..

REPORT No. 67

Recession of Wisconsinan

Glacier

from Central Saskatchewan

by

F. H. EDMUNDS

1962

DEPARTMENT OF MINERAL RESOURCES

Geological Sciences Branch

Sedimentary Geology Division

HON . A. C. CAMERON Minister

J. T. CAWLEY Deputy Minister

PROVINCE OF SASKATCHEWAN

Reprinted 1969

SASKATCHEWAN DEPARTMENT OF MINERAL RESOURCES

REPORT No. 67, 1962

RECESSION OF WISCONSINAN GLACIER FROM CENTRAL SASKATCHEWAN

F. H. EDMUNDS

University of Saskatchewan Department of Geological Sciences

Saskatoon, Saskatchewan

ABSTRACT

During the retreat of the last ice-sheet from a position in the vicinity of the Qu' Appelle River valley to one north of Saskatoon in Saskatchewan, two distinct lobes were formed, one occupying the present valley of the South Saskatchewan River and the other the Last Mountain Lake Valley. The character of surficial materials provides evidence for the existence of lakes in front of the melting ice. Delta sands mark inlets to these lakes and the outlets left distinctive channels at various levels.

Evidence for slight postglacial movements has been found.

CONTENTS

TEXT

INTRODUCTION.

ACKNOWLEDGMENTS ... .. .

TOPOGRAPHY AND SURFICIAL DEPOSITS

THEORETICAL CONSIDERATIONS ...

PHASES OF RETREAT .. .

General remarks

Early Lake Regina phase

Late Lake Regina phase

Lake Milden phase ..

Early Lake Elstow phase __ _

Late Lake Elstow phase

Lake Saskatoon phase

REFERENCES ...

ILLUSTRATIONS Figure

1. Index map ..

2. Physiography

3. Surficial Deposits

4. Glacial history-Early Lake Regina phase

5. Glacial history- Late Lake Regina phase

6. Glacial history- Lake Milden phase .

7. Glacial history- Early Lake Elstow phase

8. Glacial history-Late Lake Elstow phase

9. Glacial history- Late Saskatoon phase

Table

1. Topographic sheets . __

2. Phases of ice retrea L

3. Channel data

Page

7

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9

11

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Page

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WYOMING i

100 AREA OF REPORT ~ SCA.LE lN MILES

Figure 1- lndex Map

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INTRODUCTION

It has long been recognized that thert have been changes in the drainage patterns of Central Saskatchewan; at one time, for example, the South Saskatchewan River followed a course from The Elbow into the Qu'Appelle River Valley. This conclusion was first reached by Hind ( 1859 ) who suggested the possibility of again diverting the water of the South Saskatchewan River down the Qu'Appelle River by construction of a dam north of The Elbow. Upham (1890 ) who investigated Glacial Lake Agassiz in Manitoba, realized that parts of Central Saskatchewan were flooded in late glacial time and that the Qµ ' Appelle River valley had formed an outlet for waters of a lake which he called Lake Sask, atchewan. He also considered that other outlets might have existed and suggested a possible drainage through Last Mountain Lake valley. Johnston and Wickenden (1930, p. 46 ) described a glacial lake in the Regina area and stated that it " ... was drained by way of the Qu'Appelle River valley when the ice had retreated far enough to uncover the lower part of the valley near its junction with the Assiniboine".

It is the purpose of the present paper to offer some conclusions arrived at by the writer, with regard to the final retreat of the ice from Central Saskatchewan and to indicate the drainage channels cut at various phases. The area studied, and here referred to as Central Sask, atchewan, is in the central part of the Interior Plains of Saskatchewan and includes stretches of the South and North Saskatchewan Rivers, the Last Mountain Lake valley, and the upper reaches of the Qu' Appelle River valley (Fig. 1; Fig. 2) .

The conclusions are based on studies of topography and surficial deposits . Topographic information was obtained from the map sheets listed in Table I. The surficial deposits were examined during soil surveys and details can be gleaned from the comprehensive report by Mitchell et al. (1947) which is accompanied by soil maps.

TABLE 1

TOPOGRAPWC SHEETS

All sheets used in this study are part of the Sectional Map of Western Canada, on a scale of l inch to 3 miles, with 50 foot contours, published by the Canada Department of Mines and Technical Surveys, Surveys and Mapping Branch, Ottawa.

Number

118 119 .. 168 .. 169 .. 218 .. 219 ....

Name

Rush Lake Regina

The Elbow Touchwood Saskatoon Humboldt

ACKNOWLEDGMENTS

Year oflatest edition

1925 1921 1923 1927 1927 1929

This interpretation of the late Wisconsinan ice retreat in Saskatche, was was presented to Section IV of the Royal Society of Canada at the 1940 meeting. I ts publication at this time is due to the urging of Dr. W. 0. Kupsch and Dr. E. A. Christiansen, who made some editorial changes in the original manuscript, mainly to bring it up to date, and to whom the writer expresses his thanks.

The writer wishes to record his appreciation to his former colleagues in the Soils Department, University of Saskatchewan for the help ac,

7

Figure 2- Physiography

FIGURE 2

PHYSIOGRAPHY SCALE OF MILES

10., ...,...,.,o...,,,..,.;i'° ____ _:2;i:;o;,,,,,,..,i,j'o

LEGEND

Direction of water f low - ·

Spot levels · + 2000

NOTE: Elevations of towns and spot levels ore in feet above sea level.

corded him. He is particularly indebted to the late Dr. John Mitchell with whom he was associated during much of the field work connected with the soil surveys. Thanks are due also to Dr. J. B. Mawdsley for helpful criticism.

Publication by the Saskatchewan Department of Mineral Resources is gratefully acknowledged. Redrafting of maps, originally drawn by Mr. R. B. Cairns, has been done by the Drafting Branch of the Department of Mineral Resources.

TOPOGRAPHY AND SURFICIAL DEPOSITS

The dominant physiographic features of Central Saskatchewan are shown in figure 2; the distribution of surficial deposits is shown in figure 3. The surficial material on the uplands is till, commonly exhibiting a characteristic knob and kettle topography. The tops of many local hills are stony because the finer material has been washed into the depressions; little evidence of gullying is to be seen. While the major part of the till occurs as ground moraine, there are some end moraine belts which are generally on the flanks of the uplands. In the field it is not possible to trace these end moraines clearly over long distances. There is little in; formation on the thickness of the till on the uplands, where, as a rule, water is obtained at a shallow depth, and where consequently there are few deep wells. In the Allan Hills, however, bedrock has been encountered at depths Jess than 100 feet, and exposures of shale can be seen at re; latively high altitudes on The Coteau south of Rosetown. Therefore, it is probable that the broad topographic features of Central Saskatchewan reflect the preglacial topography and that uplands such as the Allan Hills, The Coteau, and Last Mountain, were dissected uplands prior to glaciation.

The main river in Central Saskatchewan is the South Saskatchewan which enters the area at the extreme southwest corner where it occupies a trench 400 to 500 feet deep (Fig. 2 ). Here it has an easterly course and passes through The Coteau upland. South of Riverhurst it bends sharply to the north and flows in a narrow valley some 250 feet deep. At Elbow, northeast of Riverhurst, it makes another sharp bend where the upper part of the Qu' Appelle River valley joins the South Sask, atchewan River valley. A small creek, called Aiktow Creek but referred to by Hind (1859 ) as " the River that Turns", now occupies the upper 12 miles of the Qu'Appelle River valley and flows into the South Sask; atchewan. From Elbow northward the river follows a variable course with valley walls from about 75 to 200 feet in height. The land bordering the river from Riverhurst north is relatively low. Between Outlook and Saskatoon this tract of low land is from 50 to 70 miles wide and for convenience will be referred to as the Saskatchewan Lowland.

The surficial deposits of the Saskatchewan Lowland and of some other relatively low parts of the area are mainly glacio;lacustrine in origin (Fig. 3 ). They include off-shore, near-shore, and deltaic sediments. The off-shore deposits commonly consist of clays, silty clays, and silt loams. The topography of these deposits is level or gently undulating and is dissected by a few relatively shallow gullies, some of which have been eroded down to the till. Fresh excavations in the clay show varves which are easily obscured by weathering. The deltaic deposits are gen; erally sands or sandy loams and occupy level to undulating areas except where wind action caused dunes to form. Some sandy deposits may represent abandoned beaches but, because detailed mapping was not done, the extent of these beaches is not known. At boundaries between Jacustrine material and till, the near-shore fades of the lake deposits is

9

1oe· 106° 105°

Humboldt •

5 2°

0

--+------------ ,,. #ipo,

104° 107°

Figure 3- Surficial deposits

FIGURE 3

SURFICIAL DEPOSITS

SCALE OF MILES 10 o k;;;-;;;.-.;;e;I

10 I

LEGEND

30

Locustrine c loy and silt . ~

Alluvial silt and sand k :-:·:·.·-_· .. · .. :_:] Sand modified by wind .. rt'.X-:Jt}t;i)

Modified til l (portly lacustrine) · ~

Till, including eroded till and outwash · D

commonly eroded stony clay and does not show definite beaches. It is necessary, therefore, to deduce in places the height of the former highest Jake level from the elevation of these indefinite strandlines.

Some of the most interesting topographic features are the deeply cut, wide valleys presently occupied by underfit streams. These valleys, in several places, contain a chain of lakes which almost everywhere can be accounted for by local damming of alluvium brought down into the main valley from tributaries or by slumping of the valley walls. The valleys, such as Thunder Creek in the south, the Qu' Appelle River from The Elbow of the South Saskatchewan to the southeast, the Anerley Channel between Rosetown and The Elbow, the Blackstrap Coulee southeast of Saskatoon, the Watrous and Lewis Channels to the northeast and south, east of the Allan Hills, and the Wakaw Channel in the northeast of Central Sctskatchewan (Fig. 2 ), were spillways of glacial lakes. Evidence for this contention is provided by the presence of lake clays at elevations closely corresponding to the heights of the divides through which these valleys were cut and by sand areas at the mouths of rivers which once occupied the channels. It is conceivable that under special conditions subglacial water-erosion might have taken place, but it is not possible that the above named valleys were formed in this manner.

THEORETICAL CONSIDERATIONS

At the outset of the present study it was intended to delineate the glacial lakes of Central Saskatchewan and to reconstruct the drainage of these lakes using information provided by topographic maps and field, work. As the work progressed it became obvious that definite positions of the ice front, which formed barriers to northeasterly drainage, had to be assumed in order to account for the drainage pattern at any one time. As far as possible, the distribution of surficial deposits and drainage was explained on the one premise that blocking by the ice front had occurred. Only if the drainage history and the distribution of sediments could not be explained that way, was it assumed that earth movements had taken place. The possibility of local re-advances was considered, but as definite proof of these in Central Saskatchewan is still lacking, they are not used in the explanation of anomalous features or events.

In figures 6 and 7 the ice front is shown with two lobes and a marked re-entrant. Comparison with figure 2 shows that the lobes occupy low, lands and that the re-entrant corresponds to an upland area. This re, construction is based on many field observations and map interpretations and, to some extent, also on theoretical considerations. Preglacial topo, graphy must have exerted a great influence on the local movement of the glacier, particularly near the ice front, where the ice was not sufficiently thick to override the uplands. The invading ice tends to advance further in the lowlands, forming Jobes. During recession the ice will also form lobes in the lowlands as it disappears first from the uplands where it is thinner.

The position of the center of accumulati.on of the glacier also influ, ences the shape of an ice sheet and its front . There is no evidence for the former presence of local centers of accumulation anywhere in Central Saskatchewan, and the center was apparently remote during the phases of deglaciation discussed in the present paper. The influence of this remote center of accumulation was much less pronounced than the influence of the local topographic relief.

11

1oa0 101• 105• 10 4•

// /~

,,.

~

- ~ }:::; N

Figure 4- Glacial history- Early Lake Regina phase

52 •

FIGURE 4

GLACIAL HISTORY EARLY LAKE REGINA PHASE

SCALE OF MILES 10 0 ~ 20 ~

L EGEND

Ice front

Ice front of 2400 to 2350 foot . . . . . . . . ..., , Lake Stewart Volley ,

Ice · ····E~ Glacial lake ( elevation in feet) · · · · · · ~~ a Meltwoter channel · · · · · · ~

Direction of meltwater flow

Sand ·

NOTE: Outlet of water from Loke Stewart Volley until the level hod follen to obout 2350 feet , and the ice front retreated to neor Beechy · · · · · · 2400\

PHASES OF RETREAT

General Remarks

It was found convenient to designate the phases of ice retreat by reference to the glacial lakes in existence at that time. No attempt is made to correlate these phases with others recognized outside Central Saskatchewan because lack of detailed investigations in most neighbour, ing areas prevents any reasonably certain correlations. It is hoped, how, ever, that the phases discussed here may be of value in deciphering the late glacial history, not only of Central Saskatchewan but also of other parts of the Interior Plains.

No attempt was made to estimate the actual time in years occupied by the various phases; only their chronological order is discussed. Table 2 provides a summary of the phases recognized, indicating the drainage conditions. Each phase is illustrated by a map (Figs. 4,9 ) showing the paleogeography at the time.

Name of Phase

Youngest

Lake Saskatoon

Late Lake Elstow

Early Lake Elstow

Lake Milden

Late Lake Regina

Early Lake Regina

Oldest

TABLE 2

PHASES OF ICE RETREAT

Figure

9

8

7

6

5

4

Drainage

North, through Wakaw Channel

East, through Watrous and Last Mountain Lake Channels to the Qu'Appelle River Valley.

From Saskatchewan Lowland through the Qu'Appelle River valley. From Lake Elstow through Lewis and Las t Mountain Lake Channels.

East, through Qu ' Appelle River Valley.

From Lake Rosetown through Anerley Channel to Lake Regina.

East, through Thunder Creek to Lake Regina.

Early Lake Regina Phase

During the time of the Early Lake Regina phase only a small area in the southwest of Central Saskatchewan was free from ice, and, therefore, much of the following description refers to conditions outside the map area shown in figure 4. When the ice was at the position shown by the broken line in figure 4, slightly prior to the Early Lake Regina phase, it ponded the drainage to the west and Lake Stewart Valley formed. The occurrence of lake clays in this southwestern corner of Central Sask, atchewan indicates that the highest level of Lake Stewart Valley was at an altitude of 2400 feet. On retreat, the ice margin moved northeasterly and a spillway of Lake Stewart Valley cut a short channel (now occupied by the South Saskatchewan River ), of fairly steep gradient through The Coteau, to drain Lake Stewart Valley eastward and to flood the country near Beechy to an altitude of 2200 feet. Lake Beechy drained through Thunder Creek, an ice-marginal channel, into Lake Regina which was then in existence as a glacial lake to the southeast and which in turn drained south,easterly through the Souris River channel. It seems likely that the sands shown at the mouth of Thunder Creek in figure 4 represent deltaic deposits of the Early Lake Regina phase and that the till directly north of Thunder Creek represents a recessional moraine formed during

13

Figure 5- Glacial his tory- Late Lake Regina phase

FIGURE 5

GLACIAL HISTORY LATE LAKE REG INA PHASE

SCALE OF MILES 10 10 2,0

LEGEND

Ice front ·

Ice front of 2050 feet . Lake Rosetown

Ice

Glacial lake { elevation in feet) ·

Meltwoler channels

Direction of mettwoter flow

Sand ·

,o

... ... , '

·· ~

-F~l[~~3

this phase. Thunder Creek valley was eroded almost to its present depth, which means a downcutting of about 170 feet, before the ice moved far enough north to permit drainage along the ice front at a lower elevation than during the Early Lake Regina phase. Once retreat started in this part of the area it was probably fairly rapid until the ice was just north of the Q u' Appelle River valley, where another recessional moraine was formed during the next phase (Fig. 5 ).

Late Lake Regina Phase The Late Lake Regina phase commenced when the ice had retreated

north of the Qu' Appelle River valley and thus allowed Lake Regina to expand along the Saskatchewan Lowland to near Elbow, and from there south where the part of the South Saskatchewan River valley to River­hurst became flooded (Fig. 5 ).

Northwest of Elbow the largest lake was Lake Rosetown which drained to the southeast through the Anerley Channel, which was cut through a nort herly projecting spur of The Coteau. The Anerley Channel is a trench about 150 feet deep and could only have been formed when an almost stationary ice front lay directly adjacent to it to the northeast. A retreat of the ice over a distance of 6 miles would have exposed land lower than the level of Lake Rosetown and would have permitted all the water from that lake to join Lake Regina. The height of the divide at the inlet of the Anerley Channel is 2050 feet and this is the approximate height of the highest strandline of Lake Rosetown as corroborated by the altitude of lake deposits on the flank of The Coteau to the west. The bottom of Anerley Channel is at about 1880 feet, so that final erosion of the channel must have taken place at the end of the Late Lake Regina phase when Lake Regina had almost completely drained down the Qu'­Appelle River valley. On the west side the ice front was retreating more rapidly than near the inlet of Anerley Channel, and two positions of the ice front relating to the 2050-foot and the 1950-foot levels of Lake Rose­town are indicated in figure 5.

To the east, outside the map area of Central Saskatchewan, a lake was evidently in existence in the Qu' Appelle River valley area north of Indian Head. From the location and altitude of this lake it can be con­cluded that it could have existed only before Lake Regina drained down the Qu' Appelle River. Another smaller lake near Cu par (Fig. 5 ) can be explained as an ice-marginal lake with the ice front trending almost north-south. When Lake Cupar existed, the eastern part of the Qu' -Appelle River valley was free from ice which formed a lobe occupying the Saskatchewan Lowland, overriding the Allan Hills, and filling the Last Mountain Lake valley. The moraine north of the Anerley Channel and the Qu 'Appelle valley, extending towards Chamberlain can be considered the recessional moraine of the Late Lake Regina phase.

Lake Milden Phase Lake Rosetown, which existed during the previous Late Lake Regina

phase, diminished when drainage was possible around the northern edge of the Anerley spur of The Coteau, and its place was taken by a lower, and smaller lake, here named Lake Milden (Fig. 6 ). The strandlines of Lake Milden are ill-defined, but in figure 6 the lake is depicted as it is thought to have been at the 1850-foot level. Some indication of the presence of the lake at this level is given by the altitude of lake clays along the edge of Eagle Hills; some deltaic sands confirm the position of the lake's strandline at the 1850-foot contour. Lake Milden drained south along the South Saskatchewan River channel to Elbow and thence down the Qu'Appelle River valley.

15

108°

52•

6 Glacial history Figure -

,o,;_-_·---~----;--

~ 104°

Touchwood •

- Lake Milden phase

FIGURE 6

GLACIAL HISTORY LAKE MILDEN PHASE

SCALE OF MILES 10 0 10 20 ,o

LEGEND

Ice front

Ice ·

Glacial loke ( elevation in feet) .

Meltwater chonnels . ····---~

Direction of meltwoter flow

Sand

It is probable that during the Lake Milden phase a re-entrant formed in the ice front to the south of and on the Allan Hills and that lobes of ice extended south on either side of the hills; the eastern lobe occupying Last Mountain Lake valley, and the western, the Saskatchewan Lowland (Fig. 6 ). Squaw Creek and Arm River, both at present underfit streams occupying large valleys, drained the re-entrant.

Early Lake Elstow Phase It is desirable to make reference to the surficial deposits of the Elstow

area before discussing the drainage of the Lake Elstow phases (Figs. 7 & 8 ). Directly north of the Allan Hills the deposits are variable. Typical glacio,lacustrine clays, in places with varved banding, occupy the lower areas up to an elevation of 1750 feet . Above this elevation there are mixed lacustrine and till deposits. Silty sediments on the tops of local hills show that flooding must have reached the 1850 foot level, although there is no clear evidence of a shoreline at that level.

At present, a lowland occupies the area west of Lake Elstow, and it could be inferred that the Elstow district was flooded by an .easterly projecting arm of a lake in the Saskatchewan Lowland when the ice stood at about the latitude of Saskatoon. This interpretation is, however, unlikely because Blackstrap Coulee, which leads into the Elstow district, can be explained only by assuming an ice barrier between the coulee and the lowland to the west. Moreover, a moraine area near Saskatoon shows no signs of flooding above the 1750,foot level, whereas the Elstow district shows flooding up to 1850 feet. Therefore, during the Early Lake Elstow phase, Lake Elstow is regarded as an ice-marginal lake dammed by ice on the west and east with bordering lands to the south.

Three drainage channels were connected with Lake Elstow; two on the east side and one on the southwest side. One of the channels on the east side of Lake Elstow, here named the Lewis Channel, lies about 3 miles west of Simpson and trends nearly south. The other channel on the eastern side of Lake Elstow is the Watrous Channel (Fig. 8 ) which has a west to southeast direction, and part of which is now occupied by Little Manitou Lake. The third channel, on the southwest side of Lake Elstow, is Blackstrap Coulee, a deeply cut drainage way now occupied by a series of shallow lakes. For each of the three drainage channels the altitude of highest flooding was determined as well as the altitude of the lowest part of the valley bottom near the head of the channel (Table 3 ). The top altitude of a channel provides the level at which a lake first spilled over, and the bottom altitude gives the minimum depth to which downcutting ultimately was achieved. Not enough information could be obtained to determine the thickness of alluvial fill in the valleys. The presence of such alluvium would indicate downcutting to a greater depth than the min, imum.

Name of Channel

Youngest Watrous .. . Lewis Blackstrap

Oldest

T .

32 28-31 31-33

TABLE 3

CHANNEL DATA

Top LOCATION altitude

near head R. W.Mer. (feet)

24,26 2 1780 26 2 1850 3-4 3 1850

17

Bottom altitude Length of

near head channel (feet) (miles)

1660 15 1780 28 1730 9

-co

Figure 7- Glacial history- Early Lake Elstow phase

FIGURE 7

GLACIAL HISTORY EARLY LAKE ELSTOW PHASE

SCALE OF MILES 10 10 20

LEGEND

Ice front

Ice

Glacial lake (elevation in feet) ·

Meltwater channels · ·

Direction of meltwa ter flow

Sand

,o

' ··· ~

Study of the topographic data of Table 3 and of the field relation, ships suggests the following sequence of events for Lake Elstow. Lacus, trine clays a short distance west and south of Hanley occur to an altitude of slightly over 1850 feet which is also the approximate height of the divide through which Blackstrap Coulee was cut, and which is somewhat higher than the level of Lake Els tow. It is therefore suggested that north-flowing water from the lake near Hanley commenced the erosion of Blackstrap Coulee which is situated across a local height of land in a characteristic side,hill position that can only be explained if the channel was ice,marginal to a lobe separating the Hanley area from Lake Swanson in the Saskatchewan Lowland (Fig. 7 ). Lake Swanson, at a level about 50 feet lower than the lake near Hanley and Lake Elstow and separated from them by a lobe of ice, drained southward through the South Sask, atchewan River valley into the Qu'Appelle River valley. Lake Elstow also drained south into the Qu'Appelle River valley, but the water followed a route through the Lewis Channel and the Last Mountain Lake valley, thus cutting the Lewis Channel down to about 1780 feet. When the ice lobe in the Last Mountain Lake valley retreated farther north and opened up land lower than 1780 feet, the Lewis Channel was abandoned in favor of the Watrous Channel which was eroded down to 1660 feet, during the next or Late Lake Elstow phase (Fig. 8 ). This allowed Lake Elstow to drain and Blackstrap Coulee to be cut down to 1730 feet.

As depicted in figure 7, during the Early Lake Elstow phase, when the Saskatchewan Lowland was occupied by a broad ice lobe, the Elstow district lay in a pronounced re-entrant, and a narrow lobe filled the upper part of the Last Mountain Lake valley. Justification for the postulation of the Last Mountain Lake lobe can be found also in the surficial geology of the area now occupied by the Quill Lakes in the eastern part of Central Saskatchewan. At present the Quill Lakes lie in an interior drainage basin at an altitude of 1703 feet. A slight rise in water level would cause the lakes to overflow to the southwest into the Last Mountain Lake valley. During glacial times lake clays were deposited in the Quill Lakes basin to a height of 1750 feet and the westerly drainage into Last Mountain Lake valley must have been blocked by ice for the water to rise to this level. A now abandoned outlet of the Quill Lakes to the east can be traced along a wide channel which connects the lakes with the White Sand Creek valley.

The assumed presence of a Jobe in the Last Mountain Lake valley is, therefore, not only justified by the damming of the Watrous Channel area of Lake Elstow to permit erosion of the Lewis Channel in an ice, marginal position on the west side of the lobe, but also on the east side by the damming of the outlet of the Quill Lakes into the Last Mountain Lake valley to raise the lakes above the level of their present outlet and to force them to drain to the east through the White Sand Creek channel.

Late Lake Elstow Phase The Late Lake Elstow phase commenced when the ice had retreated

far enough north from the Last Mountain Lake valley to permit the water of Lake Elstow to pass over the Watrous divide at about 1780 feet altitude (Fig. 8 ) . When downcutting of the Watrous Channel commenced and the channel was lowered below 1780 feet, Lake Swanson instead of draining south (Fig. 7 ), started to drain northeasterly through the Blackstrap Coulee into Lake Elstow and from there through the Watrous Channel into the Qu'Appelle River valley (Fig. 8 ). The reach of the South Saskatchewan River valley between Elbow and Outlook now became temporarily dry because the South Saskatchewan River con, tinued to flow from Elbow southeasterly into the Qu' Appelle River valley (Fig. 7).

19

Biggar

Rosetown

Milden•

c-_-_-_-_:, \_-_----~

,:-=-=-=-=~ ,,.... ,:::._ :_-_-_-_-_-_; ----= LAKE :...-_-,,

,=-':.WAKAW:!, i----_ 1eso -:...-_] ,:_-_----?---_-_,

/~~, ::-..;;, -..,

Figure 8 - Glacial history- Late Lake Elstow phase

FIGURE 8

GLACIAL HISTORY LATE LAKE ELSTOW PHASE

SCALE OF MILES 10 10 20 30

LEGEND

Ice front ·······················'-

Ice ~ Glocial loke {elevation in feet) · ··[ R~§:3 Meltwoter channels · · · · · · • · · • · · • · - · · · · · ~

Direction of meltwoter flow

Sand

This sequence of events is likely because the level of the South Saskatchewan River at The Elbow during the initiation of the Late Lake Elstow phase is believed to have been 1780 feet or about the same height as the Watrous Channel when that channel was first opened up. The level of the South Saskatchewan River at The Elbow is arrived at by extrapolation of the height of the present divide in the Qu' Appelle River valley, which is 12 miles southeasterly of The Elbow at an elevation of 1750 feet. If the same gradient as the present 2.6 feet per mile for the lower Qu' Appelle River is assumed for the upper 12 miles, a height of 1780 feet at The Elbow can be derived.

The lowering of the level of Lake Swanson was accompanied by the development of a stream in the abandoned reach of the South Saskatche, wan River valley between The Elbow and Outlook. This stream flowed north in the valley and drained into Lake Swanson. I ts head moved gradually from Outlook to The Elbow by headward erosion and finally captured the South Saskatchewan River at The Elbow, thus diverting the South Saskatchewan River to the north and reversing the gradient of the channel previously occupied by the south-flowing stream which drained Lake Swanson. The upper reaches of the Qu' Appelle River then ceased to be an important drainage channel. This diversion was accom, plished sometime at the beginning of the Early Lake Saskatoon phase (Fig. 9 ), when the water of the South Saskatchewan River could drain into Lake Saskatoon and from there to the northeast to lower ground.

It is believed that during the Late Lake Els tow phase the Last Mountain Lake ice lobe separated from the still active glacier in the Saskatchewan Lowland, stagnated, and finally wasted away. This allowed flooding of the Carrot River valley area, north and east of Central Sask, atchewan, by a westerly projecting arm of glacial Lake Agassiz. The northern part of Lake Elstow (Fig. 7 and Fig. 8 ) then separated from the southern part and formed a separate lake, here named Lake Wakaw which drained northeasterly into the Carrot River valley. The deposits of Lake Wakaw are shown in figure 3 as modified till, in part lacustrine. Although the exact origin of these deposits is not fu lly understood they are regarded as having been covered by a Jake because deposits in this belt of relatively low, rolling country are commonly silty, and banded silts can be seen on the tops of some hills .

Lake Saskatoon Phase The last phase in the retreat of the Wisconsinan glacier from Central

Saskatchewan, here termed the Lake Saskatoon phase, was initiated when the drainage of the Saskatchewan Lowland was through the Wakaw Channel to the northeast into glacial Lake Agassiz (Fig. 9 ). The main feature of this phase, Lake Saskatoon, was an extensive lake fed from the west by the North Saskatchewan River and from the south by the South Saskatchewan River. Both rivers formed sandy deltaic deposits where they entered the lake. In figure 9 the probable extent of Lake Saskatoon as it existed at the 1700,foot level is shown, with a small projection of the Saskatchewan Lowland ice lobe still in the area. On the southeast side of the lobe a relatively narrow border was flooded and lacustrine clays and silts were deposited. A series of morainic ridges at the present location of the South Saskatchewan River were probably formed during the Lake Saskatoon phase. An extensive tract of fairly level land underlain by gravel west of the present South Saskatchewan River valley near Saskatoon, probably represents outwash from the retreating ice where the lake was shallow.

It is not clear why the North Saskatchewan River eventually took a course to the north instead of joining the South Saskatchewan River near

21

,,. r---------- ---' - -1--------+----- -j"" e Cupor

Figure 9- Glacial history- Lake Saskatoon phase

FIGURE 9

GLACIAL HISTORY LAKE SASKATOON PHASE

10

Ice front

Ice

SCALE OF MILES 10 20 ,o

LEG END

········ ··· ··· '-. ~

Glociol loke (elevation in feet) · .... [~§:3 Meltwoter channels ·

Direction of meltwater flow

Sand ····· ··· ········· ·· ··· ·· ·~

Saskatoon. The divide through which the North Saskatchewan has cut north of its elbow is at least 1700 feet in altitude, whereas a course to the southeast from the elbow to Saskatoon would be in country as low as 1650 feet (Fig. 2 ). It is possible that postglacial uplift in the northern part of the Saskatchewan Lowland has to be invoked to aid in the solu, tion of this problem, but as long as the area north of Central Saskatche­wan has not been studied it is too early to rule out other possibilities, such as capture.

Most of the features and postulated events in Central Saskatchewan during Wisconsinan deglaciation can be explained without recourse to earth movements. As discussed above, uplift to the north in the Sask, atchewan Lowland could be suggested to account for the present channel of the North Saskatchewan River through a high morainic belt north of the area. Similarly, the cessation of drainage through the Wakaw Channel and the establishment of the present South Saskatchewan River valley farther to the west could imply postglacial uplift in the northern part of Central Saskatchewan. Neither locality, however, has been studied in detail and, moreover, detailed contour maps are sti ll lacking.

The present relief features of Last Mountain Lake also suggest post, glacial differential movement (Fig. 2 ). From Little Manitou Lake in the Watrous Channel to the north end of Last Mountain Lake there is no eroded valley, but the country here is a rather fl a t, sandy plain. It is possible that in Late Lake Elstow time, the water fo llowed a varied course over this plain as a braided stream. The northern part of Last Mountain Lake is less than 10 feet deep and there are no high banks. In the middle part, soundings show that the depth increases to a maximum of 90 feet (Anonymous. 1954 ), and here there are no banks. Farther south, there is a gradual rise in the banks to 150 feet and a shallowing of the water to 10 feet or less. Considering that this channel was cut by erosion and that it presumably had a fairly uniform gradient, the features now present could be explained by warping, with a relative downward movement near the middle of the lake. Further work is necessary before a clear idea of the nature and magnitude of this warping can be given. Particularly, a study of local readvances during the general retreat of the Wisconsinan glacier, to be accomplished through stratigraphic investigations, appears to be necessary. The writer is well aware that the history of retreat as outlined in this paper is based on continuous retreat and that possible disturbances by local readvances have not been considered, mainly because the necessary informa tion is still lacking.

REFERENCES ANONYMOUS, 1954, Last Mountain Lake, Depth soundings in feet : Prov. Sask ., Tourist

Branch, map. BRETZ, J . HARLEN, 1943, Keewatin end moraines in Alberta, Canada: Geo I. Soc. America

Bull., v. 54, p. 31-52. EDMUNDS, F. H ., 1940, Some stages in the recession of the Pleistocene ice from Saskat,

chewan (abstract) : Royal Soc. Canada Proc., 3d ser., v. 34, app. D, sec. 4, p. 161.

HIND, H . Y., 1859, Northwest Territory. Reports of progress together with a prelim, inary and general report of the Assiniboine and Saskatchewan exploring expedition: Toronto, 201 p.

JOHNSTON, W. A. and W1cKENDEN, R. T . D ., 1930, Glacial Lake Regina, Saskatchewan, Canada: Royal Soc. Canada T rans. , 3d ser. , v. 24, sec. 4, p. 41-49.

MITCHELL, J ., Moss, H . C., and CLAYTON, J. S., 1947, Soil survey of Southern Sask, a tchewan from township I to 48 inclusive : Univ. Sask., Sask. Soil Survey Rept. 12 (sec. ed .).

UPHAM, WARREN, 1890, Exploration of the glacial Lake Agassiz in Manitoba : Geol. Survey Canada Ann. Rept. (New ser. ) , v. 4, 1888,1889, Rept. E, 156 p .

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REGINA, SASKATCHEWAN

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Reprinted 1969