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IOt1 Perneability Gas Reservoirs in Marine Cretaceous Sandstones of Saskatchewan: 8. Viking Fo:nm.tion (Upper Albian) of Fast~ntral Saskatchewan

by F. Simpson

Stratigraphy The study area extends northwards fran the northern limit of 'To,mship 20 to the erosional edge of l.DNer Colorado strata and is further delimited by the Third Meridian and the Manitoba border {Fig. 1) .

In this paper, the relationship between the Viking Fonration (upper Albian) and the enclosing Joli Fou and Big River RUdstones and shales is discussed. The data presented here supplerrent the previous work of Sinpson (1979a, 1979b, in press).

The lower Colorado (Middle Albian to Cencrcanian) strata of east-central Saskatchewan are divi­sible into ~ three main units, recognized throughout the remainder of the province: the Joli Fou, Viking and Big River Fonration, listed from oldest to youngest. Glauconitic, rrostly fine-gr ained sandstones, of the Joli Fou Fonration in the western part of the area, are genetically related to the Spinney Hill Sandstone of west-central Saskatchewan. Other

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sandsta1es and siltstones, in the lower half of the Big River Fonnation in the northv.estem part of the study area, are tentatively assig­ned to the St. Walliurg Sandstone; their relationship to the Viking Formation is at present unclear. The Okla Sandstone (S.inpson, 1979b) forms a southward-thinning tongue of shaly, fine-grained sandstone and siltstone in the eastern half of the area under consi­deration. The Viking Fonnation, which separates the daninantly argillaceous Joli Fou and Big River Fonnations throughout rrost of the area, is the rrost extensive arenaceous sequence and is similar to the Vi.king of southeastern Sas.1<.atchewan, in terms of both lithologic associations and relationships with the enveloping shales and nuistones. 'As noted by Price (1963) , in sane parts of eastern Saskatchewan the Viking Fonnation

undergoes marked attenuation , to be replaced laterally by shale. At these locations, where the Big River shales and IlUldstones rest upon lithologically similar Joli Fou strata, differentation of the two units is difficult.

Facies relationships, which are to a large extent typical for the Ia-Ae.r Coloracb succes­sion of the central part of the study area are sh::Jwn in figure 2. In the north-central part of the area, the total thickness of the Ia-Ae.r COlorado arrounts to 70 m or less . The succession thickens southwards (to 117 min Well 6 of figure 2) and beyond the area to nore than 140 m. Along the line of section within the study area, the Joli Fou Fonration nore than doubles its thickness, fran 21 m to 48 m, whereas the Big River Fonnation undergoes a rrore gradual increase fran 69 m to 117 m.

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Fi g. 2 - North-south cross-section f rom Cali fornia Standard Bannock No. 15-5 we l l (lsd 15-5-46-9W2 ) to Homestead Amarillo W Benson 15- 20-6-9 well (Lsd 15-20-6-9W2}, showing lithologic variation i n Viking Formation (upper Alb ian) of east-cent ral Saskatchewan.

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The Viking Fonnation exhibits pronounced variation in thickness, which bears no si.nple oonsistent relationship to changes in thick­ness of the enveloping argillaceous units. In many instances an increase in Viking thick­ness between two wells along a line of section is readily denonstrated as being at the expense of the Joli Fou section , whereas the Big River shale underg:,es little or no change. This is typified in figure 2, Wells 4 and 5, within the study area and for Wells 9 and 10 farther south: in both cases, a northward thickening of the Viking Fonnation is accxmp.3nied by a decrease in Joli Fou thick­ness. However, the southerly increase in thickness of the Lower COlorado succession as a whole is such that a southward increase in Viking thickness may be accunpanied by thick­ness increase for the two argillaceous units. There appears to be lithologic oontinuity beh-leen the distal part of the Bow Island.­Viking succession of western Saskatchewan and the Viking strata in the southwestern comer of the stuly area. The detailed oorrelation of well logs is made nore di fficult, because of the shaly nature of the fine-grained sand­stones and sil tstones, but preliminary oorrelations suggest that the eastern Viking i s in the ui:per part of the spatially restric­ted, "ccriµ:>si te Viking" section.

An exanple of the northern Viking lithologies within the study area is provided by the section fran The Choiceland No. 1 well (Lsd 13-3-50-18W2}, which penetrate the Viking Formation between 119 . 8 m and 136. 8 m. At this location, the unit is ccriµ:>sed of kao­linitic, fine-grained sandstone and alterna­ting layers of san:lstone and mudstone . Flattened, sand-lined and mul-filled, tubular burrows are cx:mron and the trace fossil Spirophyton was observed near the base of the unit. The sequence is characterized by upward fining from the base, followed by a net upward decrease in intercalated mxlstone in the upper half of the unit. Fining-UfMard sequences are more distinctly defined in the rnultistorey arran~ts of sandstone bodies in the southern parts of the study area. Teichichnus and Phycodes are the dominant trace fossils of type - III and -IV sequence eleirents, whereas Chondrites occurs camonly in the upper parts of sandstone and siltstone layers belonging to type - II elerrents . The trace-fossil asserrblages are closely conparable to those reoorded fran Viking strata laid cb,m in a proximal-shelf setting in western SaskatchEWan (Slll{)son, 1975) . The strata discussed above include the rocks , designated "Ashville Sand" in the Kamsack-Hudson's Bay Junction area by Wickenden (1945) . H~ver, at present it is not known whether or not these beds are continuous with the Ashville Sand of south­western Manitoba (Sinpson , 1980) , and which

appears to pinch out east of the Manitoba border.

Discussion

The Viking sarrlstones and siltstones were laid davn on a s hallow, marine shelf. Joli Fou -Viking relationships suggest that at least a part of the Viking sequenoe was deposited in channels cut into the Joli Fou argillaceous deposits. The presence of a relatively thick Viking succession in the northern part of the stu:iy area indicates that the W'lit nust extend into a subcrop beneath the drift. This renders the sequence an unlikely prospect for c:nmrer­cial hydrocarbons there . On the other hand, in the central and southern parts of the area, this Fornation appears to be prospective . Pronounced thickness variation of the unit provides updip pinch-outs of sandstones into the Joli Fou shale s. Multi story arrangerrents of good reservoir sandstone and siltstone bodies, with shale breaks and strongly indu­rated sandstones as possible capping litho­logies, may contain ccmrercially significant quantities of petroleun. This vie.v is reinforced by nl.lll'erous reports of oil and gas sh<:Mings in the south .

References

Price, L.L. (1963) : Lower Cretareo.1s rocks of southeastern SaskatchEWan : Geol. Survey Canada, Paper 62-29, 55 p .

Silllpson, F . (1975) : Marine lithofacies and biofacies of the COlorado Group (middle Albian to Santonian) in Saskatchewan: p . 553-588, in caldwell, W.G.E . (Editor), The Cretaceous System in the Western Interior of North Anerica, Geel. Assoc . Canada, Special Paper 13, 666 p .

( 19 79a) : Low-penreabili t y gas reservoirs in marine, Cretaceous sarrl­stones of Saskatchewan: 1. Project out­line and rationale: p . 174-180, in ChristoEher, J.E. and Macrlonald, R. (Editors), SaskatchEWan Geel. Survey, Sumn:u:y of Investigations, 1979, Saskat­chewan Mineral Resources, Misc. Rept. 79-10, 227 p.

(1979b) : I..cM-perrooability gas reservoirs in marine, Cretaceous sand­stones of Saskatchewan : 3. Lower COlorado (middle Albian to Cenananian) strata of east-central Saskatchewan: p . 186-190, in Christopher, J .E. and Macdooald, R-:-(F.ditors), Saskatchewan Geel. Survey, Surmary of Investigations, 1979, Saskatchewan Mineral Resources, Misc. Rept . 79-10 , 227 p .

Sinp.3on, F. (in press): Lithologic descri1r tions of selected cored sections fran the Coloraoo and t-bntana Groups (midlle Albian to Carrpanian) of Saskatchewan: Saskatchewan Mineral Resources, Rept . no. 233.

Wiclcenden , R.T.D. (1945): Mesozoic strati­graphy of the eastem plains, Manitoba and Saskatchewan: Geol. Survey ca.naia, Man. 239 I 87 P•

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