M. Timothy Corkery
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GEOLOGY AND LANDFORM5 OF MANITOBA 2 M. Timothy Corkery The geological history of Manitoba abundant). Each of these eons was the southwest of the province and in spans more than 3.5 billion years. hundreds of millions of years long, the Hudson Bay Lowlands, in the By studying the rocks of the prov- so they are further divided into northeast. ince, geologists can deduce what the eras: the Precambrian is divided In south-central Manitoba, rocks landscape of Manitoba was like mil- into the Archean and Proterozoic, deposited in shallow seas during lions, or hundreds of millions, of and the Phanerozoic is divided into several periods of the Paleozoic are years ago. At times seas covered the the Paleozoic (the time when early found; these periods are, from old- whole province; at other times the forms of life existed in the seas and est to youngest, the Ordovician, province was covered by up to 1.5 then spread onto the land); the Silurian, Devonian, and Mississip- km of ice. There were volcanic is- Mesozoic (often called "the age of pian. For the Mesozoic era, we have lands in the area that is now Flin reptiles"); and the Cenozoic (the rocks deposited during the Jurassic Flon, and two continents collided in time when warm-blooded animals and Cretaceous periods, and in the Thompson area. Rocks can re- — mammals — became dominant) some locations these are overlain by veal whether it was warm or cold (Table 2.1). The Phanerozoic eras Cenozoic rocks from the Tertiary pe- and indicate when our province was are further subdivided into periods. riod. Of most recent origin are gla- close to the equator. Also, by study- Manitoba's geological history is so cial sediments from the Quaternary ing fossils we can even deduce rich that much of the geological period that cover much of the prov- something about the animals that time scale is represented in our ince. lived here long before there were rocks. people. The rocks and minerals that HISTORY IN Geologists partition the history formed at different times in the past THE ROCK RECORD of the earth in the same way that occur in different places throughout historians subdivide and name dif- the province (Figure 2.1). The oldest Precambrian ferent periods of human history, rocks in Manitoba were formed dur- Rocks in the Precambrian Shield such as the Bronze Age and the ing the Precambrian eon, and are are predominantly igneous in origin Renaissance. In the earth's history, exposed in the Precambrian Shield but include areas of metamor- the two major time divisions, that stretches from southeastern phosed volcanic and sedimentary termed eons, are the Precambrian Manitoba northwestward to Sas- rocks called greenstone belts. Broad (the time when there was little liv- katchewan and the Northwest Ter- areas of igneous rocks were formed Copyright @ 1996. University of Manitoba Press. All rights reserved. May not be reproduced in any form without permission from the publisher, except fair uses permitted under U.S. or applicable copyright law. ing) and the Phanerozoic (the time ritories. Younger sedimentary rocks by the cooling and crystallization of when evidence suggests life was of the Phanerozoic eon are found in extremely hot melted rock material EBSCO : eBook Collection (EBSCOhost) - printed on 9/19/2018 2:34 PM via UNIVERSITY OF MANITOBA AN: 497392 ; Stadel, Christoph, Everitt, John C., Welsted, John E..; The Geography of Manitoba : Its Land and Its People Account: s5519424.main.ehost 12 THE GEOGRAPHY OF MANITOBA called magma. After the old rocks of Table 2.1 Geological Formations of Manitoba the Precambrian Shield were formed, AGE' ERA PERIOD EPOCH FORMATION MEMBER THICK BASIC LITHOLOGY («) QUATER- they were buried deeply in the earth 0 RECENT NARY Top soil, dune sands E and changed by heat and pressure PLEISTOCENE N GLACIAL DRIFT 140 Clay, sand, gravel, boulders, peal to metamorphic rocks. However, 0 PLIOCENE Z UKKSIE this explanation is oversimplified; 0 OLIGOCENE TERTIARY the rocks are able to tell us more 50 I EOCENE C TURTLE MTN. PALEOCENS 120 Shale, clay and sand. Liqnite beds — located only in Turtle Mountain about the distant past. They tell of 65 continents colliding, volcanoes erupt- BOISSEVAIN 30 Sand and sandstone, greenish grey — located only in Turtle Mountain 0 COULTER Grey shale — non-calcareous, local ironstone, R RIDING MTN. ODANAH 310 ing, and great wandering rivers in MILLWOOD bentonite near base, gas found E PEMBINA T VERMILION Shale, dark grey carbonaceous ram-calcareous; bentonite bands mountains that may have been as UPPER 155 A CRETACEOUS RIVER 30YNE Shale, arev speckled calcarous. bentonitic: sliohllv petroliferous majestic as the Rockies today. At C MOftOEN Shale, dark arev non-calcareous, concretions, local sand and silt E M FAVEL Grey shale with heavy calcareous specks, times the area that is now Manitoba 0 40 E U bands of limestone and bentonite was even in a different global posi- 100 S S ASHVILLE 115 Shale, dark grey non-calcareous, silty quartz sand or sandstone 0 LOWER ASHVIllESAND tion from that which it occupies to- CRETACEOUS Z SWAN RIVER 75 Sandstone and quartz sand, pyritic shale — grey non-calcareous day. 0 1 WASKADA u UPPER Banded green shale and calcareous sandstone R 200 c JURASSIC Bands of limestone, vari-coioured shafe 150 A MELITA Archean S S RESTON 45 Limestone, buff, and shales, grey 1 MIDDLE The rock record of Manitoba starts UPPER: EVAPOflTfE JURASSIC 45 White anhydrite and/or gypsum and banded dolomite and shale C AMARANTH in the Precambrian eon about 3.5 200 LOWER: RED BEDS 40 Red shale to siltstone, dolomitic, oil producing TRiASSIC ST. MARTIN billion years ago. In the eastern 250 PERMIAN 300 Carbonate breccia, traehyandesite (crypto-expiosion structure) PENNSYL- COMPLEX Permian-Trtassic (?) part of the Precambrian Shield, in VANIAN 300 CHARLES M 20 Massive anhydrite and dolomite the area known as the Superior i S g MISSION Limestone, light buff, oolitic, iossiiiferous fragments!, cherty, Geologic Province, rocks were S 120 1 g CANYON bands of shale and anhydrite, oil producing S formed during the Archean era and s Limestone and argllaceous limestone, light brown and radish 1 M LODGEPOLE are more than 2.5 billion years old. f IBS mottled. Zones of shaly, oolitic, crinoidal and cherty limestone p Oil producing Early in the Archean, from about i A BAKKEN 20 Two black shale zones separated by siltstone. Oil show 2.7 to 3 billion years ago, there was N 350 p QU-APPSLL6 1, ... .--„., GROUP ILYLETQN 35 Red siltstone and shale, dolomitic no large continent as there is today. A NISKU 40 Limestone & doiomite, yellow-grey fossiferous, porous, some anhydrite L D » ft At that time ocean basins existed E a§ DUPEROW 1 E 170 Limestone and dolomite, arailaceous and anhvdritic in places 0 V a. SOURIS RIVER with black pillowed basalts being 33 1st RED 120 Cyclical shale, limestone and dolomite, anhydrite Z 0 S S tAWSONtiAY formed along ocean ridges, much 0 N 2nd RED 65 Limestone and dolomite, porous, anhydrite — local shale red & green 1 1 1 \ PRAIRIE A S ^-v. EVAP 120 Salt, potash and anhydrite, dolomite interbedded like mid-ocean spreading ridges c N | MNNIPEGOSIS Dolomite, light yellowish brown, reefy found in the Atlantic and Pacific to- 75 £ ^^s^eM POINT Limestone, fossiliferous high-calcium day. Also, chains of volcanic islands 400 3 ASHEHN 12 Doiomite and shale, brick red known as island arcs were being SILURIAN INTEHLAKE GROUP 135 Dolomite, yeilowish-orange to greyish-yellow, fossiliferous silty zones formed. Remnants of rocks formed STONEWALL 15 Dolomite, greyish-yellow, bedded 0 during these times are preserved in R WILLIAMS Dolomite, yellowish-grey, shaly D STONY GUNTON 30 the greenstone belts. Very old areas 0 MOUNTAIN PENITENTIARY Dolomite, dusky yellow, fossiliferous V mm 20 Shale, red-green, fossiliferous, limestone bands 1 FORT GARRY of continental granites are pre- C 450 SELSP.K served, indicating that some conti- 1 RED RIVER 170 Dolomitic limestone, mottled, and dolomite A CATHEAD nental land masses must also have N DOG HEAD WINNIPEG 60 Shale, green, waxy; sandstone interbedded existed in the early Archean era. Sand and sandstone, quartzose 500 CAMBRIAN 60 Glauconitic sandstone and siltstone, and shale; green-grey Very slowly, the forces that move DEADWOOD to black; very edge of S.W. Manitoba only continents today were at work mov- 550 ing the various segments of the PRECAMBRIAN (EON) Acid and basic crystalline and metamorphic rocks 'millions of years before present crust together to form the Superior Source: Geological Highway Map of Manitoba 1994, 2nd ed. (Winnipeg: Manitoba Craton (Continent) by about 2.7 bil- Minerals Division, 1994). lion years ago. Geological forces are impercepti- Geologic Province were formed, and Proterozoic bly slow but never idle, and 2.7 bil- tremendous heat and pressure The Proterozoic era started some lion years ago a major geological metamorphosed the rocks beneath 2.5 billion years ago. There is evi- event called an orogeny began. Dur- the high mountains. dence that a portion of the western ing the next 60 million years high Thus, by the end of the Archean, margin of the Superior Geologic mountains were thrust up and 2.5 billion years ago, the Superior Province was rifted away westward great rivers ran through deep val- Province of Manitoba had changed about 2.2 billion years ago, creating leys. Gravel and sand deposited by from oceanic basin and islands in an oceanic basin in the same fash- these rivers are preserved in some some unnamed sea — similar to the ion that the Atlantic Ocean has of the greenstone belts. Also during East Indies of today — into a conti- opened and spread to separate the this period of mountain building, nent with mountains along the Americas from Africa and Europe.