Exposures of Late Paleozoic sedimentary deflation take place. Glaciers of this type, with rocks are restricted to three areas: Mt. Le- only a dry snow facies and a dry ablation facies, Schack, the area immediately west of the glacier are confined to the interior of Antarctica, and that isolates Mt. LeSchack, and the major the term, "High Antarctic" glacier is used escarpment between Camp Reedy and the herein. Olentangy Glacier. Sedimentary rocks may also be present beneath the ice elsewhere. These ACKN'OWLKDGMKNTS rocks consist of tillite resting on a striated ero- This work was supported by National Science sion surface; the tillite is overlain by shales and Foundation Grant GA-136 awarded to The sandstone containing a sparse Glossoptens flora. Ohio State University Research Foundation. Near the Olentangy Glacier these sediments are The field study was from November 1964 to about 600 m thick including 140 m of tillite at February 1965. Aircraft of the U. S. Navy pro- the base, but at the other two localities less than vided transport to and from the field, and re- 200 m are present, all of which is tillite. The

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sediments are generally flat-lying except near Glacier down to about 400 m above, all the Olentangy Glacier, where they have been granitic boulders on the surface have deep downfaulted an estimated 600 meters or more cavernous weathering. Between 400 m and 260 and are often vertical near the north-trending m, boulders weathered to the same color, but fault contact. with no cavernous weathering, partially cover No bedrock younger than these sediments is the older drift. Between 260 m above the glacier known from the Reedy Glacier area, except for and the edge of the ice-covered cliff adjacent to compact till dating from the early part of the the glacier (PL 1, fig. 2), fresh, angular boulders present glaciation and exposed at the top of the lie in about 15 cm of sand and gravel covering escarpment to the east of the Olentangy ice; the upper margin of this drift does not form Glacier. This till is described in detail later. a conspicuous ridge, indicating that the ice is thin. The present margin of the glacier from the GLACIAL GEOLOGY Queen Maud Mountains has receded a few Several ice-free areas having surfaces of low meters from a fresh ice-cored moraine ridge (PL to moderate slope border the Reedy Glacier as l,fig.2). it cuts through the Transantarctic Mountains: Thus in this area three Reedy Glacier drifts these are, moving upglacier, the Quartz Hills, of decreasing age can be distinguished by the the Caloplaca Hills, the Camp Reedy-Olen- weathering of granitic boulders on their sur- tangy Glacier area, and the Metavolcanic faces. They are here called the Reedy I, II, and Mountain area. The glacial geology of these III drifts. Boulders on Reedy I drift, the oldest areas is described below. and highest, are stained by ferric oxide and have deep cavernous weathering; on Reedy II drill Quartz Hills they are similarly stained but cavernous weath- An area of mature alpine sculpture about 20 ering is absent or incipient; on Reedy III drift km long and between 1 and 18 km wide lies on they have a fresh surface with little or no oxida- the left side of the Reedy Glacier (PL 1, figs. 1 tion of ferrous compounds. The differences are and 2), extending from 1400 m to about 2400 so clear that drifts elsewhere bordering the m elevation. It is named the Quartz Hills be- Reedy Glacier are correlated on the basis of cause of the abundant rose quartz in the drift. surface weathering. Lateral erosion by the Reedy Glacier has Stratified drift. In an empty cirque near the truncated two empty cirques along the east side southeastern end of the Quartz Hills the Reedy and formed precipices 1000 m high. Ice from 1 end moraines, consisting of one or two ridges, the Queen Maud Mountains has steepened part lie along the backwall 730 m above the Reedy oi the northwest side. Glacier (PL 2, figs. 1 and 2). A platform that Former ice levels. End moraines he as much slopes across the cirque floor from 120 m to 180 as 750 m above the present ice surface. In the m above the ice is the surface of a thick drift de- northwest, above the glacier from the Queen posit that has been exposed in section. Compact Maud Mountains, they extend along the hill- stratified drift forms a cliff 90 m high and may side, and above the Reedy Glacier they extend extend below the present ice surface (PL 2, fig. along the backwalls of the two truncated 1). The lower part was inaccessible, but 50 m of cirques. At the confluence of these two glaciers horizontally bedded clay alternating with a lobe of ice flowed back into a cirque-headed micaceous sand and containing many pebbles valley and deposited several closely spaced, mas- and boulders up to 50 cm in diameter was ex- sive end moraines, as much as 45 m high (PL 1, amined (PL 3, figs. 1 and 2). This stratified drift fig. 2—Reedy I moraines), A pit was dug to a was evidently deposited in an ice-marginal lake depth of 1.5 m on the crest of a ridge without containing floating ice. Scattered boulders of reaching an ice core. About 3 m of stony till on Reedy III age lie on the surface of the platform, bedrock is exposed at the top of the cliffs over- indicating that the lake existed before Reedy looking the Reedy Glacier. Although cavernous III time, but because many weathered boulders weathering of exposed granitic boulders is far have fallen from the cirque backwall, it is not advanced, no weathering is evident below the clear whether the stratified drift covers, or is surface of the till. covered by, drift of Reedy II and Reedy I age. The slope below the moraines is drift- When the lake existed, the climate must have covered and nearly flat (Fig. 4). From the high- been much warmer than it is today. At present, est end moraine at 750 m above the Reedy small ice-marginal ponds are frozen solid during

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EXPLANATION

•• STRATIFIED DRIFT ROCK DEBRIS REEDY I END MORAINE REEDY I END MORAINE - REEDY IE END MORAINE -V^H-KC- RIDGE PRECIPICE ^TTT, ICEFALL FIELD OF VIEW, PL I, FIG 2 TC TRUNCATED CIRQUE

Figure 2. Map of Quartz Hills, Rccdy Glacier, Antarctica, showing glacial geology.

most of the summer; on a few calm, sunny days the genus present. The hills extend about 8 km only, after snow has fallen on the hare rocks, by 6 km and arc 1600 m to 2500 m above sea mcltwater covers these frozen ponds to a depth level, about 600 m lower than the escarpment of of a few centimeters for a few hours while the the Queen Maud Mountains 10 km away (Fig. direction of the sun is favorable. 3). The area is one of alpine topography, but the Independent glacier. A valley glacier 4 km cirques are now empty or occupied by tinderfit long is connected to the glacier to the south but glaciers, fee from the Queen Maud Mountains receives no ice from H and is therefore an inde- flows along all sides of the hills except the east pendent "High Antarctic" glacier (PL 1, fig. 2). and has not appreciably modified the landforms, It appears to be advancing; a small amount ol but lateral erosion by the Reedy Glacier along unweathered drift is being deposited at the con- the eastern side has formed a precipice over 400 vex margin of the glacier, but drift on the sur- m high. Cavernous weathering of granitic rock face beyond is weathered. The terminus, most on the precipice face shows that cliff recession ol it masked by a snow bank, is only about 300 has been virtually at a standstill for a long time. m from the Reedy III moraine ridge of the main On the other side of the Reedy Glacier, faceted glacier. This apparently advancing glacier spurs are gullied (PI. 2, fig. 2). tongue contrasts with the evident recent reces- Former ice levels. Six meters of stony Reedy sion of the local ice from the Queen Maud 1 till cap the cliff 420 m above the Reedy- Mountains nearby (PI. 1, fig. 2). Glacier. This drift thins rapidly to the west, where sparse ice-transported material lies on the Caloplaca Hills surface both inside and outside the cirques for The Caloplaca If ills contain the most south- 500 m above the present ice margin. No erly known occurrence of lichen: Caloplaca is morainal ridges of Reedy t age were found.

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Figure 2. Vertical aerial view of north part of Quartz Hills, Reedy Glacier, Antarctica, showing Reedy moraines. U. S. Navy photo.

REEDY GLACIER AND QUARTZ HILLS, ANTARCTICA

MERCER, PLATE 1 Geological Society of America Bulletin, volume 79

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 I'lgure 1. Truncated cirque, Quart/. Hills, Rcccly Glacier, Antarctica, from the Reedy Glacier, looking southwest. Reedy [ moraine ridge with snow slope behind is same as in Plate 2, Iigurc 2. Stratified drift at bottom right.

Figure 2. Reedy I moramal ridge in foreground, 730 m above the surface of the Reedy Glacier, Antarctica; view to east. Note gullied, truncated spurs on the other side of the glacier. END MORAINES AM) GLACIOLACUSTRINE DEPOSITS, QUARTZ HILLS, ANTARCTICA MERGER, PI,ATK 1 Geological Society of America Bulletin, volume 79

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 Aerial view of Polygon Ridge and part of the Wisconsin Plateau, Reedy Glacier area, Antarctica; view to northeast. Note the Reedy I and II moraines, the Queen Maud surlacc, and the situation of the Horlick drill exposure. Solifluction (low is at the lower right. U. S. Navy photo, Operation Highjump.

GLACIAL AND PERIGLACIAL DEPOSITS, REEDY GLACIER, ANTARCTICA

MERCER, PLATE 4 Geological Society oi America Bulletin, volume 79

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 Figure 1. Horlick drift exposure on edge of Wisconsin Plateau, Reedy Glacier area, Antarctica; view to west, Tillite Ridge left middlcground and Reedy Glacier behind. Note metavolcanic cobbles and granitic boulder on surface, right foreground. Arrow marks position of mass-wasted layer.

Figure 2. Aerial view to south-southwest over Metavolcanic Mountain, Reedy Glacier area, Antarctica, and nunataks behind. Arrow marks position of drift lying 600 m above subjacent ice. GLACIAL DEPOSITS AND GROUP OF NUNATAKS, REEDY GLACIER, ANTARCTICA

MERCER, PLATE 5 Geological Society of America Bulletin, volume 79

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 Figure 1. Lowest part of Horlick drift exposure, Reedy Glacier, Antarctica. Vertical sandstones in foreground, mass- wasted layer by hammer handle, Early Horlick drift between hammer head and large granitic boulder, Middle Horlick drift above.

Figure 2. Disconformity between Early Horlick and Middle Horlick drifts; edge of Wisconsin Plateau, Reed)- Glacier area, Antarctica. GLACIAL DFPOSITS, REEDY GLACIER, ANTARCTICA

MERCER, PLATE 6 Geological Society of America Bulletin, volume 79

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Camp Reedy-Olentangy Glacier Area Queen Maud erosion surface. The Wisconsin Plateau surface is ice-free for about 25 km southeast of the Olentangy Glacier, the width of the exposed portion varying from a few meters to two kilometers (Fig. 4). The surface bevels horizontal and vertical sediments of Late Paleozoic age, and basement granitic rocks (PI. 4), indicating that it is an old erosion surface. It is proposed here that the name Queen Maud

SMALL GLACIER Surface be applied to this erosion surface that ROCK DEBRIS now forms the upper levels of the various REEDY I ICE LIMIT plateau areas. This surface was raised and locally REEDY I END MORAINE offset during uplift of the Transantarctic Moun- REEDY H END MORAINE tains, and is the surface that the earliest glaciers OTHER END MORAINES formed upon. The Queen Maud Surface is RIDGE 0 du nil PRECIPICE L- widespread in the Queen Maud Mountains, the ICEFALL 0 Horlick Mountains (Mercer, 1963, p. 8), and the Thiel Mountains (Andersen, 1963, p. B140), gure 3. Map of Caloplaca Hills, Reedy but it is generally ice-covered and thus visible icr, Antarctica, showing glacial geology. only in profile in ice-free escarpment faces. Some of the Queen Maud Surface may be es- sentially the exhumed and replaned Lower A cirque-headed valley about 5 km long ex- Paleozoic Kukri Peneplain of Debenham (1921. tends parallel to the Rccdy Glacier anil a de- p. 105) or the Mid-Paleozoic erosion surface ol bris-covered lobe of ice, originating in the Mirsky (1964, p. 372). The exposure southeast Queen Maud Mountains, enters the mouth. In of the Olentangy Glacier is exceptional, not front of this lobe is an expanse of flat-lying drift only for its extent but also for the variety ol. of Reedy II age, covered by unsorted polygons, rock types and attitudes that the surface bevels apparently the ablation moraine left by the lobe Moderately rugged hills of basement rocks that: as it wasted away from a level 275 rn above the rise about 300 m above the exposed erosion sur- present level. Reedy III drift extends 100 m face were perhaps former topographic highs above the present ice margin, and an undis- turbed recessional end moraine of Reedy II age lies about 10 m below the Reedy 111 ice limit. Independent glaciers. An independent "High Antarctic" glacier about 1 km long lies at. the head of the 5-km-long valley, and its convex debris-covered margin gives the impression that it is advancing. An unvveathered ice-cored moraine lies 30 m ahead of the glacier, and two moderately weathered moraines containing no ice within 30 cm of the surface lie 80 m and 100 m ahead. When the glacier reached the outer moraine its volume was about one third greater than it is today. A very small glacier lies in the angle between the flat-lying Reedy It drift and the hillside, its upper part extending onto the Reedy I drift. Polygons on the Reedy II drift appear to extend beneath it, and some weathered rock is being brought to the surface along a shear plane, the weathering showing that the glacier has not been present continuously since Rccdy 1 time. Figure 4. Map of Camp Rcedy-Olentangv Where the shear plane reaches the surface, the Glacier area, Antarctica, showing glacial geology. accumulation ol debris is small, indicating that Labeled arrow shows location of measured section the activity of the glacier is extremely low. described in Table 1.

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standing above a plain of degradation: with the TABI.F 1. ShonoN or 1 IORLICK Dim-r ON Enor greater part of the Queen Maud Surface ice- WISCONSIN Pi,.vrt;Ar (LOCATION OF SI-.CTION INDICA covered, its real nature remains uncertain. Some HV LAIU'.LKH ARROW IN FK;IIKF. -1) ol the suriace is covered hv highly weathered glacial drill and other parts by a fclsenmcer de- Approx. rived from the underlying rock. This weathered Stage Unit Thicknes' material extends up to the margin of ice bodies ((>) i.oose drift containing of inactive appearance occupying the angle many mctavolcamc cobbles between these hills and the Queen Maud Sur- REEDY I and fragments of staurolitc face. .schist. Granitic boulders on the suriace ate cavcrnously The Queen Maud Suriace bevels some faults weathered. but is offset by others (PI. 4). The younger laults probably date from uplift of the range. LATE POSSIBLE DISCON- Variations oj the tec cover. About 450 m be- IIOKL1CK EORMITY (a surface of low the Queen Maud Surface a more uneven nomlcposition) ice-free suriace slopes down toward the Reedy (:>) Til!, grittier and less com- 6 in Glacier. Cirque-headed valleys extending back pact lhan unit (4). Pebbles to the escarpment divide it into two flat-topped and cobbles of sandslonc, ridges Red and Tillite spurs - and one more shale, and granitic rock and extensive ice-free area, Polygon Spur (Fig. 4). a few black metavolcainc All the bare ground has been ice-covered in the cobbles. past, either by more extensive \Visconsm MIDDLE (4) Very compact till, rich in 30 i IIORLIOK- clay minctals and conlaining Plateau ice, or by a thicker Reedy Glacier, or pebbles anil cobbles ot by both. The glacial deposits will be described sandstone, shale and gtaninc and discussed starting on the edge ol the Wis- rock. Many pebbles of Ime- consin Plateau and descending to the Reedy gi'amcd sedimentary rocks Cilacier margin. are striated. The upper half Massive, almost horizontal sandstone beds conlams grannie boulders. underlie the Queen Maud Suriace above Red and Tillite spurs, except above the eastern end I )1 SCON LOR MIT Y ol 'I illite Spur where the underlying fine- (?) Discontinuous stratihed 1-2.Sm grained, thin-bedded sandstones are abruptly fines and lenses of clay. folded almost vertically (PI. 4. below arrow EARLY (2) tJnwcathcrcd, nnsorted pointing to I ioilick drill). A shallow depression HORLICK granitic fragments in all in the Queen Maud Suriace, probably a valley six.es up to one meter in that was excavated along these weaker beds, diameter, some rounded, has been Itlled \\itli a drill deposit. A thickness others angular, in a matrix moslly of sand and sill. ol 40 m ol this drill is exposed in the escarpment A lew Iragments of unit lace (Table IK most ol the deposit, apparently (1) near the base. including the valley floor, is hidden by ice. Unit (1 j consists entirely of fragments of the PRE- (1) Well-cemented bedrock 1 m underlying line-grained sandstone cemented I lORLICls. fragments lying on nearly vertically bedded fine- together. Many ol the fragments are imbricated grained sandstones. and no trace remains ol the original bedding (PI. 6, fig. 1). Some horizontal movement has evidently taken place, but the material was derived Irom the immediate vicinity; no frag- Unit (2) is also hthologically homogeneous, ments ol the massive sandstone that constitutes but consists entirely oi granitic material whose the edge ol the depression between 50 and 100 closest outcrop is the hill that stands about 1.5 m away were recognized. I.nit (1) is interpreted km to the northeast (PI. 4). This unit may be as Irosi-shaltcrcd bedrock, or perhaps the C- landslide material from that hill, or till from a honzon ol a lormer soil that has undergone small glacier in the angle between the Queen creep. Clay coatings around rock Iragments are Maud Surface and the hill. A glacial origin visible in thin section, indicating that water seems more likely because small glaciers must percolated throughout; therefore the material have preceded the general ice cover of the originated under penglaeial or nonglacial con- Wisconsin Plateau that deposited the overlying ditions. unit (4). The existing glacier m this situation is

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inactive and dry-based, and appears to deliver glacier became established and was later in- no drift to its margin, but unit (2), if of glacial corporated into a plateau ice cap that formed origin, was deposited by temperate, wet-based on the Wisconsin Plateau. Because extensive ice. Unit (3) was deposited in pools of water and areas of the plateau are at almost the same ele- is thus a surface deposit, indicating that unit (2) vation, glacierization was probably rapid once is not subglacial in origin but probably an over- it had begun, so that unit (2) represents a short ridden end moraine. A discontinuity, ac- time interval. Clay-rich lodgment till is best companied by an abrupt change in facies, explained as having been deposited beneath the separates units (2) or (3) from unit (4) (PL 6, plateau ice cap while it was temperate and wet- fig. 2). based, but when the ice became "cold" and Units (4) and (5) are interpreted as lodgment dry-based, deposition of this type of till ceased. till, because of the great thickness, the compact After a long interval, unit (6) was deposited as nature and the common occurrence of striated uncemented ablation till at the margin of the pebbles. The lithology is heterogeneous; the slowly receding ice. matrix is predominantly of sedimentary rock The numerous cirques in the Reedy Glacier origin, pebbles and cobbles are of sedimentary area that are now empty must have lost their and crystalline rocks, and all the boulders are glaciers as the result of decreased snowfall, be- crystalline. This indicates a much more exten- cause temperatures are continuously far below sive ice cover than in unit (2) time, covering freezing. The events in the Wisconsin Range of much or all of the Wisconsin Plateau. Although the Horlick Mountains, from the birth of local proof is lacking, deposition of lodgment till is glaciers to their shrinkage because of starvation, generally thought to take place as the result of are here referred to as the Horlick Glaciation. slow pressure-melting of the basal ice and thus It is subdivided into Early Horlick time that to be confined to temperate glaciers (Flint, ended with the establishment of extensive wet- 1957, p. 120; Carey and Ahmad, 1961, p. 879). based ice caps on the plateaus and the first Unit (6), apart from the highly weathered cirque and valley glaciers on their flanks; Mid- material on the surface, is similar in composition dle Horlick time when local glaciers were at to modern glacial deposits along the margins of their maximum and the ice was still wet-based; the Reedy Glacier, although it is thicker. It is and Late Horlick time, a period of increasing not lodgment till and may be ablation till left cold and aridity and of shrinking local glaciers. at the margin of the receding Wisconsin Most of the glacial erosion probably took plac; Plateau ice. In contrast to the restricted oc- in Middle Horlick time and virtually ceased currence of the lower drift units that it covers when the ice became dry-based in Late Horlick at this locality, unit (6) drift is widespread, and time. elsewhere rests directly on bedrock. Its com- According to the above interpretation, unit position varies slightly from place to place. (1) is pre-Horlick, units (2) and (3) Early Metavolcanic rocks which crop out on the Horlick, and units (4) and (5) Middle Horlick Wisconsin Plateau are absent from unit (6) in age. Above unit (5) is a probable surface of drift on the Queen Maud Surface due west of nondeposition representing the cessation of the outcrop, but are present in the drift lying lodgment till deposition when the ice became to the southwest and south (Fig. 4). This sur- dry-based in Late Horlick time. Unit (6) is face distribution suggests that the metavol- probably of Reedy I age because it occurs not canic rock was derived from this known out- only on the escarpment edge but also on the crop and its probable continuation beneath the highest parts of Tillite and Polygon spurs (Fig. ice to the east or southeast. Ice was thus flowing 4), 490 m above the present ice surface. The off the plateau toward the south or southwest. drift covers flat surfaces separated from the Metavolcanic rock is absent from unit (4) present glacier by precipices, and it is difficult either because the direction of ice flow off the to understand how drift from the Wisconsin plateau was different at that time, perhaps Plateau could have been deposited in such toward the west, or because the ice had not yet situations except when the surface of the Reedy removed the sedimentary rock cover from the Glacier was much higher than it is today ia present outcrop area. Reedy I time. In the Quartz Hills and Caloplaca The above suggests that this part of the Hills, however, Reedy I end moraines were de- Wisconsin Plateau was at one time ice-free but posited in empty cirques, indicating that starva- with a periglacial climate that allowed water to tion of local glaciers was far advanced at the percolate at least a meter below the surface Reedy I maximum. The local thinning of Wis- when unit (1) was formed. A small, temperate consin Plateau ice in unit (6) time may, there-

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lore, have been the result of headward erosion flows are younger than the Reedy I drift, which by the Olentangy Glacier (Fig. 1), rather than they incorporate or cover, and the longer flow ol increased aridilv. is older than the Reedy II end moraine, which The distribution ot unit (6) drift elsewhere crosses it without distortion. on Tillite, Red, and Polygon spurs indicates The Reedy II end moraine extends across that the drift was deposited before the Reedy 1 Polygon Spur, approximately parallel to the maximum. The lower part of the top surface of present margin of the glacier and between 170 Tillite Spur and all of the top surface of Red m and 210 m above it. In places it forms a con- Spur are devoid ol drilt containing metavol- spicuous single or double ridge 2 m high (PI. 4). canic rock Irom the Wisconsin Plateau but have The Reedy III end moraine ridge is one meter scattered cavcrnously weathered granitic boul- high and lies 100 m to 140 m above I he ice mar- ders that were probably deposited by the Reedy gin. Its composition is deceptive; in places, most (ilacier later in Reedy 1 tune, when ice Irom the of the constituent boulders and cobbles are of Wisconsin Plateau was no longer flowing over Reedy II age, and only a few boulders and most: the edge of the escarpment. On Polygon Spur ol the smaller material are virtually umvealh- I he situation is more complicated. A subdued ered. This can be explained by observing proc- end moraine lies about 400 in above the ice esses near die ice margin today, where forward margin, and above the moraine is unit (6J drift movement of t he ice is balanced by sublimation. with metavolcanic cobbles, granitic boulders up In some places only weathered drilt from be- to 2 m in diameter and well-developed tin- ncaih the glacier reaches the surface along shear sorted polygons. The moraine itself and the planes, but elsewhere, only unwcathered drill on the slope below it are interpreted as supraglacial material of similar composition Reedy I drill, deposited by the Reedy (Ilacier; reaches the margin. In other places mixed drift they contain granitic boulders up to 4 m in from both sources is being deposited. Weath- diameter, no metavolcanic cobbles and polygons ered boulders beneath the glacier, and weath- are poorly developed. This ridge is more ap- ered bedrock surfaces extending up to and parent Irom the air than Irom the ground (PI. apparently beneath the ice, are evidence that 4). About 100 m below this moraine, however, the glacier surface was lower than it is today lor the Reedy I drill is sparse in places, and thin a considerable period before Reedy III lime. unit (6) drill containing metavolcanic cobbles Blue ice field and independent glaciers. The lies on bedrock, indicating that elsewhere it is cirque-headed valleys adjacent to Red, Tillite, covered by the Reedy 1 drilt. Unit (6) was, and Polygon spurs have undcrfit "High therefore, probably deposited in early Reedy I Antarctic" glaciers at their heads, separated by time; ice Irom the Wisconsin Plateau was (low- a belt ol ice-cored end moraines (rom blue ice ing over the escarpment above Tillite and lobes of the Reedy Glacier thai enter the valley Polygon spurs while (he Reedv (ilacier was mouths (PI. 4). A blue ice field extends lor thickening but had ceased to do so by the about: 5 km m front of the ridges, sloping down Reedv 1 maximum. toward the exposed rock. Twelve nails set into On the lower, eastern part ol Polygon Spur the ice were measured at fortnightly intervals; are features lhal are believed to be inactive on an average, aboul 7.5 mm of ice a week was solifluetion (lows. They are known to be in- lost by sublimation in the eight weeks between active because they are covered by a network mid-November 1964 and mid-January 1965. ol unsorled polygons (I'l. 4); temperatures arc This is a much higher rate than has been now much loo low lor the existence ol an active measured m Queen Maud Land: in the nine layer, probably averaging below 15° G lor the months from 7 February to 12 November, 1951 warmest monlh. One flow extends at least: as at hit 72°W S., Iong3°45' \V., an average of 1.3 low as the Reedv III ice limit, and is partly mm a week was lost (Schyll, 1961, p. 188) ami covered by a shorter flow ending within 300 m over a 21-month period m the Sc/jr Rondane of the escarpment in a lobate (ront about 1.5 m Mountains near lat 72° S., long 25° E., an high, whose surlace consists of rocks averaging average of about 3 mm a week was losl (Auten- 20 cm in length. The Hows extend Irom some boer/1964, p. 87). small ice bodies that may have been the source The independent underlit glacier between of bolh water and debris. Solifluetion (lows Polygon and Tillite spurs ends near the loot ol were not seen elsewhere in the Reedy Glacier the escarpment (['1. 4); it is in contact with a area, even at lower elevations, perhaps because fresh ice-cored moraine with its crest 7 m above such lavorable circumstances are rare. Both the ice. Three older contiguous ice-cored

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moraines lie outside. Weathering indicates that drift patch lies at about 2700 m above sea level the oldest is older than Reedy III drift, but no and 600 m above the subjacent surface of the older than Reedy II drift; it is partly covered Reedy Glacier, but level with the lower by Reedy III drift from the Reedy Glacier lobe. plateau of the Wisconsin Range to the east. Narrow bands of sparse rock debris that come This setting suggests that it was deposited by to the surface of the blue ice field as the surface ice from the lower plateau, not by a thicker is lowered by sublimation consist mainly of un- Reedy Glacier. If so, it was before the plateau weathered angular granitic fragments of all remnant forming the summit of Metavolcanic: sizes up to several meters in diameter. These Mountain had been isolated from the lower have not fallen Irom rock faces bordering the plateau by glacial erosion, which probably took glacier and are evidence that glacial plucking place in Middle Horlick time when the ice was is in progress upglacier, perhaps beneath the ice temperate. This suggests an early Middle that descends steeply from the plateau. All this Horlick age for the till on Metavolcanic Moun- material eventually reaches the ice margin on tain. Similar silty till was found in a comparable Polygon Spur, and the amount that has been setting on the summit of Mount LeSchack, a deposited since Reedy II time is small. promontory at the northern end of the Wis- Many small recessional moraines lie between consin Range (Fig. 1). the Reedy III moraine ridge and the ice mar- South of Metavolcanic Mountain are several gin, and in places the ice is in contact with an small nunataks, precipitous or steep on their ice-cored moraine 6 m high that appears to western sides, and sloping gently beneath the mark the only significant readvance since Reedy ice on the east. Reedy III drift with no visible III time. weathering extends 40 m above the present level of the ice and covers nunataks a, c, and d (Fig. Metavolcanic Mountain Area 1; PI. 5, fig. 2); it lies on a highly weathered Several nunataks, part of the exposed edge surface that extends up to and apparently be- of the lower plateau of the Wisconsin Range, neath the present ice cover. Nunatak b rises 120 border the upper Reedy Glacier (Fig. 1; PI. 5, m above the ice; no ice-transported material fig. 2). Their surfaces are remnants of the Queen was found more than 40 m above the ice. Maud Surface, modified by ice action. The Nunatak e is a north-trending ridge about largest is Metavolcanic Mountain which ex- 2700 m above sea level, 30 m above the ice to tends about 15 km east-west and 6 km north- the east and 360 m above the ice to the west. A south. The summit area is rolling, with about small concave platform is attached to the west- 150 m of relief, and the edge is scalloped by ern side of the northern end, about 90 m below cirques, whose original glaciers have in most the level of the ridge, and bounded on three cases been replaced by inward-flowing lobes of sides by precipices. The whole of the nunatak ice from the Reedy Glacier. Slopes are steep except for this platform was ice-covered in or precipitous on all sides except the east, where Reedy III time, and virtually unweathered a narrow neck of land connects Metavolcanic drift lies on a weathered bedrock surface tlw: Mountain with the ice-covered lower plateau. extends to the ice margin and apparently be- In the cirques occupied by distributary lobes of neath it. This Reedy III drift is absent from the the Reedy Glacier, drift covering the ice ex- platform, but cavernously weathered granitic tends 120 m above the glacier margin and is boulders and black metavolcanic cobbles of probably of Reedy III age; on the north-facing Reedy I age or older and of unknown proven- escarpment granitic boulders perched 200 m ance are scattered on the surface. No Reedy II above the Reedy Glacier are perhaps of Reedy stage was recognized on these nunataks. II age. The surface of Metavolcanic Mountain, DISCUSSION where not covered by permanent ice and snow, Field evidence shows that the ice cover in the is a fclsenmeer of the dark metavolcanic bed- vicinity of the Reedy Glacier has varied greatlv rock on which scattered erratics of highly in both thickness and extent. Interpretation is weathered granite show up clearly. Over most complicated because independent local glaciers of the surface erratics are very sparse, not more would have responded only to local climatic than one to a square kilometer, but a concentra- variations, whereas the surface level of the tion of them lies in a saddle, partly embedded in Reedy Glacier would have depended both on at least 1 m of light-colored silty till containing the amount of ice flowing into it from the Polar cobbles of granitic and sedimentary rock. This Plateau, and also on the position of the ground-

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ing line of the Ross Ice Shelf toward which it shrinking. Tn colder intervals reduced sublima- (lows. tion may have caused growth, or reduced snowfall may have caused shrinkage. Age of the Horlick Glacialion The Wisconsin Range combines great eleva- Variations of the Reedy Glacier tion and high latitude, and must have supported While the ice caps on the Transantarclic some of the earliest glaciers in Antarctica. Most Mountains were temperate, temperatures of the Wisconsin Plateau lies between 2900 and would still have been too high for the East 3600 m above sea level and would be about 450 Antarctic Ice Sheet to build up on low ground. m higher without the isostatic depression caused In Middle I lorlick time the Reedy must have by the ice sheet (see Bentlcy and Ostenso, 1961 , been a local glacier, draining the plateau ice p. 893). The first glaciers would have formed on caps on either side. Some cirques and cirque- the plateau when the mean temperature of the headed valleys that were probably cut at that warmest months had (alien to near freezing time and arc tributary to the valley occupied point, or slightly higher il the precipitation was by ihe Reedy Glacier arc now occupied bv in- very heavy (Ahlmann, 1948, Fig. 32). There- ward-flowing lobes of ice that slope down as fore, temperatures were at least 25° C higher much as 200 m from the main glacier. Ex- than they arc today on the Wisconsin Plateau amples are around Metavolcanic Mountain and when the Early Horlick drift was laid down, between Red Spur and Camp Reedy. This in- and not much lower in Middle Horlick time dicates that the surlace level ot Reedy was while temperate ice was depositing lodgment lower than it is today when these valleys were till. occupied by outward-flowing glaciers. Later, The Council of the International Geological when temperatures had fallen enough for the Congress in 1948 proposed that the criterion East Antarctic Ice Sheet to build up on low for the Pliocene-Pleistocene boundary he ground and local glaciers were shrinking changes in marine faunas at the base of the through starvation in Late Horlick time, the Calabrian formation in the type-area in Italy. Reedy became an outlel ot the ice sheet. It Migliorini (1950, p. 69) notes that this horizon thickened and in Reedy I time reached its separates strata laid down under warmer condi- highest known level; as it expanded, it was in- tions than prevail today from strata laid down vading new territory and the abundance of: under colder conditions; in other words, at the Reedy I drift suggests that spur faceting and transition, temperatures were roughly similar lateral erosion in general were more active than to those of the present lime and (ailing. Ac- in later expansions. cording to this definition. Early and Middle Ihe sohlluction flows on Polygon Spur in- Horlick time in the Reedy ( ! lacier area was pie- corporate or cover the Reedy I drift and the Pleistocene and, therefore, presumably Pli- longer flow is crossed by the undislorted Reedy ocene. Sea level stimniei temperatures prevail- 11 moraine and was, therefore, active only in ing at the foot of the Transantarctic Mountains the Reedy EU interval. It extends down at in Early Horlick time at lat 85° S., calculated least to the Reedy III ice limit, indicating that from the present elevation of the Wisconsin during the Reedy I-II interval, the surface of Plateau, would have been more than 20 C, a I he Reedy Glacier dropped at least to that level. figure so high that the I loiiick Glacialion may Weathered bedrock surfaces which extend to have begun before uplift of the Trausantarctic the present ice margin and apparently con- Mountains was complete. tinue beneath it, perhaps were exposed during the Reedy 1-11 interval. Variations of Independent Glaciers After the warm episode m the Reedy I-II The independent "High Antarctic" glaciers interval, solilluclion ceased, indicating that the thai now end on land were incorporated into climate had grown colder again, and the surface the thickened Reedy Glacier in Reedy I time. o( the Reedy Glacier rose to the Reedy II level. Since then they have fluctuated several times; The weathering of the Reedy 11 drift could at least one has been about a third greater in have taken place only during the Reedy H-III volume than it is today, and at least one has interval. On Polygon Spur, weathered Reedy been smaller. They may have varied in or out ol II drift is being brought to the surlace along phase with the Reedy Glacier and also with shear planes within a lew meters of the ice mar- each other; today, some appear to be in gin, indicating that during the Reedy II-IIl equilibrium or growing, while others are inlet val the surface of the Reedy Glacier

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dropped to below the present level. In Reedy TABI.E 2. HEIGHT i.\ METERS OF REEDY KNI> III time it rose once more. MORAINES ABOVE PRESENT GLACIER SURFACE It is uncertain whether all the deposits that formed under \varmer conditions date from the Polygon Caloplaca Quartz Reedy I-II interval, or whether some date from Nunataks Spur Hills Hills the Reedy II-III interval. Both solifluction Reedy I 400 500 750 flows have similar weathering on their surface Reedv II 190 275 400 boulders, but the weathering history of these Reedy III 40 120 100 260 boulders is uncertain. The shorter flow may date from the Reedy I-II interval, or from the upglacier Reedy II-III interval. The lake sediments in the Quartz Hills are older than the Reedy III drift which covers them and younger than the most as soon as they leave the mountains despite intense cirque cutting in Middle Horlick time great differences in velocity and volume. because the lake occupied an empty cirque; Lowering of the glacier bed by erosion has been they were laid down when the surface of the suggested by many workers (e.g., Trail, 1964, Reedy Glacier was low, suggesting either the p. 150) as an explanation for stranded moraines. Reedy I-II interval or the Reedy II-III interval. Spurs faceted by the Reedy Glacier show that The inactive solifluction flows lie between glacial erosion has been active in the past, and 2000 m and 2300 m elevation where the esti- fresh angular boulders and rock fragments, un- mated 1964-1965 average midsummer tempera- weathered on all faces, exposed by ablation in ture was about -15° C. This is at least 10° C the blue ice field near Camp Reedy, are too low for the development of an active, evidence that a small amount of plucking is tak- thawed layer, so that summer temperatures ing place today. Thus, the bed of the Reedy must have been at least 10° C higher when the Glacier has been lowered to some extent by flows were active. The ice-marginal lake glacial erosion, but this mechanism could not probably had a climatic environment similar have caused the great oscillations in level that to the present Lake Radok situated at a low are known to have occurred. elevation 300 km from the sea, in about lat At present, the surface profile of the Reedv 71° S., at the head of the Amery Ice Shelf. It is Glacier is largely determined by the position described by Mellor and McKinnon (1960, p. of the grounding line separating the West 32). Average midsummer temperature on the Antarctic Ice Sheet from the Ross Ice Shelf, and coast in that part of Antarctica is about 0° C only changes in the position of this line could (Bureau of Meteorology, 1964, pp. 1 and 13), have caused the known variations of the profile. and at the lake is probably about -2° C. If the If the portion of the ice shelf that the Reedy- estimated 1964—1965 midsummer temperature Glacier now joins had once been part of the of -15° C at 2050 m on the Reedy Glacier is grounded West Antarctic Ice Sheet and had normal, at 1400 m it is about -8° or -9° C, built up to about 1500 m above sea level, which taking the lapse rate as 1° C per 100 m in this is the present surface elevation of the West area of descending winds. At a rough estimate, Antarctic Ice Sheet north of the Ohio Range, therefore, midsummer temperature was at least the surface of the Reedy Glacier would have 6° C higher than it is today when the ice- risen to the Reedy I level (Fig. 5). This mech- marginal lake existed. anism has been suggested by Voronov (1960) Causes of the variations of the Reedy Glacier. and Hollin (1962) to account for Pleistocene The Reedy Glacier has been thicker than it is variations of ice thickness in coastal Antarctica. today on at least three occasions, and it has also They have pointed out that because the posi- been thinner. When it was thicker, the surface tion of the grounding line is at present de- gradient was less than it is today (Table 2). By termined by sea level, it would have been extrapolation, where the glacier leaves the East affected by the repeated waxing and waning of Antarctic Ice Sheet it has changed little in the northern hemisphere ice sheets during the thickness. In any case, no increase in the amount Pleistocene. Thus, the high levels of the Reedv of ice flowing into the glacier from the East Glacier perhaps reflect northern hemisphere Antarctic Ice Sheet could account for the glaciations and low levels the mterglacials. This former high surface levels of the Reedy Glacier, interpretation receives some support from the because at present all the outlet glaciers from solifluction and ice-marginal lake episodes which the ice sheet merge with the Ross Ice Shelf al- presumably took place during a northern

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/79/4/471/3432435/i0016-7606-79-4-471.pdf by guest on 25 September 2021 484 ]. H. MHKCEK GLACIAL GEOLOGY, REEDY GLACIER, ANTARCTICA

1RANSANTARC MTS 2300 M

ROSS ICE SHELE EXTENDING 900 KM

APPROXIMATE SCA^E 1'igurc 5. Diagrammatic sketch showing the effect of a rise and a fall in sea level on the thickness of the Reedy Glacier.

hemisphere interglacial and which are inferred ticularly early in the Pleistocene before the to have happened when the glacier surface was glacier bed had a mature profile and cross sec- low. However, the problem is complicated by a tion. possible nonglacially controlled eustatic Jail in sea level throughout the Pleistocene, by SUMMARY AND CONCLUSIONS changes in the isostatic depression of Antarctica that accompanied changes in the volume oi the In the Reedy Glacier area, the first glaciers ice sheet, and by the multiple nature of each formed on the Transantarctic Mountains, per- northern hemisphere glaciation. Correlation ol haps before uplift was complete. At first, with Reedy Glacier stages with northern hemisphere inferred high temperatures and abundant snow- events must await absolute dating, perhaps oi fall, the ice was temperate and glacial erosion ice in ice-cored moraines. was active. With increasing cold and decreasing The Reedy Glacier leaves the mountains snowfall, the ice became dry-based and local slightly to the east of the grounding line of the glaciers shrank, resulting in the empty cirques Ross Ice Shell, and for a short distance it is a that exist at present. The establishment of the grounded ice stream within the West Antarctic local ice cover, its increase to a maximum, and Ice Sheet. If the grounding line was farther east its later decrease constitute the Horlick Glacia- because of higher sea level, and the Reedy tion, which was probably Pliocene in age. joined the ice shelf directly, it would be shorter By the time that local ice was shrinking be- and steeper and its surface level would be lower cause of starvation, the Reedy Glacier had be- (Fig. 5). The weathered surfaces extending become an outlet of the East Antarctic Ice Sheet, neath the ice may, therefore, date from the and variations in its surface level thereafter Reedy I-II and Reedy II-III intervals, if sea depended mainly on the position of the ground- levels were then higher. The Reedy is the only ing line ol the Ross Ice Shelf, superimposed on outlet glacier that would be affected in this lowering of the glacier bed by erosion. The way. The others, being far from the grounding grounding line is determined largely by sea line, would thicken slightly as a result of the level, and perhaps the three progressively lower higher surface level of the ice shell. maximum levels of the Reedy Glacier cor- The main factor in the variations of surface respond to times when sea level was eustatically level of the Reedy Glacier since it has become lowered by northern hemisphere ice sheets. an outlet of the East Antarctic Ice Sheet has, Data are insufficient to attempt correlations. therefore, probably been the change in the During one or two warm intervals, solifluc- position of the grounding line of the Ross Ice tion was active and ice-marginal lakes existed, Shelf and the resultant change in the extent of indicating summer temperatures much higher the grounded West Antarctic Ice Sheet. A than at present. This took place when the sur- lowering caused by widening and deepening of face of the Reedy Glacier was low, suggesting the glacier bed by glacial erosion has very likely high sea level and a northern hemisphere inter- been superimposed on these oscillations, par-

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REFERENCES CITED Ahlmann, H. W., 1948, Glaciological Research on the North Atlantic Coasts: London, Royal Geog. Soc., 83 pp. Andersen, B. G., 1963, Preliminary report on glaciology and glacial geology of the Thiel Mountains, Antarctica: Article 37 in U. S. Geol. Survey Prof. Paper 475-B, pp. B 140-B 143. Autenboer, T. van, 1964, The geomorphology and glacial geology of the S0r Rondane, Dronning Maud Land: pp. 81-103 in Adie, R. J., Editor, Antarctic Geology: First Internal. Symp. Antarctic Geology Proc., Capetown, 1963, New York, John Wiley and Sons, Inc., 758 pp. Benson, C., 1962, Stratigraphic studies in the snow and firn of the Greenland Ice Sheet: SIPRE (Snow, Ice, and Permafrost Research Establishment) Research Rept. no. 70, 93 pp., plus Appendix. Bentley, C. R., and Ostenso, N. A., 1961, Glacial and subglacial topography of West Antarctica: Jour. Glaciology, v. 3, no. 29, pp. 882-911. Bureau of Meteorology, 1964, Meteorology: Davis, Macquarie Island, Mawson and Wilkes, 1961: ANARE Reports Series D, v. 14, Antarctic Division, Dept, of External Affairs, Melbourne, 440 pp. Carey, S. W. and Ahmad,Naseeruddin, 1961, Glacial marine sedimentation: pp. 865-894, v. 2 in Geology of the Arctic: G. O. Raasch, Editor, Univ. of Toronto press. Crary, A. P., Robinson, E. S., Bennett, H. F., and Boyd, W. W., 1962, Glaciological studies of the Ross Ice Shelf, Antarctica, 1957-1960: IGY Glaciological Report No. 6, IGY World Data Center A: Glaciology, Am. Geog. Soc., New York, 193 pp. Debenham, Frank, 1921, The sandstone etc., of the McMurdo Sound, Terra Nova Bay, and Beardmore Glacier regions, no. 4a o/The sedimentary rocks, South Victoria Land, in British Antarctic ("Terra Nova") Expedition, 1910: British Museum (Nat. Hist.), Geology, v. 1, no. 4, pp. 104-119. Flint, R. F., 1957, Glacial and Pleistocene geology: New York, John Wiley, 553 pp. Hollin, J. T., 1962, On the glacial history of Antarctica: Jour. Glaciology, v. 4, no. 32, pp. 172-195. Mellor, M., and McKinnon, G., 1960, The Amery Ice Shelf and its hinterland: Polar Record, v. 10, no. 64, pp. 30-34. Mercer, J. H., 1963, Glacial geology of Ohio Range, Central Horlick Mountains, Antarctica: Rept. no. 8, The Ohio State University, Inst, of Polar Studies, 13 pp. Migliorini, C. I., 1950, The Pliocene-Pleistocene boundary in Italy: pp. 66-72 in International Geol. Con- gress, Rept, of the 18th session, 1948, Pt. 9, Proc. of Sect. H, 130 pp. Minshew, Velon, 1966, Stratigraphy of the Wisconsin Range, Horlick Mountains, Antarctica: Science, v. 152, no. 3722, pp. 637-638. Mirsky, A., 1964, Reconsideration of the "Beacon" as a Stratigraphic name in Antarctica: pp. 364-378 in Adie, R. J., Editor, Antarctic Geology: First Internal. Symp. Antarctic Geology Proc., Capetown 1963, New York, John Wiley and Sons, Inc., 758 pp. Robinson, E. S., 1964, Some aspects of subglacial geology and glacial mechanics between the South Pole and the Horlick Mountains: Geophysical and Polar Research Center, Univ. of Wisconsin, Research Report Series no. 64-7, 88 pp. Rubin, M. J., and Giovinetto, M. B., 1962, Snow accumulation in Central West Antarctica as related to atmospheric and topographic factors: Jour. Geophys. Research, v. 67, no. 13, pp. 5163-5170. Schytt, Valter, 1961, Blue ice-fields, moraine features and glacier fluctuations: Pt. E, p. 183-204, of Glaciology II, Norwegian-British-Swedish Antarctic Expedition, 1949-52, Scientific Results, v. 4, Norsk Polarinstitutt, Oslo. Swithinbank, C. W. M., 1964, To the valley glaciers that feed the Ross Ice Shelf: Geog. Jour., v. 130, pt. 1, pp. 32-48. Taylor, L. D., 1965, Glaciological studies on the South Pole traverse, 1962-1963: Rept. no. 17, The Ohio State University, Inst, of Polar Studies, 13 pp. Trail, D. S., 1964, The glacial geology of the Prince Charles Mountains: pp. 143-151 in Adie, R. J., Editor, Antarctic Geology: First Internal. Symp. Antarclic Geology Proc., Capetown 1963, New York, John Wiley and Sons, Inc., 758 pp. Voronov, P. S., 1960, Attempt to reconstruct the ice sheet of Antarctica at the time of maximum glaciation on earth: Information Bulletin of ihe Soviet Antarctic Expedition, no. 23, pp. 15-19 (in Russian).

MANUSCRIPT RECEIVED BY THE SOCIETY JULY 7, 1966 REVISED MANUSCRIPT RECEIVED SEPTEMBER 7, 1967

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