A stratigraphic framework for Late Jurassic Early Cretaceous gas-bearing strata (Monteith Formation) in the subsurface of northwest Alberta

Transcription

1 A stratigraphic framework for Late Jurassic Early Cretaceous gas-bearing strata (Monteith Formation) in the subsurface of northwest Alberta Abstract The entire Late Jurassic Early Cretaceous stratal package between the Fernie Formation and the Cadomin Formation, from Townships in the subsurface of northwestern Alberta, is assigned to the Monteith Formation (Minnes Group). Three mappable units are present, informally termed Monteith A, B and C, from youngest to oldest. The Monteith C was deposited in a marginal marine deltaic depositional setting. Upward, the transition to coastal plain (Monteith B) and fluvial (Monteith A) depositional settings records a continuous progradation of a long-lived depositional system. Mapping of these units is aided by identification of regionally extensive marine flooding surfaces in the Monteith C, which are used as stratigraphic datums. The thickness of the Monteith Formation decreases from 450 m in the southwestern portion of the study area to a zero-edge in the northeast. The Monteith A, B and C are up to 160 m, 100 m and 200 m thick, respectively. Depositional thinning to the northeast is prevalent, but the primary reason for gross stratal thinning is substantial incision associated with the overlying sub- Cadomin unconformity. The Monteith Formation in Alberta was deposited in a foredeep setting. Regional thickness trends suggest increased accommodation to the southwest and the strata are interpreted to have accumulated on the cratonward side of the foredeep axis. These observations, as well as evidence for basin axial channel flow to the northwest during deposition of the Monteith C, support an interpretation that the foreland basin had initiated prior to Monteith Formation deposition. Basin physiography, as well as uplift and denudation of the Cordillera, affected the depositional evolution of units in the study area. Ultimately, these factors strongly influenced the distribution of reservoir rocks (primarily sandstones of the Monteith A and C), which are part of the Deep Basin Gas System. The presence or absence of permeability enhancing fractures also impacts reservoir quality and well deliverability in the Monteith Formation. Brett D. Miles 1 Department of Geoscience University of Calgary 2500 University Drive NW Calgary, AB T2N 1N4 Ross B. Kukulski Department of Geoscience University of Calgary 2500 University Drive NW Calgary, AB T2N 1N4 M. Keegan Raines 2 Department of Geoscience University of Calgary 2500 University Drive NW Calgary, AB T2N 1N4 John-Paul Zonneveld Department of Earth and Atmospheric Sciences University of Alberta Edmonton, AB T6G 2E3 Andrew L. Leier Department of Geoscience University of Calgary 2500 University Drive NW Calgary, AB T2N 1N4 Stephen M. Hubbard Department of Geoscience University of Calgary 2500 University Drive NW Calgary, AB T2N 1N4 Résumé Tout le corps rocheux du Jurassique tardif et du Crétacé précoce situé entre la Formation de Fernie et la Formation de Cadomin, à partir des cantons dans la subsurface du Nord-Ouest de l Alberta, est attribué à la Formation de Monteith (groupe de Minnes). Trois unités cartographiables y sont présentes que l on nomme officieusement Monteith A, B et C, c est-à-dire de la formation la plus jeune à la plus âgée. La Monteith C a été déposée dans un cadre sédimentaire marindeltaïque marginal. Vers le haut, la transition vers la plaine littorale (Monteith B) et le cadre sédimentaire fluvial (Monteith A) présente une progradation continue d un système sédimentaire de longue durée. La cartographie de ces unités est favorisée par l identification de surfaces d inondation régionale considérables dans la Formation de Monteith C, que l on utilise comme données stratigraphiques. L épaisseur de la Formation de Monteith diminue de 450 m dans la partie sud-ouest de la région d étude pour atteindre zéro en bordure nord-est. Les Formations de Monteith A, B et C atteignent des épaisseurs de 160 m, de 100 m et de 200 m, respectivement. Au nord-est, l amincissement sédimentaire est prévalent, mais la principale raison de l amincissement brut des strates est due à une incision importante associée à la discordance sub-cadomin sus-jacente. 1 Present address: ConocoPhillips Canada 401-9th Avenue SW Calgary, AB T2P 3C5 2 Present address: Imperial Oil 237-4th Avenue SW Calgary, AB T2P 3M9 BULLETIN OF CANADIAN PETROLEUM GEOLOGY Volume 60, Number 1 March 2012 Pages 3 36 Page 3

2 La Formation de Monteith en Alberta a été déposée dans un contexte d avant-fosse. L évolution de l épaisseur régionale suggère un espace d accommodation accru au sud-ouest et l on pense que les strates se sont accumulées sur le côté du craton de l axe de l avant-fosse. Ces observations, ainsi que les preuves d écoulement en chenal longitudinal du bassin vers le nordouest durant la sédimentation de Monteith C soutiennent une interprétation voulant que le bassin d avant-pays ait commencé avant la sédimentation de la Formation de Monteith. La géographie physique du bassin ainsi que le soulèvement et la dénudation de la cordillère ont affecté l évolution sédimentaire des unités de la région d étude. En bout de ligne, ces facteurs ont fortement influencé la répartition des roches-réservoirs (principalement les grès de Monteith A et C), lesquelles font partie du système de gaz du Deep Basin. La présence ou l absence de fractures facilitant la perméabilité ont également des effets sur la qualité des réservoirs et la productivité des puits dans la Formation de Monteith. Michel Ory Introduction The Late Jurassic Early Cretaceous Nikanassin Formation and Minnes Group accumulated in the incipient foredeep of the preserved Alberta Basin (Price and Mountjoy, 1970; Monger et al., 1982; Cant and Stockmal, 1989; Leckie and Smith, 1992). These initial foreland basin deposits comprise potential gas reservoirs in the well-established Deep Basin gas system in the Alberta and British Columbia subsurface (Masters, 1979; Law, 2002; Zaitlin and Moslow, 2006). The relationship between depositional environments, facies and reservoir properties is crucial to understanding the resource potential of these strata (Shanley et al., 2004; Zaitlin and Moslow, 2006). The primary objective of this study is to establish robust and practical lithostratigraphic correlations for Late Jurassic Early Cretaceous strata in the subsurface of northwestern Alberta. Stratigraphic nomenclature, as previously defined and applied, is cumbersome and will be revised. A secondary objective is to provide a general facies framework and depositional system interpretation for each of the lithostratigraphic units identified in order to deduce a paleogeographic reconstruction. The final objective is to provide a preliminary investigation of the hydrocarbon potential of tight gas sandstone reservoirs in Late Jurassic Early Cretaceous strata of northwestern Alberta. Geological Setting A major phase of foreland basin development in Western Canada began in the Middle to Late Jurassic, as terranes were accreted to the western margin of the continent (Price, 1973; Monger et al., 1982; Stott, 1984; Cant and Stockmal, 1989; Fermor and Moffat, 1993; Evenchick et al., 2007). Basin geometry during this phase of subsidence is poorly constrained as extensive deposits from this time period have been removed through subsequent erosion or remain deeply buried under the fold and thrust belt. The timing of foreland basin initiation has recently been placed during the Late Oxfordian (Late Jurassic), during which time the Omineca Belt was uplifted and sediment was shed from pericratonic terranes and displaced continental margin strata into the foreland basin (McMechan and Thompson, 1993; Ross et al., 2005; Evenchick et al., 2007). Based on the dominance of phosphatic and fossiliferous cherts in the foreland basin strata, Stott (1998) suggested that the major western sediment sources tapped early thrust sheets of Paleozoic strata (e.g. Price and Mountjoy, 1970). Potential sources of siliciclastic detritus were also exposed in the east, which included Paleozoic sedimentary rocks and crystalline Precambrian units of the craton (Stott, 1998). Late Jurassic Early Cretaceous strata have been studied extensively in other portions of western North America (Fig. 1; e.g. Hamblin and Walker, 1979; Leckie et al., 2004; Turner and Peterson, 2004; Fuentes et al., 2009; Dickinson et al., 2010). The position of ancient shorelines mapped to the south of the study area in southern Alberta and northern Montana indicate that the basin filled northward along the axis of the foreland, parallel to the orogenic front, during the initial stages of accommodation development (Hamblin and Walker, 1979; Leckie and Smith, 1992; Poulton et al., 1994; Turner and Peterson, 2004). Recent studies of Middle to Late Jurassic deposits in northern Montana (Ellis Group and Morrison Formation) suggest that early foreland basin sediments were deposited in the backbulge depozone and not in the foredeep (Fuentes et al., 2009, 2011). Fuentes et al. (2009, 2011) postulated that evidence for foredeep sedimentation was completely eradicated during subsequent mountain building and denudation in their study area. Study Area and Methods The study area is in the Alberta subsurface, bounded by Townships 62 and 74, and Ranges 5W6 and 14W6 (Fig. 2). Approximately 8,300 km 2 is included, with a database that consists of approximately 1200 wireline log suites and 65 drill cores (Fig. 2). The study area was chosen because it contains significant natural gas resources, including the Elmworth, Knopcik, Wapiti, Chinook Ridge, and Narraway gas fields, and relatively dense well and core distribution (Fig. 2). The regional scale stratigraphic architecture of Late Jurassic Early Cretaceous strata was established through wireline log correlation. Important contacts were analyzed in cores where possible, validating wireline log-based correlations. Wireline logs were selected with an emphasis on those from wells that penetrated the entire stratigraphic interval from the uppermost Fernie to Cadomin formations. The stratigraphic database was used to generate isopach maps for three lithostratigraphic units identified in the study area. Net sandstone maps for selected intervals relied on a gamma ray cutoff of 60 API, which was established through core calibration. Sedimentological analysis of cores through the various lithostratigraphic units led to the delineation of major facies and facies associations. Facies are presented for each stratigraphic unit, based on observations of lithology, physical sedimentary structures, biogenic structures and bed bounding surfaces. Page 4 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

3 Stratigraphic Framework for the Monteith Formation, Alberta Page 5 Figure 1. Late Jurassic Early Cretaceous lithostratigraphy from northeast British Columbia to northwest USA. Younger ages associated with the basal sandstone deposit are assumed based on northward progradation of the system as insufficient fossil evidence exists to determine age.

4 Page 6 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard Figure 2. Overview of study area and regional stratigraphic nomenclature context. (A) Regional map of subsurface Late Jurassic Early Cretaceous well penetrations, subsurface deformation front, and Minnes Group zero edge. Spatial extent of lithostratigraphic units defined by Stott (1998) and corresponding type sections in the foothills are shown. Inset map of Canada with study area location included. (B) Detailed study area map with wells used for mapping; locations of core and subcrop edges of the three Monteith Formation units are indicated.

5 Lithostratigraphy and Nomenclature Issues In northwestern Alberta, the strata of interest are up to 500 m thick adjacent to the fold and thrust deformation front and erosionally thin to 20 m or less eastward (Figs. 1 and 2). The strata conformably overlie the Jurassic Fernie Formation and are unconformably overlain by Early Cretaceous conglomeratic deposits of the Cadomin Formation (Fig. 1; Stott, 1967, 1998; Poulton et al., 1990, 1994; Cant, 1996). The lithostratigraphic units in and adjacent to the study area have variably been assigned to the: 1) Nikanassin Formation, the type area of which is approximately 200 km to the south of the study area near Cadomin, Alberta (Fig. 2; Mackay, 1929; Kryczka, 1959); and 2) Minnes Group, a portion of which was originally named at Mt. Minnes ( Minnes Formation ), approximately 50 km to the southwest of the study area (Fig. 2; Ziegler and Pocock, 1960). The basal formation of the Minnes Group is the Monteith Formation, which is overlain by the Gorman Creek Formation at Mt. Minnes (Fig. 2; Stott, 1998). The type section of the Monteith Formation is in the Carbon Creek Region, approximately 200 km to the northwest of the study area, where it is overlain by the Beattie Peaks, Monach and Bickford formations that are also defined in that area (Figs. 1 and 2; Stott, 1998). The boundaries of Late Jurassic Early Cretaceous lithostratigraphic units have been inconsistently applied to the subsurface of Alberta. This may stem from the fact that the subsurface units are distant from each of the areas where type outcrop sections were first defined (Fig. 2). The most comprehensive study on the Minnes Group is the integrated outcrop and subsurface analysis of Stott (1998). We review and build upon this work in order to propose an informal, unifying stratigraphic framework for this and future studies in the Alberta subsurface. Historic Lithostratigraphy and Nomenclature In the subsurface of Alberta, the stratigraphic section between the Fernie and Cadomin formations is most typically referred to as the Nikanassin Formation (MacKay, 1929; Kryczka, 1959; Poulton et al., 1990, 1994). The Nikanassin Formation in the type area consists primarily of marine sandstone (Fig. 2; MacKay, 1929; Kryczka, 1959; Stott, 1998). Farther northward, approximately at Township 52, Stott (1998) proposed that the Nikanassin Formation changes into the Monteith and Gorman Creek formations (Figs. 2 and 3). The nature of the transition was not defined. Stott (1998) mapped the Gorman Creek Formation (Fig. 3), which consists of interbedded siliciclastic and coal layers (Figs. 2 and 3), from Township 52 northward to the vicinity of Townships 62 and 63 in the subsurface and outcrop (Figs. 2 and 3). In this area, Stott (1998) delineated an additional lithostratigraphic transition; although the Monteith Formation persists, the overlying Gorman Creek Formation is replaced by the Beattie Peaks, Monach and Bickford formations (Figs. 2, 3 and 4). Farther north, in the Carbon Creek region where the formations are defined (Fig. 2), the Beattie Peaks Formation comprises deep-marine shale and siltstone, the Monach Formation variably consists of marine and fluvial sandstone, and the Bickford Formation is dominantly carbonaceous sandstone and siltstone (Fig. 4; Stott, 1998). Lithostratigraphy and Nomenclature in this Study The Beattie Peaks and Monach formations, as they were defined in northeastern British Columbia, do not in fact correlate into the subsurface of Alberta as had been interpreted by Stott (1998) and Miles (2010) (Figs. 3 and 4). Careful review of cross-sections by Stott (1998) reveals that a key well location used to correlate these upper formations of the Minnes Group into Alberta was interpreted differently in two sections, and therefore correlated inconsistently with surrounding wells (Figs. 3 and 4). In this well (i.e W6 in Fig. 4; and figs. 9 and 20 of Stott, 1998) the top of the Monteith Formation was defined lower than in surrounding wells, leading to erroneous correlation of the Beattie Peaks and Monach formations into the subsurface of Alberta (Fig. 4; see fig. 20 of Stott, 1998). Effectively, this resulted in strata lithostratigraphically equivalent to the Monteith Formation in the type area (Carbon Creek) to be subdivided into the Monteith, Beattie Peaks and Monach formations in Alberta (Figs. 3 and 4). Importantly, regardless of the nomenclature, the lithostratigraphic units in Alberta identified by Stott (1998) and mapped by Miles (2010) are widespread, and correlatable from south of the area studied herein, north and westward into British Columbia (Fig. 3). In this study, we propose the use of Monteith A to account for an upper sandstone-dominated unit (referred to as the Monach Formation in Alberta by Stott [1998] and Miles [2010]); Monteith B for a middle heterolithic unit (referred to as the Beattie Peaks Formation by Stott [1998] and Miles [2010]); and Monteith C for a lower sandy unit (referred to as the Monteith Formation by Stott [1998] and Miles [2010]; Fig. 3). Correlation of Jurassic Cretaceous Monteith units from the Carbon Creek area of British Columbia for >370 km southward, beyond the Alberta study area, is demonstrated in Figure 3. The three Monteith Formation units can be readily identified in the southern portion of the study area, where Stott (1998) delineated the Gorman Creek Formation (Fig. 3). Therefore, the use of Gorman Creek Formation in the subsurface of Alberta is deemed unnecessary. The Nikanassin Formation to the south of the Alberta study area is considered to be lithostratigraphically correlative with the Monteith C (Fig. 3). Notably, the informal lithostratigraphic units in the subsurface are consistent with the stratigraphic framework defined in outcrop by Stott (1998) and the revised framework does not invalidate the previously defined formations. The Origin of Correlation Difficulties Jurassic Cretaceous strata between the Fernie and Cadomin formations are characterized by a paucity of preserved fossils in many areas, which has hindered correlations in and adjacent to the study area. Fossils that have been collected in the Minnes Group of British Columbia range in age from Tithonian (Late Jurassic) to Late Valanginian (Early Cretaceous; see Stott, 1998 for a detailed discussion; Warren and Stelck, 1958; Ziegler and Pocock, 1960). More than 75 km to the north of the area of interest for this study (Fig. 2), Stott (1998) placed the Jurassic Cretaceous boundary within the Monteith Formation. Fossils recovered from the basal beds of the Monteith Formation lie within the Buchia terebratuloides s. lato Zone of Late Tithonian age (Late Jurassic), and those recovered from the uppermost beds lie within the Buchia uncitoides Zone of Late Berriasian age Stratigraphic Framework for the Monteith Formation, Alberta Page 7

6 Page 8 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard Figure 3. Regional strike oriented gamma radiation log cross-section (A A ) featuring the stratigraphic correlation scheme adapted in this study indicated by solid lines, as well as previous stratigraphic picks from Stott (1998) and Legun (1988), indicated by bars adjacent to gamma radiation curves. Complex stratigraphic architecture led to incorrect application of the Monach, Beattie Peaks and Monteith formation nomenclature, developed in northeastern British Columbia, to strata in Alberta by Stott (1998). Late Jurassic Early Cretaceous strata in the Alberta subsurface are lithostratigraphically equivalent to the Monteith Formation in northeastern British Columbia. The Nikanassin Formation is correlative with the Monteith C. Extent of the Alberta study area is shown in grey. Cross-section location shown in Figure 2A.

7 Figure 4. Regional dip oriented gamma radiation log cross-section (B B ) featuring the stratigraphic correlation scheme adapted in this study indicated by solid lines, as well as previous stratigraphic picks from Stott (1998) and Legun (1988), indicated by bars adjacent to gamma radiation curves. Progressive downcutting and erosion of the Minnes Group associated with the sub-cadomin unconformity in northeast British Columbia was substantial. The differential application of stratigraphic picks by Stott (1998) in W6 in part, caused miscorrelation of units into the Alberta subsurface; note the very limited spatial extent of the Bickford, Monach and Beattie Peaks formations. The section location is shown in Figure 2A. Stratigraphic Framework for the Monteith Formation, Alberta Page 9

8 (Early Cretaceous; Stott, 1998). In the north, the Beattie Peaks Formation ranges from the Polyptychites cf. P. keyserlingi and Buchia cf. B. keyserlingi Zone to the Buchia n. sp. aff. B. inflata Zone corresponding to an early to late Valanginian (Early Cretaceous) age. Stott (1998) deduced the Monach Formation to be within the Buchia n. sp. aff. B. inflata Zone and of late Valanginian (Early Cretaceous) age. To the south of the study area, the age of the Nikanassin Formation has been estimated to range from Kimmeridgian to Tithonian/Volgian, based on the bivalve Buchia mosquensis, found in the Smoky River region (Irish, 1965; Stott, 1998). Biostratigraphic delineation of stratal ages was beyond the scope of this study, although ages in the north are demonstrated to be younger than in the south. The stratigraphic architecture of the Monteith Formation in the Alberta subsurface, as delineated in this study (Figs. 1 4), has historically been poorly constrained as a result of issues with internal correlations. Selection of a datum for this Jurassic Cretaceous interval is particularly difficult, compounded by a diachronous, gradational basal contact with the underlying Fernie Formation and erosional truncation associated with the overlying sub-cadomin unconformity (Fig. 5). The contact between Jurassic Cretaceous strata and the Cadomin Formation is a particularly poor datum choice for regional scale correlations, despite the fact it is recognizable in logs and cores (Fig. 5). The issues with this surface as a datum stem from the differential degree of erosion associated with this surface, which variably places the Cadomin Formation in contact with the Monteith A, B or C (Figs. 2 and 5). The implications of using the sub-cadomin unconformity as a datum include miscorrelation of Monteith A sandstone bodies to Monteith C sandstone bodies (Fig. 5). This problem is not inconsequential, as the Monteith A and C differ with respect to lateral sandstone distribution patterns, composition, and natural gas potential. The base of the Cadomin Formation is a useful datum when studying a local area, particularly when the Monteith A is the primary target or where wells do not penetrate beyond this interval. Another obvious datum choice is the contact between the Fernie Formation and Monteith Formation. However, the contact is gradational and relies on the amount of sandstone present in the lowermost portion of the Monteith Formation, which is variable (Fig. 5). The Fernie Formation contact can also be difficult to utilize because many wells do not penetrate deeply enough, commonly only encountering Monteith C at the base of the wellbore. Other major internal lithostratigraphic contacts, between Monteith C and B, and Monteith B and A, are not well suited as datums as they are gradational and erosional contacts, respectively. Through detailed analysis of core and regional wireline log correlations, more consistent and useful stratigraphic datums are recognized. The datums represent widespread surfaces within the Monteith C, interpreted to have been generated during major marine flooding events associated with rapid rises in relative sea level (Figs. 5 6; Van Wagoner et al., 1990). The marine flooding surfaces are recognized on wireline logs and in core by a change from sandy deposits to overlying interbedded siltstone and sandstone, distinguished on gammaradiation logs by a serrated profile (Figs. 3 6). These datums are most useful for constraining stratigraphic correlations in the Monteith A and B, and are reasonable for mapping the Monteith C at the reservoir scale (Fig. 5). The origin of these datums and other similar surfaces is discussed in this study. A secondary datum, useful for reservoir scale correlations in the Monteith A, is the first occurrence of coal in the Monteith B. Sedimentology The Monteith Formation and lithostratigraphically equivalent units have been the focus of few detailed sedimentological investigations. The majority of studies have focused on broader paleogeographical topics or large scale reservoir studies, in which Monteith Formation or Nikanassin Formation sedimentology is only briefly discussed (e.g. Spivak, 1949; Warren and Stelck, 1958; Masters, 1979; Poulton et al., 1990, 1994; Boettcher et al., 2010; Solano et al., 2010). Centimetre-scale analysis of cores has led to identification of a series of sedimentary facies and facies associations in the Monteith Formation, summarized in unit-specific (i.e. A C) facies schemes (Tables 1 4). The discussion of facies and facies associations presented herein are not intended to be comprehensive, but rather a general overview of dominant sedimentological characteristics. The analysis focuses on observations from core, followed by process-based interpretations. Subsequently, the entire facies association assemblage for each lithostratigraphic unit is considered and a depositional setting proposed. Facies architecture and sandstone distribution is included in the analyses. The stratigraphic units are discussed from oldest to youngest (i.e. C to A) in order to illustrate the evolution of depositional systems. Monteith C Facies Association Descriptions and Interpretations Monteith C facies association one (MC-FA1) is dominated by thinly (cm-scale) interbedded muddy, silty and sometimes sandy, normally graded beds (MC-F1), punctuated by planar laminated or hummocky cross stratified sandstone units m thick (MC-F2; Figs. 7A, B and 8; Table 2). MC- FA1 is commonly m thick and grain-size ranges from mudstone to very fine-grained sandstone. Fine-grained intervals are commonly characterized by evidence for softsediment deformation, including loading structures (Fig. 8B). The graded beds of MC-F1 are sharp-based, and the sandstone of MC-F2 is characterized by hummocky cross-stratification and symmetric and asymmetric current ripples. Phycosiphon is the most common trace fossil present in MC-F1, with locally abundant Chondrites and Thalassinoides (Fig. 8; Table 2). Cosmorhaphe, Skolithos, and Teichichnus are rare. The trace fossil assemblage in MC-F2 includes fugichnia, as well as rare and diminutive Palaeophycus and Skolithos. The trace fossils within MC-FA1 are often present in monospecific to low diversity suites, with highly variable abundances (Bioturbation index [BI] = 0 4; BI scheme adapted from MacEachern and Bann, 2008). Physical structures of MC-F1 are interpreted to have been deposited rapidly under waning turbulent flow conditions (Mulder et al., 2003; Nakajima, 2006; Bhattacharya and MacEachern, 2009), whereas sandstone of MC-F2 underwent reworking by unidirectional or oscillatory currents (Hamblin and Walker, 1979; Duke et al., 1991; Dumas and Arnott, 2006). Page 10 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

9 Figure 5. (A) Regional stratigraphic gamma radiation log cross-section (C C ) hung on the top of the middle Monteith C upward-coarsening package, which is demarcated by a regional scale marine flooding surface. This datum is an ideal internal stratigraphic marker within the Monteith Formation. (B) Regional stratigraphic cross-section C C hung on the base of the Cadomin Formation (top of the Monteith Formation), which is a commonly used datum for this strata. The base of the Cadomin Formation is a basin wide angular unconformity and is not an ideal datum for regional mapping purposes. Cross-section location shown in Figure 2B. Stratigraphic Framework for the Monteith Formation, Alberta Page 11

10 Page 12 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard Figure 6. Regional stratigraphic gamma radiation log cross-section (D D ) hung on the top of the middle Monteith C. This section is oriented in a SW-NE direction, perpendicular to the axis of the foreland. In this section, the Monteith A is most affected by erosion associated with the sub-cadomin unconformity. Cross-section location shown in Figure 2B. Note the upward-coarsening packages in the Monteith C as delineated with grey arrows in W6.

11 A link between the deposits of storms (HCS beds of MC-F2) and river floods, as recorded by possible hyperpycnal flow deposits (MC-F1), has been established in studies on modern day continental shelves and pro-deltaic settings (Bentley and Nittrouer, 2003; Friedrichs and Scully, 2007). Analysis of modern sedimentary processes has shown that in low gradient settings, wave action can play a role in generating near bed turbulence, thus promoting suspension of fine-grained sediment that is driven down slope by gravity as a hyperpycnal plume (Bentley and Nittrouer, 2003; Bhattacharya and MacEachern, 2009). The trace fossil suite in MC-FA1 is dominated by opportunistic burrowing behaviours (cf. Phycosiphon; Wetzel and Wijananda, 1990; Wetzel and Uchman, 2001). Opportunistic ethologies and low diversity trace fossil assemblages suggest that periodic stresses affected the environment, perhaps as a result of high current and wave energy, rapid sedimentation, high suspended sediment concentrations, and possibly lowered salinity (Dörjes and Howard, 1975; Wightman et al., 1987; MacEachern et al., 2005, 2010). Monteith C facies association two (MC-FA2) is characterized by climbing ripple-dominated sandstone (MC-F3), massive sandstone with local fluid escape structures (MC-F4), organicrich ripple laminated sandstone (MC-F5), and rare inclined heterolithic strata (MC-F6; Figs. 7C, D and 8; Table 2). MC-FA2 is commonly between 5 10 m thick and grain-size ranges from lower-fine to upper-medium sandstone. Evidence for traction processes associated with unidirectional flow is dominant, including aggradational current ripples (Fig. 8G, H). Trace fossils are rare in MC-FA2. Where present the trace fossil suite is generally dominated by thin ( cm diameter) Cylindrichnus with rare Palaeophycus, Skolithos and Rosselia. Overall, the trace fossil suite is impoverished and comprised of diminutive forms; bioturbation indices are generally low (BI=1 2). Thick, massive sandstone beds with fluid escape structures are consistent with rapid sedimentation and dewatering (Fig. 8E; Allen, 1973; Martin and Turner, 1998). Siltstone drapes and inclined heterolithic stratification are suggestive of tidal influence (e.g. Thomas et al., 1987; Smith, 1988; Hovikoski et al., 2008). The dominance of simple, diminutive structures in low diversity ichnological suites indicates that this trace fossil assemblage was strongly influenced by physio-chemical stresses, and the suite consists of forms typical of brackish-water deposits (Pemberton et al., 1982; Gingras et al., 1998; MacEachern et al., 2005). Monteith C facies association three (MC-FA3) is characterized by fine-grained facies with thinly interlaminated sandstone and mudstone (MC-F7) common (Figs. 7C, D and 8; Table 2). MC-FA3 can be up to 5 m thick, generally characterized by lenticular beds and starved current ripples with abundant carbonaceous detritus, and local syneresis cracks. Soft sediment deformation is present, including ball and pillow structures. Trace fossils present include small Cylindrichnus, (?) Ophiomorpha, Planolites, Skolithos, Teichichnus, and Thalassinoides. Bioturbation index is variable (BI=0 3), with generally higher values in mudstone and siltstone beds. The sedimentary processes recorded in beds of MC- FA3 reflect suspension deposition with periodic, short-lived unidirectional currents that were responsible for sand transport. The environment of deposition was sand-poor, as indicated by the common development of starved current ripples (Fig. 8). Syneresis cracks are consistent with subaqueous shrinkage, commonly attributed to salinity fluctuations (Fig. 8I; Plummer and Gostin, 1981; Wightman et al., 1987). Overall, MC-FA3 is characterized by an impoverished and variable trace fossil suite, with components that are consistent with the brackish water model (Pemberton et al., 1982; Gingras et al., 1998; MacEachern et al., 2005). Monteith C facies association four (MC-FA4) is dominated by sandstone, with sharp-based packages that range from 5 10 m thick. Sandstone is fine- to medium-grained (MC-F8), however, organic-rich mudstone and siltstone is locally present (Figs. 7C, D and 8; Table 2). Physical structures include low- to mediumangle cross-stratification; finer grained facies are massive to thinly laminated, with abundant carbonaceous laminae. MC- F8 commonly grades upwards into structureless organic-rich mudstone and siltstone (MC-F9a/b). Trace fossils are absent from MC-FA4. The sharp base and fining upwards character of MC-FA4, coupled with evidence for unidirectional currents, suggests that deposition occurred in a channelized setting (i.e. on point bars). The sandstone of MC-F8 records high-energy channelized flow whereas MC-F9 is interpreted to represent overbank or channel abandonment deposits based on their fine grained nature, absence of bioturbation and the local abundance of organic matter (Allen 1978; Cant, 1984; Jones and Hajek, 2007). Depositional Setting Monteith C facies associations constitute a complex stratigraphic architecture attributed to deltaic sedimentation. Table 1. Legend for symbols used in measured sections (Figs. 7, 9 and 11). Stratigraphic Framework for the Monteith Formation, Alberta Page 13

12 Figure 7. (A) Gamma radiation, density porosity, and neutron porosity wireline logs and location of core description through the Monteith C ( W6). Note the upward-coarsening packages in the Monteith C as delineated with grey arrows. (B) Detailed sedimentologic description of interpreted prodelta deposits, specifically MC-LA1 and MC-LA2. Note the sharp contact at the top of the MC-LA1 prodelta lithofacies association. The location of the core shown is denoted by the filled black box in part A. (C) Gamma radiation, density porosity, and neutron porosity wireline logs and location of core description through the Monteith C ( W6). Note the upward-coarsening packages in the Monteith C as delineated with grey arrows. (D) Detailed sedimentologic description of interpreted delta front deposits, specifically MT-LA2 (delta front/ mouthbar deposits), MT-L3 (interdistributary bay deposits) and MT-L4 (distributary channel deposits). See Table 1 for legend of symbols and Table 2 for detailed facies descriptions. Page 14 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

13 Stratigraphic Framework for the Monteith Formation, Alberta Page 15 Table 2. Lithofacies of the Monteith C. Trace fossil abbreviations are Arenicolites (Ar), Asterosoma (As), Chondrites (Ch), Cosmorhaphe (Co), Cylindrichnus (Cy), Gyrolithes (Gy), Ophiomorpha (Oph), Palaeophycus (Pa), Planolites (Pl), Phycosiphon (Ph), Rosselia (Ro), Skolithos (Sk), Teichichnus (Te) and Thalassinoides (Th).

14 Figure 8. Monteith C facies photographs. (A) Thin sandy to muddy graded beds with Phycosiphon (Ph) and Chondrites (C) (MC-L1; W5, m). (B) Soft sediment deformation (MC-L1; W5, 3069 m). (C) Undulating parallel lamination and combined flow ripple (MC-L2; W6, m). (D) Rip up clasts (normally graded) (MC-L8; W6, m). (E) Massive sandstone with dish structures indicative of rapid sedimentation and dewatering (MC-L4; W6, m). (F) Hummocky cross-stratification (MC-L8; W6, 2061 m). (G,H) Current ripples defined by organic detritus (MC-L5; W6, m, W6, m). (I) Interlaminated sandstone and siltstone with starved ripples and syneresis cracks (MC-L9b; W6, m). (J) Bioturbated heterolithic sandstone and mudstone with notable Cylindrichnus (Cy), and Planolites (Pl) (MC-L7; 102/ W6, 2161 m) (K) Intensely bioturbated heterolithic sandy mudstone overlying a marine flooding surface with pebbles (p) of transgressive lag present at lower right (MC-L7; W6, m). Trace fossils identified include Cosmorhaphe (Co), Palaeophycus (Pa), Planolites (Pl), and Teichichnus (Te). Page 16 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

15 MC-FA1 comprises the basal portions of three widely correlatable upwards-coarsening packages (Figs. 5 and 6). It is characterized by facies deposited from sediment-laden discharge associated with river flooding (MC-F1), punctuated by sandstone beds attributed to storm events (MC-F2) in the prodeltaic region of a strongly flood influenced delta (Figs. 7A and B). Prodelta deposits typically are sharply overlain by delta front sandstone deposits, which are dominated by sedimentary structures indicative of unidirectional currents and high sedimentation rates (MC-FA2). The lithofacies (MC-F3 to MC-F6) are consistent with deposition in deltaic distributary channels and mouthbars (Wright, 1977; Bhattacharya and Walker, 1991; Olariu and Bhattacharya, 2006; Bhattacharya and MacEachern, 2009), where rapid sediment fallout from suspension is characteristic (Martin and Turner, 1998; Fielding et al., 2005b, 2006; Bhattacharya and MacEachern, 2009). The sharp contact between the sandstone of the delta front (MC-FA2) and the underlying fine-grained prodelta deposits (MC-FA1) is caused by flood-induced rapid progradation of the delta front (Fielding et al., 2005b). MC-FA3 contains facies associated with brackish water, interpreted to have been deposited in protected interdistributary bays or the coastal plain. Occasionally, these low energy environments received sand via crevasse splays, generated by flood events in adjacent distributary channels (Bhattacharya and Walker, 1991a; Gingras et al., 1998). MC-FA4 is dominated by large-scale sedimentary structures generated by unidirectional currents overlain by organic-rich mudstone and siltstone. It is interpreted to represent deposition in proximal distributary channels (e.g. Bhattacharya and Walker, 1991; Plint et al., 2001; Ambrose et al., 2009; Li et al., 2010). The upward-coarsening packages of the Monteith C record the shift from prodelta (MC-FA1), to delta front/mouthbar environments (MC-FA2), and cross-cutting deltaic distributary channels (MC-FA4); delta plain and interdistributary bay deposits are preserved in MC-FA3 (Fig. 7; Table 2). Thus, the Monteith C is considered a river-dominated, floodinfluenced, wave and tidal affected deltaic deposit (Ainsworth et al., 2011). Monteith B Facies Association Description and Interpretation Facies analysis of the Monteith B is limited by a paucity of cores (Fig. 2B). The wireline log characteristics, calibrated with core where possible, indicate that the strata are dominated by thinly interbedded fine grained siltstone, mudstone and coal with localized sandstone intervals (Figs. 9 and 10; Table 3). Monteith B facies association one (MB-FA1) is the only facies association defined for the unit, and includes organic detritus-rich cross-stratified sandstone (MB-F1), carbonaceous siltstone, mudstone and coal (MB-F2), bioturbated heterolithic mudstone and sandstone (MB-F3), and finely laminated mudstone (MB-F4; Table 3). The interval is m thick and dominated by fine-grained facies (MB-F2 and MB-F4), with coal beds increasingly abundant upward (Figs. 5, 6 and 9). Where present, sandstone beds are generally thin (cm-scale) and sporadically distributed, associated with starved symmetric and asymmetric ripple cross lamination, indicative of periodic and variable input of sand into the depositional setting. Figure 9. (A) Gamma radiation, density porosity, and neutron porosity wireline logs and location of core description through the Monteith B and A and Cadomin Formation ( W6). Note the abundant coal beds at the top of the Monteith B, indicated by bold arrows. (B) Detailed sedimentologic description of interpreted coastal plain deposits. See Table 1 for legend of symbols and Table 2 for detailed facies descriptions. Stratigraphic Framework for the Monteith Formation, Alberta Page 17

16 Upward-fining sandstone units of MB-F1 are 2 3 m thick in cores, however 5 6 m thick upward-fining units are evident in some wells (Fig. 9). Syneresis cracks and soft-sediment deformation structures are locally preserved. Trace fossils are rare, including roots in MB-F2 and MB-F4, and a low diversity suite comprising diminutive Cylindrichnus, Palaeophycus, Skolithos and Teichichnus in MB-F3 (Table 3). Biogenic and physical sedimentary structures suggest slight marine influence on portions of the depositional setting (Wightman et al., 1987). Depositional Setting Monteith B deposits are dominantly fine grained (MB-F2, MB- F3, MB-F4), with localized fining upwards sandstone packages (MB-F1; Table 3). Fine-grained facies of MB-FA1 are considered floodplain or coastal plain deposits, with local marine influence (Corbett et al., 2011). Thin sandy upward-fining successions are attributed to migration of point bars and channels. Overall, the facies association records large-scale progradation of the depositional setting from the underlying marine (Monteith Figure 10. Monteith B facies photographs. (A) Box photographs of a heterolithic succession ( W6; m). (B) Current ripples (MB-L1; W6, m). (C) Heterolithic sandstone and siltstone with starved current ripples (MB-L4; W6, m). (D) Bioturbated sandstone and siltstone from (MB-L3; W6, m). Page 18 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

17 C) to coastal plain (Monteith B) deposits (Coleman and Prior, 1982). Notably, through the vertical profile of MB-FA1, coal horizons and channels are more common upward (Fig. 9) and associated with an overall decrease in trace fossil abundance and the occurrence of syneresis cracks (Figs. 9 and 10). These observations are considered to correspond to an upward reduction of marine influence on the coastal plain deposits of the Monteith B (Coleman and Prior, 1982). Monteith A Facies Association Descriptions and Interpretations Monteith A facies association one (MA-FA1) consists of massive appearing sandstone with siltstone clast dominated intervals (MA-F1), planar to inclined tabular cross-stratified and rippled sandstone (MA-F2), and very-fine sandstone (MA-F3; Figs. 11A,B and 12A D; Table 4). MA-FA1 ranges from 5 30 m thick, and is proportionally more important in the southern to southwestern portion of the study area. MA-FA1 consists primarily of moderately well sorted, rounded to sub-rounded, upper fine- to upper coarse-grained sandstone. Traction-structured sandstone indicative of high-energy unidirectional flow (MA-F2) is the most abundant facies. Massive appearing sandstone (MA-F1) is often associated with angular to rounded siltstone clasts that are interpreted as lags deposited at channel bases (Fig. 12B). Overall, sandstone beds within MA-FA1 are often amalgamated, resulting in a thick, blocky gamma-radiation log signature (Fig. 11A and B). However, sandy units grade upward into fine-grained units of MA-FA2 in many instances. Biogenic structures are sparse in MA-FA1, limited to rare Planolites and Skolithos. Monteith A facies association two (MA-FA2) consists of very fine-grained sandstone with interbedded siltstone (MA-L3) and organic-rich siltstone and coal (MA-F4). Siltstone and sandstone characterized by soft sediment deformation and syn-sedimentary faults are also present (MA-F5). MA-FA2 ranges from 5 20 m thick, with individual sandstone, siltstone or mudstone beds typically <1 m thick. MA-FA2 is characterized by increased preservation of facies associated with lower energy, relative to MA- FA1, and is most abundant in the northern portion of the study area. In finer grained facies (i.e. MA-F3 and MA-F4), lamination is not common; when present it is mainly planar to wavy and generally discontinuous. Bioturbation in MA-FA2 is rare, with Planolites, Skolithos and Teichichnus locally present. Depositional Setting Thick-bedded sandstone of the Monteith A (MA-FA1) contains features, including high-angle cross-stratification, which suggest that deposition occurred by accretion of channel bar-forms and dunes within a fluvial channel system (Miall, 1978, 1992; Cant, 1984). Evidence for traction dominated unidirectional current flow also includes abundant trough and planar cross-stratification; the lack of evidence for biogenic reworking and the general absence of fine-grained material is consistent with deposition in a high energy fluvial setting with limited to no marine influence. MA-FA2 is characterized by the preservation of fine-grained facies and coal, and indicates a decrease in current velocity or transport capacity compared to MA-FA1. MA-FA2 is interpreted to represent floodplain or bar top (inter-channel) deposition. Thick successions of organic-rich siltstone and coal of MA- FA2 in the north are generally attributed to more stable channel Table 3. Lithofacies of the Monteith B. Trace fossil abbreviations are Cylindrichnus (Cy), Palaeophycus (Pa), Skolithos (Sk), Thalassinoides (Th), Teichichnus (Te). Stratigraphic Framework for the Monteith Formation, Alberta Page 19

18 Figure 11. (A) Gamma radiation, caliper, density porosity, and neutron porosity wireline logs and location of core description through the Monteith A interval ( W6). The caliper log remains in gauge through the Cadomin Formation and is out of gauge in the Monteith A, an important observation for differentiating the stratigraphic units. (B) Detailed sedimentologic description of interpreted fluvial deposits, overlain by the Cadomin Formation. This section highlights features of MA-LA1, which are characterized by a high net/ gross ratio and cross bedded sandstone (MA-L2). (C) Gamma radiation, density porosity, and neutron porosity wireline logs and location of core description through the Monteith A interval ( W6). (D) Detailed sedimentologic description of interpreted fluvial overbank deposits. Page 20 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

19 banks, or possibly an overall decrease in sediment supply or an increase in subsidence in the area. In either case, the result is increased preservation potential of fine-grained facies (Fig. 11; Miall, 1996; Catuneanu, 2006). In summary, the Monteith A consists of non-marine, fluvial deposits (Figs. 11 and 12; Table 4; Miall, 1978; Cant, 1984; Bridge and Tye, 2000; Bridge, 2006; Gibling et al., 2011). Facies associations are largely differentiated by grain size, with MA-FA1 sandstone-dominated and MA-FA2 composed of a high proportion of finer grained material and coal. MA-FA1 is generally attributed to intrachannel sedimentation and MA-FA2 to interchannel deposition. The two associations characterize regionally distinctive and mappable portions of the fluvial system across the study area (Figs. 5 and 6). Stratigraphic Architecture The focus of this section is description of the lithostratigraphic organization of the Monteith Formation, although the sequence Figure 12. Monteith A facies photographs. (A) Box photographs of an upward-fining succession ( W6, m). (B) Clast lag composed of siderite clasts overlying a sharp, erosive contact (MA-L1; 200d-60-G/093-I-16, m). (C) High angle trough crossstratification (MA-L2; W6, 3089 m). (D) Current ripple laminated sandstone (MA-L3; W6, m). (E) Rooted siltstone and overlying coal (MA-L4; W6, 2560 m). Stratigraphic Framework for the Monteith Formation, Alberta Page 21

20 stratigraphic significance of key surfaces and stratal packages is also considered. The underlying Fernie Formation and overlying Cadomin Formation are also briefly discussed, as they provide stratigraphic context. Table 4. Lithofacies of the Monteith A. Trace fossil abbreviations are Planolites (Pl), Skolithos (Sk), Thalassinoides (Th). Fernie Formation The Fernie Formation directly underlies the Monteith C in the study area and consists of interbedded siltstone, mudstone and local sandstone (Figs. 1 and 13); it is referred to as the Upper Fernie shale and sandstone (Stronach, 1984; Marion, 1984; Poulton et al., 1994; Asgar-Deen et al., 2004). The Fernie Formation is tectonostratigraphically important, as it is postulated to record the change from easterly derived passive margin sediments to foreland basin deposits sourced from the uplifting Cordillera in the west (Leckie and Smith, 1992; Asgar-Deen et al., 2004). In southwest Alberta, the uppermost informal unit within the Fernie Formation consists of the Passage Beds, which mark the transition from the relatively fine-grained units to a sandstonedominated interval that makes up the overlying shallow marine to continental deposits of the Kootenay Group (Fig. 1; Hamblin and Walker, 1979; Leckie and Smith, 1992 ; Ross et al., 2005). Monteith C Overview In the study area, the Monteith C is characterized by three upward-coarsening packages (lower, middle, and upper) separated by regionally extensive bounding surfaces (Figs. 6 and 13). These surfaces are associated with a marked change in facies from nearshore to offshore deposits (MC-L7 9 overlain by MC-L1), indicating a sharp rise in relative sea level. This facies shift is characterized by thorough biogenic reworking of the flooding surface, including robust trace fossils of marine affinity and the presence of rare pebble-sized clasts (Fig. 8K). Sequence stratigraphically, the three widely distributed upwardcoarsening units are thought to be equivalent to parasequence sets (Van Wagoner et al., 1990). Monteith C Fernie Formation Contact The contact between the Upper Fernie shale and sandstone and the Monteith Formation is typically placed at the base of the lowermost >3 m thick sandstone unit in the Monteith Formation (Stott, 1998). This contact is straightforward to recognize in the central portion of the study area as the lower Monteith C sandstone is thick and sharp based; northwards, however, sandstone of the lower Monteith C gradationally pinches out (Figs. 6 and 13). The lithostratigraphic base of the Monteith Formation effectively transitions along a diachronous surface and is progressively more difficult to discern (Fig. 13). This challenge is exacerbated where sandstone beds are present in the uppermost part of the dominantly fine-grained Upper Fernie shale and sandstone (Figs. 5, 6 and 13). Consistent with the interpretations from this study, Stott (1998) concluded that the Upper Fernie shale and sandstone was transitional with the lowermost portion of the Monteith Formation. The Upper Fernie shale and sandstone consists of prodeltaic units (MC-FA1; Table 2), which represent the distal progradational expression of genetically linked overlying coarser grained deltaic sandstone of the lower Monteith C (Figs. 1, 4, 13). The base of the upward-coarsening cycle in the Upper Fernie shale Page 22 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

21 and sandstone, demarcated by a relatively high gamma radiation reading, is considered a marine flooding surface (Fig. 13). Thickness Trends and Internal Stratigraphic Architecture The Monteith C thickens to the west and southwest, a trend also apparent within each of the Monteith C packages (Figs. 5, 6, 13, and 14A, D F). The thickness of the Monteith C to the east of the Monteith B erosional edge is a partial thickness, affected by erosional truncation associated with the sub-cadomin unconformity (Figs. 5 and 14A). Notably, the eastern extent of the Monteith C is not an erosional limit, but rather it is the edge beyond which the upward-coarsening packages and their bounding flooding surfaces can no longer be reliably defined due to amalgamation of sandstone units (Figs. 14D F and 15). In the lower Monteith C, the northwest limit of sandstone is interpreted to represent the major depositional edge of the deltaic system (Fig. 16). The depositional edges of overlying upward-coarsening packages have not been recognized, as they are presumably beyond the study area. Internally within each of the packages, laterally offset sandstone bodies, interpreted to represent deltaic complexes, are recognized (Fig. 16; Coleman and Gagliano, 1964; Anderson and Fillon, 2004). The internal facies architecture is complex, possibly attributed to the dominance of floods during deposition. Fielding et al. (2005a, 2005b, 2006) has demonstrated significant flooding in deltaic systems can cause rapid progradation, incision and delta front reworking. Despite the complex internal stratigraphic architecture, in some areas deltaic complexes can be further differentiated into smaller lobate bodies, separated by higher order, semi-regional marine flooding surfaces (Fig. 13). This degree of high order mapping was not a focus of this study and is difficult in most portions of the study area due to limited well penetrations; however, where recognized, it is clear that the internal complexity leads to substantial reservoir heterogeneity and compartmentalization (Fig. 13). Further sequence stratigraphic analysis will likely be useful for future natural gas exploration and development in the region. Figure 13. Genetically correlated dip oriented cross-section (E E ) through the lower Monteith C. This section is hung on a regionally correlatable flooding surface in the Monteith C that defines the top of the middle Monteith C upward-coarsening package. Southeast to northwest progradation is evident. Internal higher order flooding surfaces within the Monteith C sepa rate deltaic sedimentary bodies. The genetic relationship between the Monteith C and the Upper Fernie shale and sandstone is evident. Angles on the shoreline clinoforms, as interpreted, are between 0.1 and 0.3. Surfaces in the Fernie Formation after Poulton et al. (1990) and Asgar-Deen et al. (2004). The section location is shown on Figure 2A and Figure 16. Stratigraphic Framework for the Monteith Formation, Alberta Page 23

22 Page 24 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard Figure 14. Isopach maps for (A) Monteith C, (B) Monteith B, (C) Monteith A, (D) lower Monteith C, (E) middle Monteith C, and (F) upper Monteith C intervals as defined in text. The location of the Monteith A and B subcrop edges, amalgamation edge of the Monteith C and edge of the deformation front are indicated on the maps. Trends in the cross-hatched area in the eastern portion of the Monteith C maps (A, D F) are less certain due to amalgamation of units and erosion associated with the sub-cadomin unconformity.

23 Monteith B Overview The lithological character of the Monteith B does not change markedly across the study area (Fig. 6). The dominantly finegrained nature of the unit is locally interrupted by thin upward fining sandstone bodies, which are up to 6 m thick. The upper portion of the Monteith B is characterized by numerous coal horizons (0.5 1 m thick) that are readily identifiable on porosity and sonic logs (Fig. 9). Internal stratigraphic boundaries are difficult, if not impossible, to recognize as core and well control is lacking for the unit. Due to the lack of internally correlatable surfaces, the Monteith B is not sub-divided. However, the first occurrence of coal is successfully utilized as a stratigraphic datum for correlation of the Monteith A (Fig. 17). Monteith B Monteith C Contact The base of the Monteith B is a gradational contact placed at the top of the uppermost upward-coarsening package in the Monteith C. The top of the Monteith C is defined by the uppermost thick (>4 m), clean sandstone (>60 API cut-off; Figs. 5 and 6). Recognition of this contact provides a useful division between deltaic deposits and those of the overlying coastal plain, and distinguishes reservoir sandstone (Monteith C) from heterolithic non-reservoir intervals (Monteith B). Thickness Trends and Internal Stratigraphic Architecture The thickness of the Monteith B increases from 0 m in the east at its erosional edge beneath the sub-cadomin unconformity to >100 m in the west-southwest (Fig. 14B). To the east of the Monteith A erosional edge, the thickness of the Monteith B is strongly linked to erosion associated with the overlying sub- Cadomin unconformity and does not represent a depositional thickness (Figs. 5, 6 and 14B). Monteith B thickness is variable in the northern portion of the map area (Figs. 2 and 14B) due to the inconsistency in sandstone thickness in the underlying upward-coarsening package of the Monteith C, which has a thickness distribution that is inversely proportional to that of the Monteith B (Fig. 14B). Monteith A Overview The Monteith A is the uppermost lithostratigraphic unit of the Monteith Formation in the Alberta subsurface (Fig. 1). The internal stratigraphy is difficult to discern due to a lack of correlatable markers, further compounded by eastward erosional truncation associated with the overlying sub-cadomin unconformity (Figs. 5 and 14C). Wireline log signatures of the Monteith A are variable, with gamma-radiation logs showing blocky (up to 75 m thick) and upward-fining stratal packages (up to 30 m thick; Figs. 11 and 17). In the southern and southeastern portions of the study area, the net sandstone/gross thickness ratio is generally high ( ) and blocky log signatures are associated with MA-FA1 (Figs. 11, 12 and 17). To the northwest, the unit is more heterogeneous, due to greater preservation of MA-FA2 (Figs. 11, 12, 17). Figure 15. Dip oriented cross-section (F F ) that highlights the increasing difficulty in identifying the flooding surfaces that define individual units in the Monteith C towards the eastern portion of the study area, where amalgamation of sandstone bodies is notable. The section location is shown in Figure 2B. Monteith A Monteith B Contact The contact between the Monteith A and B typically is sharp and may be slightly erosional. The contact is difficult to define in the northwest where the Monteith A is characterized by upward-fining log signatures separated by siltstonedominated intervals, similar to the upper portion of the Monteith B (Figs. 11C, D, 12 and 17). A number of laterally extensive thin coal seams and sandstone beds with relatively high siltstone content (higher gamma-radiation response and lower resistivity) distinguish the top of the Monteith B in this region. Generally, the Monteith A B contact is placed at the Stratigraphic Framework for the Monteith Formation, Alberta Page 25

24 base of the lowermost thick and clean (>60 API) sandstone package (Figs. 5, 6 and 17). This contact can be interpreted as either: 1) a facies contact between two sub-environments that existed lateral to one another that resulted from continued progradation of the depositional system; or 2) a sequence boundary associated with rapid base level fall and associated fluvial incision. The simpler progradational interpretation of this transition from Monteith B to A is favoured as similar facies are present in each unit. Thickness Trends and Internal Stratigraphic Architecture The Monteith A varies in thickness from approximately 150 m adjacent to the deformation front to the zero edge in the east (Fig. 14C). Minor perturbations in the thickness of the Monteith A are attributed to erosion associated with the overlying sub-cadomin unconformity. Such variations do not reflect fluvial incision into the underlying Monteith B because thin zones of Monteith B strata do not correspond to thick zones in the overlying Monteith A (Figs. 14B and C). Areas where the Monteith A is over-thickened are considered to be erosional remnant highs, attributed to differential erosion on the unconformity surface or the result of thrust faulting (Fig. 14; McLean, 1977; Gies 1984; Varley, 1984; Hayes et al., 1994). Cadomin Formation The Cadomin Formation is characterized by conglomeratic alluvial facies throughout the study area (McLean, 1977; Gies 1984; Varley, 1984; Hayes et al., 1994; Leier and Gehrels, 2011). It unconformably overlies the Monteith Formation (Fig. 1). The sub-cadomin, or sub-cretaceous, angular unconformity is present across most of Alberta (McLean, 1977; Schultheis and Mountjoy, 1978; Smith et al., 1984), and it truncates progressively older units eastward (Figs. 5 and 14A C). The contact between the Monteith Formation and Cadomin Formation can be difficult to delineate and map because some of these units have similar wireline log responses. Although the signature of the boundary can be variable, the Cadomin Formation can typically be differentiated from the underlying Monteith Formation by: 1) an in gauge caliper log; 2) a slightly cleaner gamma-radiation log response (1 5 API units); 3) a shift in porosity; and 4) a shift in resistivity (e.g. Fig. 11A and B). Figure 16. (A) Net sandstone distribution in the lower Monteith C upward-coarsening package showing the north-northwesterly pinch out of sandy deltaic sediments. Trends in cross-hatched area are less certain due to amalgamation of units (Fig. 15). (B) Line drawing trace of main features in part A emphasizing the distributive channel system and the basinward pinch out of sandstone (>5 m). Page 26 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

25 Tight Gas Sandstone Reservoir Potential The Monteith Formation contains substantial natural gas reserves in low porosity and permeability (tight) sandstone reservoirs (Energy Resources Conservation Board, 2005; Boettcher et al., 2010; Solano et al., 2010). The tight sandstones are part of the basin centered gas system that extends from northwestern Alberta to northeastern British Columbia (Masters, 1979). More than 200 wells in the study area have reported gas production from the Monteith Formation, although most of these are comingled with up-hole reservoirs and contribution from the Monteith Formation is difficult to assess. Production is primarily from the Monteith A and C; local contribution from channel deposits within the Monteith B is also plausible. Although an extensive petrographic analysis was beyond the scope of this study, a preliminary investigation of reservoir petrography was undertaken. Thirteen randomly selected thin sections (eight Monteith C and five Monteith A) were analyzed for their composition, porosity characteristics, and diagenetic properties. Monteith C Production from the Monteith C is concentrated in the Deep Basin and to date has not been a major target in the Foothills belt in the southwest of the study area (Fig. 2). Production is likely controlled by primary sedimentary facies and diagenesis as no major structures have been identified in the Deep Basin (Fig. 2; Masters, 1979; Shanley et al., 2004; Zaitlin and Moslow, 2006). Sandstones of the Monteith C are mainly quartz arenite to sub-litharenite (Fig. 18A, C and E). The major component of all Monteith C sandstones is quartz, with minor lithic and chert grains and traces of feldspar (Fig. 18A, C, and E). No compositional differences have been observed between sandstone units of the three Monteith C packages. Monteith C strata record silica cementation and burial compaction (e.g. stylolites and strained quartz grains with undulose extinction), which eliminated portions of the primary intergranular porosity (Fig. 18C). Leached lithic grains are notable locally, and where present contribute secondary porosity; however, this porosity may be unconnected (Fig. 18E). A link between facies and diagenesis is noted in the Monteith C. Well-sorted quartz rich facies (MC-F5) tend to be more affected by silica overgrowths due to the abundance of quartz-on-quartz contacts (Figs. 18A and 19A, B, D). Conversely, facies with significant primary mud in the sand matrix (MC-F4) tend to have fewer silica overgrowths and were more prone to development of clay rims (Figs. 18A and 19A, C, E). Intragranular microfractures and slot pores are also observed locally in sandstones of the Monteith Formation (Figs. 19E and 20D), however, their regional distribution and contribution to production from the formation is poorly constrained. They may be an important control on the permeability and porosity in Monteith C sandstone (Shanley et al., 2004; Aguilera, 2008). All of the upward-coarsening packages in the Monteith C have produced gas; however, spatial variations in the petroleum potential within each package are present, with certain upwardcoarsening packages more productive in a given field than others. The controls on regional variation in production and hydrocarbon potential from within the Monteith C have not been well constrained and remain an avenue for future research. Monteith A Gas production from the Monteith A is concentrated in the deformed belt with limited contribution from the Deep Basin region to date. The high net:gross ratio (N:G) in the unit, up to 50 70% (Fig. 17), is an important consideration as reservoir simulations from other channelized deposits indicate that high N:G values (>60 75%) significantly increase the chance for vertically and laterally connected reservoir bodies (e.g. Allen, 1978; Bridge and Tye, 2000; Larue and Hovadik, 2006). In the Foothills portion of the study area, high N:G values are associated with a thick sandstone reservoir interval proven to contain a significant tight gas resource (e.g. Chinook Ridge; Figs. 2, 14 and 17). Figure 17. Strike oriented stratigraphic cross-section (G G ) through the Monteith A hung on the first coal in the Monteith B, utilizing gamma radiation and sonic logs, with net sandstone (>60 API) shown in yellow. Net to gross (labelled) progressively decreases towards the northwest with an associated decrease in channel amalgamation. The section location is shown in Figure 2B. Stratigraphic Framework for the Monteith Formation, Alberta Page 27

26 Figure 18. Thin section photomicrographs from the Monteith Formation. (A) Sublitharenite to quartzarenite sandstone of the Monteith C. This sandstone had mud incorporated into the matrix during deposition, which limited silica overgrowth. The majority of the porosity in this sample is moldic, formed by the secondary dissolution of primary grains (02/ W6; m; PPL). (B) Chert grain from the Monteith A. The chert grain is composed of sponge spicules. Because of the polycrystalline nature of the chert grain silica overgrowth is inhibited. In the lower left there is dolomite cement present. Dolomite cement is more common in the Monteith A than the Monteith C ( W6; m; PPL). (C) Silica cemented quartz grain from the Monteith C. The initial dust ring (red arrow) highlights the initial quartz grain and the primary porosity filled by silica cement. The silica overgrowth on this grain has euhedral boundaries, a common characteristic of Monteith C sandstones where there are abundant quartz/quartz contacts ( W6; 2030 m; XPL). (D) Litharenite of the Monteith A. This sandstone has a high percentage of chert grains (blue arrows), and limited to no porosity ( W6; m; PPL). (E) Sublitharenite of the Monteith C. Note the dissolution of primary lithic grains and the associated ineffective moldic porosity (orange arrows). Some larger slot pores are developed (black arrows; Shanley et al., 2004), which increases porosity and permeability although the development of these slots in the subsurface is poorly constrained ( W6; m; PPL). (F) Litharenite of the Monteith A that is dominated by microfractures (purple arrows). Microfractures contribute to porosity and permeability, although the occurrence and contribution of microfractures at reservoir conditions is not well constrained ( W6; m; PPL). Page 28 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard

27 Figure 19. (A) Regional porosity and permeability core data from the upper Monteith C (grey X s) and from well W6 (black squares). The thick black trend line shows the regional porosity/permeability relationship. The two circled regions on the graph fall within different Monteith C facies (MC-F4 and MC-F5). (B) Core photo of MC-F5, organic rich cross bedded sandstone, with a major horizontal stylolite. This facies is fairly well sorted and was deposited under the influence of traction in a distributary channel ( W6; m). (C) Core photo of MC-F4, massive sandstone with local fluid escape structures. This facies was deposited rapidly from suspension and was therefore not well sorted and contains a large amount of primary interstitial mud ( W6; m). (D) Thin section of MC-F5, showing the dominance of quartz overgrowths in this sample. The quartz overgrowths are dominant because of the abundant quartz-quartz contacts in this well sorted facies. The presence of slot pores in this sample leads to high permeability (60 70 md) relative to porosity (0.15; W6; m; PPL). (E) Thin section photograph of MC-F4. The rapid sedimentation from suspension allowed for the incorporation of a significant amount of interstitial mud, which limited quartz overgrowths in this sample and led to development of secondary moldic porosity. The preclusion of quartz overgrowths did not allow for slot pores to form resulting in low permeability (0.4 md) relative to porosity (0.12; W6; m; PPL). Stratigraphic Framework for the Monteith Formation, Alberta Page 29

28 Page 30 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard Figure 20. (A) True vertical depth (TVD) gamma radiation, density porosity, neutron porosity, resistivity logs and cored intervals from the Monteith A in a deviated well in the foothills ( W6). Five separate hydraulic fracture stimulations were applied to the Monteith A in this well, with the amount of gas flared from each flow test shown. Hydraulic fracture stimulation #4 over an interval associated with more abundant natural fractures returned the largest amount of gas and had measurable flow rates of to 2934 Mcf/d. (B) Core description through interval of fracture stimulation #4 (MD; m) with high angle bedding, fault breccia and abundant natural fractures. (C) Box photographs (MD; m) with highly fractured sandstone and siltstone. (D) Highly fractured interbedded sandstone and siltstone with fractures filled with quartz cement (MD; m). (E) Open fractures in sandstone with well developed quartz mineralization, likely representing important permeability conduits (MD; 3485m).

29 Chert and quartz are the major mineralogical constituents of Monteith A litharenite (Fig. 18B, D and F). Porosity of the unit is greatly reduced as a result of quartz cementation, with secondary chert and dolomite locally present as pore filling cements (Figs. 18B and D). The overall porosity contains a moldic component, associated with the dissolution of primary grains, generating both effective and ineffective porosity (Fig. 18F). Fractures are important permeability conduits in the Monteith A, helping overcome ineffective porosity generated by grain dissolution (Figs. 18 and 20). The role of fractures is emphasized by the significantly higher initial production rates from wells within the fold and thrust belt (e.g Mcf/Day from Chinook Ridge fields; Fig. 20) compared to those in the Deep Basin (e.g. approximately 750 Mcf/Day from Elmworth, Wapiti fields). Intergranular microfractures are locally present in the Monteith A (Fig. 18F). As with Monteith C sandstones, the role of microfractures within reservoirs is unknown. However, they are likely an important contributor to permeability and production rates in strata within or adjacent to the deformed belt (Shanley et al., 2004; Zaitlin and Moslow, 2006; Aguilera, 2008). Discussion Basin Setting The tectonostratigraphic information recorded within the Monteith Formation provides important insight into depo-centre evolution during an early phase of foreland basin development. The timing of loading in the Omineca fold and thrust belt (Late Oxfordian, Late Jurassic) is fairly well established (Monger et al., 1982; Cant and Stockmal 1989; Fermor and Moffat, 1993; Evenchick et al., 2007); however, the associated foreland basin deposits are less well studied. The relatively undeformed strata have been penetrated by thousands of well-bores and the resultant dataset represents a rare opportunity to generate well constrained isopach maps, which provide insight into the early foreland basin architecture. Each of the informal Monteith Formation units (A, B and C), as well as each of the individual Monteith C packages (lower, middle and upper), show an appreciable increase in thickness towards the west-southwest (Figs. 14 and 20). The significant thickening towards the orogenic belt suggests that accommodation was greater in the west than in the east. Regional cross-sections oriented SW-NE highlight the southwestward thickening of the Monteith A, B and C; however, apparent westward thickening is exaggerated in the east by erosion associated with the sub-cadomin unconformity (Fig. 15). The Monteith C is particularly useful in regional thickness correlations because it is not affected by erosion over most of its regional extent (Fig. 14A). Regional correlations within the upward-coarsening packages of the Monteith C show an increase in gross thickness towards the southwest, perpendicular to the axis of the foreland basin, consistent with studies of directly overlying strata (McLean, 1977; Gies, 1984; Hayes et al., 1994; Stott, 1998). However, sandstone thickness and N:G decrease along the same trend as abundant finer grained prodeltaic deposits are preserved (Figs. 14 and 15). N:G is higher in the east as individual sandstone packages are characterized by increased amalgamation and therefore limited preservation of the intervening finer grained prodelta material (Figs. 5, 13, 14A and 15). This eastward amalgamation of units within the Monteith C suggests an eastward decrease in accommodation, precluding the development or preservation of thick prodelta deposits. Based on thickness trends increasing southwestward, accommodation is interpreted to have been generated in response to flexural loading in a foredeep (DeCelles and Giles, 1996). The greater thickness in the southwest indicates that the axis of the foredeep had developed at least as early as the onset of Monteith Formation deposition. Precise paleogeographic reconstruction is hampered by the limits of the study area and data assessed but the continued thickening to the west suggests that the study area is on the cratonward side of the foredeep axis (Fig. 21). Amalgamation of Monteith C packages to the east and northeast suggests proximity to the basin margin during deposition, where accommodation was significantly reduced (DeCelles and Giles, 1996). A potential cause for this reduced accommodation is proximity to the forebulge, where distal uplift in response to flexural loading is manifested (Fig. 21; DeCelles and Giles, 1996). Basin Evolution The Monteith Formation represents an important phase of deposition in response to flexural loading in the Canadian Cordillera during the Late Jurassic Early Cretaceous (Cant and Stockmal 1989; Evenchick et al., 2007). A particularly interesting aspect of the Monteith Formation is that the associated units (A, B and C) represent a continuous cycle of basin filling with no apparent major sequence stratigraphic breaks in the overall depositional history. The depositional evolution in the study area is recorded in: 1) prodelta deposits of the Upper Fernie shale and sandstone; 2) deltaic units of the Monteith C; 3) coastal plain deposits of the Monteith B; and 4) fluvially dominated facies of the Monteith A. The overall evolution of the system is punctuated by a number of widespread marine flooding events within the Monteith C; however, on a broader scale the entire system is progradational (Fig. 21). Stratigraphic correlations (Fig. 13) and sandstone distribution (Fig. 16) in the Monteith C indicate that a north-northwestward flowing basin axial drainage system was established prior to or synchronous with the onset of coarse-clastic deposition (Fig. 21). Similar drainage patterns recognized in the overlying Cadomin and Gething formations may indicate that this basin axial flow persisted throughout deposition of the Monteith Formation (Smith et al., 1984). Major axial drainage systems are typical of both ancient and modern foredeeps (e.g. DeCelles and Giles, 1996; Garcia- Castellanos, 2002; Clevis et al., 2003; Romans et al., 2011). If the overlying Cadomin Formation and Gething Formation paleogeographic reconstructions, as well as that for the Kootenay Group to the south, are considered analogous, the axial drainage was likely intersected by tributaries sourced from both the Cordillera and craton (Hamblin and Walker, 1979; Smith et al., 1984; Stott, 1984, 1998). The presence of spiculitic chert in thin sections from the Monteith A is consistent with a westerly catchment, which contained uplifted Paleozoic carbonates (Fig. 18B, D and F; Stott, 1998). Overall there is a change in sediment composition through the system Stratigraphic Framework for the Monteith Formation, Alberta Page 31

30 from quartz arenite in the Monteith C to litharenite in the Monteith A (Fig. 18). A number of possible mechanisms are proposed for this compositional shift: 1) Sequential unroofing of new source terranes in the uplifted belts to the west may have caused a change in sediment source during evolution of the system. Given the proposed paleogeography and a dominantly Cordilleran source in the west and south (Fig. 21), an evolution in catchment area would potentially be reflected across successive northward progradational wedges of the system. The detritus shed during Monteith C deposition may have been quartzrich, however, by the time the Monteith A fluvial system was active in the study area, a new source may have been uplifted that contributed substantial Paleozoic chert-rich detritus to the system; 2) Sediment winnowing and breakdown of chert may also explain sandstone composition changes. Harrell and Blatt (1978) suggest that chert has less survival potential compared to monocrystalline quartz in that it is more susceptible to chemical weathering. The fluvial systems of the Monteith A and equivalent chert rich intervals in the Kootenay Formation to the south may have provided residence times long enough for chemical weathering to weaken the chert grains, making them less likely to pass through the non-marine realm and reach the deltaic system in the Monteith C; 3) Lastly, a change from a dominantly eastern cratonic catchment to a western catchment containing abundant chert may also explain the increase in chert content through Monteith Formation strata. Some combination of these processes likely was active but more work is needed to definitively interpret source-area evolution. Figure 21. Proposed paleogeographic evolution and tectonic setting of the Monteith formation and equivalent strata in northwestern North America. (A) Paleogeography during the Late Tithonian (Late Jurassic) with an extensive axial fluvial system, sourced from the USA (after Dickenson et al., 2010), providing sediment to mapped deltaic deposits of the Monteith C in the study area. Late Berriasian drainage divide from Evenchick et al. (2007). The extent of the foreland basin is estimated from Poulton et al. (1994) and Stott (1998) in the north and central portion of the map, and Fuentes et al. (2011) and Turner and Peterson (2004) in the south. The position of the Barremian Fox Creek Escarpment is from Smith et al. (1984), outcropping chert rich conglomeratic deposits from McMechan et al. (2006), Middle Jurassic Early Cretaceous J2/J3 Paleovalley of Hopkins (1981), Late Kimmeridgian shoreline from Turner and Peterson (2004) and the proposed positions of the Late Oxfordian-Kimmeridgian and Aptian forebulges in Montana from Fuentes et al. (2011) are shown for context. (B) Paleogeography during Berriasian (?) time showing progradation of the Late Tithonian shoreline in a northwestwards direction and dominantly fluvial deposition of the Monteith A in the study area. (C) Schematic cross-section oriented SW-NE through the Early Cretaceous foreland basin that accounts for the stratal thickening to the west and the internal amalgamation of the strata to the east (after Decelles and Giles, 1996; Ross et al., 2005; Evenchick et al., 2007). Cross-section line indicated by straight black dashed line in B. Page 32 B.D. Miles, R.B. Kukulski, M.K. Raines, J-P. Zonneveld, A.L. Leier and S.M. Hubbard