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Physiographic Division | Geology of the Kazan Upland | Physiography of the Kazan Upland | Manitoba Lowland | Ancient Erosion | Tertiary Erosion | Glacial Erosion and Deposition | Glacial Lake Deposits | Postglacial Events

Physiographic Division

The Precambrian Shield forms the core of Canada and is composed of old, massive crystalline rocks. The surface of this core "resembles that of an inverted dinner plate with its flat, slightly depressed centre (Hudson Bay Basin) and an outward shelving rim terminated by a steep edge" (Bostock 1970: 10).

The geological boundary between the Precambrian Shield and the area underlain by Phanerozoic rocks is also the boundary between the two main physiographic divisions of the study area: the Shield and the Borderlands. [This boundary follows a line from La Ronge south-east to Wapawekka Lake, Ballantyne Bay, and Amisk Lake.]

Bostock (1970-map) divides the Shield into several regions. The Churchill-Reindeer rivers area is part of the Kazan Region. The latter can be further divided into various physiographic units, of which only the Kazan Upland concerns us here, as the entire Shield portion of the study area lies within its boundaries.

Similarly, the Borderlands have their regions and units. Only the Interior Plains Region, and within it the Manitoba Escarpment, is of interest in the following discussion.

The Interior Plains Regions is part of a chain of lowlands, plains, and plateaux of gently dipping, Phanerozoic sedimentary rocks overlying the rim of the Shield. Within the study area, Manitoba Plain is the term used for the lowlands to the south of the Shield. It is separated from the higher Saskatchewan Plain to the west by the Manitoba Escarpment, of which the Wapawekka Hills, south of the lake of the same name, are a part (Map 2).

The boundary between the Manitoba Plain and the Saskatchewan Plain may be drawn best at the 1,450-foot contour, the height of the upper strandline of Glacial Lake Agassiz south of Lac La Ronge (Langford 1973: map). The Manitoba Plain is covered by some washed till but mainly by extensive lacustrine sediments laid down in Lake Agassiz. These surficial deposits in turn lie on rocks of Ordovician and Silurian age in the eastern part of the study area. Farther west they lie on Cretaceous rocks. The presence of Devonian rocks on the south-west side of Lac La Ronge is uncertain. No outcrops have been encountered, but the occurrence of erratics containing Devonian fossils may indicate rocks of that age beneath the drift.

The Manitoba Escarpment is the erosional edge of gently westward dipping sedimentary rocks, mainly sandstones and shales, of Late Cretaceous age. Seven major re-entrants in the escarpment, formed by preglacial river systems, divide it into a series of cuestas each from 20 to 100 miles long. Major streams flowed through these re-entrants during deglaciation and discharged north-eastward into the Hudson Bay region (Elson 1967: 40)

The lowest elevation of the study area is 855 feet, at The Pas in the south-east corner. The highest is in the Wapawekka Hills, which reach a maximum altitude of 2,500 feet. The Foster Lakes are at approximately 1,687 feet and Reindeer Lake at 1,106 feet.

The drainage of Wapawekka, Deschambault, Wood, Pelican, and Amisk lakes, all south of the Churchill River, is in a south-easterly direction through the Sturgeon-Weir River into the Saskatchewan River. The northern part of the study area drains into the easterly flowing Churchill River. One of the largest tributaries of the Churchill, the Reindeer River, drains Reindeer Lake and the surrounding country.

Wollaston Lake, in the north-western corner, occupies a unique position; it drains by the Cochrane River into Reindeer Lake and by the Fond-du-Lac River into Lake Athabasca. Both of these rivers are outside the study area, but they are mentioned here to call attention to the fact that some water flows from Wollaston Lake south and east to Hudson Bay via the Churchill River and some flows north-west to reach the Arctic Ocean via the Mackenzie River.


Geology of the Kazan Upland

The Canadian Shield has been divided into several structural provinces based on overall geological differences in regional structural trend and style of folding. These provinces have been rendered more distinctive by the isotopic dating of orogenies that occurred within them (Stockwell et al. 1970: 44-45).

The Churchill Province includes the Precambrian Shield of the Churchill-Reindeer rivers area. In contrast to adjacent provinces it exhibits pronounced northerly or north-easterly trends of gneissic and schistose structure, bedding, formational boundaries, and narrow magnetic anomalies, all contributing to a well-developed "grain" in the landscape. Linear trends commonly represent the surface traces of major faults or long tight folds. Curved ones (which are well developed in some parts of the area) may represent more open folds or, most commonly, the convex margins of intrusive masses, such as batholiths and stocks.

Among the oldest rocks recognized are lavas that flowed out of fractures on to the sea floor, near Flin Flon. The individual flows were several feet to several tens of feet thick. Some sediment, derived from islands arranged in an arc, was deposited between successive outpourings of lava, but most sediment appears to have been laid down after the main period of volcanic activity.

Younger Precambrian rocks, probably formed in a north-easterly trending geosyncline or marine depositional basin bordering older Precambrian rocks of the Superior Province to the east. Eventual compaction and consolidation of the sediments resulted in their becoming sedimentary rocks.

The Aphebian sedimentary succession generally consists of a basal quartzite with lenses of conglomerate and greywacke over lain by argillite, carbonates, thinly bedded greywacke, and impure quartzite. Basic volcanic rocks occur locally near, or at, the top of the sequence (Stockwell et al. 1970: 86). Individual layers of sedimentary rock range from a fraction of an inch to several feet in thickness.

Following this period of sedimentation the volcanic and sedimentary rocks were crumpled and, in places, broken and sheared by large fractures or faults during an episode of folding and mountain building known as the Hudsonian Orogeny. Isotopic or radiometric dating shows that the Hudsonian Orogeny spanned a time interval from about 2,000 to 1,600 million years ago and had its culmination approximately 1,735 years ago.

During the Hudsonian Orogeny granitic magrna, or molten rock, rose from deep within the earth, filling fractures and partly replacing the volcanic and sedimentary rocks. This material cooled and crystallized before reaching the surface, thereby forming intrusive igneous rock bodies of various types, such as large batholiths or smaller stocks (DMR 1974: 8). The granitic intrusive rocks in the study area are mainly biotite or hornblende-biotite granodiorite or quartz diorite.

The rocks were subjected to varying degrees of change or metamorphism as a result of intense heat and pressure during the Hudsonian Orogeny. The sedimentary rocks became gneisses and schists, the volcanic rocks greenstone and hornfels, and the granitic rocks gneisses. In those places where gneisses, Archean in age, became rejuvenated, it is impossible to separate them from Aphebian rocks. Maps, therefore, may show Aphebian-Archean complexes.

Occupying a large area between Flin Flon and Reindeer Lake, gneisses occur which are referred to as the Kisseynew Gneisses. Deformation and metamorphism during the Hudsonian Orogeny obliterated the stratigraphic relationships of these gneisses to the surrounding rocks, destroying evidence for the age of the rocks.

The following summary of the history of sedimentation and deformation in the Shield, which is the basement complex of Precambrian rocks in northern Saskatchewan, is provided by Byers, Caldwell, and Kupsch (1969 ):

Some of the older rocks of the basement complex are volcanic in origin and accumulated as lava flows, ash beds, and thick lenses of fragmental rock blown out during eruptions of explosive violence. The volcanoes formed chains of islands in an ancient sea, and one such chain extended in a great arc from Flin Flon to La Ronge and then north-eastward to Reindeer Lake. Muds, sands, and gravels, derived from the weathering and erosion of these volcanic rocks, were deposited on the sea floor surrounding the volcanic belts. Near the volcanoes, as at Flin Flon, for example, these sediments became intertongued with the lava flows and other volcanic rocks, but farther away, as between Foster and Wollaston Lakes, they formed an uninterrupted sedimentary sequence.

Toward the close of this period of volcanism and sedimentation, the region was uplifted and the rocks were subjected to folding and fracturing. Weathering of exposed rocks was rapid, and rivers eroded the land surface, carrying loads of mud, sand, and gravel into adjacent shallow seas. The Missi Series, near Flin Flon, is one group of rocks probably produced by this sequence of events.

There followed a long period of earth movement. Huge mountain ranges were formed and, over much of Saskatchewan, the landscape was, similar to that of the western mountains of North America today. The north-easterly trend of these ancient ranges is evidenced by the relict "grain" of the present-day topography.

Accompanying deformation, molten material welled up from depth, forced its way into the volcanic and sedimentary rocks, and there cooled slowly, much of it crystallizing to form large masses of pinkish-grey granite (composed mainly of feldspar and iron- magnesian silicates). Since this activity occurred well within the crust, where temperatures and pressures were high, many of the sedimentary and volcanic rocks were recrystalized or even completely reconstituted to form metamorphic rocks, such as gneisses and schists.

Development or regional fractures or faults, in three prominent sets trending north-east, north, and north-west, marked the final episode in the deformational history. Along some of these faults, relative movement of the order of thousands of feet vertically or horizontally took place.

Erosion over a period of hundreds of millions of years then reduced the rugged landscape to a gently undulating plain. In this process, the masses of granite, schist, and gneiss were exhumed, and, at the close of Precambrian time, the land surface exhibited a complicated pattern of rocks similar to that of today.


Physiography of the Kazan Upland

All parts of the Canadian Shield from the Northwest Territories to Labrador, are remarkably similar in their subdued regional relief. The Kazan Upland typifies this characteristic (Figure 1). "Viewed from some prominent summit the landscape presents an even, monotonous skyline interrupted by round or flat-topped monadnocks and ranges of hills. The smooth horizon is evidence of an old . . . erosion surface . . . " (Bostock 1970: 10).

The Shield is a terrain of great areas of massive rocks which form broad sloping uplands, plateaux, and lowlands - a rather expressionless, rolling surface, with lakes, swamps, or muskegs occupying the valleys and depressions between the low hills and ridges.

Water occupies as much as 35 to 40 per cent of the surface of the study area. The great number of lakes on the Shield often is attributed to the glaciations that affected the region during Pleistocene time. The Shield and the Interior Plains were covered equally by ice, but they show distinctive differences, both in numbers and outlines of their lakes. The amount and type of water coverage is clearly dependent on the reaction of the bedrock to glacial erosion. The Shield, with its hard, much folded, faulted, and fractured rocks of differing resistance to erosion, had its "grain" etched by the glaciers. The softer, areally homogeneous Paleozoic rocks, in which prominent structural weaknesses are absent were overridden by the ice with little or no modification. The generally loose, poorly indurated Cretaceous sands and shales on the Interior Plains supplied much of the finer fraction of the material deposited by the glaciers.

Kettle FallsAlthough the surface of the Shield is rough and knobby in detail with small vertical cliffs or precipitous slopes of solid rock along some valleys and lake shores, the local relief in the study area generally does not exceed 300 feet; it is mostly under 200 feet. The horizon of this surface appears almost as a straight line when viewed from a distance. Its complex erosional history, with which we shall later concern ourselves, is not yet understood in detail. (See photo left: Precambrian terrain, Kettle Falls, Churchill River. Photo: W.O. Kupsch, 25/06/1974).

Streams on the Shield exhibit a more or less crudely developed trellis pattern in which the main lines follow long straight lineaments, major fracture zones, or dominant joint systems in massive rocks. Differences in the resistance to erosion of layered rocks also may control a drainage pattern, the streams, guided by the sinuous twists of the folds, developing S-shaped lakes and curving valleys (Bostock 1970: 11).

Ambrose (1964: 821), who discusses the relationships between lithology, structure, and topographic relief, remarks of the Flin Flon area:
Even the smallest details of locations and forms of hills, streams, and lakes are controlled by structure ... Relief is small, with few hills rising more than 75 and none more than 200 feet above the encircling depressions. The country in general is nearly a plane, but in detail the surface is extraordinarily uneven, for it consists of a continuous succession of low, rounded rock hummocks, each a few tens of feet high, separated from each other by narrow strips of moss-filled swamp.

The larger relief features, apart from a few valleys along faults, result from differences in resistance to erosion of the three principal rock types: granite, greenstone, sedimentary rocks. The smaller relief features developed on each type have an individuality of form which expresses the structural peculiarities of the rock. Granite tends to form uplands with swampy surfaces broken by low isolated outcrops, whose rounded, more or less equidimensional shapes are controlled in part by steeply-dipping ,joint planes. Gneissic granite tends to form ridges parallel with the foliation. The greenstones form uplands with uneven surfaces, though locally, where rocks are well jointed or schistose, the forms of the hummocks are evidently controlled by foliation planes.

These remarks are applicable to all of the Churchill-Reindeer rivers area, as are the following words of Alcock (1920: 9) who wrote about northern Manitoba:

The topography of the region is in close harmony with the geological structure. The dominant trend of the rocks is north-east and their general direction is expressed by parallel strike ridges and by the main drainage lines. There is also a close relation between the topography and the type of bedrock. As a rule, the streams and lakes lie in the softer gneisses and schists, whereas the interstream areas are composed of the more resistant granite.

In the immediate impact area of the Churchill River Study (along the Churchill River from Drinking Lake in the west to Wintego Lake in the east and along the Reindeer River to Reindeer Lake), Roed (1973) recognizes four main physiographic patterns. From west to east these are:
(A) a predominantly arcuate physiographic pattern in intrusive igneous rocks of granitic composition,
(B) a strong, northerly trending, linear pattern with rectangular lakes along fault zones west of and parallel to the Reindeer River,
(C) joint-controlled benches, or terrace-like landforms in bedrock, bounded by short linear scarps and valleys developed in the metamorphosed rocks belonging to the Kisseynew Gneisses which are exposed east of the Reindeer River,
(D) distinctly north-east trending valleys in the Kisseynew Gneisses to the east of (C).


Manitoba Lowland

Two of the most obvious physiographic distinctions between the Kazan Upland and the Manitoba Lowland are the presence of fewer lakes and the absence of any visible structural control in the area south of the Shield. Rather than the elongated irregular lakes with much indented shorelines found on the Shield, the lakes of the flat-lying Paleozoic rocks tend to be round or oval with smooth shorelines. This "contrast in shorelines is so marked that an approximate geological boundary between the Precambrian and the Paleozoic areas might be drawn from a drainage map alone" (Ambrose 1964: 821-822).

The presence of outliers of Paleozoic rocks on the Precambrian Shield in Ontario and Manitoba leaves little doubt that the sea covering Western Canada at that time extended across the Shield and connected the Interior with the Hudson Bay depositional basin. It has been known for some time that the Precambrian Shield was thus formerly extensively covered by Ordovician, Silurian, and possibly Lower Devonian rocks. More recently it has been found that the Cretaceous rocks in Saskatchewan and Manitoba, of which the erosional edge is the Manitoba Escarpment, extended much farther north and east than they do at present (Caldwell 1974: personal communication). The evidence for this is twofold:
(1) some 600 feet of sediments containing Cretaceous fossils overlie Precambrian rocks in Deep Bay of Reindeer Lake,
(2) the sediments exposed in the Manitoba Escarpment do not indicate a proximate coastline but were deposited in marine waters some distance from the shore of Late Cretaceous time.

Relief in the Manitoba Lowlands is even less than in the Kazan Upland: it does not exceed 100 feet, and local rock knobs, bosses, and hillocks are absent. The Manitoba Escarpment (at the Wapawekka Hills 1,400 feet above the lake) thus stands out as a prominent feature of the landscape.


Ancient Erosion

During the time of the Hudsonian Orogeny the rocks of the Shield already were subjected to subaerial weathering and erosion that lasted millions of years, long after mountain building waned and ceased. Thus the mountain chains were reduced to a flat erosional plain, a peneplain, characterized by a topography much like that which we see at present on the Kazan Upland, although there are some indications that local relief may have been more pronounced. In the Montreal Lake area, for example, information obtained from wells indicates that the unconformity between the Precambrian and the Paleozoic rocks in the area has a relief in the order of 800 feet (Hutt: 1963).

Thousands of feet of material were worn away, exposing intrusive rocks that were formed at a considerable depth below the surface. These intrusive rocks, mainly granitic, form the bulk of rocks now exposed. Metamorphosed sedimentary rocks and schists and gneisses which were probably sedimentary rocks originally, rank second in abundance. They occur in north-easterly-trending bands and, as remnants in the intrusive rocks, represent the downfolded roots of the former mountain chains. Metamorphosed volcanic rocks are least abundant. They occur with the other rocks mainly in a broad zone extending from Flin Flon to La Ronge and from La Ronge to the south end of Reindeer Lake (DMR 1974).

In late Proterozoic time the Precambrian peneplain of northern Saskatchewan became, at least in part, gently downwarped. Shallow waters and fluctuating, migrating streams occupied depressions, in which sands and gravels were deposited. Evidence of this deposition can still he seen in the Athabasca Sandstone to the north-west of the Churchill-Reindeer rivers area. The present edge of the Athabasca Sandstone is undoubtedly erosional, but it is not known how far the deposits extended originally and whether or not they covered extensive additional parts of the Kazan Region.

After the stripping of parts of the Athabasca Sandstone by erosion near the end of Precambrian time, the rocks of the Shield again were subjected to weathering. Such weathering may have taken place under hot, humid climatic conditions and proceeded without the soil-forming influences of plant life as land plants were not to develop until Silurian time. Paleosols, or old soils, are still preserved from this time of Late Precambrian weathering and erosion. In places they are represented by layers of kaolinite between the Precambrian granitic rocks and the overlying sedimentary rocks of Ordovician age. The weathered upper part of the Anglo-Rouyn ore body, near La Ronge, which has an abundance of secondary chalcocite, also may have formed at this time (John Randall 1974: personal communication).

As mentioned above, where it is possible to study the surface of the Precambrian rocks beneath the overlying Ordovician rocks, it is found that the topography of the buried rocks is similar to that of the present Shield. This led Ambrose (1964:81 8) and some earlier geologists to regard the present Precambrian surface an an exhumed peneplain, or paleoplain. This concept now appears to be generally accepted, but controversies still exist with regard to when and how stripping of the Phanerozoic cover took place.

Ambrose (1964: 849) held that the cover may have been stripped partly in Late Devonian time and that probably the Shield was never again completely covered as the only outliers known to him to be younger than Early Devonian were two of Cretaceous strata south-west of James Bay. To these we now must add the Cretaceous sediments discovered in Deep Bay at the south end of Reindeer Lake, which cover the bottom of a round, steep-walled, crater-shaped depression believed by some to have been caused by the impact of a meteorite (Innes et al. 1964). Deep Bay, which is 7-1/2 miles wide, is the largest known crater in North America. Its maximum depth is 720 feet, whereas most of the rest of Reindeer Lake does not exceed 200 feet in depth.

Another indication of pre-Cretaceous erosion is the general northward thinning of the Paleozoic rocks between those of Mesozoic age above and of Precambrian age below, as well as the fact that the Cretaceous rocks in the Wapawekka Hills area lie directly on Precambrian rocks. The source of coarse quartz grains cemented with white kaolin, so common in the Cretaceous rocks in this area, is probably a deeply weathered Precambrian Shield (Langford 1973: 2-3).

For the Churchill-Reindeer rivers area, then, it appears reasonable to assume that a cover of Ordovician and Silurian rocks was removed by streams, that the sea covered this exhumed Shield surface again in Cretaceous time, and that the area was subjected to further subaerial erosion before it was invaded by the successive glaciers of Pleistocene time. How much or how little these glaciers contributed to the stripping process is still a subject of debate.

In some places the effects of weathering and erosion in pre-Cretaceous time can still be seen: "The contact between the Precambrian and Cretaceous rocks can be located along the south shore of Wapawekka Lake. In this area, unlike the Deschambault or Egg Lake areas to the east and west, no Paleozoic rocks are present. Instead, a quartz and kaolin sandstone lies on the Precambrian rocks. This sandstone is apparently the lowest unit of the local Cretaceous sequence, probably correlative with the Swan River Formation of western Manitoba, and deposited in a very broad channel formed by removal of the Paleozoic rocks" (Langford 1973: 2).

Subaerial erosion by streams, which first removed Ordovician-Silurian and later Cretaceous rocks from the Precambrian, adjusted itself to the structure and lithological differences in the older rocks. Erosion thus accomplished the reactivation of an old drainage system, not once but at least twice. "The Precambrian surface as whole has been lowered very little since the cover was removed, and such lowering as did occur was accomplished by reactivated pre-Ordovician adjusted drainage, thus preserving the drainage pattern and hill forms virtually intact" (Ambrose 1964; 850).

If this concept of the erosional history of the Shield is close to the truth, it follows that the stream pattern now exposed on the Shield is virtually unchanged since it was buried in early Paleozoic time. The drainage pattern, then, is at least as old as pre-Ordovician. Once adjusted to the structure of the Precambrian rocks, it persisted through at least two periods of burial, each followed by times of exhumation.


Tertiary Erosion

Stream erosion in Tertiary time was responsible for the retreat of the Manitoba Escarpment to its present position. Although the preglacial drainage system of the Shield remains to be deciphered, maps depicting the inferred preglacial drainage system of Western Canada show that at the end of the Tertiary Period a mature, dendritic drainage system existed on the Interior Plains. Whereas in several places the preglacial South Saskatchewan River system deviated substantially from its present course on the Saskatchewan Plain, the Saskatchewan River followed its present course rather closely in the southern part of the study arena. Then, as now, it flowed eastward through the gap between the Pasquia Hills in the south-east and the Cub and Wapawekka Hills in the north-west.

The ancestral Montreal River occupied the next, more westerly gap between the Cub and Wapawekka Hills on the one side and the Thunder Hills on the other. Through this gap it flowed north toward the north end of Lac La Ronge; from there it is believed to have turned east to follow the Churchill River to Hudson Bay, which was already a topographic depression in preglacial time. The gaps in the Manitoba Escarpment were cut by these streams during the Tertiary period of erosion.

The preglacial drainage system of Western Canada has become known mainly from the study of buried valleys in the Saskatchewan and Alberta Plains. In the Shield portion of the study area only one buried valley is presently suspected to exist. Innes (1969) alluded to the presence of thick drift deposits in a linear depression trending south-south-westerly across Deep Bay. Limited field work done to date may explain why more such features are not known (Alley 1975: personal communication).

The Tertiary drainage system of the Shield is to be regarded, therefore, as highly conjectural. Nevertheless its inferred configuration, as a continuation of the much better known system on the Interior Plains, lends strong support to the contention that an ancestral Churchill River was already developed in late Tertiary, preglacial time and that it followed more or less its present course.

There may then have been other, older rivers where the Churchill River now flows. What is envisaged is the presence of a drainage system on Cretaceous rocks in Tertiary time which covered both the Interior Plains and the Shield. An ancestral Churchill River was a major stream of this system; with its tributaries, it was to a large extent responsible for the removal of the Cretaceous rocks from the Shield. This superimposed stream flowed in a general west to east direction across the dominant structural trend of the Precambrian rocks which, as previously mentioned, is south-westerly. When cutting through the cover of Cretaceous rocks the river largely maintained this cross-structural course but in detail adjusted itself to local structural and lithological differences.

When the Churchill River flowed across Phanerozoic rocks from its source to its mouth it is believed to have displayed the valley characteristics of a normal stream through its entire extent. Now these characteristics can be seen only in the upper and the lower reaches where the river is incised in Cretaceous and Paleozoic rocks, neither of which exert much structural control. In its middle reaches, where the Churchill flows on the Shield, it consists of a string of structurally controlled lakes separated by short stretches of fast water over rapids and falls, the positions of which are again governed by geological structures and lithological differences that control the resistance to erosion.

The most striking regional characteristic of the Churchill River, its tripartite division (into upper reaches having a normal stream valley, middle reaches that are strongly structurally controlled in detail but which trend transversely to the "grain" of the country, and lower reaches off the Shield that show a normal stream valley), can thus be understood in light of the erosional history of the river.


Glacial Erosion and Deposition

The youngest time division recognized by geologists is the Quaternary which spans approximately the last 2 million years. During this period, which commenced with a deterioration of the climate, almost all of Canada became covered by a succession of ice sheets. These sheets were several thousands of feet thick at their centre west of Hudson Bay and north of the study area. A complex history of advances and retreats of these glaciers (there were likely four main ones) has been pieced together (for a summary and further references see Prest 1970), but the study area has contributed little information essential to a better understanding of this history. There are two main reasons for this. Firstly, the detailed study of Quaternary deposits on the Shield is in its infancy. Only in 1974 did the Saskatchewan Research Council begin the systematic mapping of the La Ronge Sheet, using augering to obtain much-needed stratigraphic information. Secondly, because of its hard, resistant rocks, the Shield was an area of glacial scouring which produced little material suitable for local deposition; except for some protected areas, any thin deposits left behind by one glaciation were easily removed by later ones.

Multiple till sections may be present in the study area. Some indications have been found by the Saskatchewan Research Council in the La Ronge area, and an oxidized layer in till is reputed to occur in the Reindeer Lake area (Alley 1974: personal communication). However, information on these occurrences as yet is insufficient to establish a detailed stratigraphy of the Quaternary deposits. Moreover, it is not known with certainty whether such oxidized layers are a definite indication of exposure to the air. Some may have formed within glacial deposits, the oxygen being supplied by circulating groundwater. Only the effects of the last (Late or Classical Wisconsin) glaciation, therefore, can be considered further in the present review. . .

The effect of glaciation on the Shield was mainly one of scouring with little attendant deposition. Glacial striae and other erosional features on bedrock show a dominant south-westerly direction of ice movement across the study area. This direction is parallel to the "grain" of the bedrock surface, which consequently has been emphasized by glacial erosion. At several locations, however, crossing striations can be seen. North of Otter Rapids, for example, the striae run transverse to the dominant south-westerly direction and may indicate a late, topographically controlled re-advance, which postdates the Classical Wisconsin (Alley 1975: personal communication).

Although the glaciers generally moved in a south-westerly direction in the study area, the pre-existing bedrock relief caused some local deflections. This is particularly evident along the Manitoba Escarpment, where prominent hills and valleys brought about lobations of the late ice fronts with consequent changes in the direction of flow during retreat of the glaciers (Prest 1970: 739). Fluted till deposits, restricted to the tops of the Wapawekka and Cub Hills, indicate a south-easterly direction of ice movement; in the lowlands, drumlinoid moraine indicates a southerly direction of movement. These divergent directions are held by Langford (1973: 8) to "indicate that while the thick ice was moving southward down the Montreal Lake plains, the upper part was spilling south-eastward over the tops of the Wapawekka Hills and Cub Hills into the lowlands east of Big Sandy Lake." Local deflections also have been observed on the Shield. Alley (1975: personal communication) noted from airphotographs that, north of Deep Bay, ice-flow features indicate a southerly direction.

The ice front of the retreating glacier was sub-parallel to the boundary of the Precambrian Shield . . . and ice flow was approximately perpendicular to this boundary. A halt in northern Saskatchewan is marked by the Cree Lake Moraine, which has been traced by means of airphotographs for about 500 miles north-westward from Cree Lake to the western end of Lake Athabasca and eastward into Manitoba (Prest 1970: 745). It varies from an end moraine-outwash complex to a single discrete ridge or a series of minor ridges. Deep, steep-sided, funnel-shaped kettles, which are a prominent feature of the morainal hills south-east of Reindeer Lake suggest sand and gravel rather than till. They have been noticed on airphotographs but have yet to be studied in the field (Alley 1974: personal communication). Their depth suggests that the deposits are not likely to exceed 300 feet in thickness. Exposures on the shore of Fafard Lake (at the southern end of Reindeer Lake) show the presence of glacier-induced deformations in the morainal deposits.

There are some eskers in the study area, particularly in the north-western part. Generally, they are oriented approximately parallel to the direction of ice movement and are believed to have originated during the last waning stage of the continental glacier, when the ice had become so thin as to be immobile (Kupsch, 1969).

Other deposits of ice-contact stratified drift, such as outwash plains and kames, also are distributed unevenly across the study area. A discontinuous esker-kame complex, which has abundant sand and gravel, stretches from La Ronge to the McLennan Lake area (Alley 1975: personal communication), but in the immediate impact area of the Churchill River Study, however, sand and gravel, which are essential to large construction projects, appear to be deficient.

Few analyses of the composition of tills on the Shield are as yet available. In general, such tills appear to be composed mainly of sand and silt, with little or no clay, and therefore to differ markedly from the typical tills of the Interior Plains. There are notable exceptions to this rule, particularly in areas that have both till and lacustrine clay deposits. During the 1974 field mapping of the La Ronge sheet by the Saskatchewan Research Council, extensive areas were mapped as being mantled by a clayey, re-advance till (Alley 1975: personal communication). Ten samples analysed showed approximate values of 29% sand, 46% slit, and 25% clay. This till may be related to the ice sheet which left the set of striations oriented transverse to the dominant direction of ice flow. Langford (1974: personal communication) regards some of the clayey, unsorted, non-stratified deposits to be seen along the Churchill River as flow tills, which slid from higher ground into the lacustrine environment below. In several localities an inter-tonguing of lacustrine clays and the flow tills is evident. In others a mixing can be noticed which has enriched the till in its clay component.

The effects of glacial erosion in northern Saskatchewan were discussed by Kupsch (1969):
The broadest physiographic division of Saskatchewan that can be made is between the Precambrian Shield, with its fringe of Palaeozoic rocks, in the north and the Mesozoic-Cenozoic sediments of the Prairies in the south. The two divisions show pronounced differences in their response to the advance and retreat of glaciers during the Pleistocene. These differences can be explained by the predominance of hard rocks in the north and largely unconsolidated shales and sands in the south. The Precambrian-Palaeozoic region can be regarded as having been affected most intensely by glacial erosion - it can be described as an ice-scoured plain - whereas the Mesozoic-Cenozoic regions shows the effects mainly of glacial deposition. This does not mean that deposits laid down by glaciers are absent over the Precambrian-Palaeozoic bedrock or that a thick mantle of glacial deposits entirely covers that part of Saskatchewan underlain by Mesozoic-Cenozoic sediments.

Many outcrops of the hard rocks in northern Saskatchewan display highly polished surfaces created by the former passage of glacier ice over them. In particular, fine-grained rocks, such as limestones and dolomites, show well-developed polished surfaces. They, and to a lesser extent the coarsely crystalline granites and granite-gneisses so common in the Precambrian Shield, also have been scratched by rocks held in the ice. These glacial scratches or striations indicate the direction of former ice movement. The sense of this direction is generally inferred from other evidence such as streamlined rock bosses ("roches moutonnees") with their gently sloping, striated, and polished upstream side and their rough, steep downstream ends where rocks were plucked away by the ice. The striations may range from barely visible scratches to large grooves several feet deep and wide. Again, such grooves are particularly well developed in carbonate rocks which are fine grained, solid, yet relatively soft, and thus constitute ideal surfaces for ice scouring. Some striations and grooves are accompanied by lunate marks or friction cracks that are oriented at right angles to the direction of movement.

Features such as striations, most grooves, and friction cracks are too small to be detectable on airphotos. Other glacial lineations parallel to the ice-flow direction and resulting from abrading of the rock pavement may, however, be large enough to be seen on aerial photographs; some "roches moutonnees" and rock basins, for example, show up well on airphotos of ice-scoured terrain. In general it can be said that the flowing ice emphasized the structural grain of the rock terrain parallel to the direction of its movement. Planes of weakness, particularly joints are generally oriented more or less at random over large areas; those that are traverse to the ice movement are largely unaffected by the overriding glacier while those that are parallel to it are widened and deepened. . . .The main structural trends of the Precambrian Shield are oriented in a northeast-southwest direction, which is also the direction of ice movement. Glacial scouring during the Pleistocene, thus, emphasized the Precambrian grain of the country.

The glacial features of the Shield, therefore, are dominated by those that owe their origin to glacial erosion rather than deposition. However, there are substantial disagreements as to the effectiveness of glacial erosion and how much bedrock has been removed by it. We have already seen that Ambrose (1964: 849-850) is very specific on this point: the present surface of the Shield was produced by stream erosion long before glaciation, which effected only minor, negligible modifications by some scouring of hill tops and some deposition of till in the hollows. A different view is presented by White (1972: 1037) who makes a case for deep erosion by continental ice sheets, and who holds that "glaciation skinned Paleozoic rocks off crystalline basement." Although he is aware of the thinness of the drift on the Shield, which can be used as an argument against the effectiveness of glacial erosion, he fails to direct himself to the composition of that drift. If it was glaciation that removed the Paleozoic rocks, would one not expect Ordovician erratics on the Shield? Such erratics are not encountered, not even downstream from Paleozoic outliers in any substantial numbers. Moreover, no Cretaceous erratics are present on the Shield, although there is now substantial evidence that Cretaceous rocks extended much farther onto the Precambrian Shield than they do at present and lay directly on basement rocks, indicating that the basement was exposed when they were laid down. On the other hand both Cretaceous and Ordovician erratics are conspicuous in the drift on the Interior Plains south of the Shield boundary.

The geological map of Saskatchewan . . . reveals that re-entrants of the Manitoba Escarpment coincide with the gaps cut through the upland by Tertiary streams and where gaps are absent the Cretaceous rocks extend as salients onto the Precambrian Shield (Wapawekka Hills). This relationship (which holds true for the gap through which the Saskatchewan River flows, as well as for the one occupied by the Montreal River) demonstrates that the removal of rocks younger than Precambrian is closely related to the Tertiary drainage.

Although White's (1972) concept of stripping Paleozoic and younger cover rocks from the Precambrian appears to be incompatible with other evidence regarding the erosional history of the Shield since Precambrian time, he well may be correct in his assumption that glacial erosion his been more effective locally than some geologists have assumed. Where the ice movement coincided with the "grain" of the terrain. glacial scouring may have deepened pre-existing valleys and lakes. With the limited topographic relief of the Shield, such deepening may not have been severe in absolute terms, possibly in the order of a few tens of feet at the most. For instance, the depth of Lac La Ronge is only about 80 to 90 feet, and the height of the surrounding hills above the lake is about 200 feet.

Reindeer Lake thus may have been both deepened and widened. Tributaries of the Churchill River, themselves adjusted to the south-westerly trending structure, became deepened and lengthened by south-westerly flowing ice, thus transforming the ancestral west-east trending Churchill River valley into a series of lakes with their long axes parallel to the valley but with arms and embayments transverse to it and parallel to the direction of ice movement.

Similarly, glacial erosion may be responsible in large measure for the modification of pre-existing rivers and lakes along the border of the Canadian Shield, and thus it may account not for their origin but for their prominence. Lac La Ronge, in the ancestral valley of the Montreal River, a tributary to the Churchill, would be an example of this.

Prest (1970: 690) mentions the disagreement concerning the degree to which glaciation has affected the gross topography of Western Canada. Contour maps of the present topography of the Interior Plains also give a general picture of the preglacial topography, but it must be kept in mind that as much as 1,000 feet of drift is present locally in some buried valleys. On the Shield, conversely, where drift is thin and glacial erosion has removed little bedrock (at least according to most geologists), the correspondence between the present relief and the preglacial topography is believed to be very close. [Topographical maps], therefore, depict the gross features and some of the detail of both past and present.

The history of glacial erosion and concomitant minor deposition has been summarized as follows (DMR 1974: 4-5):
The glaciers moved in a general south-westerly direction, parallel with the general structures in the underlying bedrock, and south-westerly trending valleys, basins and shallow depressions were left where the rocks were softer and more deeply weathered. The harder, less weathered rocks were left as bare rocky hills, and south-westerly-trending ridges, Much of the weathered material was carried away by ice and deposited in the Plains region, but a small amount was also deposited as thin, discontinuous cover over the Precambrian rocks.

Water from the melting of the vast ice sheets flooded much of the region, and, although most of this water was drained into the ocean some was trapped in the numerous rock-rimmed basins and depressions. These very shallow bodies of water were soon filled with vegetation and with soil washed from the adjacent hills, giving rise to innumerable muskegs and swamps, while the deeper bodies of water remained as thousands of lakes, many of which were dotted with islands where the tops of hills and ridges rose above the surface. Many of the lakes and swamps developed as long, narrow bodies in the valleys, giving an overall north-easterly trend to the drainage pattern, but in areas underlain by massive, uniform rocks, the lakes and swamps developed rounded or very irregular outlines . . .

The drainage system developed on this glaciated surface consists of small, irregular creeks joining thousands of lakes and swamps and draining their excess water into the larger streams which lie in some of the more prominent valleys. These creeks and streams are generally shallow and are characterized by numerous rapids and falls. The larger streams, such as the Churchill River, consist mainly of chains of lakes connected by short stretches or rapids or falls where the water spills over from one lake basin to another.


Glacial Lake Deposits

As the glacier retreated in a northerly direction, the meltwater drained mainly to the east but in certain places and at certain times became ponded in front of the ice. Extensive parts of the study area were covered by clays deposited in these glacial lakes. By far the largest of these was Glacial Lake Agassiz, the complex history of which now has been worked out in detail (Elson 1967). A series of progressively lower lake levels can be recognized, which are related to the successive operation of southern, north-western, eastern, and northern outlets, with some rises in lake levels due to ice-marginal fluctuations in the spillway areas (Prest 1970: 732).

In the study area, the northern boundary of Lake Agassiz between longitudes 100 degrees and 104 degrees is difficult to determine (Elson 1967: 39). From airphotograph interpretation the lake basins enclosed by rock ridges did not appear to Elson to contain lacustrine clays. Neither could he determine the northern boundary of Glacial Lake Agassiz from the available geological literature. West of longitude 104 degrees, however, the rock basins do appear to contain clays. The boundary shown by Elson (1967: 38) is based in part on the intersection of a water plane (defined by the well-marked strandline on the escarpment that formed the south side of the lake at the Wapawekka Hills) with the topography on the north side of the basin at longitude 105 degrees (at and west of Lac La Ronge).

Combining the information presented in Map 4 with that of Elson (1967: 83), it appears possible that about 10,750 years ago Glacial Lake Agassiz extended all over the area south of a line running approximately from Flin Flon to La Ronge. At that time the lake is believed to have drained southward (through the Minnesota Valley outlet), and slightly later, about 10,500 years ago, to have drained north-west through the Flatstone Lake-Clearwater River system. The strandline of Lake Agassiz is well marked on the eastern and northern slopes of the Wapawekka Hills where Langford (1973: 2) placed it between 1,425 and 1,450 feet. This corresponds to the Campbell phase of Elson (1967: 83). It should be emphasized, however, that evidence from the field is as yet very fragmentary and that any history of glacial lakes and drainage is speculative .

Although it has been recognized for some time that the area west of the Wapawekka Hills was covered by the waters of a glacial lake, authors prior to Elson regarded this lake as separate and distinct from Glacial Lake Agassiz. Writing about the Peter Pond Lake-Methy Portage area, Kupsch (1954: 10) mentioned that Tyrrell "was the first to notice that most of the lakes and rivers in this general area once stood higher than they do at present. Tyrrell concluded that this was true at the time immediately subsequent to the retreat of the Pleistocene continental glaciers when these larger lakes lay between the face of the waning ice sheet and the higher land over which the water flowed in great rivers. Tyrrell proposed to add the prefix hyper to the name of the present lake or river to designate the former high-level waterbody that occupied its basin or valley. He therefore speaks of Hyper-Churchill Lake, the drainage of which was to the south in the direction of Green Lake outside the Peter Pond Lake area."

The Sturgeon-Weir River sedimentary basin lies in the area between the Wapawekka Hills and Namew Lake. This basin, like others, has characteristic sediments related to certain events in the history of Glacial Lake Agassiz, and records fluctuations in water level (Elson 1967: 45, 46). The sediments in the Sturgeon-Weir Basin, for instance, record the deepening water after an important re-advance of the glacier margin about 10,500 years ago. First the water became shallower. It appears that the re-advance may have been caused by a reduction in the rate of wastage, possibly in response to climatic change. Finally, the sediments of the Sturgeon-Weir Basin were overridden by the re-advancing ice.

A detailed description of the Sturgeon-Weir sedimentation basin is provided by Elson (1967: 57-58 ):
The Sturgeon-Weir sedimentation basin is along the edge of the Precambrian Shield mainly in Saskatchewan west of Flin Flon. It includes the area from Ballantyne Bay of Deschambault Lake east to Amisk Lake and might be extended to include Athapapuskow Lake and the Goose River drainage basin (Longitude 101' 20'). Thus its length from west to east is roughly 90 miles and its width about 30 miles, less at the west end. There is little or no closure of the south side of the eastern half of this area, as a result of crustal warping. Geological reports on the region north of the Saskatchewan River here are few and information on surface deposits is sparse. Where they have been exposed in the new road cuts, the lake sediments are thin.

The altitude of this basin ranges from about 965 feet (Amisk Lake) to about 1 200 feet . . . Shallow road cuts and borrow pits along Route 106 (Hanson Lake Road). and on Route 167 from Flin Flon south-west to Denare Beach on Amisk Lake, expose 6 to 10 feet of lake sediments. Between latitude 54'40' and 54'50' the stratigraphic sequence has at the top contorted clay with abundant stones, or else a sandy till from 2 to 3 feet thick, overlying 2 to 3 feet of varved clay comprising as many as 80 couplets. The varved sediments tend to be coarse and are sandy near the base. In exposures at an altitude of about 1050 feet or 1ower the varves rest on stratified sand and till. At altitudes above about 1100 feet (for example about two miles west of the Sturgeon-Weir River crossing on the Hanson Lake Road) the varves grade downward into well sorted sand with ripple marks and a few pebbles. The altitude here is about 1200 feet. In places pebbles are concentrated at a horizon 1.5 to 3 feet below the surface: many are faceted ventifacts. The upper part of the sand has been reworked by wind action, though dunes are rare.

The Sturgeon-Weir basin appears to have functioned for a relatively-short time if the couplets observed are true varves. Initially proximal varves were laid down and these were overridden by an ice re-advance. Evidently there was little or no deep water sedimentation when the ice retreated so this basin may have been drained when the retreat occurred. Furthermore, present observations have not entirely eliminated the possibility that some or all of the upper till-like layers are the result of periglacial solifluction when the lake floor was first exposed. Early in the history of this basin there was a rise of water level, perhaps from about 1100 feet to 1200 feet.

North of the extensive area that was covered by Glacial Lake Agassiz in the southern part of the study area other deposits of lake clays are encountered on the Precambrian Shield, particularly along Reindeer Lake, Reindeer River, and the Churchill River below the confluence with the Reindeer. In the latter area lacustrine clays were shown on an early map by Mclnnes (1913: 124). who regarded them as having been deposited in Lake Agassiz. Antevs (1931: 46), however, excluded this area from Lake Agassiz because the lacustrine clays and sands on the Southern Indian Lake "extended to an altitude of about 875 feet and, therefore, probably were laid down in a separate lake standing at a higher level than did Lake Agassiz," which he regarded at that time as "standing at a level that now lies about 800 feet above the sea and that lay about 350 feet above the then sea-level." Elson (1967: 39) accepts Antevs' conclusion and mentions that the basin which is in the Churchill River drainage basin, is "separated from the rest of Lake Agassiz (about 50 to 100 miles to the south-east) by high ground and an end moraine that is unwashed on the west side but has wave-formed features on the east side." Elson goes on to state that the "lake formerly present in the Churchill drainage does not seem to have been confluent with Lake Agassiz . . . although it may have been contemporary. "

During his fieldwork for the Churchill River Study in 1974, Langford found indications of a former lake level along the shores of Iskwatam Lake (east of Wintego Lake and west of the confluence of the Churchill and Reindeer Rivers) at a height of approximately 1,100 feet above present sea-level. He also found lacustrine clay deposits as high as 1,300 feet. The conspicuous strandlines on the north-east side of Reindeer Lake, which are developed as beaches, are close to 1,150 to 1,200 feet. This higher lake, however, may have drained southward to the lower Glacial Lake Agassiz over ground now occupied by Manawan Lake and Frog Portage. But because recent drilling during dam site investigations for the Saskatchewan Power Corporation has revealed the presence of clays and the absence of sands and gravels in both these localities, the water may have drained south through rather broad, shallow lakes rather than through narrow stream channels. Stressing that he has only limited information, Langford (1975: personal communication) believes that a much larger area along the Churchill and Reindeer Rivers was flooded than previously was assumed; that this lake was at a much higher level than reported by Antevs; and that this northern lake may have been an extension of Glacial Lake Agassiz when the lake stood at 1,450 feet.

Prest (1970: 746) holds that the Reindeer Lake basin was occupied by meltwater when the ice front receded from the Cree Lake Moraine at its south end, that the outlet was at about 1,200 feet above sea-level, and that it led directly to Glacial Lake Agassiz lying south of the moraine.

The lake clays of Glacial Lake Agassiz in the La Ronge area are reported to contain the mineral montmorillonite, the source of which is believed to be the Cretaceous shales of the Interior Plains (Alley 1974: personal communication). Whether the high-level clays of the Reindeer-Churchill River area also contain this mineral remains to be determined. At present, given the above considerations, this appears to be likely. If montmorillonite is absent, it would be a useful tool for distinguishing Lake Agassiz clays of southern derivation from clays of separate, higher-level lakes in which the sediments were derived locally from the north, probably from older glacial deposits. If montmorillonite is present, on the other hand, the question of this mineral's derivation and of the origin of the lakes and the history of drainage changes needs re-examination. Further work on lake levels and drainage channels, particularly in northern Manitoba, then would be needed.

Streams from the Interior Plains to the west entered Glacial Lake Agassiz and formed deltas. The Bear River delta, west of the Wapawekka Hills, was deposited in a bay cut off from the Main body of the lake by bayhead beaches (Elson 1967: 65). The Saskatchewan River formed a large delta in the Cumberland House region, but as yet has not been studied geologically in sufficient detail to ascertain whether it formed in Glacial Lake Agassiz or in an earlier glacial lake in the Saskatchewan valley (Elson 1967: 61 ).

A large ice sheet is believed to constitute a load greater than the strength of the material of the upper mantle beneath the Earth's crust. The crust subsides beneath the ice in basin-like fashion. This deformation is chiefly plastic: flow from within the mantle transfers material outward, away from the depressed area, in compensation for the extra load. Conversely, with deglaciation a period of postglacial uplift or warping starts, and a return flow within the Earth's mantle bulges the crust upward. Eventually conditions are restored to normal (Flint 1971: 344).

Evidence for postglacial uplift is provided by the study of tide gauges, the determination of former positions of sea-level as preserved in abandoned beaches, and the accurate surveying of lacustrine strandlines which show a progressively greater upwarping northward where the ice was thickest. Much work has been done on the deformation of the former strandlines of Lake Agassiz where tilting amounts to about 1-2 feet per mile (for a summary, see Elson 1967), but geologists have contributed little or no data from the study area. The lakes farther north than Lake Agassiz also remain to be surveyed in detail to determine the present configuration of the abandoned strand lines that surround them. In the absence of such data only general statements can be made about postglacial warping in the study area.

Using the closest available data (west of Lesser Slave Lake, Alberta), the thickness of ice covering the study area was at least 600 m (Flint 1971: 485). As subsidence beneath a large ice sheet equals approximately one-third of the ice thickness, it follows that depression and subsequent uplift approximated 200 m. During the last 10,000 years, which is the time interval in which the central part of the study area has been free of ice (Map 4), that much uplift of the land has occurred. The rate of uplift was fast in the beginning, perhaps as much as 100-150 m during the first 4,000 years, which is analogous to rates determined in East Greenland (Flint 1971: 355). Since that time the rate has slowed to about 45 m (+- 5m) during the last 6,000 years. This can be deduced by extrapolation of uplift contours for North America (Flint 1971: 363, after unpublished data provided by J. T. Andrews). Sea-level 6,000 years ago was some 13 m lower than at present, and it is from this datum that the 4 5-m uplift has been calculated.


Post Glacial Events

Map 4 shows the positions of northerly retreating ice fronts in postglacial time. As the land in front of the glacier became free of ice and as much of the water that covered part of the land drained off, plants, animals, and following them, man invaded the Churchill-Reindeer rivers area. During this time the climate changed from that prevailing around an ice cap to the present one, but that change was not a smooth, gradual transition; it was interrupted by periods of both warmer and colder climate than that prevailing today.

Vegetation

The best record of postglacial vegetation change, which reflects climatic change, is provided by an analysis of the pollen and spore content of cores taken from bogs. Wood encountered in such cores can be analysed by the radiocarbon method and provides dates in years, to which the events can be related. During the 1974 field season the Saskatchewan Research Council obtained samples suitable for radiocarbon dating. The results obtained from these samples are not yet published and therefore cannot be given here, although it can be stated that they are compatible with the previously published dates.

Based on radiocarbon dates and field evidence indicating former positions of the ice front, Prest (1969) constructed a map of Canada showing where the glacier front was located at different times in the past. Map 4 shows the portion of this map covering the study area. It should be mentioned that this map is an approximation only and that further dating and field work can be expected to contribute much to its refinement. Mott (1971: 127) regards Prest's date for the Cree Lake moraine as "somewhat speculative" but mentions that the radiocarbon dates obtained subsequent to the publication of the map neither verify nor negate the suggested age.

As the ice retreated northward changes in vegetation cover took place. Within the Shield portion of the study area these events are demonstrated by the various pollen zones into which the cores taken at Cycloid Lake near La Ronge have been divided ( Mott 1973). The lowest pollen assemblage is characterized by spruce (Picea), birch (Betula) and willow (Salix), as well as herb pollen types, especially Artemisia, grasses, sedges, and chenopods. Soapberry (Shepherdia canadenses is a shrub pollen type consistently present in small amounts, as is aspen (Populus). This assemblage, although it provides only meagre evidence, is the only indication that a tundra-type vegetation preceded the invasion of spruce after the retreat of the glacier. The next higher zone shows an increase in the relative abundance of spruce pollen to such an extent that it indicates the dominance of that tree and the existence of a closed spruce forest in the La Ronge area about 8,500 years B.P.

Following the Picea-zone, which is widespread throughout Western Canada, birch and to a lesser degree alder (Alnus) increased greatly as spruce, shrubs, and herbs declined.

About 6,000 years ago, with a warmer and drier climate, jack pine (Pinus banksiana) began to invade the area and rapidly, until this tree was then much more abundant (50% ) than it is now (30%). Following a decline, a resurgence, and again a decline in pine pollen, accompanied by increases in the percentages of birch (to about 35%), alder, and spruce, the modern forest type came into being in response to a period of cooling and increased precipitation.

Rowe (1959) includes the forest of the La Ronge area in the Northern Coniferous Section of the Boreal Forest Region, the taiga. He also recognizes other sections in the study area. The following quotes from Brown (1965) are based on Rowe's descriptions of the vegetation that characterizes these sections:

[In the Northern Coniferous Section the] predominant tree is black spruce, which forms stands on the thin soils of the rock knob uplands and on the poorly-drained lowland depressions; it is associated on both positions with jack pine and tamarack, respectively. Frequent fires have favoured the spread of jack pine and are probably responsible also for the general although scattered representation of white birch over the majority of sites. In river valleys, around some of the lakes, and on south-facing slopes where more favourable conditions of soil and local climate occur, white spruce, balsam fir, aspen and balsam poplar form mixed stands of good growth.

The low areas are characterized by bog vegetation - open bogs with scattered stunted black spruce growing on deep accumulations of Sphagnum and sedge bogs. The best black growth occurs where the organic accumulation is relatively thin and drainage is improved: this is a characteristic of both sedge and Sphagnum bogs. The tallest black spruce grow to about 30 ft. Tamarack is common, either mixed with black spruce or less frequently in pure stands. Scattered jack pine growing to 20 ft. are encountered in drier bogs. The ground cover consists, predominantly of Sphagnum, with patches of feather and club mosses, Lichen and Labrador tea. There are also extensive wet sedge meadows.

The high areas with moderate to good drainage support a mixed cover of trembling aspen, white spruce and jack pine, with undergrowth of willow and alder. The tallest trees grow to 80 and 100 ft. in dense stands averaging about 5 ft. between trees. Areas with more level relief, poorer drainage and finer textured soils have white spruce as the major cover, with occasional aspen. Improved drainage, coarser grained soils and more irregular relief results in an increase in aspen and a decrease in white spruce, ultimately giving rise to relatively pure aspen stands with occasional white birch on the crests of high areas in soils of sand-clay-loam textures. Mixed aspen-jack pine forest growth is common in regions of well-sorted sands. The ground vegetation consists of various berry plants, grasses, Labrador tea, discontinuous cover of feather and club mosses, and some Lichen.

Scattered burned over areas occur in the study area. Following a fire it appears that aspen is the main species to regenerate on medium to fine-grained soils, and jack pine the main post-fire species on sandy areas.

In the Manitoba Lowlands Section the prevailing vegetation on the flat, poorly drained land consists of patches of black spruce (Picea mariana) and tamarack (Larix laricina), with intervening swamps and meadows. Good stands of white spruce (Picea glauca), aspen (Populus tremuloides), and balsam poplar (P. balsumifera), sometimes in mixture with balsam fir (Abies balsamea) and white birch (Betula papyrifera) occur on the better-drained alluvial strips bordering rivers and creeks. Low ridges throughout are generally forested with jack pine (Pinus banksiana) or aspen.

The Wapawekka Hills lie in the Mixedwoods Section. Tree growth on the well-drained uplands consists of a mixture, in varying proportions, of aspen and balsam poplar, white birch, white spruce and balsam fir, the last two species especially prominent in old stands. The cover type of greatest areal extent is the aspen, a result of the ability of this species to regenerate readily following disturbance. In addition to its usual dominance on sandy areas, jack pine enters into the forest composition in the drier till soils, and mixes with black spruce on the plateau-like tops of the high hills. Lower positions and the upper water catchment areas develop black spruce and tamarack on shallow peat.

North and west of the Wapawekka Hills the forest is included in the Upper Churchill Section. There extensive stands of jack pine occupy the sand plains and low ridges, and intervening poorly-drained areas are forested with black spruce and tamarack. White spruce and aspen are of less importance here than on the upland tills of the Mixedwood Section, although both species, as well as balsam poplar, are well represented where drainage conditions are favourable. Balsam fir and white birch are present but not abundant. Large areas of swamp and bog are common.

East of Cranberry Portage, north of Manitoba highway 38, in the area occupied by Reed and File Lakes, is the westernmost portion of the Nelson River Section where stands of black spruce constitute a large part of the forest cover, but proximity to the numerous and extensive swamps that lie back from the rivers is reflected in a restriction of growth. Where drainage is better, along the sides of rivers, on islands or on low ridges, good stands of white spruce with some balsam poplar, white birch, aspen and balsam fir are customary. Extensive and repeated fires, however, have fragmented all the forest cover, and large areas support small-growth aspen, white birch, and scattered white and black spruce or jack pine and aspen or grassy scrub on rocky barrens. Tamarack is present with black spruce in the swamps.

Climate

A subarctic climate with a mean annual temperature of 30.9 degrees Fahrenheit characterizes the La Ronge area at present (Mott 1973: 4). The January mean daily temperature of -10 F contrasts with that in July of 62 F. Wind directions are variable with no seasonal preferences. Because of the forest cover, wind speeds are lower than on the prairies. Of the mean annual total precipitation of 15 inches, 10 inches fall as rain. The large difference between summer and winter air temperatures, together with the occurrence of most of the precipitation during the summer, is testimony to the continental character of the climate (Brown 1965: 5-7). Although the eastern boundary of the study area is only some 300 miles west of Hudson Bay, this large body of water has little influence on the weather patterns because of the prevailing west to east circulation of air masses and disturbances. Its cooling influence on the climate is manifested, however, by the southward trend of isotherms from west to east. The 30'F mean annual isotherm approximately coincides with the boundary of the Shield: the 25'F mean annual isotherm parallels this but traverses the study area at about the middle of Reindeer Lake. The weather pattern during the summer is characterized by frequent cool periods in the rear of eastward moving cyclones.

Total precipitation values are slightly higher in the eastern part of the area: at Island Falls the total is 19.56 inches. The snowfall pattern does not have the same trend but varies at random from one location to another. The highest totals are 67.9 inches at Island Falls and 57.1 inches at La Ronge. The highest monthly totals of snowfall occur in the late fall during November and December (Brown 1965: 6).

Climate is the most important factor influencing the formation and continued existence of permafrost, a temperature condition which requires that the ground remains below OC for at least two consecutive years. Between the 30'F and the 25'F mean annual isotherms the distribution of permafrost is patchy and greatly influenced by local terrain conditions. Brown (1965: 24) mentions that in the study area permafrost occurs only in peat bogs in low ground and is restricted to dry Sphagnum moss areas. It does not exist where marsh sedge grows and water lies at or near the ground surface.

Langford (1974: personal communication) encountered small clay hummocks, about 2-3 feet in diameter, during his field studies for the Churchill River Study in July, 1974, in a forest-covered upland along the shore of Iskwatam Lake. Excavations in August demonstrated that there was no ice in the ground. Possibly the hummocks were formed under permafrost conditions which no longer prevail.

In a bog occupying low ground near Iskwatam Lake, Langford (1974: personal communication) noticed some peat mounds, which likely are palsas (low hills or knolls of perennially frozen peat about 10 feet or less in height occurring in peat bogs).

It is not known whether permafrost conditions existed when glacier ice covered the area. Some glaciers have frozen ground underneath them in some places and during certain times of their existence, others do not. Regarding the origins of permafrost in the study area Brown (1965: 21) mentioned that, "permafrost, particularly in the southern portion, may have formed when air temperatures were lower than they are at present, and perhaps it is now degrading. In any event, present air temperatures appear to be sufficiently high to render the formation of permafrost virtually impossible except in the peat bogs. In this particular type of terrain its existence is being maintained by the moss and peat."

Soils

The time available for the formation of soils in the study area has been short (approximately between 11,500 and 9,000 years; see Map 4) and therefore the soil-forming factor provided by the parent (geological) material plays a greater role than in other regions where the effects of climate, weathering, and erosion have been operating long enough to determine the kind of soil that develops. Yet differences in climate and vegetation are reflected in the colour and other characteristics of the surface layers of soils if a comparison is made between soils in northern Saskatchewan and those on the prairies (Moss and Clayton 1969). Light (greyish) colours are associated with the forested areas, where both vegetation and other biological conditions are less favourable to the accumulation of organic matter than in southern Saskatchewan where brown and black soils prevail.

Grey Wooded soils and the Podzols represent typical forest soils. The Grey Wooded soil profile has a thick, light-greyish A horizon, and a clayey B horizon: the C horizon usually contains lime carbonate. The Podzol soils have a thin, light-grey to white A horizon and a light-brown B horizon; lime carbonate is lacking and the Podzols are more acid than the Grey Wooded soils. Regosolic, or weakly developed, soils have thin or no A horizons, and no B horizons; thus in many places only the parent material (C horizon) is present. Many Gleysolic or poorly drained mineral soils have a surface layer of peat over thin to thick, dark A horizons. The B horizon (not present everywhere) and the C horizons are dull in colour and marked with rusty, yellowish, and bluish streaks and stainings. Organic soils have a thick layer of peat (18 inches or more) over a poorly drained mineral subsoil (Moss and Clayton 1969: 72).

In the Manitoba Lowland the predominantly clayey and loamy soils show the influence of the carbonate rocks that underlie the glacial drift. They are mainly Gleysolic and Organic soils, which show high-lime peat profiles. On the Manitoba Escarpment, Grey Wooded soils predominate with some organic deposits of deep moss peat in places. The moderately rolling to hilly flanks of the uplands may also show some Podzols locally.

To a large extent, the Shield exposes rough bedrock land. Soils have developed on glacial, lacustrine, and fluvial parent material only. Mixed sandy and loamy soil textures prevail. Moss and Clayton (1969: 70-71) show that Podzols are dominant with a significant occurrence of Regosols (soils that are weakly developed or absent) and deep moss peat in poorly drained depressions. Grey Wooded soils occur on the clayey lacustrine deposits along the Churchill River.

Beaver pondSignificant changes in the landscape were brought about by beavers. Their dams caused extensive flooding in some areas, and a subsequent filling of the ponds thus created were subsequently filled by vegetation. (See photo: F. F. Langford, August, 1974).

Ice-shoved boulders The effects of floating lake and river ice, although minor, can be seen on some shores. The "stone figures" mentioned by Roed (1973: 13, photos 23-24) as occurring in one locality on the floodplain of the Reindeer River, and which he regarded as possibly man-made, are almost certainly the result of grooving, pushing, and redistribution of the pebbles and boulders that compose the shore by ice floes during spring break-up. (See photo: M. Roed, Summer, 1973).

Although man may have occupied the Churchill-Reindeer Rivers area for the past 8,000 years (Millar 1973: 52), his direct effects on the landscape remained insignificant until the 20th century. At this time roads, towns, and dams were built, mainly to provide services to various mines. Among man's in-direct effects, however, has been the accidental setting of forest fires that have wrought great changes in some parts of the area.

Fires, 90% of which presently result from natural causes (lightning), not only affect the vegetation but also may be the cause of increased erosion of surgical material following damage to the protective vegetative cover. In turn, this may alter the sediment load carried by the streams draining the area. J. B. Tyrrel, who in 1894 travelled from Lac La Ronge down the Churchill River and up the Reindeer River to Reindeer Lake and beyond, provides the following description (in Glover 1962: 110, footnote 1): "Reindeer river is a beautiful clear stream draining the waters of Reindeer lake southward into the Churchill river. At the confluence the waters of the two streams are very distinct, that of Reindeer river being beautifully clear and white in contrast to the dark brownish water of the Churchill river . . ." Observations made in 1973 and 1974, however, show the influence of landscape disturbances, which in turn have had an impact on the turbidity of the streams. The changed river regime caused by the building of the Whitesands Dam at the southern end of Reindeer Lake in the early 1940's, as well as the extensive fire damage to a large forested area south-west of the lake, are believed to be significant factors in any variations in sediment load in the Reindeer River.


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31 May 96