A Revised Lithostratigraphic Framework and Characteristics of the Upper Devonian Duperow Formation, Southeastern Saskatchewan

Home , Manitoba Group, Saskatchewan Group

X.C. Cen 1 and O. Salad Hersi 1

Cen, X.C. and Salad Hersi, O. (2006): A revised lithostratigraphic framework and characteristics of the Upper Devonian Duperow Formation, southeastern Saskatchewan; in Summary of Investigations 2006, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2006-4.1, CD-ROM, Paper A-9, 17p.

Abstract The Duperow Formation in southeastern Saskatchewan forms the lower part of the Upper Devonian Saskatchewan Group and consists of three members: Saskatoon, Wymark, and Seward, in ascending order. The Saskatoon Member (17 to 37 m thick) consists of stromatoporoid floatstone, bioclastic wackestone/mudstone and subordinate dolomudstone, and anhydrite. Bioclasts include globular stromatoporoids, corals, brachiopods, bivalves, and crinoids. The Wymark Member (77 to 145 m thick) is also dominated by stromatoporoid/Amphipora floatstone/bafflestone and bioclastic packstone to mudstone with minor dolomudstone and anhydrite interbeds. A thin (0 to 6 m thick), discontinuous halite unit (the Flat Lake Evaporite) locally caps this member. Bioclasts in the carbonate portion of the member include globular stromatoporoids, Amphipora branches, corals, brachiopods, gastropods, and crinoids. The Seward Member (31 to 78 m thick) contains burrow-mottled bioclastic rudstone, packstone, wackestone, mudstone, dolomudstone, and rare anhydrite layers. Gastropods, bivalves, brachiopods, and crinoids form the most abundant framework grains in the member. The three members are internally organized in a shallowing-upward rhythmic sedimentation defined by recurring intervals of bioclast-rich, normal-marine, subtidal to inter-tidal lithofacies grading upward into more restricted lime-mudstone and dolomudstone, and evaporites. The restricting-upward rhythmic sedimentation is attributed to be the result of high-order, relative sea- level fluctuations affecting a broad lagoonal basin (the Duperow Embayment) separated from the open-marine Alberta Basin by coeval carbonate build-ups (e.g., the Leduc reefs).

Keywords: southeastern Saskatchewan, Upper Devonian, Duperow Formation, Saskatoon Member, Wymark Member, Seward Member, Flat Lake Evaporite, lithostratigraphy, carbonate-evaporite cycles, Williston Basin.

1. Introduction The Duperow Formation is a Late Devonian carbonate-dominated stratigraphic unit that accumulated in the Williston Basin and occurs in the subsurface of southern Saskatchewan, North Dakota, and Montana. Despite the formation’s chronostratigraphic equivalence to strata that host and produce significant amounts of hydrocarbons (e.g., the Leduc reefs of Alberta and the Duperow Formation of North Dakota and Montana), no substantial petroleum-producing reservoirs have yet been recognized in Saskatchewan. Also, as the stratigraphic, sedimentological, and diagenetic characteristics of the Duperow Formation in Saskatchewan are poorly known in comparison to those of equivalent intervals in the nearby regions, our studies are expected to improve our understanding of the reservoir potential of the formation, and may eventually kindle exploration interest. This paper presents the results of a detailed stratigraphic subsurface investigation of the Duperow Formation of southeastern Saskatchewan. The study area occupies the north-central and northeastern parts of the Williston Basin. It comprises a rectangular area bounded to the east by the Saskatchewan-Manitoba border, to the west by the Third Meridian, to the south by the Canada-U.S.A. border, and to the north by Township 20 (Figure 1). Our findings are based on data collected from 27 cores and 66 wireline logs (Table 1 and Figure 2). More detailed sedimentological information and microfacies examination of the Duperow Formation in southeastern Saskatchewan are provided in another paper in this publication (see Cen and Salad Hersi, this volume).

1 Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2; E-mail: [email protected] or [email protected].

Saskatchewan Geological Survey 1 Summary of Investigations 2006, Volume 1 0 km 300 2. Geological Setting n The Duperow Formation and the a w e conformably overlying Birdbear h Alberta tc Formation form the Upper a k Devonian Saskatchewan Group. s Calgary a Manitoba n S The Duperow conformably i overlies the Souris River s a Regina Formation of the Manitoba B Group (Figure 3). It was Study area deposited during the Late BC a t Devonian in the southeastern r e Western Canada Sedimentary b Duperow Basin (WCSB) in a backreef l setting southeast of the Leduc A Embayment reef barrier of the Alberta Basin. North Dakota The WCSB, a large, northwest- Montana southeast–oriented basin extending from the northwestern South Northwest Territories to Dakota southwestern Manitoba, was, in Idaho Devonian times, dominated by Wyoming accumulation of thick carbonate deposition (Moore and Richards, Figure 1 - Map showing location of the study area in southeastern Saskatchewan 1989; Wendte, 1992a, 1992b). (boxed area) (modified from Ehrets and Kissling, 1985). The strata are made up of thick, carbonate-dominated rhythmic Table 1 - Well localities in the study area in southeastern Saskatchewan referred to megasequences that indicate in this paper. large-scale sea-level fluctuations. These megasequences include, in Core ascending order, the Upper Elk Location Well Number Wymark Point (Gedinnian to Givetian), Sasktoon Seward lower middle upper the Beaverhill Lake (Givetian to Lower Frasnian), the Woodbend 1 131/11-36-22-1W2 x x x x x (Lower to Middle Frasnian), the 2 16-10-3-25W2 x x x x Winterburn (Upper Frasnian to 3 15-28-12-2W2 x lowermost Famennian), and the 4 6-33-7-8W2 x x x Wabamun (Lower to Upper 5 9-32-7-6W2 x Famennian) (Campbell, 1992; Stoakes, 1992a; Wendte, 1992a, 6 1-8-2-6W2 x x x 1992b, among others). They are 7 8-30-7-8W2 x well developed in the Alberta 8 2-11-10-9W2 x Basin (Figure 4) and become 9 16-34-6-11W2 x x thinner eastward into 10 12-2-7-11W2 x x Saskatchewan. This eastward 11 7-29-6-11W2 x x thinning is accompanied by pronounced lithological changes 12 3-26-4-20W2 x x that warrant application of 13 1-10-3-21W2 x different lithostratigraphic terms 14 11-19-5-28W2 x x x for strata in the eastern regions, 15 16-11-6-25W2 x x x x e.g., Saskatchewan (North 16 7-36-7-25W2 x American Commission on 17 11-14-22-6W2 x x Stratigraphic Nomenclature, 1983). The Beaverhill, 18 6-29-22-6W2 x Woodbend, and Winterburn 19 6-34-14-12W2 x megasequences correlate with, 20 1-28-24-10W2 x respectively, the Manitoba 21 9-20-20-25W2 x x x Group, the Duperow Formation 22 14-10-17-22W2 x x x and the Birdbear Formation of 23 16-10-21-25W2 x x southern Saskatchewan (Figure 4; Stoakes, 1992b). The 24 1-24-20-33W1 x x x x x Beaverhill, Woodbend, and 25 4-16-18-23W2 x Winterburn megasequences of 26 4-21-7-22W2 x 27 141/11-36-22-1W2 x x x x

Saskatchewan Geological Survey 2 Summary of Investigations 2006, Volume 1

104 102 106 1 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 25 20 24

23 18 1 27 22 17 23 21 21 24 20

18 25 22 17 MOOSE JAW REGINA 16 2 15 1 re 1 14 u 19 ig d 1 F n 13 ,a 0 3 12 , 1 11 , 9 s 8 8 10 re u 9 ig F WEYBURN 8 10 4 5 7 16 26 7 6 15 9 11 14 5

4 12 2 3 13 6 2 ESTEVAN 1 49 Figure 2 - Location of the study wells (filled circles represent wells with cores; open circles represent wells with no cores; both types of wells have wireline logs that are examined in this study). the Alberta Basin are dominated by reefs, open-marine carbonates, and deep-marine shales (Campbell, 1992; SOUTHERN PERIOD STAGE/ Stoakes, 1992b, 1992c). Toward the east, typical AGE SASKATCHEWAN depositional sites include reef-sheltered, shallow- BAKKEN marine to lagoonal settings where cyclic sedimentation THREE of open to restricted carbonates and evaporites FORKS BIG VALLEY FAMENNIAN GROUP predominate. The Duperow Formation, which is the TORQUAY focus of this study, is characterized by rhythmically R BIRDBEAR E bedded, shallow-marine limestones, dolostones, and P

P SASKATCHEWAN evaporites organized in a shoaling-upward pattern U GROUP DUPEROW N FRASNIAN (Andrichuk, 1951; Wilson, 1967; Kent, 1963, 1968; A

I Dunn, 1975; Wilson and Pilatzke, 1987). The formation

N SOURIS RIVER MANITOBA was deposited in a south-southeast–oriented, shallow- O GROUP marine, inner platform setting termed here the V DAWSON BAY

E “Duperow Embayment” (Figure 1). Besides E GIVETIAN

L PRAIRIE D

D ELK EVAPORITE correlations with known Late Devonian strata (e.g., D I POINT Stoakes, 1992a), recent biostratigraphic conodont M EIFELIAN WINNIPEGOSIS GROUP ASHERN dating (McCracken and Kreis, 2003) has indicated that DALEJAN the Duperow Formation is Late Devonian (Frasnian) in R EMSIAN E age.

W PRAGIAN O

L LOCHKOVIAN

Figure 3 - Chart showing Devonian stratigraphic succession of southwestern and southeastern Saskatchewan (after Sask. Industry Resources, 2003).

Saskatchewan Geological Survey 3 Summary of Investigations 2006, Volume 1

east EWAN S W South HERN

RK R RO

FO EA PE

E DB DU SOUT

RE BIR

SASKATCH

ER IV NATE-

NAL R

R CESSIO U

C SO CARBO E BASI DU IC SUC LE of the Alberta Basin to west (modified ONATE ICTED OW WATER MARIN N O OPEN RESTR EVAPORIT CARB SHALL ET

E E AK

LEDUC

L ILL

D RH

EN VE

UP A DB

ta RO BE O er G O lb W

UP A

rata of southern Saskatchewan and those RN GROUP RN RO EON C G E DU UN LE AM LAK STURG

AB WINTERBU W ON C OF SECTI DU LE TE CROSS LINE GRANI WASH the lateral relationship between Devonian st PEACE RIVER A IS K A ,K R E RN IV UMBIA R T N U

O HO O R IE EASTE PS TC ,T H COL O AR FE IM KO H S NI C M T RT TE DK AN NORTH FO BRITIS

RE JE Northwest from Stoakes, 1992b). Figure 4 - Schematic cross section showing

Saskatchewan Geological Survey 4 Summary of Investigations 2006, Volume 1 3. Lithostratigraphy of the Duperow Formation a) Previous Work The earlier lithostratigraphic work on the Late Devonian strata of southern Saskatchewan includes Andrichuk (1951), Powley (1951), Baillie (1953), and Sandberg and Hammond (1958) (Figure 5). In southern Saskatchewan, Andrichuk (1951) recognized cyclic limestone, dolomite, and anhydrite strata that he divided into two units: Upper Dolomite-Evaporite and Lower Limestone units (Figure 5), the latter being roughly equivalent to the actual Duperow Formation, as used in more recent publications (e.g., Kent, 1963, 1968; Dunn, 1975; and this paper). Andrichuk (1951) used the evaporite cycles for basin-wide correlations. The first work to use the name Duperow Formation was that of Powley (1951); it was applied to strata that are not equivalent, but rather slightly older than Andrichuk’s (1951) Dolomite-Evaporite succession (Figure 5). Baillie (1953) subdivided the Devonian system of the Williston Basin into four different groups, i.e., Elk Point, Manitoba, Saskatchewan and Qu’Appelle groups. His Saskatchewan Group contained a lower unnamed unit and an upper Nisku Formation (Figure 5). Later, Sandberg and Hammond (1958) revived the name Duperow, but applied a stratigraphic interval roughly equivalent to the “unnamed” unit of Baille (1953). This stratigraphic interval is different from that originally assigned by Powley (1951). Sandberg and Hammond’s (1958) Duperow Formation included the lower part of the Saskatchewan Group. It spanned the upper contact of the Souris River Formation (upper unit of the Manitoba Group) and the lower contact of the Birdbear Formation (upper unit of the Saskatchewan Group, Figure 5). Sandberg and Hammond (1958) selected the Mobil Producing Co. Birdbear No.1 well in North Dakota as the reference section for the Duperow Formation and picked up argillaceous dolomudstones that exhibited high-gamma kicks as marker beds. Six of these high-gamma argillaceous dolomudstones were recognized to occur within the Duperow Formation. These marker beds are relatively extensive and were later used by Wilson (1967), Dunn (1975), Kent (1968), and Ehrets and Kissling (1985) to enhance the Duperow Formation correlation.

The most prominent lithostratigraphic partition within the Duperow Formation was based on regional studies by Wilson (1967), Kent (1968), and Dunn (1975). Wilson (1967) mainly addressed the Duperow Formation of North Dakota and, to a lesser extent, southern Saskatchewan; he recognized two informal units: lower and upper (Figure 6). Later, Wilson and Pilatzke (1987) subdivided the lower Duperow into five informal units (1 to 5) with further stratigraphic, lithofacies, and sedimentary cycles in the lower Duperow Formation. Kent (1968) studied the Duperow Formation of southwestern Saskatchewan. He identified four stratigraphic intervals that include, in ascending order, the Saskatoon, Elstow, Wymark, and Seward members (Figure 6). The Elstow and Seward members are lithologically similar and contain argillaceous carbonate rocks, whereas the Saskatoon and Wymark members are predominantly non-argillaceous, clean carbonates. Dunn (1975) studied the Duperow Formation of southeastern Saskatchewan; he did not use Kent’s (1968) nomenclature, instead proposing four informal units (1 to 4). To justify his rejection of Kent’s terminology, Dunn stated that the Elstow Member could not be readily traced into southeastern Saskatchewan because of facies change and that the Wymark-Seward contact is not clearly discernible everywhere. In a short course report, Kent (1983) indicated that a modified version of his nomenclature for southwestern Saskatchewan (Kent, 1968) could also be applied to the Duperow Formation of southeastern Saskatchewan. He recognized that the two lower members (Saskatoon and Elstow members) could not be differentiated and, therefore, combined them (Figure 6).

b) Revised Andrichuk (1951) Powley (1951) Baillie (1953) Sandberg and Hammond Southeast Sask. Central Sask. Williston Basin (1958) Williston Basin Lithostratigraphy Detailed subsurface e

l lithostratigraphic mapping of the M1 l e Post-Evaporite Unit p p u Duperow Formation in p o Three Forks Formation p r A ’

u southeastern Saskatchewan and G

u o

r M2 Q Dolomite-Evaporite comparison with that of G

Unit M3 Nisku Fm. southwestern Saskatchewan w

n Birdbear Formation n a enabled us to trace the members, a a J i

M4 w e

e except the Elstow Member n p h s c u o t o M5 which disappears toward the o a r v o

k Unnamed Unit

G Duperow Formation east, defined by Kent (1968), s e

Lower-Limestone a

D Unit M6 into southeastern Saskatchewan. The lithostratigraphic attributes Duperow of the three members of the Formation Duperow Formation in a b p

o southeastern Saskatchewan are u t i Souris River Formation o n r discussed below. We propose Hudson Bay a G

Basal Devonian Unit M Formation that the core of well 11-36-22- Figure 5 - Previous Duperow Formation lithostratigraphic classifications.

Saskatchewan Geological Survey 5 Summary of Investigations 2006, Volume 1 Southwest Southeast Saskatchewan WILLISTON BASIN Saskatchewan GR 11-36-22-1W2 SONIC (Wilson, 1967) (Kent, 1968) Kent (1983) Dunn (1975) This Paper (LOC. 1)

SEWARD SEWARD SEWARD UNIT 4 MEMBER MEMBER MEMBER 1900' UPPER DUPEROW

N A O I

T UNIT 3 UPPER A UPPER UPPER R M R E R E R B E B B B M O P1 M E M F E E

M M

W P2

K K R

O M M R

A M R ID ID ID A A

R D D UNIT 2 M D X L L L M

E Y M E

E E Y Y W P W W

U LOWER D DUPEROW C1 LOW LOW LOW ER ER ER 2200' C2

ELSTOW MEMBER ELSTOW UNIT 1 MEMBER + ? SASKATOON SASKATOON MEMBER SASKATOON MEMBER MEMBER

Anhydrite Stromatoporoid floatstone/ bafflestone Dolostone Argillaceous dolomudstone Limestone

Figure 6 - Stratigraphic nomenclature applied to the Duperow Formation in southeastern Saskatchewan.

1W2 be the reference section for the formation and its three members in southeastern Saskatchewan.

The Saskatoon Member The Saskatoon Member is the lowermost unit of the Duperow Formation and conformably overlies the Souris River Formation of the Manitoba Group. The basal boundary is defined by a firmground surface that separates highly burrowed bioclastic wackestone (upper Souris River Formation) from overlying argillaceous dolomudstone (lower Saskatoon Member, Figure 7). The upper boundary of the Saskatoon Member is placed at the base of the argillaceous dolomudstone noted as the C2 marker bed by Sandberg and Hammond (1958). The thickness of the member in the study area ranges from 17 to 37 m; in the reference core, it is 26.98 m (from 2203 feet [671.47 m] to 2291.5 feet [698.45 m], Figure 8). The member consists of various lithofacies of limestone, dolostone, and anhydrite. The limestone lithofacies includes light to dark brown stromatoporoid floatstone/bafflestone, bioclastic wackestone, and mudstone. The member is thin to medium bedded with beds locally separated by dark argillaceous seams. Bioclasts in the limestones include tabular and globular stromatoporoids, corals, brachiopods, bivalves, and crinoids. Wavy to horizontal laminations, horizontal burrows (Planolites and Thalassinoides), firmgrounds and minor mudcracks are observed in wackestone and mudstone lithofacies. Diagenetic features in the limestones include stylolites and secondary anhydrite crystals. The dolostone lithofacies includes two sublithofacies: light to

Saskatchewan Geological Survey 6 Summary of Investigations 2006, Volume 1 dark brown, thinly bedded to A wavy- to microbially-laminated, stromatolitic dolomudstone and grey-green, indistinctly laminated argillaceous dolomudstone. The argillaceous dolomudstone is characterized by a high-gamma kick, which is typical of the Duperow B sublithofacies throughout the Formation formation and is therefore used to identify them as marker beds for correlation (this includes Sandberg and Hammond’s Souris River (1958) C marker layer). The anhydrite lithofacies is defined Formation by nodular or mosaic, bluish white anhydrite beds. The upper contact of anhydrite is sharp to erosional to the overlying argillaceous dolomudstone. The latter locally contains small horizontal burrows and thin wavy to lenticular bedding/laminations. The three lithofacies are arranged Figure 7 - A) Core photograph showing the contact between the Souris River in a cyclical pattern where Formation and the Duperow Formation; B) the contact is marked by a firmground surface with burrows penetrating the upper part of the Souris River Formation (1- limestones are generally followed 24-20-33W1, LOC. 24, 2495.5 feet [760.63 m]). by the dolostone lithofacies, which is, in turn, overlain by the anhydrite lithofacies. The high- gamma argillaceous dolomudstone either lies at the top of the erosional to sharp upper contact of the anhydrite lithofacies or occurs between beds within the limestone lithofacies. The argillaceous lithofacies is interpreted to represent a marine flooding surface that heralded the start of a new (high order) relative sea-level rise (Cen and Salad Hersi, 2005).

Cyclicity within the Saskatoon Member

Seven complete and incomplete cycles (S1 to S7 in ascending order) can be identified in the Saskatoon Member. Figure 8 shows the Saskatoon Member lithologies in cores from two widely separated wells, 11-36-22-1W2 in the northeast and 16-10-3-25W2 over 300 km to the southwest. The predominance of limestone is evident in each cycle. The thickness of cycles is variable.

In the reference well, only cycles S2 and S7 are complete. Bioclastic wackestone-packstone containing brachiopods, bivalves and crinoids, and interbedded stromatoporoid-constructed floatstone/bafflestone are overlain by nodular crinoidal wackestone and mudstone. The capping unit of the cycle is stromatolitic dolostone and anhydrite with nodular and laminated structures. This is generally followed by grey-green argillaceous dolomudstones attributed as the basal “transgressive” unit of the overlying cycle (Cen and Salad Hersi, 2005). Sedimentary cycles S1, S3, S4, S5, and S6 in the Saskatoon Member are incomplete, and anhydrites are generally not well developed. Cycle S3 is poorly defined, because of lack of the anhydrite and the argillaceous dolomudstone lithofacies. Lithoclastic breccias lie at the top of the S3 cycle, possibly indicating desiccation-related mud chips. The cycles of S5 and S6 are poorly defined in 11-36-22-1W2 due to the absence of the cycle-capping dolomudstone and anhydrite lithofacies, but are relatively well developed in 16-10-3-25W2. They mainly contain stromatoporoid floatstone/bafflestone, nodular wackestone, and mudstone.

The Wymark Member This member is the thickest unit of the Duperow Formation in southeastern Saskatchewan, its thickness ranging from 77 to 145 m. The upper boundary of the Wymark Member is placed at the base of the predominately argillaceous dolomudstone noted as “marker bed A” by Sandberg and Hammond (1958) (Figure 6). This member is informally subdivided into lower, middle, and upper units.

Saskatchewan Geological Survey 7 Summary of Investigations 2006, Volume 1 16-10-3-25W2 11-36-22-1W2 (LOC. 2) (LOC. 1) CYCLE 7544' 2203' S7

S5 LEGEND

S4 Lime mudstone

Lime wackestone ?

S3 Lime packstone

Lime grainstone and rudstone 7605' Lime floatstone/bafflestone

Dolostone

t m

1 S2

1 . Dolomitic limestone 3

Dolostone and anhydrite interlayer ?

Anhydrite S1 ? Argillaceous dolostone 2291.5'

Algal head Laminated Contorted bedding Bivalves Bioclasts Wavy laminated Bioturbation (light/intensive) Gastropods Lithoclasts Stylolite Crinoids Thin bedded Ooids Medium bedded Desiccation cracks Brachiopods Peloids Fracture Stromatoporoids Thick bedded Firmground Burrowing Evaporite nodulars Coral (undifferentiated) Vuggy porosity Amphipora Organic seams Mottle Breccia

Figure 8 - Lithostratigraphic strip-log and cycles of the Saskatoon Member across the study area.

Saskatchewan Geological Survey 8 Summary of Investigations 2006, Volume 1 The Lower Unit of the Wymark Member The lower Wymark lies between 2203 feet (671.47 m) and 2170 feet (661.42 m) in 11-36-22-1W2 (Figure 9). Its upper termination is marked by the base of an argillaceous dolomudstone (Sandberg and Hammond’s (1958) C1 marker bed). This unit is dominated by various limestones lithofacies that include light to dark brown, laterally persistent, stromatoporoid floatstone/bafflestone (cf. Kent, 1998), and nodular wackestone and mudstone. Minor burrow-mottled and argillaceous dolomudstone and interbedded nodular anhydrite are also present. Bioclasts in the limestones include tabular, bulbous and branching stromatoporoids, corals, brachiopods, bivalves, and crinoids. Clay seams and horizontal burrows give the unit a somewhat nodular appearance. Diagenetic features in the limestones include vuggy porosity filled with various generations of anhydrite cements. The dolostone lithofacies is mostly overlain by the anhydrite lithofacies with mainly gradational contacts seen either as a mixture of dolomite and nondiagenetic anhydrite nodules or as contorted bedding possibly due to growth of anhydrite crystals in the upper part of the dolomudstone in a hypersaline environment. The anhydrite lithofacies is rare and characterized by light bluish white, nodular or mosaic anhydrite beds.

Cyclicity within the Lower Unit of the Wymark Member Only one complete, well defined cycle (W1) has been recognized in this unit (Figure 9). It begins with bioclastic wackestone and stromatoporoid floatstone/bafflestone containing tabular and branching stromatoporoids, corals, branchiopods, bivalves, and crinoids. They are followed by generally nodular to medium- and thin-bedded wackestone to mudstone lithofacies. The cycle is capped by dolomudstone interbedded with anhydrite.

The Middle Unit of the Wymark Member

This unit is represented by the strata between 2034 feet (619.96 m) and 2170 feet (661.42 m) in 11-36-22-1W2 (Figure 10). Throughout the study area and beyond the Saskatchewan border, its upper boundary is well recognized on wireline logs by the gamma-ray signature denoting the base of marker bed B (Wilson, 1967; Kent, 1968). The

16-10-3-25W2 CYCLE 11-36-22-1W2 (LOC. 2) (LOC. 1)

7507' 2170'

t e m

e f

1 0

. 1 3

2203'

7544'

Figure 9 - Lithostratigraphic strip-log and cycles of the lower Wymark across the study area. See Figure 8 for the legend.

Saskatchewan Geological Survey 9 Summary of Investigations 2006, Volume 1 middle unit consists of lower and 16-10-3-25W2 CYCLE 11-36-22-1W2 (LOC. 2) (LOC. 1) upper parts separated by the base of an argillaceous dolomudstone 7325' (P1 marker bed of Sandberg and Hammond, 1958), which exhibits good lateral persistence in southeastern Saskatchewan.

t The lower part of the middle

3.13 m Wymark is characterized by

0 1 rhythmic successions of light to dark brown, stromatoporoid floatstone/bafflestone, bioclastic ? packstone, wackestone, and W11 mudstone. Dolostone and anhydrite beds are also present. 2034' Bulbous, tabular, and branching stromatoporoids are the predominant skeletal grains. Other bioclasts include brachiopods, gastropods, bivalves, and crinoids. Wavy to irregular clay seams and vertical W10 burrows are common. Diagenetic features include vuggy porosity and anhydrite nodules. The dolostone lithofacies includes two main sublithofacies: buff- coloured, thin-bedded to W9 microbially laminated, microcrystalline dolomudstone, and indistinctly laminated, grey- W8 green argillaceous dolomudstone. The anhydrite lithofacies is W7 characterized by medium- bedded, light blue, laminated to nodular anhydrite beds. These W6 lithofacies show a rhythmic pattern that defines a restricting- W5 upward succession (see below for further discussion). W4 The upper part of the middle Wymark mainly consists of W3 bioclastic packstone, wackestone, and mudstone with minor dolostone and anhydrite. W2 Stromatoporoid floatstone/ 2170' 7507' bafflestone is rare. The limestone lithofacies is partially dolomitized. The bioclasts in the Figure 10 - Lithostratigraphic strip-log and cycles of the middle Wymark across the limestone include bivalves, study area. See Figure 8 for the legend. gastropods, brachiopods, and crinoids. Non-fossiliferous framework grains include peloids, intraclasts, and rare ooids. Firmgrounds and rare desiccation cracks are present. Bioturbation is locally intensive. The dolostone lithofacies mainly consists of grey-green argillaceous dolomudstone that is laterally extensive and persists beyond the study area (Sandberg and Hammond, 1958; Wilson, 1967; Dunn, 1975).

Cyclicity within the Middle Unit of the Wymark Member Figure 10 illustrates the lithological succession of the middle unit and its lateral variations. Ten incomplete and complete sedimentary cycles (W2 to W11), of which eight occur in the lower part and two in the upper part, have been identified in this unit. The two cycles in the upper part of the unit (W10 and W11) are dominated by bioclastic

Saskatchewan Geological Survey 10 Summary of Investigations 2006, Volume 1 wackestone and packstone with brachiopods, gastropods, bivalves, and crinoids. The anhydrite lithofacies is rarely developed. The cycles of W2 to W9 are better defined in 16-10-3-25W2 than in 11-36-22-1W2. Where complete, the cycles begin with bioclastic packstone, stromatoporoid floatstone/bafflestone overlain by dolostone which is in turn capped by anhydrite. These cycles are relatively poorly defined in 11-36-22-1W2 because the cycle-capping dolostone and anhydrite lithofacies are generally absent. The limestone lithofacies mainly includes tabular or bulbous stromatoporoid floatstone interbedded with branching stromatoporoid floatstone and nodular wackestone and mudstone. Branching stromatoporoid (Amphipora spp.) floatstone with an organic-rich matrix indicates deposition in a more restricted environment than that suggested by tabular and bulbous stromatoporoids, which imply higher energy environments such as banks. The 16-10-3-25W2 CYCLE 11-36-22-1W2 tops of these cycles are, (LOC. 2) (LOC. 1) therefore, discerned by the ? presence of branching 7230' stromatoporoid floatstone and nodular wackestone/mudstone.

t m

e 3

. The Upper Unit of the Wymark

0 3 1 Member W17 The upper unit of the Wymark 1952' Member lies between 1952 feet (594.97 m) and 2034 feet (619.96 m) in 11-36-22-1W2 (Figure 11). The upper boundary of the unit, which is also the W16 boundary of the Wymark Member, is defined by the base of a widespread argillaceous dolomudstone that Sandberg and W15 Hammond (1958) identified as the “A marker bed”. The Flat Lake Evaporite consists of laterally discontinuous lenses, 0 to 6 m thick that may be present as the uppermost unit of Wymark Member; where the Flat Lake W14 Evaporite is missing, due to either non-deposition or dissolution, wackestone and/or mudstone make up the uppermost beds. The Flat Lake Evaporite, named by Dunn (1975), is almost exclusively formed of halite. It appears to have been deposited during a near-complete dry-out of the basin before the return of normal marine conditions that prevailed during deposition of W13 the overlying the Seward Member. Thus, due to the presence or the absence of the Flat Lake Evaporite, the thickness of the upper unit of the Wymark Member varies. The unit is dominated by light to dark brown, bioclastic mudstone, wackestone, packstone, and sparse stromatoporoid W12 floatstone/bafflestone. Bioclasts 7325' 203 4' in the limestones include brachiopods, gastropods, bivalves, stromatolites, tabular Figure 11 - Lithostratigraphic strip-log and cycles of the upper Wymark across the stromatoporoids, and crinoids. study area. See Figure 8 for legend. Wavy to irregular clay seams,

Saskatchewan Geological Survey 11 Summary of Investigations 2006, Volume 1 firmground, and vertical burrows are present in wackestone and mudstone lithofacies. Small stylolites are a common diagenetic feature in these limestones. Minor dolostone of two types, wavy laminated stromatolite dolomudstone and distinctly laminated argillaceous dolomudstone, and anhydrite lithofacies are also developed. The anhydrite content increases in the upper part where two thick (1.5 and 4.5 m) anhydrite layers exhibit good lateral persistence and can be traced in most of the study area. As for other units of the formation, lithofacies of the upper Wymark are arranged in rhythmic successions with overall “restricting-upward” depositional settings (e.g., the Flat Lake Evaporite).

Cyclicity within the Upper Unit of the Wymark Member Six complete and incomplete sedimentary cycles (W12 to W17) have been identified in this unit. All the cycles are well developed in core from both wells (Figure 11) and are clearly discernable. W14 to W17 cycles are incomplete and dominated by anhydrite and argillaceous dolomudstone. The anhydrite layers exhibit lateral persistence and can be traced through most study Composite area. Cycles W12 and W13 are Core log thicker than the other cycles of 4-16-18-23W2 (LOC. 25) this unit. At their base, the cycles 16-1 1-6-25W2 (LOC. 15) CYCLE 11-36-22-1W2 are formed of bioclastic (LOC. 1) wackestone and packstone associated with stromatoporoid ? 1816' floatstone; these are overlain by nodular wackestone and ? mudstone suggesting semi- Se7 restricted to restricted ? depositional environments. The Se6 cycles are normally capped by Se5 anhydrite.

The Seward Member

t The Seward Member occurs m

e e 3 f

between 1816 feet (553.52 m)

1 . 0 1 3 and 1952 feet (594.97 m) in 11- 36-22-1W2 (Figure 12). The upper boundary of the member, which is also that of the Se4 Duperow Formation, is conformable with the overlying Birdbear Formation (Dunn, 3970' 1975). The base of a reddish brown to greenish grey argillaceous dolomudstone marks the top of the Seward Member over much of the study area (Figure 13).

The thickness of the Seward Se3 Member ranges from 31 to 78 m. This member is characterized by 4008' its high argillaceous content 6374’6" Se2 compared with that of other members of the formation. Its lithology is dominated by limestone of various sublithofacies, but dolostone and Se1 rare anhydrite lithofacies are also present. The limestone lithofacies includes medium- to thick-bedded, burrow-mottled, 6406' 1952' buff to light brown bioclastic rudstone and laminated to thin- Figure 12 - Lithostratigraphic strip-log and cycles of the Seward Member across the bedded bioclastic mudstone to study area. See Figure 8 for legend. packstone. Vuggy porosity, in

Saskatchewan Geological Survey 12 Summary of Investigations 2006, Volume 1 places partly filled by evaporite minerals and calcite, is particularly well developed. The mudstone to packstone sublithofacies contains intraclasts and bioclasts. The latter include gastropods, bivalves, brachiopods, and crinoids. Like n

o the Wymark Member, the i n t o a dolostone lithofacies in the i t m

a Seward Member consists of two r o m sublithofacies: thinly to r F

o microbially laminated, buff- w F

r coloured microcrystalline r a e dolomudstone and grey-green e p b

u argillaceous dolomudstone. d r D i Fractures and vuggy porosity in B the microcrystalline dolomudstone are mainly filled by anhydrite and/or halite.

Cyclicity within the Seward Member

Cyclicity within the Seward Member is similar to that in the Contact Wymark except that the anhydrite component appears to be much less developed. Seven cycles (Se 1 to Se 7), some complete, are recognized (Figure 12). The lithological strip-log shown for the southwest (the short section on the left in Figure 12) is a composite from two cores, the upper half from 4-16- 18-23W2, the lower from 16-11- Figure 13 - Contact between the Birdbear and Duperow formations (8-30-7-8W2, 6-25W2. Cycle Se4, the thickest LOC. 7, 5590 feet [1703.83 m]). one, starts with bioclastic wackestone-packstone at the base overlain by nodular wackestone and mudstone. The uppermost part of cycle is made up of microcrystalline dolomudstone. Anhydrite beds are rare. Other sedimentary cycles (Se1, Se2, Se3, Se5, Se6, and Se7) are incomplete, but can be clearly discerned by beds of fossiliferous – and in places calcareous – argillaceous dolomudstone, which is much more abundant than in other cycles of the Duperow Formation.

Correlations

The Duperow Formation of southeastern Saskatchewan can be lithostratigraphically correlated with the equivalent strata in southwestern Saskatchewan, North Dakota, and Manitoba. The Elstow Member is not readily traceable from southwestern to southeastern Saskatchewan because of facies change from argillaceous carbonate in the southwest to clean carbonate in the southeast (Dunn, 1975). In the southeast, the Elstow-equivalent carbonate unit is lithologically similar to the underlying Saskatoon Member and is, therefore, considered as part of this member (Figure 14A). In North Dakota, the Duperow Formation consists of five informal cycles [I to V, Wilson (1967)]. The Saskatoon Member in southeastern Saskatchewan is correlative with cycle I, the Wymark Member with cycles II, III, IV, and lower part of cycle V, and the Seward Member with the upper part of cycle V (Figure 14B). Because the Duperow Formation in southwestern Manitoba is continuous with, and lithologically similar to, the Duperow Formation of southeastern Saskatchewan, the lithostratigraphic subdivisions and nomenclature proposed in this study can be applied there also.

4. Conclusions The Duperow Formation is an Upper Devonian succession that was deposited in a large epicontinental basin lying south-southeast of the Leduc barrier reefs of the Alberta Basin. The formation mainly consists of mixed carbonate

Saskatchewan Geological Survey 13 Summary of Investigations 2006, Volume 1

SONIC chewa 2 . 1)

Study Saskat (LOC A 1900' 2200' 11-36-22-1W B This C2 P1 C1 astern P2 GR d Southe on rk southwestern Saskatchewan (A) and North B Sewar Wyma Saskato ) LATEROLOG (1967 Dakota A B 7400' 7800' GR C2 P2 P1 Wilson North C1 IIIa IIIb Ivb Iva I II V

uivalent strata in the adjacent regions of

III

W O R E P U D R E P P U W O R E P U D R E W O L

CYCLO- THEMS

n o i t a m r o F W O R E P U D IC N an O S hew y 2 ) atc 1 W tud . C -1 ask O 2 is S (L -2 6 rn S ' ' ' ' Th 0 0 0 0 -3 0 0 0 0 y 9 9 2 2 1 a 1 1 2 2 1 A

R aste 1 a 2 1 B 2 P P m C C the m a tion of southeastern Saskatchewan with eq G Sou n o rk to rd a a a k A s w m y e a S S W w an to ls hew E n o atc tr u e N ask 3 W 68) rn S -1 4 (19 -3 este 2 ' ' ent 0 -2 0 0 0 y 6 5 2 thw A 2 a 2 K 1 B R 1 C a 2 P m C Sou

m Figure 14 - Correlation of the Duperow Forma Dakota (B). a G

Saskatchewan Geological Survey 14 Summary of Investigations 2006, Volume 1 and anhydrite lithofacies with a subordinate, discontinuous halite unit. The nomenclature proposed here for the Duperow Formation in southeastern Saskatchewan (i.e., the Saskatoon, Wymark, and Seward members in ascending order) is a modified version of the four-fold lithostratigraphic subdivision into the Saskatoon, Elstow, Wymark, and Seward members applied by Kent (1968) to equivalent strata in southwestern Saskatchewan. This modification is based on the facts that the Elstow Member disappears eastward into the study area and that the other three members can be recognized and correlated with their counterparts in the southwest. The lateral facies change of the Elstow Member has also been recognized in previous studies by Dunn (1975) and Kent (1983). The Saskatoon Member conformably overlies the Souris River Formation and is mainly made up of stromatoporoid floatstone/bafflestone, bioclastic wackestone and mudstone, and minor stromatolitic and argillaceous dolomudstone interbedded with nodular to thin-bedded anhydrite. Bioclastics include corals, brachiopods, bivalves, and crinoids. The Wymark Member is the thickest member of the Duperow Formation in southeastern Saskatchewan and includes three informal units: lower, middle, and upper. The lower Wymark is dominated by stromatoporoid floatstone/bafflestone and bioclastic wackestone and mudstone. The middle Wymark mainly consists of stromatoporoid floatstone, bioclastic packstone, wackestone and mudstone, and minor dolomudstone and anhydrite. Sedimentary structures include wavy to irregular clay seams and burrows, as well as firmgrounds and minor mudcracks. Bioclasts include tabular and branching stromatoporoids, corals, brachiopods, bivalves, and crinoids. In the upper Wymark, anhydrite and bioclastic wackestone and mudstone are the dominant lithofacies. A discontinuous halite layer, the Flat Lake Evaporite, is locally preserved in the uppermost part of the unit. The Seward Member is the uppermost unit of the Duperow Formation and is conformably overlain by the Birdbear Formation. It is argillaceous and contains burrow-mottled, bioclastic rudstone, packstone, wackestone, mudstone, and argillaceous dolomudstone. Rare anhydrite beds are also present. Bioclasts include gastropods, bivalves, brachiopods, and crinoids.

The three members of the Duperow Formation are internally organized in shallowing-upward, rhythmic sedimentation patterns defined by recurring intervals of bioclast-rich, normal marine, subtidal to intertidal lithofacies grading upward into more restricted lime- and dolo-mudstone and evaporite. A total of 31 cycles (seven in the Saskatoon Member, 17 in the Wymark Member, and seven in the Seward Member) have been recognized within the Duperow Formation of the study area.

5. Acknowledgments We extend our thanks to Saskatchewan Industry and Resources (SIR), Petroleum Geology Branch, for funding this project. We also acknowledge the support we have received from the staff of SIR’s Subsurface Geological Laboratory, Regina. This paper has been reviewed by Drs. Hairuo Qing and Guoxiang Chi of the University of Regina and their suggestions and comments have helped to improve the paper. We thank AGAT Laboratories, Calgary, for support in the preparation of thin sections studied in this project. We also thank Mosaic Potash Esterhazy for allowing us to study core from 1-24-20-33W1.

6. References Andrichuk, J.M. (1951): Regional stratigraphic analysis of Devonian system in Wyoming, Montana, southern Saskatchewan and Alberta Western Canada Sedimentary Basin; in Clark, L.M. (ed.), Western Canada Sedimentary Basin, Amer. Assoc. Petrol. Geol., Tulsa, p68-108. Baillie, A.D. (1953): Devonian System of the Williston Basin Area, Manitoba; Dept. Mines Nat. Resour., Publ. 52- 5, p1-105 Campbell, C.V. (1992): Beaverhill Lake Megasequence; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence- Stratigraphic Framework, Soc. Sed. Geol., Short Course No. 28, Calgary, p163-181. Cen, X.C. and Salad Hersi, O. (2005): A preliminary report on sedimentology and stratigraphy of Late Devonian mixed carbonate-evaporite succession of the Duperow Formation, southeastern Saskatchewan; in Summary of Investigations 2005, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2005- 4.1, CD-ROM, Paper A-9, 12p. Dunn, C.E. (1975): The Upper Devonian Duperow Formation in Southern Saskatchewan; Dep. Miner. Resour., Rep. 179, 151p.

Saskatchewan Geological Survey 15 Summary of Investigations 2006, Volume 1 Ehrets, J.R. and Kissling, D.L. (1985): Deposition, diagenesis and paleostructural control of Duperow and Birdbear (Nisku) reservoirs, Williston Basin; in Longman, M.W., Stanley, K.W., Lindsay, R.F., and Eby, D.E. (eds.), Rocky Mountain Carbonate Reservoirs, SEPM Core Workshop No. 7, Golden, p183-216. Kent, D.M. (1963): The Stratigraphy of the Upper Devonian Saskatchewan Group of Southwestern Saskatchewan; Sask. Dep. Miner. Resour., Rep. 72, 224p. ______(1968): The Geology of the Upper Devonian Saskatchewan Group and Equivalent Rocks in Western Saskatchewan and Adjacent Areas; Sask. Dep. Miner. Resour., Rep. 99, 224p. ______(1983): Carbonate and associated rocks of the Williston Basin: Their origin, diagenesis, and economic potential; Rky. Mtn. Section, SEPM, short course notes, May 14 to 15, Denver, p72-87. ______(1998): Diagenetically altered Stromatoporoid banks: Seals for dolomiticrite reservoirs in Birdbear and Duperow rocks of southern Saskatchewan; in Kreis, L.K. (ed.), 8th International Williston Basin Symposium Core Workshop Volume, Sask./North Dak./Mont. Geol Socs., Spec. Publ. 13A, p105-142. McCracken, A.D. and Kreis, L.K. (2003): A preliminary report of Upper Devonian conodonts from the Birdbear and Duperow formations of southeastern Saskatchewan; in Summary of Investigations 2003, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.1, CD-ROM, Paper A-6, 14p. Moore, P.F. and Richards, B.C. (1989): The Kaskaskia Sequence: Reefs, platforms and foredeeps, the lower Kaskaskia Sequence – Devonian; upper Kaskaskia Sequence – uppermost Devonian and Lower Carboniferous; in Ricketts, B.D. (ed.), Western Canada Sedimentary Basin - A Case History, Chap. 9, Can. Soc. Petrol. Geol./The Open Univ., Spec. Publ. No. 30, p139-201.

North American Commission on Stratigraphic Nomenclature (1983): North American Stratigraphic Code; Amer. Assoc. Petrol. Geol., Bull. 67, p841-875.

Powley, D. (1951): Devonian stratigraphy of central Saskatchewan; unpubl. M.Sc. thesis, Univ. Saskatchewan, Saskatoon, 98p.

Sandberg, C.A. and Hammond, D.R. (1958): Devonian system in Williston Basin and central Montana, AAPG Bull., v42, p2293-2334.

Saskatchewan Industry and Resources (2003): Geology, and Mineral and Petroleum Resources of Saskatchewan; Sask. Industry Resources, Misc. Rep. 2003-7, 173p.

Stoakes, F.A. (1992a): Nature and succession of basin fill strata; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence- Stratigraphic Framework, Soc. Sed. Geol., Short Course No. 28, Calgary, p127-144.

______(1992b): Woodbend megasequence; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence- Stratigraphic Framework, Soc. Sed. Geol., Short Course No. 28, Calgary, p183-205.

______(1992c): Winterburn megasequence; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence- Stratigraphic Framework, Soc. Sed. Geology, Short Course No. 28, Calgary, p207-224. Wendte, J.C. (1992a): Overview of the Devonian of the Western Canada Sedimentary Basin; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence-Stratigraphic Framework, Soc. Sed. Geol., Short Course No. 28, Calgary, p1- 24. ______(1992b): Cyclicity of Devonian strata in the Western Canada Sedimentary Basin; in Wendte, J.C., Stoakes, F.A., and Campbell, C.V. (eds.), Devonian–Early Mississippian Carbonates of the Western Canada Sedimentary Basin: A Sequence-Stratigraphic Framework, Soc. Sed. Geol., Short Course No. 28, Calgary, p25- 39. Wilson, J.L. (1967): Carbonate-evaporite cycles in the lower Duperow Formation of Williston Basin; Bull. Can. Petrol. Geol., v15, p230-312.

Saskatchewan Geological Survey 16 Summary of Investigations 2006, Volume 1 Wilson, J.L. and Pilatzke, R.H. (1987): Carbonate-evaporite cycles in lower Duperow Formation of Williston Basin; AAPG Bull., v69, no5, p870-871.

Saskatchewan Geological Survey 17 Summary of Investigations 2006, Volume 1