Diagenesis of the Middle Devonian Winnipegosis Carbonates ...€¦ · The Middle Devonian Winnipegosis carbonates have been extensively altered by diagenesis. Dolomitized calcrete

Saskatchewan Geological Survey 1 Summary of Investigations 2005, Volume 1

Diagenesis of the Middle Devonian Winnipegosis Carbonates in South-central Saskatchewan 1

Qilong Fu 2, Hairuo Qing 2, and Katherine Bergman 2

Fu, Q., Qing, H., and Bergman, K. (2005): Diagenesis of the Middle Devonian Winnipegosis carbonates in south-central Saskatchewan; in Summary of Investigations 2005, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2005-4.1, CD-ROM, Paper A-7, 11p.

Abstract The Middle Devonian Winnipegosis carbonates have been extensively altered by diagenesis. Dolomitized calcrete profiles and paleokarst structures formed during subaerial exposure are the most striking diagenetic features of Winnipegosis mounds. The calcrete profiles are interpreted to have formed from diagenetic alteration of the host carbonate deposits in vadose zones. Paleokarst of the Winnipegosis mounds is characterized by extensive solution features, cavity sediments, and speleothems. Dolomite is a dominant carbonate phase in the Winnipegosis rocks. Petrographic, stratigraphic, and Sr-isotopic constraints suggest that microcrystalline to finely crystalline dolomite (Type 1) formed in the near-surface, evaporative marine environment. Medium-crystalline dolomite (Type 2) is interpreted to have precipitated from upward-migrating basinal fluids evolved from Devonian evaporitic seawater and postdated, or occurred coevally with, early stylolitization during burial. Two types of gypsum cement, macrocrystalline and selenite, are identified based on petrographic observations. Gypsum cements occurred in vugs and fractures and postdated the Late Cretaceous to Early Tertiary Laramide Orogeny.

Keywords: Diagenesis, Winnipegosis carbonate, Middle Devonian, calcrete, paleokarst, dolomitization, gypsum cementation, diagenetic sequence.

1. Introduction Strata of the Middle Devonian Winnipegosis Formation were deposited in Manitoba, Saskatchewan, south-western Alberta, North Dakota, and Montana in the Elk Point Basin south of the Peace River-Athabasca Arch (Figure 1). Hydrocarbon discoveries in the Estevan area in 1986 led to a renewed interest in Winnipegosis rocks (e.g., Rosenthal, 1987; Martindale and MacDonald, 1989; Teare, 1990; Kent and Minto, 1991; MacDonald et al., 1994; Yurkowski, 1995; Minto, 1996; Jin et al., 1997; Fu et al., 2004). In southern Saskatchewan, the Winnipegosis carbonate is an attractive target for hydrocarbon exploration. Diagenetic events that are imposed on the Winnipegosis deposits have significantly influenced the development of hydrocarbon reservoirs, and the study of these diagenetic processes is of great importance for development of effective exploration and production strategies.

The major diagenetic processes that have influenced porosity evolution in the Winnipegosis deposits are subaerial alteration, dolomitization, sulphate cementation, compaction, and fracturing (Wardlaw and Reinson, 1971; MacDonald et al., 1994; Yurkowski, 1995). This study documents the diagenetic history of the Winnipegosis carbonates in the Saskatoon area (Figures 1 and 2), based on the examination of more than 300 thin sections and over 40 cores. The petrography of diagenetic anhydrite in the Winnipegosis Formation has been described in detail in a previous study (Fu et al., 2002) and is not repeated here. This paper is a summary of a Ph.D. project on diagenesis of the Winnipegosis carbonates. More detailed descriptions and discussion can be found in the thesis by Qilong Fu (2005), a copy of which will be available in the libraries of the University of Regina and the Subsurface Geological Laboratory, Saskatchewan Industry and Resources.

The study area is located in the subsurface of southern Saskatchewan and covers approximately 47 160 km2, from Tp 28 to 50 and from Rge 15W2 to Rge 10W3 (Figures 1 and 2). In this region, the Winnipegosis Formation is composed of well developed mud mounds. Exploration for both hydrocarbon and potash deposits has made a number of high quality cored intervals and well log data available for this study.

1 This project is funded by an NSERC IOR grant to K. Bergman and J. Jin with matching funds from the Potash Corporation of Saskatchewan as well as an NSERC Discovery grant to H. Qing. 2 Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2; E-mail: [email protected] or [email protected]).


Figure 1 - Sketch map of the Devonian Elk Point Basin showing related tectonic elements, facies distribution of the Winnipegosis Formation in Manitoba and Saskatchewan and equivalent strata in Alberta, and thickness of Elk Point Group strata in metres (modified from Holter, 1969; Kent, 1994; and Meijer Drees, 1994). The study area is outlined by the pink rectangle in the Saskatoon area.

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Figure 2 - Isopach map (contours in feet) of the Winnipegosis and Ratner rocks in the study area. The Winnipegosis mud mounds are well developed in this area. Locations of sampled borehole cores are represented by solid blue circles.

2. Geological Setting In the study area, the Winnipegosis Formation disconformably overlies the Ashern Formation (Eifelian in age) and is overlain by the Prairie Evaporite (of Givetian age; see Figure 3). The Winnipegosis Formation has been divided into Lower Winnipegosis, Upper Winnipegosis, and Ratner members (Jones, 1965; Reinson and Wardlaw, 1972). The Ratner rocks consist of laminated dolostone changing gradually upward into interlaminated dolostone and anhydrite, and have been more recently elevated to formation status (Jin and Bergman, 2001). In inter-mound basinal areas, deposits of organic-rich laminate with interbeds of mound-derived detritus were named as the Brightholme Member (cf. Campbell, 1992; Jin and Bergman, 2001).

The Lower Winnipegosis Member is composed of mottled, sparsely to moderately fossiliferous, dolomitized or dolomitic mudstone to packstone. In the study area, the Upper Winnipegosis Member consists of dolomitized build-ups of mudstone, wackestone, packstone, floatstone, grainstone, and rudstone. The build-ups have a vertical height of up to 95 m and, based on core examination, appear to lack conspicuous, in-place, frame-building organisms. These build-ups are regarded as mud mounds rather than reefs (Reinson and Wardlaw, 1972; Gendzwill and

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Figure 3 - Stratigraphic nomenclature of the Elk Point Group in southern Saskatchewan and equivalent strata in northern Alberta.

Wilson, 1987). On the basis of well-log and seismic data, Gendzwill (1978) suggested that the Winnipegosis mud mounds are relatively steep sided and, at their tops, range in diameter from 0.5 to 6 km.

The Elk Point Basin extended over 3000 km in length from the present-day Northwest Territories in Canada to North Dakota in the United States (Figure 1), and is interpreted to have been located between latitudes 0° to 15°S of the equator during Middle Devonian time (Vander Voo, 1988; Witzke, 1990). The Tathlina High and the Presqu’ile Barrier Reef complex separate an open-marine shale basin to the north from the Elk Point Basin to the south. The Winnipegosis mud mounds developed on the low-relief slopes and basin floor of the Saskatchewan Sub-basin in moderate water depths, probably several tens of metres (Kendall, 1975).

Thermal history of the cratonic platform and foreland basin sequences in Saskatchewan records cycles of heating and cooling that follow the pattern of the regional burial history (Osadetz et al., 2002). In contrast to previous constant heat flow models, a study of apatite fission-track thermochronology suggests temporal variations in thermal history (Osadetz et al., 2002). A recently recognized Late Paleozoic heat-flow anomaly in the Saskatchewan Sub-basin was geographically close to an area of Middle Devonian to Carboniferous Kaskasia subsidence, and roughly coincident in time with the Antler Orogeny (Koehler et al., 1997; Osadetz et al., 2002). A second Phanerozoic peak temperature occurred during the Late Cretaceous-Paleogene Laramide Orogeny when the Winnipegosis carbonate was buried at maximum depth (Figure 4).

3. Paragenetic Sequence The Winnipegosis deposits have been extensively altered by diagenetic processes. The diagenetic history can be roughly divided into three stages: near-surface, early burial, and late burial (Figures 4 and 5). The transitions between stages are gradual and some diagenetic processes, such as pressure solution and anhydrite infilling, may occur in multiple stages. The following paragenetic sequence is generalized and is based on the compilation of the petrographic fabrics and geochemical data documented in the previous studies (Fu et al., 2004; Fu, 2005).

a) Early Near-surface Diagenesis In the near-surface stage, diagenetic alteration of the Winnipegosis carbonate is related to marine and early meteoric processes. Submarine lithification/cementation includes occurrence of isopachous, fibrous and micritic calcite cement rimmed peloids, and skeletal fragments. Calcrete profiles are present in the top portions of many Winnipegosis build-ups. Growth of pisolites was interrupted by leaching, in situ brecciation and non-tectonic fracturing. Solution channels and vugs are elongate, sub-parallel to bedding, and truncate pisolite and laminations (Fu et al., 2004). Such vugs are lined with a rind of dolomite crystals. All the calcrete features were dolomitized, indicating that early massive dolomitization postdated subaerial diagenesis. Karstification occurred during subaerial exposure (Fu, 2005). Crystallotopic anhydrite displacement is interpreted to be coeval with early dolomitization because the anhydrite crystals contain dolomite inclusions and dolomitization enhances lithification.

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Figure 4 - Burial history model of the Middle Devonian strata in the Baidon well (2-11-15-26W2) showing three diagenetic stages (age-depth data are after Osadetz et al., 2002).

Figure 5 - Paragenetic sequence for the Winnipegosis Formation illustrating the relative timing of the major diagenetic phases.

Winnipegosis-Prairie Sequence

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b) Early Burial Stage Physical compaction begins in the first several metres of burial (Shinn and Robbin, 1983, Choquette and James, 1990). Early generations of stylolitization are interpreted to occur in the latest Devonian to Permian when the Winnipegosis Formation was buried to a depth of between about 500 and 1500 m. The onset of stylolitization in limestone defines intermediate burial and occurs at 500 to 1000 m depth (Lind, 1993; Nicolaides and Wallace, 1997). The depths of stylolitization in dolostone is deeper because of the increased resistance to pressure solution (Mountjoy and Amthor, 1994). Lath-shaped anhydrite is replaced by acicular anhydrite in places. Acicular replacive anhydrite and acicular anhydrite cement are geochemically and petrographically similar. Acicular anhydrite occurred after early-stage dolomitization (see Section 5), and probably formed simultaneously with or postdated early stylolitization (Fu, 2005). Replacement and cementation of medium- to coarsely crystalline dolomite by acicular anhydrite has not been observed, implying acicular anhydrite predates late-stage dolomitization. The early crystallization of microcrystalline dolomite and the late-stage dolomitization are interpreted to have occurred during Carboniferous to Permian time.

c) Late-burial Stage Pressure solution (stylolitization) continued into the late-burial stage. Medium- to coarsely crystalline dolomite is locally cemented and replaced by blocky anhydrite, indicating blocky anhydrite cementation and replacement postdated the formation of medium- to coarsely crystalline dolomite. Late-stage fractures truncate stylolites and most diagenetic fabrics, and probably formed in response to tectonism associated with the Laramide Orogeny. Gypsum cement in fractures and solution vugs postdates the Laramide Orogeny because gypsum cannot survive burial temperatures greater than 60°C (cf. Testa and Lugli, 2000). Hydration of anhydrite and gypsum cementation are the latest diagenetic events. Anhydrite and gypsum cementation are critical processes in the reduction of porosity and permeability in the Winnipegosis rocks.

4. Subaerial Diagenesis Dolomitized calcrete profiles and paleokarst structures are the most striking diagenetic features related to subaerial exposure in the Winnipegosis mounds. Calcrete is widespread in the uppermost parts of the mounds with vertical relief greater than approximately 65 m and typically contains multiple (up to three) discrete profiles (Figure 6A). A well developed calcrete profile is generally composed of two to five layers that include (in descending order) laminar crust, massive, pisolitic, breccia, chalky, and transitional layers (Figure 6A). The dolomitized calcrete profiles are interpreted as pedogenic in origin due to diagenetic alteration of the host carbonate deposits in the vadose zones during subaerial exposure (Fu et al., 2004). This interpretation is based on the occurrence of an orderly set of well differentiated layers, disconformities, vadose pisoids, micritic stringers, circumgranular cracks, linkage coatings, and gradational contacts between the calcrete and underlying host carbonate rocks. In striking contrast to most Quaternary pedogenic calcrete, root-related structures such as rhizoconcretions and alveolar-septal structures are not observed, suggesting that the Winnipegosis calcrete has not been influenced significantly by macrophytes.

Paleokarst in the Winnipegosis Formation is characterized by extensive solution features as well as fractures, cavity sediments, and speleothems. Caverns and various sizes of vugs were developed in both calcrete successions and underlying host carbonate rocks (Figure 6B). The caverns, large vugs, and highly porous “Swiss-cheese” fabrics are interpreted to have formed in freshwater-saltwater mixing zones and/or to have occurred at or just below the water tables in the phreatic zones during subaerial exposure (Fu, 2005). Caverns and large vugs extend to 55 m below the top of the Winnipegosis mounds, indicating that the mixing zone has extended downward to this depth in response to the lowering of water-level in the Elk Point Basin.

Subaerial exposure of the Winnipegosis mounds was induced by drops in sea level (allocyclicity) and not by vertical accumulation of deposits into the subaerial realm (Fu et al., 2004). Growth of the Winnipegosis mounds was interrupted by at least three periods of subaerial exposure caused by drops of water level in the basin, as represented by three dolomitized calcrete profiles in the upper parts of many mounds. Periodic subaerial exposure and repeated changes in water-level have led to the development of karst features at various depths in the mounds corresponding to occurrence of the vadose, phreatic freshwater, and mixing zones at different levels.

5. Dolomitization In the study area, the Upper Winnipegosis build-ups are completely dolomitized, whereas the lower Winnipegosis and Brightholme members are either completely or partially dolomitized. Two major types of replacive dolomite are distinguished based on petrographic observations. Microcrystalline to finely crystalline dolomite (Type 1) displays nonplanar-a to planar-s textures, and mimetically replaces the precursor limestone (Figure 7). Medium-crystalline

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Figure 6 - Column sections showing three dolomitized calcrete profiles (A), and anhydrite-filled solution vugs and caverns (B) in the core 12-19-36-23W2. The mound is about 93 m (305 ft) thick.

Figure 7 - Photomicrograph showing textures of Type 1 and Type 2 dolomites. A) Very finely to finely crystalline, nonplanar-a, Type 1 dolomite [12-19-36-23W2, 1064.4 m, plane-polarized light]. B) Medium-crystalline, planar-s, Type 2 dolomite; note dolomite is cross-cut by stylolite [16-11-33-1W3, 1278.2 m, plane-polarized light].

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dolomite (Type 2) is fabric destructive, and shows nonplanar-a to planar-e textures (Figure 7B). Where dolomitization is incomplete, this type of dolomite preferentially replaces the finer matrix and allochems are preserved as calcite (Fu, 2005).

Type 1 dolomite occurs in the Upper Winnipegosis mounds, in the Lower Winnipegosis Member directly underlying the mounds, and, less commonly, in the Lower Winnipegosis and Brightholme deposits in the basin areas between the mounds. Generally, Type 1 dolomite decreases downward in abundance. Type 2 dolomite is dominantly present in the Lower Winnipegosis and Brightholme carbonate in the basin areas between the mounds, and less commonly in the Lower Winnipegosis deposits underlying the build-ups. The intensity of type 2 dolomite replacement decreases upward.

The average δ13C value of Type 1 dolomite (2.8‰ VPDB, n=32) is slightly higher than the corresponding limestone (1.7‰ VPDB, n=15). The negative shift in δ18O values of the dolomite (mean=-6.5‰ VPDB) compared to Middle Devonian marine dolomite (mean=-2.7‰ VPDB) is interpreted as the result of recrystallization at elevated temperatures during burial (cf. Qing, 1998; Fu, 2005). The 87Sr/86Sr ratios of Type 1 dolomite (mean=0.70802, n=8) coincide with the associated limestone (mean=0.70795, n=4) and fall within the range for Middle Devonian marine carbonate, suggesting that Type 1 dolomite precipitated from Middle Devonian seawater. Stratigraphic, petrographic, and geochemical data constrain the formation of Type 1 dolomite to hypersaline seawater in a near-surface environment, after marine cementation and subaerial diagenesis, and prior to the precipitation of the Leofnard salts (Fu, 2005). The hypersaline condition required for early massive dolomitization was established during precipitation of the Whitkow salts (Fu, 2005). The potential for dolomitization would have persisted until the build-ups were completely encased in the Prairie Evaporite that formed an aquitard preventing evaporative seawater from flowing downward into the carbonate deposits. Movement of dolomitizing fluids was driven by elevation head between inlet and distal part of the basin maintained by continuous evaporation and by density difference.

Type 2 dolomite has higher 87Sr/86Sr ratios (mean=0.70861, n=9) than the corresponding Middle Devonian marine carbonate, suggesting that the dolomite probably formed from basinal fluids enriched in radiogenic 87Sr (Fu, 2005). The δ13C values of Type 2 dolomite (0.7‰ VPDB, n=19) are comparable to those of the Lower Winnipegosis and Brightholme limestone (0.3‰ VPDB, n=4), and interpreted to be inherited from the precursor sediments. The lower δ18O values of Type 2 dolomite (-6.7‰ VPDB) are interpreted to be the result of elevated temperatures (Fu, 2005). Petrographic and geochemical evidence suggests that Type 2 dolomite was precipitated from upward-migrating basinal fluids, and dolomitization postdated, or occurred coevally with, stylolitization during the burial (Fu, 2005).

6. Gypsum Cementation Two types of gypsum cements, macrocrystalline and selenite, are identified based on petrographic observations. Macrocrystalline gypsum is only identified in thin sections and commonly occurs as single crystal cement filling solution vugs, channels and fractures in the Winnipegosis Formation (Figure 8A). Crystals of macrocrystalline gypsum cement range in size from less than a millimetre to tens of millimetres and display uneven or diffuse extinction in some samples. The gypsum crystals contain smaller anhydrite crystals and/or their residues (Figure 8A). Macrocrystalline gypsum cement is interpreted to be related to incomplete hydration of the blocky anhydrite cement (Fu, 2005).

Figure 8 - A) Gypsum cement (Gc) encloses remnants of anhydrite (An) [5-34-34-3W3, the Lower Winnipegosis Member, 1175.3 m, cross-polarized light]. B) Selenite gypsum cement (Gc) poikilotopically includes dolomite crystals and fragments [12-30-38-7W3, the Upper Winnipegosis Member, 1135.8 m, plane-polarized light].

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Crystals of selenite gypsum cement in the Winnipegosis rocks are up to tens of millimetres in size (Figure 8B). Selenite gypsum in several adjacent voids commonly forms a single crystal and shows uniform extinction. The gypsum crystals may poikilotopically include dolomite crystals or carbonate fragments (Figure 8B). Selenite gypsum is interpreted to have been derived from remobilized Middle Devonian anhydrite, and the more radiogenic Sr (mean = 0.70866, n = 4) is probably derived from basinal fluids (Fu, 2005). However, sulphate in the selenite gypsum may have a multiple origin associated with a complex geochemical history. Oxygen isotopic exchange and partial isotope equilibration between ambient water and aqueous sulphate had probably occurred before precipitation of selenite gypsum (Fu, 2005).

7. Summary The Winnipegosis carbonate deposits have been extensively altered by diagenetic processes. Dolomitized calcrete profiles and paleokarst structures are the most striking diagenetic features of Winnipegosis mounds formed during subaerial exposure. The calcrete profiles are interpreted to have formed from syn-depositional diagenetic alteration of the host carbonate deposits in vadose zones during periodic subaerial exposure of the Winnipegosis mound and are interpreted as pedogenic in origin.

Paleokarst of the Winnipegosis is characterized by extensive solution features, fractures, cavity sediments, and speleothems. Periodic subaerial exposure and repeated changes in sea level led to the penecontemporaneous development of karst features at various depths in the mounds corresponding to the occurrence of vadose, phreatic freshwater, and mixing zones at different levels.

Dolomite is a dominant carbonate phase in the Winnipegosis rocks. Petrographic, stratigraphic, and Sr isotopic constraints suggest that microcrystalline to finely crystalline dolomite (Type 1) occurred syn-depositionally in the near-surface, evaporative marine environment. The downward flux of brines was induced by gravity. Medium-crystalline dolomite (Type 2) is interpreted to have precipitated from upward-migrating basinal fluids evolved from Devonian evaporitic seawater. This late stage of dolomitization postdated, or occurred coevally with, early stylolitization during burial.

Two types of gypsum cement, macrocrystalline and selenite, are identified based on petrographic observations. Gypsum cements occurred in vugs and fractures and postdate the Late Cretaceous to Early Tertiary Laramide Orogeny. Macrocrystalline gypsum cement is interpreted to be related to incomplete hydration of the blocky anhydrite cement. Selenite gypsum is suggested to have been derived from remobilized Middle Devonian anhydrite, and sulphate in the selenite gypsum may have a multiple origin associated with a complex geochemical history.

8. Acknowledgments This project is funded by a NSERC (Natural Sciences and Engineering Research Council of Canada) IOR grant to K. Bergman and J. Jin with matching funds from the Potash Corporation of Saskatchewan and by a NSERC Discovery Grant to H. Qing. The Subsurface Geological Laboratory of Saskatchewan Industry and Resources (SIR) provided access to the cores and examination facilities at no charge. Guoxiang Chi at the University of Regina and Fran Haidl at SIR critically reviewed the manuscript.

9. References Baille (1953): Devonian System of the Williston Basin Area, Manit. Mines Branch, Publ. 52-5, 105p.

Campbell, C.V. (1992): Upper Elk Point megasequence; in Wendte, J., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian-Early Mississippian carbonates of the Western Canada Sedimentary Basin: A sequence stratigraphic framework; Soc. Econ. Paleontol. Mineral., Short Course 28, p145-162.

Choquette, P.W. and James, N.P. (1990): Limestones – burial diagenetic environments; in McIlreath, I.A. and Morrow, D.W. (eds.), Diagenesis, Geosci. Can., Reprint Series 4, p75-112.

CoreLab (2001): Stratigraphic Correlation Chart; Core Laboratories Calgary, poster.

Fu, Q. (2005): Diagenesis of the Middle Devonian Winnipegosis and Ratner deposits in southern Saskatchewan, Canada; unpubl. Ph.D. thesis, Univ. Regina, Saskatchewan, 210p.


Fu, Q., Qing, H., and Bergman, K.M. (2002): Petrography of diagenetic anhydrite in the Middle Devonian Winnipegosis and Ratner formations, south-central Saskatchewan; in Summary of Investigations 2002, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2002-4.1, CD-ROM, p15-23

__________ (2004): Calcrete in the Upper Winnipegosis Member in the subsurface of south-central Saskatchewan, Canada; Sed. Geol., v168, p49-69.

Gendzwill, D.J. (1978): Winnipegosis mounds and Prairie Evaporite Formation of Saskatchewan - seismic study; Amer. Assoc. Petrol. Geol. Bull., v62, p73-86.

Gendzwill, D.J. and Wilson, N. (1987): Form and distribution of Winnipegosis mounds in Saskatchewan; in Peterson, J.A., Kent, D.M., Anderson, S.B., Pilatzke, R.H., and Longman, M.W. (eds.), Williston Basin: Anatomy of a cratonic oil province; Rky. Mtn. Assoc. Geol., Denver, Colorado, p109-117.

Holter, M.E. (1969): The Middle Devonian Prairie Evaporite of Saskatchewan; Sask. Dept. Miner. Resour., Rep. 123, 134p.

Jin, J. and Bergman, K.M. (2001): Revised stratigraphy of the Middle Devonian (Givetian) Winnipegosis carbonate–Prairie Evaporite transition, Elk Point Group, southern Saskatchewan; Bull. Can. Petrol. Geol., v49, p441-457.

Jin, J., Bergman, K.M., Haidl, F., Blair, M., and Ricci, A. (1997): Vadose diagenesis of the Winnipegosis carbonate and the origin of the Ratner laminate and Whitkow anhydrite, Middle Devonian, southern Saskatchewan; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p197-212.

Jones, L.J. (1965): The Middle Devonian Winnipegosis Formation of Saskatchewan; Sask. Dep. Miner. Resour., Rep. 98, 101p.

Kendall, A.C. (1975): The Middle Devonian Winnipegosis and lower Prairie Evaporite formations of the commercial potash areas; in Summary Report of Investigations 1975 by the Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., p61-65.

Kent, D.M. (1994): Paleographic Evolution of the Cratonic Platform—Cambrian to Triassic; in Mossop, G. and Shetsen, I. (eds.), Geological Atlas of the Western Canada Sedimentary Basin, Can. Soc. Petrol. Geol./Alta. Resear. Counc., Calgary, Alberta, p68-87.

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Diagenesis of the Middle Devonian Winnipegosis Carbonates ...€¦ · The Middle Devonian Winnipegosis carbonates have been extensively altered by diagenesis. Dolomitized calcrete