•••••••••••••••••••••••••••••••••••••••••• GEOLOGY AND LANDFORMS OF MANITOBA M. Timothy Corkery The geological history of Manitoba abundant). Each of these eons was the southwest ofthe province and in spans more than 3.5 billion years. hWldreds of millions of years long, the Hudson Bay Lowlands, in the By studying the rocks of the prov­ so they are further di vided into northeast. ince, geologists can deduce what the eras: the Precambrian is divided In south-central Manitoba, rocks landscape ofManitoba 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 ears 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 Phanerozoi c 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 inee. 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 fe rent 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 reas of igneous rocks were formed 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 fo und in extremely hot melted rock material 12 THE GEOGRAPHY OF MANITOBA call ed m agma. After the old rocks of Table 2.1 Geological Formations ofManiLoba the Precambrian Shield were formed, AGE' ERA PERIOD EPOCH FO~ MATlON n«'. 8ASIC lrTHOlOGY MEMBE R 'I they were buried deeply in the earth C QUATER· ..;fa}'T Tot> soil dun asand• E NARY and chang d by heat and pressure .J,r,g')t;(;F.IE N GLACL'.L DRIFT 140 Clay, sand, gravel. 1J1der ~.a l to metamorphic rocks. However, 0 Z ~():£I,'( this expla nation is over implified; ~ 'lC .,.:. 0 t.1~·fl' TERl IAAY the rocks are able to tell us more 50 I t :.cFl,;,r C p'lf(Wj[ TURTl£ MTN . 120 Shale. clav and saM LI(tOile b. d. - localed onl In TUllia MDunla! about the distant past. They tell of OS continents olliding, volcanoes erupt­ BOISSEVAlN 30 Sanaand saMSIOns, glO<llllsli gray - \Qcaled only In TuM'e Mounlain C . Gray shalo non-calcarS()IJS lOcallronSiona. ing, and gre t wandering rivers in R Alm~ G 1.\lN. 310 ,,·U\'fX~ benlonl" Mar tlase. gas louod E mountains that may have been as T lJP1'fR V ERM.LIO ~ S~al. da,. yrey e," bonaceous non·ealcaJ""US. l>emonne bands """'" t55 A OI!'""l>:\ RIVEfl 00''0·- I S~ale. oroy sDec1<1ed calca,,,"s OOnlonllic: s l "'~ l ly oel,ol,l.roo, maj sti c as the Rockies today. At C lo(llttt. IS~a 'EU1lir1< ~ r il'L11Qn~us ~ =. U o~s ~ 1 samlJ n~ SI·l E Gr . y s~. l o ,'illn heavy calco reous Sll.cl<~ times the area that is now Manitoba M 0 FAVEL 40 E U bandS Dlllma'loM and ben'onll' 100 5 ASHVillE was even in a different global posi­ S 11 5 Shale. oark g re ~ f1on·ca. l car~ous , :)Ilfy GUatl2 Sflnd or sa ndstone 0 C'r,rlO tStr/1llEs;..:U:;J tion from that which it. occupies to­ tR£~iCfQUS Z SWAH RI VER 75 SandS l l1"lI~ and QUartz sand pynllc snale - gray non ·c;.aI(.8rE<1us day. 0 J U WAS>\AOA BandM green ~ha19 al'!2 calca reous sand5.IQl"le R ' ....R 200 C < SandS llrmes~one yaI1-co[ouII:td shale Archean 15') A " MEUTA S RESTON .5 Limestone bull. and ,Mias. gray u , The rock record of Manitoba tarts I uPf'f-!l ~• .:. r ..,ff ,~ WMe aoll)'d nla and'or g~m snd banoed dolomila aM ,hale C IU~!.· AMA!1ANHf in the Precambri n eon about 3.5 200 I ..HI fTal.E~ ot() Red sha.11.!: to slClstona dolomrbc. 011 prOOuctng ST MARTIN billion years tigO . In the eastern Ip~; &n Ca,bor.3l. breCCia If.c~y.ndB5J le {cryp!o·e< plosion SlruClu r ~1 25() O'.H'lEX 300 P E N~SYl Permlan- Tna-59i (?) part of the Precambrian Shield, in VANIAN JOO the area known as the Superior CHARLES 2Q M.s~". anh,dnlo and ~O!omi t a "I '" MISSION i.JmesIOM. lig hl bu ~. ool<1 ,c, 10, s.IIlelOus Ilagmonl.1 eIl.tty. Geologic Province, rocks were •S g 120 C ~ Y ON bands 01 shale and anhydnlo 011 ploouclng formed dur ing th Archean era and '"2 ,; LImestone and argllacea'-l$ llmeswne. Ilgll' brown aM {edisl1 • l OOGEPOt.E I ~ 165 re more than 2.5 billion years old. § mollled Zones 0' shaly. oolilic C,,"Oldal and cherty II....lon' D" 0·1 pro<lue,ng Early in the Arch an, from about I BMKEN 20 Two blacl< sha lo ' ''''•••oba ralod by ,:lIslone. 0,1SIlO w 2.7 to 3 billion years ago, there was " ~ D · OVG~!..lf, !l'flETON J5 Red. siltstone anD sl1ale, dolommc no large continent as there is today. A NISKU ~ Umesl"". ~ doIom,". yellow'll'.Y I.,., I.'...., porOU$. some aMytjnl8 At th t time ocean basins existed l 0 ~g E E DlJP£ROW 170 Limeslone .od dOlom,l. ero'I. r.eous and . nhvdn l ~ rn otec,," l with black pillowed basalts being 0 V SOUAISR!V~ 120 eycll",,1 Shale. l.mosloM and dotomile. anhydnle Z 0 H!fll;' formed along ocean ridges, much ~ i& I OA"t,~,H;\Y 65 i.JrnoslOO. aM dal<mle. porous , . nhydtM ­ IOCIII ,"a). led & green I I ~...Rtt li ke mid-ocean spreading ridges A ~ ~ ". 120 Se u, po,a." and anhydrl'e, dolomll. ,nlerb edded C ~I ~ found in the Atlantic and Pacifi to­ f'/INNIPEGOSIS 75 Dolomlle. IIghl jello""h brown. ,.01\. ~ /EiUI"(tf... Limestol'le toss'llIerous htgh·eaJerum day. Also. chains of volcan ic islands 0100 '" ~ RN !2 001 mil. and shale bn~ rod kn~ wn as is1an 1 a rcs were being SILURIAN If l TEl1I..A KE GROUP 135 Dolomu•. yellowish-orange '0 greyis/t·Y9!Ow loss,IIlerous .lIty ZO nE> formed. Remnants of rocks formed !;TONEWAU. I~ Oolomile greyish-yellow bedde<J W'WW, during these time are preserverl in A Dolom.I•• y.llowiS"·~ r. y, <h. ly 0 TONY (j"r,~ 3C '.K)UNTAII< th greenstone belts. Very old areas 0 ~n.u·-, Dolomlle dusl<I.\'eUow, losstl,l&rQus V (, ~. Snale red'1ll1len, 'os""f,,,o"s. IIme9lOo" t>ands of continental grani es are pre­ "'-I~Tc..nfn C "" 450 SlLK:PtI. served indicating that some conti­ I flEDfllVEfl Fa Doloml!tc limeston e m !lled. end dolomlle A ':';'T~ n ntal land mas es must also hav N .":'u HEJ.C WINN'PEG ShaleJl!""n w' ''L .anelsIO,," 'nlerlledd«l existed in the early Archean era. eo :::ian an sa OO &o ne Quartzose 500 C~ MBR I MoJ DEAOWooD 60 Gl aU~t ' ~ ~~ :on" aM ,.IIS10n•• and ,hal., green g's)' Very slo wly, the force that move 10 blue very • 01S W Maniloba only . continents today were at work mov­ S5(j ing th var ious segments of the PflECAMBAlAN IroN) Add and bas", cry'lall'n. !fld ,....tamorph;c rockS em t together to fo rm th Superior 'mi Alons 01 years OOl or. p'.S,,"1 Source: Geological High way Map ofManitoba 1994, 2nd ed. (Winnipeg: Manitoba Craton (Contin nt) by about 2.7 bil­ Minerals Division, 1994). lion years ago. Geolo<yical forces are impercepti­ Geolog] Province were fo rm d, and Proterozoic bly slow but never idle, and .7 bil­ tremend us heat a nd pressure Th Proterozoic era sLart d some lion years ago major geol ogical metamorphosed the rocks beneath 2. 5 billion years ago.