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Lake Winnipeg Beaches: Why is There so Much Sand?

September 18, 2009
The shore at Victoria Beach

The shore at Victoria Beach

When summer finally arrived here in late August this year, we took advantage of the remarkable weather and spent time relaxing at Victoria Beach, on the eastern side of Lake Winnipeg’s south basin. As I lay stretched on that beautiful beach, below sandy scarps and dunes, I started to wonder how all the quartz grains had arrived there, on the shore of a lake in the middle of North America. Victoria Beach is not just a small patch of sand; it is part of a very substantial deposit that also includes the famous perfect shores of Grand Beach.

I assumed that, given the number of people who vacation along the margins of Lake Winnipeg, there would be clear answers to this question readily available on the internet. Sure enough, I was able to find out several things quite quickly. A Manitoba Parks website and other references explained that Grand Beach is part of the Belair Moraine, a deposit 100 kilometres in length that rises 30-50 metres above the lake. This deposit was formed as high energy outwash water moved sediment from the glaciers, perhaps 11,000 years ago. The sediment was subsequently reworked by glacial Lake Agassiz, which was for a time the largest lake in the world.

The Belair Moraine includes a lot of other material besides sand. My friend Jim Teller of the University of Manitoba has had his students study the composition of the sediment in this area, and he tells me that in some of the beaches, much of the material consists of larger fragments of igneous or metamorphic rock. But even in those places, a considerable portion is well-rounded quartz sand. Other Quaternary deposits in eastern Manitoba, such as in the pits at Beausejour that once served a glassworks, consist almost entirely of beautifully sorted and rounded quartz.

From all of this, my long-view geological mind just had to ask: if there was that much sand to be shifted here, where did the glaciers and the lake find the sand? At this point I begin to move into the realm of speculation, since I have not been able to find a definitive reference on the sediment source, and I would be grateful if anyone reading this wishes to correct any errors or inaccuracies.

There is no question that a large glacier can produce great quantities of sediment as its weight grinds and pulverizes the surface of the bedrock below. But in the case of the Lake Winnipeg area, there is also a remarkable ready-made source of sand that I think must have been a major contributor to the beautiful beaches: the Winnipeg Formation. And if some of the beach sand was derived from the Winnipeg Formation, then that makes it a physical material of wondrous antiquity. If the Winnipeg Formation is the source, then the beach that we often take for granted includes grains that could have been sand for anything from 500 million to more than a billion years. Some of those grains may have been part of a sandy beach or dune before there was any complex animal life on this planet.

Before I travel further into hyperbole and reverie, perhaps I had better give a bit of background to this suggestion. The geology of Manitoba is defined by the Canadian Shield, which forms a broadly-domed turtle back that is gently blanketed toward its edges by near-horizontal younger sediments. The Shield rocks are of deep antiquity (though they keep a lot of this information to themselves); the rocks of the Superior Craton on the east side of Lake Winnipeg were formed during times of tectonic turmoil about 2.5 to 3 billion years ago.

A fault in layered Precambrian rocks near Seymourville

A fault cuts through layered Precambrian rocks near Seymourville, on the east side of Lake Winnipeg

We have little evidence for events in this region over the two billion years or so following the formation of the Shield rocks, but it is clear that there were immense periods in which the land was subject to erosion. Much of the Shield terrain must have been tall and mountainous in the early years, but over the endless millennia it was ground down, bit by bit and grain by grain, to a shape close to that of the low-lying terrain with which visitors to northern and eastern Manitoba are so familiar.

The Winnipeg Formation is exposed in the immense sand pits on Black Island (photo taken in the early 1990s)

The Winnipeg Formation is exposed in the large silica sand pits on Black Island (photo taken in the early 1990s)

As the mountains were ground lower, those grains of sediment would have accumulated in vast bodies along their flanks. Finally, about 460 million years ago in the Late Ordovician Period, the sea intruded into the middle of what was then the ancient continent of Laurentia. The waves and currents played with the immense store of sediment, shaping it and laying it down into sandstones and shales. These would become the Winnipeg Formation, which blankets the eroded surfaces of the ancient Shield. Along the lake these rocks are not very thick, generally about 10 metres in total thickness, but they form very distinct deposits. They have been lightly touched by the forces of diagenesis, so lightly that you often do not need a hammer to collect them, but can scoop out the sand with a shovel or with your bare hands.

Variable layers of Winnipeg Formation in the pits on Black Island

A geological field party examines layers of the Winnipeg Formation in the pits on Black Island

The Winnipeg Formation is variable stuff. In places it is an ugly, grey, muddy shale. In other locations, such as in parts of the silica sand pits on Black Island, it is a sparkling golden yellow sandstone. Much of the Winnipeg yields little to no evidence of ancient life, but elsewhere there are lamp shells, or conodonts, or evidence of animal burrows. Even though it is such a soft material, easily rendered to mushy soil and covered with vegetation, the Winnipeg can still be seen in several places around the lake for which it is named. In addition to the superb exposures on Black Island, it can also be observed near Seymourville and Hollow Water, at Grindstone Point, and at the north end of Hecla Island, among other locations.

Near the north end of Hecla Island, the grey Winnipeg Formation is capped by hard dolostones of the Dog Head Member, Red River Formation. This photo was taken in the mid 1990s; I understand that this slope has slumped since then.

Near the north end of Hecla Island, the grey Winnipeg Formation is capped by hard dolostones of the Dog Head Member, Red River Formation. This photo was taken in the mid 1990s; I understand that this slope has slumped since then.

The Winnipeg Formation sediments are so soft and friable that they are almost never exposed except in places where they are capped with a much harder rock, the mottled Dog Head Member of the Red River Formation. Often, this cap is thin, only a few metres thick, but don’t be fooled by appearances! For this snippet of the Dog Head is itself just the introductory paragraph to the novel-length story of Ordovician limestone seas that was to follow. Along the lakeshore the overlying parts of the Dog Head have been eroded away, but in other places it has not been eroded, and in the subsurface (under ground) it is in the range of 30 metres (100 feet) thick. The Dog Head is itself overlain by three subsequent members of the Red River Formation, including the famously fossil-rich Selkirk Member (Tyndall Stone). Above these, the four members of the Stony Mountain Formation and the lower part of the Stonewall Formation were also deposited before the Ordovician story was complete. But the Winnipeg Formation is older than any of these, and its sandstones were already in place even before the Tyndall Stone cephalopods and Churchill horseshoe crabs were alive.

Ordovician stratigraphy in the vicinity of Winnipeg, showing stratigraphic positions of field trip stops. 1, Gillis Quarries, Garson; 2, Mowat Farm Quarry; 3, Stony Mountain quarries; 4, Stonewall Quarry Park. CHAT. = Chatfieldian Stage; G. = Gamachian Stage (after Elias, 1981, fig. 2).

Ordovician stratigraphy in the vicinity of Winnipeg. The Winnipeg Formation sits on an unconformity above the much older Precambrian rocks. CHAT. = Chatfieldian Stage; G. = Gamachian Stage (after Elias, 1981, fig. 2).

A few years ago, a detailed scientific study of Lake Winnipeg was carried out, and some remarkable discoveries were made. One of the most significant (from my perspective) is that there is virtually no Ordovician bedrock under the eastern part of the lake. Rather, the lake bed in that area consists of the ancient Precambrian rock, with Lake Agassiz sediments above it. If the Winnipeg Formation has been almost completely stripped out of the eastern part of the lakebed (where it almost certainly occurred in the distant past), then an utterly mammoth quantity of sand, silt, and clay has been shifted by the combined efforts of water and ice.

The total area of Lake Winnipeg is 24,514 square kilometers. Even if we assume that the Winnipeg has been removed from only 10% of that area (and I’m sure it would have been more than that), and if the formation is about 10 metres thick (as it is along parts of the lake), then that is still about 25 cubic kilometres of sediment.  Since quartz is remarkably durable stuff, the sand grains have tended to outlast the clay and silt, and the overlying carbonates.

This conversion of the antique Winnipeg Formation sand into modern sandy beaches is almost certainly happening still, because the Winnipeg is very close to the beach level in the eastern beaches area. Just east of the pump house at Victoria Beach, blocks of Dog Head rest high on the beach, but on a day when conditions are right, you can find bits of greenish, clayey sandstone exposed at mid beach level. On a really lucky day, you will find beautiful little Ordovician fossils in that sand: brachiopods (lamp shells), bryozoans (“moss animals”), crinoids (“sea lilies”), even trilobite components. That greenish sand is part of a thin layer, called the Hecla Beds, lying horizontally between the Winnipeg Formation and the Dog Head. So the Winnipeg itself is just below your feet. Along the shore, where pelicans glide above the windsurfers, grains of Winnipeg sand are gently washing out into the lake, beginning the next phase of their billion-year progress through the sediment cycle.

Victoria Beach

Victoria Beach

Even though this is far from being a scientific treatment of this matter, I ended up consulting quite a few references as I compiled the above piece. Some of these include:

Bannatyne, B.B. 1988. Dolomite resources of southern Manitoba. Manitoba Energy and Mines, Economic Geology Report ER85-1, 39 p.

Burt, A.K., T.A. Brennand, G.L.D. Matile, G. Keller, and H.L. Thorleifson. 2002. Reinterpretation of the Belair Moraine, southeastern Manitoba, Canada, based on a regional digital elevation model and new geological data. Geological Society of America, North-Central and Southeastern sections Joint Annual Meeting, Abstracts, Paper 29-0.

Elias, R.J. 1981. Solitary rugose corals of the Selkirk Member, Red River Formation (late Middle or Upper Ordovician), southern Manitoba. Geological Survey of Canada, Bulletin 344, 53 p.

McCabe, H.R. 1971. Stratigraphy of Manitoba, an introduction and review. In Turnock, A.C. (ed.), Geoscience Studies in Manitoba: p. 167-187. Geological Association of Canada, Special Paper 9.

Young, G.A., R.J. Elias, S. Wong, and E.P. Dobrzanski. 2008. Upper Ordovician Rocks and Fossils 
in Southern Manitoba. Canadian Paleontology Conference 
Field Trip Guidebook No. 13, Geological Association of Canada – Paleontology Division and The Manitoba Museum, 97 p.

Todd, B.J., C. F. M. Lewis, E. Nielsen, L. H. Thorleifson, R. K. Bezys, and W. Weber. 1997. Lake Winnipeg: geological setting and sediment seismostratigraphy. Journal of Paleolimnology, 19(3): 215-243.

I would also like to thank Dr. Jim Teller for kindly answering some of my questions about the Belair Moraine. Jim also pointed out to me, after he read this article, that Winnipeg Formation sand grains are so distinctive that they can be readily recognized in the glacial deposits. He says that they are much more rounded and frosted than grains derived from other rocks, except perhaps those of the Cretaceous Swan River Formation, and that the Swan River sand itself may have been derived from the Winnipeg!

© Graham Young, 2009
10 Comments leave one →
  1. Fern Saurette permalink
    November 7, 2009 10:51 pm

    Great Blog Dr. Graham, I love your informative description of the Winnipeg Formation. Regarding the origin of the sand from the Wpg Fm, I came across 3 refs that indicate that the sand was from Precambrian shield erosion from northern shores near Lake Athabaska.
    Please consult the following for details.
    Bezys, R.K. and Conley, G.C. 1998. Geology of the Ordov. Wpg FM. in Manitoba. Manitoba Energy and Mines, Stratigraphic Map Series. OW-1; 1;2 000 000.
    Andrichuk. 1959. American Assoc. of Petroleum Geologists. Bulletin. Vol. 43, p. 2333 -2398.
    Genik, G. J. 1954. A regional study of the Winnipeg Formation. Journ. of the Alberta Soc. of Petr. Geol.. Vol 2; No. 5. p.s 1-5.
    I would like to talk to you and Ed regarding the Wpg Fm shale and some of its microfossils. I am in the process of identifying some pyritized specimens, and I need your help.
    Thanks for the wonderful Blog.

    • Graham permalink*
      November 8, 2009 10:13 am

      Thanks Fern. I’m sure that the Winnipeg sand was derived from the Shield, but I think the source area was very broad. After all, the Shield comprised all the bedrock around here until the Winnipeg was formed.

      • September 6, 2010 11:47 am

        ya i kno i love winnipeg was there last month a loved it i miss canada soooooooooo much i am living in ireland at the moment with my family when i am 18 moving bk over cant wait hope the sand come bk better xxxxxxxxxxxxxx

  2. Terri Shrodi permalink
    December 31, 2009 10:49 am

    I have a print/lithograph entitled “Precambrian shores” numbered 35/200 but I cannot make out the name of the artist. It looks like Muscliff. It is a beautiful picture. I would love to know about it and where Precambrian shores are. If you could help it would be appreciatead. Thank you Terri. Shrodi.

    • Graham permalink*
      December 31, 2009 3:14 pm

      Thanks Terri. There are many Precambrian shores in the world. In North America, the best-known and most often depicted are those around the northern part of the Great Lakes. You might want to search for images of Lake Superior and Lake Huron to see if you find anything similar to your print.

  3. Sean permalink
    January 16, 2010 4:44 pm

    Thanks for the interesting article. I kayaked around Black Island one long weekend and wished I had a geologist in my back pocket. I read up as much as I could but I really need things pointed out to me in the field. I camped at the old quarry and didn’t think to question how all that sand (which I had assumed was of recent glacial origin) got inserted in all the ancient rock.

  4. September 30, 2010 4:26 pm

    Thanks for the nice article. I spent a good portion of three years studying the Winnipeg Formation for my master’s thesis (1984) – my focus was the North Dakota portion of the Williston Basin. Not haveing the luxury of outcrops, I had to rely upon oil well logs and a limited number of associated core samples. Among my findings was that the inception of deposition of the Black Island Member occurred simultaneously with the original downwarping of the Williston Basin – amn my be related to the beginings of the TransContinental Arch, farther to the east in Minnesota. I have spent most of my career working on Middle Ordo. sequences in Minnesota/Wis. but they are all related.

  5. February 7, 2016 2:29 pm

    hmmm lots of quartz, so much good energy out here, makes sense. first came to this place as a child, bonded instantly with it, big love, spent my life wanting to live here in my final years, which I am, living on the Belair Moraine, and darn proud of it ! thanks for an amazing blog/article, it’s a keeper for me !


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