H. R. McCabeGeocgist,MonitGba Dept. of Mhies and

Natural Resources,Winnipeg, Man.

Tectonic Framework ofPalaeozoic Formations

in Manitoba

Annual Western Meeting, CIM, Calgary, October, 1966

Transactions, Volume LXX, 1967, pp. 180-189

ABSTRACTThe study of a detailed series of structure and isopachmaps of the Palaeozoic strata of southwestern Manitobaindicates that the principal Palaeozoic tectonic elements

— the Williston Basin mid Elk Point Basin — have beenmodified to a considerable extent by major tectonic features of the Precambrian basement. The principal base-ment feature is the break between the Churchill and Supenor provinces, which coincides roughly with the Manitoba-Saskatchewan border. East-west-trending orogenic beltswithin the Superior crustal block may also be reflected tosome extent in later Palaeozoic movements. In addition,the Superior crustal block, as a whole, appears to havehad a slightly different response to the tectonic forces,giving rise to both basin subsidence and basin uplift.During periods of deposition, especially during Ordoviciantime, the Manitoba portion of the basin appears to haveundergone a relatively higher rate of subsidence, whereasduring periods of erosbrn relatively greater amounts ofuplift and truncation have occurred. As a result, the depositional and erosional patterns for most of the Palaeozoicformations in southwestern Manitoba are somewhat anomalous relative to the regional basin framework.Some prominent Palaeozoic structures probably are theresult of salt solution and differential compaction causeddirectly or indirectly by relatively minor tectonic move-ments related to Precambrian basement features. In par-ticular, the prominent hinge line at the edge of the De.vonian Prairie Evaporite salt basin may be due, in largepart, to salt solution. Numerous other small structurallows, structural highs and isopach thicks, probably resuiting from salt solution, occur along the salt edge andhave been important in modifying and controlling Mississippian oil accumulation in the Daly-Virden producingarea

Introduction

I HIS study is based on the examination of a detailed series of isopach and structure contourmaps* for all Palaeozoic formations of southwestern

Manitoba, as well as all available geophysical data.Selected references to the regional geologic setting arelisted at the end. Southwestern Manitoba is locatedon the northeastern edge of both the Williston andElk Point Palaeozoic sedimentary basins (Figure 1).The regional structure contours on the Precamhanbasement reflect not only the composite effect of thesetwo Palaeozoic tectonic elements but also later Mesozoic and Cenozoic subsidence. For Manitoba, onlyabout 20 per cent of the present structure is due toPalaeozoic tectonic activity ; this makes direct inter-pretation of the tectonic framework difficult.

*Most of these maps are included in the StratigraphicMap Series, issued by the Mines Branch.

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Although the over-all structural pattern appears tobe rather uniform, an examination of the isopachmaps for the various Palaeozoic formations showsthat there are a considerable number of anomalousfeatures throughout the stratigraphic succession, andthat the Manitoba portion of both the Williston andElk Point basins appears to have formed an anomalousarea within the regional basin framework. The writ-er believes that the tectonic framework has been di-rectly affected by major structural features of thePrecambrian basement (Figure 2) . The most prominent basement feature and the one that appears to

‘ have had the greatest effect on the Palaeozoic tectonic framework is the discontinuity or boundaryzone between the Churchill and Superior Precambrianprovinces. This zone is fairly well defined in theShield area, and its southwestward extension beneaththe Palaeozoic cover is indicated by the associatedhigh and low gravity anomalies, as shown in Figure2. A prominent magnetic low is also seen to occuralong this break in the southern part of the map-area.The Manitoba portion of the Williston and Elk Pointbasins is thus underlain principally by rocks of thePrecambrian Superior block, whereas Saskatchewanis underlain principaily by rocks of the Churchillblock.

As the Churchill and Superior blocks are known todiffer considerably in age, lithologic character, tectonic grain and even in average crustal thickness, it ispossible that these two major Precambrian blocks mayhave had a somewhat different tectonic response tothe forces giving rise to both basin subsidence and basin uplift.

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A further and very important factor to consider in‘ evaluating the tectonic framework is the existence of

prominent superficial or sedimentary structures whichre not formed as a result of basement deformation,but rather are the result of either salt collapse ordifferential compaction. Differentiation between superficial structures and true tectonic structures presents a major problem in the map-area.

PrecambrianThe structure map on the Precambrian surface

(Figure ) shows a relatively uniform dip to thesouthwest, ranging from 17 to 50 feet per mile. Al-though most of this reflects post-Palaeozoic deformation, any Palaeozoic tectonic features should nevertheless show on the structure map, but the relatively highsuperimposed dip coupled with the sparse deep wellcontrol make it difficult to delineate any but the mostprominent structures. The principal feature shown bythis map is the pronounced high in the vicinity ofLake St. Martin, west of the Lake Winnipeg narrows,where granitic and volcanic rocks are exposed at surface. Available data indicate that this feature is atopographic high on the erosion surface with a localrelief in excess of 700 feet, and that there has beenlittle or no associated post-Precambrian tectonic deformation. The volcanic rocks, however, are very freshlooking and not at all similar to the typical green-stones of the Superior province, which suggests thatthey may possibly represent late Precambrian or evenyounger activity. Two radioactive age determinationsfor these volcanics, by the K-Ar whole-rock method,gave an age of only 200-250 million years. However,because of the crystalline and vesicular nature of thematerial used, these results may be totally unreliableand need to be checked. The associated granitic rocksgave a normal “Superior” age of approximately 2.4billion years. Assuming that the basement high is ofPrecambrian age, it must have remained emergentthroughout Ordovician time, and all of the Ordovicianstrata must pinch out against the high.

Another prominent feature on the Precambrian mapis the northeast-trending Moose Lake syncline or flex-ure located immediately northwest of the north end ofLake Winnipeg. This pronounced flexure also shows upas a prominent bend in the outcrop belt of Ordovicianand Silurian strata, as shown in Figure 3. Because ofextensive post-Palaeozoic erosion in this area, the ageof this feature cannot be determined except that ithas affected the youngest strata in the area and con-sequently in post-Middle Silurian. The synclinal flex-ure is seen to be coincident with the boundary zonebetween the Churchill and Superior Precambrian provinces and with the trace of the gravity anomalieswhere this boundary zone extends beneath the Palaeozoic cover. This is the most direct evidence availablethat the Churchill-Superior boundary zone representsa zone of post-Precambrian tectonic movement.

PalaeozoicThe Precambrian of southwestern Manitoba is over-

lain by UP to 4,000 feet of Pa.laeozoic strata which dipgently to the southwest. Tnis wedge of Palaeozoicstrata was uplifted and partially truncated by preJurassic erosion so that the Palaeozoic formationsnow outcrop or subcrop in a series of northwest-trend-ing belts (Figure 8) . The Palaeozoic erosion surfacehas, in turn, undergone post-Middle Jurassic subsidence. but the pattei’n of subsidence, and hence thepost-Palaeozoic tectonic framework, is markedly dif

ferent, with the result that the utcrop-subcrop beltsare seen to be discordant to the present structure con-tours on the Palaeozoic erosion surface, and show apronounced structural rise to th northwest. The stratigraphic succession and formalion names are notedin the legend. The structure an isopach patterns foreach of these units will be discassed briefly.

Most of the Palaeozoic formations of southwesternManitoba are para-time-stratigraphic units delimitedby marker horizons, and conseçuently the isopach ofsuch units reflects the relative amount of tectonicsubsidence and the structure contours reflect truestructural deformation.

Ordoviciai. Ordovician strata comprise the first record of Palaeozoic sedimentation in Manitoha except for a smallarea in the extreme southwestern corner of the Province where Cambrian strata may be present. The To-tcLl Ordovician isopach (Figure 4) shows a relativelyuniform and rather rapid thi±ening to the south,with surprisingly few thickness variations. This mdi-cates deposition on a very smooth, flat Precambriansurface, with differential subidence apparently hay-ing occurred along an east-trending axis. The Willis-ton Basin, however, was the principal tectonic elementat this time, and the pattern of subsidence in south-western Manitoba is markedly discordant to the regional Williston Basin trends. The isopach patternof southwestern Manitoba appears to result from arelatively greater amount of subsidence in the Manitoba portion of the basin. The area of thickening is delimited approximately by the Churchill-Superior boundary zone, and the isopach trends are similar to thetrend of the orogenic belts within the PrecambrianSuperior province.

Although the Total Ordovicisn isopach is uniform,the isopachs of the constituent anits are not, and mostif not all of the isopach anona1ies shown by theseunits can be attributed to differential compaction ofthe basal Ordovician Winnipeg formation (Figure 5),which shows rapid lateral lithologic changes from sandto shale. The thickest and most persistent sandstoneunit within the Winnipeg is the Carman Sand, whichoccurs as an east-trending bar-dike body south of Win-nipeg. Differential compaction around this area ofhigh sand content has given rise to the isopach thickin this area as well as the stractural high associatedwith the isopach thick. It is ‘possible, however, thatslight tectonic movement, as evidenced by the flexureof the Precambrian structure contours, may havehelped to localize deposition of the Carman sand body.The easterly trend of the Carman Sand is seen to pa-rallel the trend of the Precambrian orogenic belts, although no magnetic data are available to determineif the sand body is coincident with a Precambrianfeature.

The isopach of the Red River formation (Figure 6)shows an anomalously thin area coincident with thearea of Winnipeg thickening. This indicates that most.of the differential compaction f the Winnipeg shalesoccurred during Red River time. The relatively rapidsouthwaru thickening of the Red River is accompaniedby a facies change from dolonilte to limestone anddolomitic limestone. This suggests relatively rapidsubsidence and tectonic differentiation of the basinduring Red River time.

Also worth noting is the pronounced discordancebetween the isopach trend and the trend of the out-crop belt. The isopach trend is seen to be almost at

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right angles to the outcrop belt, so that the maximumrate of change of thickness and also the maximumrate of lithofacies change occur along the outcrop belt.The outcrop belt of the Red River formation thus rep-resents essentially a dip section rather than a strikesection, as might be expected on the periphery of thebasin. This marked discordance between isopach andoutcrop or subcrop belts is evident to a greater orlesser extent for all Palaeozoic formations and is inpart the result of a post-Palaeozoic shift in the tectonic framework; it has been an important factor incontrolling oil migration and accumulation in Mississippian strata, and is also a highly important consideration for any other exploration involving similarstratigraphic traps at the Palaeozoic erosion surface.

The isopach of the Stony Mountain formation (Figure 7) reflects a continuation of the previously established tectonic framework, but with a somewhat moregradual and irregular thickening to the south, and asmall area of thickening near the Saskatchewan border. The southward thickening is accompanied by anincrease in argillaceous content and a decrease in degree of dolomitization.

The Stonewall formation (Figure 8) comprises theuppermost Ordovician strata and may possibly includesome basal Silurian strata as well, although there isno appreciable break in the stratigraphic succession.T}’e isopac pattern differs r-arkec11y from the previously described Ordovician strata in that the unitthickens to the west rather than to the south. Thisindicates a significant change in tectonic frameworkduring latest Ordovician or earliest Silurian time,‘ith the Manitoba portion of the Williston Basin nolonger undergoing differential subsidence.

The area of gypsum shown in Figures 8 and 9 asoccurring within the outcrop belts of the Stonewall

and Interlake strata is of uncertain age (possibly Jurassic) , and the exact configuration of, the outcropbelts relative to the occurrences of both the gypsumand the adjacent Precambrian irJier is uncertain.

SilurianThe top of the next unit, the Silurian interlake

Group (Figure 9) , marks a major unconformity, withall of the upper part of the Silurian strata having beeneroded from southwestern Manitoba. The Silurian iso-pach thus reflects primarily the topography of theerosion surface, and shows an almost dendritic pat-tern. There is, however, little evidence of progressivetruncation of Silurian strata, and this suggests thatpost-Silurian uplift was relatively uniform. Tentativeisopachs of marker-defined units within the Inter-lake also are relatively uniform throughout the map-area. Apparently, a relatively stable tectonic frame-work was maintained in the Manitoba portion of thebasin both during Interlake deposition and during sub-sequent pre-Middle Devonian uplift and erosion. Thisrelative tectonic stability may account in part, for thehighly dolomitized nature of the Interlake strata.

D evon ianDeposition of the basal Devonian Ashern formation

of the Elk Point Group marks the beginning of a ma-jor new depositional cycle and the establishment ofa completely different tectonic framework in south-western Manitoba. Whereas the Williston Basin wasthe controlling tectonic element during Ordovician andSilurian time, the Elk Point Bnsin became the con-trolling element during Devonian time. However, thetectonic framework of the basin is obscured to a con-siderable extent by “superficial” salt collapse features.

The most prominent feature of the Devonian mapsis the Birdtail-Waskada Axis, which comprises anorth-trending zone approximately 20 miles east ofthe Saskatchewan border (Figure 10) . As is shownin subsequent figures, this axis is the locus of a largenumber of local structure and isopach anomalies inDevonian and later strata. It marks the present east-em edge of the Prairie Evaporite salt basin ; it marksthe western edge of the Winnipegosis fringing reef;and it is coincident with the projected Churchill-Supenor boundary zone of the Precambrian basement.All of these factors probably are closely inter-related.

The complex local structures located along this axishave been important in controlling or modifying mostof the known oil accumulations i the shallower Mis-sissippian strata of Manitoba, and a correct inter-pretation of the origin and extent of these featureswill be even more important in determining the pros-pects for oil accumulation in the deeper Devonianand earlier strata along this zone. In any case, regard-less of the origin of these structurea, whether they aresuperficial salt collapse features or true tectonic features, the Birdtail-Waskada Axis certainly appearsto offer the best possibilities for future oil exploration within the map-area.

The isopachs of the basal Devonian Ashern for-nation (Figure 10) are markedly irregular and rep-resent, ia large part, an infiiljng of the previouslynoted topographic lows on the eroded Silurian surface.The structure contours on the top of the Ashern areof particular importance, as they are uniform andshow no evidence of any apprecialfie tectonic differentiation across the Birdtail-Waskada Axis. This sug

‘gests that the structure and isopach anomalies evidentin the overlying strata may be merely superficialfeatures.

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Neither of the next Devonian units, the Winnipegosis or overlying Prairie Evaporite, is a marker-defined unit, and the tectonic framework cannot be inter-preted directly from the isopachs. The top of the Win-nipegosis reflects the topography of a reef and inter-reef complex having local depositional relief of as muchas 200 to 300 feet. The Prairie Evaporite representsan infilling and overlapping of the Winnipegosis basin and is in large part a lateral equivalent of the Win-nipegosis. Despite this, the isopach of the Winnipegosis formation (Figure 11) shows several importantfeatures. The unit thickens rather uniformly towardthe west and northwest, to a maximum of 160 to 180feet. This probably represents sedimentation on arelatively stable shelf area building up to a fringingreef or bank along the southeastern edge of the ElkPoint Basin. West of the Birdtail-Waskada Axis, theWinnipegosis thins abruptly, coincident with a thick-ening of the Prairie Evaporite. This thinning is inter-preted as a facies thinning rather than a tectonicallycontrolled feature. The trend of the reef edge alongthe Birdtail-Waskada Axis is seen to be discordant tothe general basin framework, and it seems likely thatsome minor tectonic movement associated with theChurchill-Superior boundary zone occurred along theBirdtail-Waskada Axis during Winnipegosis time andwas sufficient to localize reef growth along the axis,but was not sufficient to show on the structure of theunderlying Ashern.

In the deeper part of the Elk Point Basin, alongthe northward continuation of the Churchill-Superiorboundary, further reef development is evident in theDuck Mountain, Swan River and Dawson Bay areas,where a series of patch reefs rise 250 to 300 feetabove the inter-reef platform. The original extent

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of the Elk Point Basin to the northeast is uncertain,but it must have extended for a very considerable distance inasmuch as the outcrop area on Dawson Bayrepresents a basinal facies.

The principal feature shown by the Prairie Eva-porite isopach (Figure 12) is the abrupt thinningalong the Birdtail-Waskada Axis, coincident with theedge of the fringing Winnipegosis reef. Additionaldeep well control probably would show the salt edgeto be much more irregular than indicated on this map.

The composite unit consisting of the Winnipegosis+ Prairie Evaporite (Figure 13) is an approximatemarker-defined unit ; consequently, the isopach reflectsthe true depositional framework, except for areaswhere salt solution has occurred. It shows a number0): features that are not evident on either of the Win-nipegosis or Prairie Evaporite maps. A very abruptthinning occurs at the present salt edge, and thisthinning is associated with a synclinal hinge or flex-ure which is down-warped to the east. (This featureis more easily seen if data are extended into Saskatchewan) . The synclinal flexure of the iop of the unitcoupled with the previously mentioned lack of structure on the underlying Ashern strongly suggests thatextensive salt solution has occurred along the presenteastern edge of the salt basin.

A number of factors probably have tended to local-ize the area of salt solution — notably the presenceof a thick underlying section of porous Winnipegosisreef or bank deposits that provided an aquifer for thecirculating formation waters which have cflssolved thesalt. Also, minor tectonic movement along the Bird-tail-Waskada Axis may have caused fracturing whichwould favour salt solution. The sharply defined, linearand cross-cutting structural lows in the Mississippianstrata of the field areas (Figure 21 ) are believed tobe due to salt collapse, and are certainly suggestive offracture-controlled solution channels.

Direct evidence for salt solution is noted in theseveral wells along the southern part of the BirdtailWaskada Axis, where the total section of Winnipegosis + Prairie Evaporite is locally thin. It will be seenin Figures 15, 17 and 19 that this thinning is corn-pensated for by a thickening of certain overlying strata. The northern limit of the Prairie Evaporite is alsoa solution edge, because Upper Palaeozoic strata areseen to be draped over the Winnipegosis reefs withno evidence of any change in thiciess. This drapingis best shown in the Swan River area, where the structure on the top of the Souris River formation reflectsthe underlying “reef topography” (Figure 14) . Atleast 200 to 300 feet of salt must have been removedfrom the inter-reef areas, largely during the post-Palaeozoic pre-Mesozoic erosion interval.

The Prairie Evaporite is overlain by the normalmarine strata of the Dawson Bay formation (Figure15) . Re-establishment of normal marine conditionsalmost certainly must have resulted in some solutionof salt from the top of the Prairie Evaporite, and theapparent truncation of the Prairie Evaporite potashbeds by the Davson Bay is one piece o evidence forthis.

The basal red shales of the Dawsn Bay probablyrepresent, in part, the insoluble residue from thissalt solution, and the previously mentioned areas oflocal salt solution on the southern end of the BirdtailWaskada Axis do in fact show a thickened DawsonBay section, due entirely to a thickening of the basalred beds.

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2 : i general, the Dawson Bay isopachs are quite er,4 ratic and bear little relation to the over-all basin

framework, as might be expected if pre-Dawson-Baysalt solution had occurred. In particular, note thethickening to the northeast of the Birdtail-Waskadaaxis, where Dawson Bay strata attain their maximumthickness at their erosional limit.

This thickening could possibly indicate relativelygreater subsidence in the Manitoba portion of the Ba-sin, but more likely it may represent thickening dueto solution of Prairie Evaporite salt immediately priorto or during Dawson Bay time. Structure contoursonce again indicate a synclinal flexure along the saltedge.

The isopach of the Souris River formation (Figure16) shows a relatively normal tectonic framework withuniform thickening toward an east-trending zone ofmaximum subsidence in the central part of the map-area. This probably represents the eastern end of theElk Point Basin, but to the east of the Birdtail-Waskada-Axis it is possible that salt collapse was a con-tributing factor, as the area of thick Souris Rivercoincides with the approximate edge of the Winnipeg-osis reef. Structure contours once again show thesynclinal flexure at the salt edge, and complex localstructures are evident in the northern area where Souris River strata are draped over the buried Winnipeg-osis reefs.

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pegosis - Prairie Evaporite isopach indicated salt solution, and the local thickening of the Duperow by over100 feet is almost certainly the result of salt collapseduring Duperow time. In the northern part of thesubcrop belt, the marked irregularities in isopachpattern are the result of differential truncation overthe reef-controlled structural highs noted previouslyin Figure 14.

For the Nisku formation (Figure 18) , the isopachpattern is seen to be quite irregular, possibly reflect-ing the biostromal nature of the unit, but there areno noticeable regional trends. This suggests a relative stabilization of the tectonic framwork towardthe end of the Devonian depositienal cycle.

The,. most prominent feature of this map is the1arge.ypnnber of synclinal structiwes occurring alongor peai the Birdtail Waskada Axis especially in thevicinity of the Mississippian oil fields where at leastfourteen prominent structural lo are evident. In allprobability, these structures are also present in mostof the underlying Devonian strata, but they do notappear on the preceding maps because of the lackof well control for pre-Nisku strata. Because of thislack of deep well control, it is riot possible to ascertam directly that these structures represent salt collapse features ; however, this apprs highly probable.Two closed structural highs occur along the southernpart of the Birdtail-Waskada Axi and are coincidentwith areas of earlier salt collapse. It seems likely thatthey are structural highs because of later salt solutionin surrounding areas ; such multiple-stage salt solution, giving rise to local structural highs in the areaof early salt solution, would appear to offer excellentpossibilities for Oil entrapment.

The isopach of the Duperow formation (Figure 17)is similar to that of the Souris River. However, asharply defined local thick is evident along the south-em part of the Birdtail-Waskada Axis. This is thesame area where a thinning of the combined Winni

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MississippianThe Ba,kken-Lyl&ton interval (Figure 19) represenLs

a composite unit f uppermost Devonian shales andbasal Mississippian shales, and includes the unconformable contact between the two. The isopach reflects primarily the eastward truncation of the Lyle-ton formation, but itmajor shift intheliston Basin rather than the Elk Point Basipwas the21na_flt tecLonic eiement duriiiiippian time

The main feature of the map once again is the largenumber of synclinal lows along the Birdtail-WaskadaAxis. In addition, three local isopach thicks occur alongthis axis, probably as a result of salt collapse duringBakken-Lyleton time. Two of these areas are nowstructural highs, indicating that later salt collapsehas occurred in surrounding areas.

Direct interpretation of the Mississippian tectonic- framework in Manitoba is uncertain because of the

! extensive erosion of these strata during the pre-JurasI sic erosion interval. However, regional isopachs of4 the lower Mississippian Lodgepole formation (Figure‘

20) indicate that, once again, the Manitoba portion ofthe Williston Basin, especially along the Birdtail-Was: kada Axis, underwent a slightly greater degree of

. subsidence than adjacent parts of the basin. The distrjHutjon of the piplie’al siale facies shci\v the effect of this differential subsidence.

The subcrcp map of the Mississippian erosion surface (Figure21) shows two windows of Mission Can-yon and Lodgepole strata along the southern part ofthe Birdtail-Waskada Axis. These are the result oftruncation of the previously mentioned local structural highs formed by early salt collapse. In addi

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tion, a well-defined change in orientation of the sub-crop belts is evident. Whereas the subcrop belts ofthe Lodgepole and earlier strata show a structuralrise to the northwest, the Mission Canyon and Charlessubcrop belts show a rise to the southeast. A possibleexplanation for this can be seen if the map is extended to include a somewhat larger portion of the basin(Figure 22) . A pronounced up-dip flexure of the sub-crop belts occurs along parts of the Birdtail-WaskadaAxis, indicating a synclinal structure which has beentruncated at the Mississippian erosion surface. Thisstructure may possibly be due to post-Mississippiansalt collapse, or it may indicate further tectonic sub-sidence along the Churchill-Superior boundary zone.

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Although the Manitoba portion of the Williston Ba-sin underwent greater subsidence throughout a con-iderable portion of Palaeozoic time, most notablyduring deposition of Ordovician and Mississippianstrata, this same area has been subjected to a greaterdegree of pre-Jurassic uplift and erosion, so that thethicker and more basinal facies of these strata are nowexposed at the erosion surface. This accounts in partfor the pronounced discordance between the isopachtrends and the subcrop belts previously noted for allPalaeozoic formations, and may be the result of agreater response of the Superior block to the tectonicforces giving rise to both basin subsidence and basinuplift.

In summary, then, the major tectonic elements ofthe Precambrian basement, especially the discontinuity between the Churchill and Superior provinces, andto a much lesser degree the east-trending. orogeniczones within the Superior block, apparently have beencenters of continued tectonic activity during Palaeozoic time. In addition to having had a direct effecton sedimentation at certain times, minor movementsassociated with these features have served to localizesuperficial isopach and structural features of a muchgreater magnitude, resñlting from differential corn-paction and salt solution. Differentiating between truetectonic structures and superficial structures, wherethe two are superimposed, is of critical importance in

evaluating the Palaeozoic tectonic framework and thepossibilities for oil accumulation in the Palaeozoicstrata of Manitoba.

AcknowledgmentThis paper was presented with the permission of

The Honourable Gurney Evans, Minister of Minesand Natural Resources, Manitoba.

. Selected ReferencesAlberta Society of Petroleum Geologists (1964) : “Geolo

gical History of Western Cana1a,” Alberta Soc. ofPetroleum Geol. Publication, 232 pp.

Andrichuk, J. M. (1959) : “O.rdovidan and Silurian Stratigraphy and Sedimentation in Southern Manitoba,Canada,” Amer. Assoc. Petrol. Geel. Bull., Vol. 43, No.10, pp. 2333-2398.

Baillie, A. D. (1953) : “Devonian System of the Willis-ton Basin Area, Manitoba,” Maflitoba Mines BranchPublication .52-5, 105 pp.

Bannatyne, B. B. (1966) : “Bibliography of Geology, Pa-laeontology, Industrial Minerals and Fuels in the Post-Cambrian Regions of Manitoba,” Manitoba MinesBranch Publication 66-1.

Davies, J. F., et al. (1962) : “Geology and Mineral Re-sources of Manitoba,” Manitoba Mines Branch Publication, 185 pp.

McCabe, H. R., (1959) : “Mississippian Stratigraphy ofManitoba,” Manitoba Mines Branch Publication 58-1.Porter, J. W., and Fuller, J. C. C. M. (1959) : “Lower Pa-laeozoic Rocks of Northern Williston Basin and Ad-jacent Areas,” Amer. Assoc. Petriil. Geol. Bull., Vol. 43,No. 1, pp. 124-189.

Wilson, H. D. B., and Brisbin, W. C. (1962) : “Tectonicsof the Canadian Shield in Northern Manitoba,” TheRoyal Society of Canada Special Publication No. 4,The. Tectonics of the Canadian Shield, np. 6045.

(Reprinted from The Canadian Mining and Metallurgical Bulletin, July, 1967)Printed in Canada

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