Sediment-aquifer play types in a list of 30 key Canadian

aquifers Russell, H.A.J.

1, Sharpe, D.R.

1, and Cummings, D.C.

2

1 Geological Survey of Canada, 601 Booth St. Ottawa, ON., K1A 0E8

2 DC Geosciences, 12 Decarie Street, Aylmer, QC. J9H 2M3

ABSTRACT There is a need for a classification scheme that can be applied nationally to aquifers in Canada. One approach is to adapt the ―play‖ concept, which is used extensively in the petroleum industry. Adapted to groundwater aquifer classification the play concept can be defined on the basis of aquifer geology, confining units (hydrostratigraphy) and hydrology (recharge - discharge). Identification and conceptualization of these characteristics requires knowledge of the geological evolution of the basin best achieved by basin analysis techniques. A synthesis of aquifer play types has the potential to capture key messages embodied in the existing large set of data that comprises local case studies. RÉSUMÉ Il s’avère important d’établir un système de classification qui pourrait s’appliquer à l’échelle nationale aux aquifères du Canada. L’une des approches consiste à adapter le concept de « play », couramment utilisé dans l’industrie pétrolière. Une fois adapté à la classification des aquifères, le concept de « play » peut être défini d’après la géologie des aquifères, les unités encaissantes (hydrostratigraphie) et l’hydrologie (recharge - émergence). La détermination et la conceptualisation de ces caractéristiques exige des connaissances sur l’évolution géologique du bassin, acquises au moyen de techniques d’analyse des bassins. Une synthèse des types de « play » aquifères offre la possibilité de saisir les messages clés contenus dans le considérable jeu de données fourni par des études menées à l’échelle locale. 1 INTRODUCTION There is a need for a succinct classification scheme for aquifers that is physically based and that transcends local geological – hydrogeological settings and issues, hence, that can be applied nationally across Canada. Groundwater aquifer classifications have been developed at various scales, from individual aquifer, to aquifer system, to watershed scale (Wei et al., 2009). Classification has taken a variety of approaches, including describing geologic materials, landforms, depositional environments, hydrostratigraphy, flow systems, hydrochemistry, water quality, etc. (e.g. Payne et al, 2010, references therein; Wei et al., 2009). Many of these approaches work well locally but have limited broader application due to a lack of standardization. Consequently, there remains a need for an improved hierarchical approach to aquifer classification. As geological data is generally more abundant than hydrogeological information, a classification should be geologically based and tied to an understanding of the basin history, commonly defined from basin analysis studies. Integration with basin analysis provides not only a classification scheme, but also a predictive framework and development of aquifer analogues that can be used for comparison or extrapolation to other areas (e.g. Sharpe et al., 2002).

One such approach is the ―play― concept, which is used extensively in the petroleum industry (Doust, 2010). The play concept was first introduced nearly 90

years ago in the USA. In the past 40 years it has seen extensive work toward refining the definition and application of the concept in petroleum basins around the world (see Doust, 2010 for a review).

The play is most commonly based on the concept of source, reservoir, and trap (e.g. Doust 2010). These concepts have direct parallels to aquifers within the broader water cycle; however, there is some modification required for groundwater applications. The play concept, relying on primary geological and hydrogeological data, without recourse to issues of vulnerability, land use or exploitation, provides a framework that incorporates all of the necessary information to support various facets of water management. 1.1 Objective The objective of this paper is to adapt the play concept to groundwater aquifers. Adaption of the play concept is presented within a hierarchical classification system that accommodates a range of scales from hydrogeological regions to individual play classifications for key Canadian aquifers identified by the Geological Survey of Canada (Fig. 1, Table 1). A single case study is presented from the Oak Ridges Moraine (Ontario) to illustrate how the play concept may work for a moraine subaqueous fan play.

Figure 1. Hydrogeological regions of Canada with key Canadian aquifers identified

Table 1. Key Canadian aquifers grouped according to hydrogeological regions. Note no currently designated key Canadian aquifers occur in the Permafrost region. Letters in parentheses refer to principal aquifer geology, namely bedrock (br), bedrock and sediment (br-s), or sediment (s)

Cordillera Western Canada

Sedimentary Basin

Southern

Ontario

St Lawrence

Platform

Appalachians

1. Gulf Islands (br) 2. Nanaimo Lowland (br-s) 3. Fraser Lowland (s) 4. Okanagan Valley (s) 5. Shushwap Highlands (br)

6. Paskapoo (br) 7. Buried Valleys (s) 8. Upper Cretaceous Sand (br) 9. Milk River (br) 10. Judith River (br) 11. Eastend – Ravenscrag (br)

12. Intertill (s) 13. Manitoba Carbonate Rock (br) 14. Manitoba Basal Clastic unit (br) 15 Odanah Shale (br) 16. Sandilands (s) 17. Assiniboine Delta (s)

18. Oak Ridges Moraine (s) 19. Grand River Basin (br-s) 20. Credit River (br-s) 21. Waterloo Moraine (s) 22. Upper Thames River (br-s)

25. Mirabel (br-s) 26. Châteauguay (br-s) 27 Richelieu (br-s) 28 Chaudière (br-s) 29. Maurice (s) 30 Portneuf (s)

23. Annapolis – Cornwallis (br-s)

Maritimes

Basin

24. Carboniferous Basin (br)

2 ADAPTING THE PETROLEUM PLAY CONCEPT FOR GROUNDWATER APPLICATIONS

The play concept developed for petroleum exploration and resource assessment assumes upward migration of hydrocarbons (oil, gas) from a source rock (charge) to a reservoir that is confined by a cap rock and trapped by a three-dimensional enclosure, either stratigraphic or structural (Fig. 2). By contrast, the groundwater system is inverted with respect to the petroleum flow system: the source equates to precipitation from above; recharge generally occurs by downward infiltration of water to the aquifer (reservoir); and partial to complete confinement may occur as a result of adjacent, underlying and/or overlying aquitards (Fig. 2).

Table 2. Terminology and concepts for petroleum and groundwater plays in unconsolidated sediment Petroleum

play

Groundwater

play

Comments

Source (charge)

Hydrology

"Hydrology" integrates precipitation, evaporation/transpiration, infiltration, recharge and discharge.

Reservoir Aquifer defined by formative process, most commonly the depositional setting

Seal Confining units

Aquitard units.

Trap Hydrostratigraphic architecture;

An important difference between the petroleum play

and groundwater play is the consideration of groundwater discharge from the aquifer. Because many aquifers in Canada are shallow, they commonly form part of shallow flow systems, contribute directly to surface hydrology, and groundwater has a resident period of tens to hundreds of years, a time scale of key interest to sustainable aquifer exploitation.

Doust (2010) has suggested that a standardized hierarchic system be adopted when defining plays. Three stratified characteristics are proposed that span different scales from regional to more local. These have the potential to provide a standardized context for the play definition. The first level is the source (charge) and flow path to the reservoir, second is the reservoir type, and third is the seal and trap type. Differences in fluid behaviour, fluid source, and time spans require some modification of the play concepts and terminology for groundwater (Table 2, Fig.2).

For hydrogeological applications, the source system can be termed the hydraulic system (Fig. 2). This would include precipitation, evaporation/ transpiration (ET), recharge, and discharge. The petroleum reservoir has a direct analogue in the aquifer. In glacial aquifers structural traps are not significant; however, confinement or flow barriers are important. Confinement can be summarized within a hydrostratigraphic framework and discussion of aquitards. Aquifers are commonly considered within the context of unconfined, semi-confined, and confined conditions with respect to recharge and discharge.

To adapt the play concept to groundwater requires some reorganization. In contrast to the petroleum emphasis first on source, then on reservoir, and finally on trap; for groundwater a different sequence is more appropriate. As the hydraulic system encompasses process contributing to both the recharge and discharge of aquifers with a temporal component, it may be more appropriately ranked following the aquifer and confining units. Consequently, primary emphasis is placed on the aquifer followed by the confining units and then hydrology. This succession assumes an established stratigraphic framework within which the aquifer play is being assessed.

Figure 2. Comparison of terminology for two idealized petroleum and groundwater plays

To provide for an orderly and consistent application of the play concept requires a standardized implementation. Doust (2010) has suggested that play types be defined on the basis of a single feature that most characterizes the reservoir (aquifer) or family of reservoirs (aquifers). For groundwater a compound play definition is proposed based on landforms and/or stratigraphic architecture followed by depositional environment (Table 3). Application of a compound play terminology captures regional components (landforms / stratigraphic architecture) and more detailed aspects of the play (depositional setting). This approach to the creation of a compound play definition recognizes the significance of regional setting (e.g. landform) along with the more local scale control on aquifer heterogeneity, and length scales imparted by depositional setting (e.g. subaqueous fan). It takes advantage of terminology and definitions commonly applied by regional workers, in much the same way as petroleum plays are commonly based on geological formation names (Doust, 2010). By integration of the depositional setting in the definition it also highlights the primary controls on aquifer size, scale, and heterogeneity. Integration of the depositional setting in the play definition also provides improved clarity as large landforms are commonly polygenetic with considerable stratigraphic and spatial differences in formative processes and hence aquifer characteristics.

3 KEY CANADIAN AQUIFERS

The scale and diversity of geology, groundwater regimes and hydrology of Canada provide an enormous challenge for synthesis. Sharpe et al. (2008) have subdivided the Canadian landmass into nine hydrogeological regions based on physiography, tectonic setting, bedrock geology, and permafrost extent (Fig.1). Within respective hydrogeological regions there are numerous aquifers of varying scale and productivity. Currently, with the exception of the British Columbia classification of Cordilleran aquifers (Wei et al., 2009), there is no inventory of aquifers in the regions and no compilation of the range of aquifer styles. The Geological Survey of Canada is currently working on mapping and assessing 30 key Canadian aquifers within these regions (Fig. 1, Table 1). In a general way, these 30 aquifers can be assigned to one of three classes: i) bedrock aquifers, ii) bedrock-sediment contact zone aquifers, and iii) unconsolidated sediment aquifers. Different groundwater plays are associated with each of these classes (e.g., Table 3). Implementation of the play concept for aquifer classification has the potential to capture key data embodied in the abundant but widely dispersed local case-study literature. Lessons learned from case study of particular play examples can be used as analogues to assess the benefits and risks associated with exploiting that particular play type in the hydrogeological region in question.

4 PLAY TYPES FOR UNCONSOLIDATED KEY CANADIAN AQUIFERS

Aquifers in glaciated landscapes / basins may occur in areas with relatively thin sediment cover (Canadian Shield) and areas with as much as 300 m of sediment cover (e.g. prairies). In large glaciated basins with thicker sedimentary fills, landforms on the modern landscape may overlie older glacial deposits (tills) and buried landforms that form elements of the basin stratigraphic architecture. In some of these glaciated basins, strata have been eroded and truncated over the course of multiple erosional events, as recorded by erosion surfaces (e.g., buried valleys), which can result in relatively complex, non-layer cake stratigraphic successions (e.g. Sharpe et al., 2002; Cummings et al., this vol.). The most broadly recognized and commonly well understood component of glaciated landscapes are landforms (e.g. moraine, esker). The subsurface equivalent is the stratigraphic architecture of features such as buried valleys within sediment fills or at the bedrock interface (e.g. Sharpe et al., 2002). Landforms and more commonly the basin fill may have stratigraphic complexity formed of stratal successions emplaced by multiple depositional environments (conduit fills, subaqueous fans, deltas).

Table 3. Possible play types and assignments for unconsolidated key Canadian aquifers.

Play Type Assignment of key

Canadian aquifers

(identified Figure 1) Landform

and/or

stratigraphic

architecture

Depositioinal

element

Moraine

subaqueous fan ORM, Waterloo, Credit River, Sandilands, Grand River

esker conduit ORM, Waterloo, ,

Glacideltaic Port Neuf, St Maurice

glacifluvial Grand River

Buried valley fill : bedrock interface

glacifluvial ORM, Waterloo, Mirabel,

esker – subaqueous fan

ORM, Waterloo, Mirabel, Grand River

fglaciluvial Spiritwood,

Buried valley fill: sediment hosted

subaqueous fan ORM, Sandilands,

meltwater channel

Intertill

Glacial basin : marine / lacustrine

glacideltaic Assiniboine

esker Chateaugay

glacifluvial Okanagan Valley, Grand River

Post glacial basin : marine / lacustrine

alluvial fan Okanagan Valley,

delta Fraser Lowland

Aquifers within similar landforms and depositional

environments in glacial basins may be confined, semi-confined or unconfined depending upon local basin stratigraphy. This variable basin hydrostratigraphy may affect aquifer potential for similar landforms and depositional environments. For example eskers on the Canadian Shield rarely form aquifers, except where hosted in clay basins that either partially or completely bury (confine) the esker (e.g. Bolduc et al., 2005; see

Cummings et al., 2011 for a Paleozoic basin example). Play types at the landform / stratigraphic architecture level for unconsolidated key Canadian aquifers may include, but are not limited to, bedrock interface buried valleys, sediment hosted buried valleys, glacial basin eskers, moraines, glacilacustrine deltas, alluvial fans, etc. qualified by appropriate depositional settings (Table 3). Information to characterize the play type may include data on sediment facies, physical properties (grain size, water content), geophysical signatures, geochemistry, hydrochemistry, hydrology (precipitation, discharge, water level, pump test), remote sensing (land cover, gravity) etc. This data may be integrated with a depositional setting (e.g subaqueous fan, delta) model to further refine understanding of flow pathways (recharge, discharge), aquifer heterogeneity, aquifer compartmentalization, aquifer potential (yield, storativity, sustainability), and aquifer vulnerability.

5 CASE STUDY: OAK RIDGES MORAINE

5.1 Basin stratigraphy The Oak Ridges Moraine (ORM) is a large stratified moraine north of Lake Ontario, in the Southern Ontario Lowlands hydrogeological region. The basin-fill succession reaches thicknesses of 200 m and consists from bottom to top of the Scarborough (aquifer) and Thorncliffe (aquifer/aquitard) formations, the Newmarket Till (aquitard), the Oak Ridges Moraine sediment (aquifer), and a muddy diamicton package referred to here as the Halton sediment (Fig. 3). Multiple regional unconformities dissect the stratigraphic succession, most notably, the unconformity that defines the upper surface of Newmarket Till, from which numerous tunnel channels subtend (Fig. 3; Sharpe et al. 2002). The ORM is up to 150 km long, 50 km wide and 160 m thick (Sharpe et al. 2007).

The three-dimensional shape and internal heterogeneity of the ORM sediment body have been mapped at coarse resolution using water wells(Logan et al., 2006; Russell et al., 2004). The ORM is underlain locally by two leaky confining units, Newmarket Till and Thorncliffe Formation muds (Desbarats et al., 2001). Breaches in the Newmarket Till (e.g., tunnel valleys) provide flow paths to stratigraphically lower aquifers (Fig. 3). The ORM is partially confined by the overlying muddy Halton sediment (Sharpe et al., 2002).

The ORM consists of a number of depositional elements that include esker conduit fills, grounding-line subaqueous fans, and rare ice-contact deltas (Patterson and Cheel, 1997; Barnett et al., 1998; Russell et al., 2004). One approach is to consider each of these elements as a separate groundwater play type within the ORM (Table 3). Few of the individual aquifer extents have been mapped out in detail; however there is considerable data on the subaqueous fan play, particularly from the western ORM (Russell and Arnott, 2003; Russell et al., 2004).

The western part of the ORM in the Humber River watershed ranges in width from 3 to 24 km, has a surface area of 645 km

2, is <50 m thick over 75% of the area, and

reaches a thickness of 245 m locally (Fig. 4; Russell et al., 2004). Most of the strata that comprises the thinner (<50 m) part of the ORM, is inferred to have been deposited in a subaqueous fan depositional environment (Russell et al., 2004). The extent of individual fans has not been mapped in detail, but based on existing well and outcrop data, they are envisioned to form a stacked succession. The following section details the elements of the subaqueous fan play in the western Oak Ridges Moraine (Figs. 3, 5).

Figure 3. Stratigraphic model of Oak Ridges Moraine and basin sedimentary succession (Sharpe et al. 2002)

Figure 4. A) Isopach map of western ORM in the Humber River watershed (from Russell et al., 2004). B) Stream baseflow data for the Humber River. Bold red (dark) colour indicates highest baseflow (Hinton et al., 1998)

5.1.1 ORM Subaqueous Fan Aquifer Play Continuous drill cores from the western ORM consist of 56% graded fine-sand to silt and 17% ripple-scale cross-laminated fine sand, and 27% gravel and dune cross-stratified medium to coarse sand. The deposit is interpreted to have been deposited in multiple subaqueous fan settings (Russell et al., 2004). Outcrop data suggest that proximal subaqueous fan deposits consist of dune-scale cross-stratified, horizontally bedded and massive sand and gravel (Russell and Arnott, 2003). More distal fan deposits consist predominantly of small-scale (ripple) cross-stratified fine sand and, silt, and rare clay laminae. (Figs. 5, 6).

Figure 5. Illustrative sections of a subaqueous fan model showing transition from coarse proximal sediment to fine distal sediment

The proximal part of the fan is lithologically diverse and consists of various gravel deposits that may extend headward to merge with even coarser esker conduit fills (Russell and Arnott, 2003). Hydraulic conductivity (K) values are estimated to be 10

-1 to 10

-3 m s

-1 (Fig. 6).

Downflow of gravel rich proximal fan, sediment facies can change rapidly to cross-stratified sand. The transition from gravel to 100 % sand can occur over distances of less than 10 m. Laterally flanking sediment consists of various styles of cross-stratified sand with minor gravel and K values of 10

-2 to 10

-3 m s

-1 (Fig. 6). Locally, these

strata are truncated by steep-walled scours downflow of the proximal gravel (Fig. 6). The steep-walled scours are up to 10 m wide and 3 m deep and are filled mostly with diffusely graded sand with K values of ~10

-3 m s

-1. The

steep-walled scours define an important hydraulic boundary in the downflow facies arrangement, beyond which no gravel was transported (Russell and Arnott, 2003). Downflow, medium sand forms ~10 m thick gently-inclined bedsets (10

-2 to 10

-3 m s

-1) that are overlain and

grade laterally downflow to small-scale (ripple) cross-laminated fine sand (10

-4 to 10

-6m s

-1; Fig. 6). Locally,

distal fan fine sand deposits are truncated by shallow channels with depth-width ratios <1:5. These channels are mostly filled with medium sand and extend out from the proximal fan as isolated, permeable fingers (10

-2 to

10-3

m s-1

) that provide potential preferential flow paths.

Subaqueous fan deposits are commonly capped by onlapping, rhythmically bedded silt and clay (mud) with hydraulic conductivities of 10

-7 to 10

-8 m s

-1. Although

seldom exposed in outcrop, it is suspected that mud deposited in distal fan settings commonly forms flow baffles and causes compartmentalization of the stacked fan successions. More proximally in the fans, the muds are absent due to non-deposition or erosion by higher-energy flows.

Based on an understanding of jet-efflux dynamics and common esker conduit dimensions, the proximal parts of the association likely can extend 10s to 100s of metres in a downflow direction, whereas the finer, more distal parts likely extend for 1000s of metres beyond this. An individual fan association can be 10s of metres thick, but they are typically <30 m thick. Transverse to flow, the width of the association is highly variable depending upon the scale of discharge, conduit diameter, and periodicity of discharge. In the proximal zone, widths are probably 10s of metres expanding to 100s of metres downflow and eventually 1000s of metres distally. In general, a plane-wall jet and a plane-wall jet with jump have a broad semi-circular geometry (Russell and Arnott, 2003); however at higher supercritical velocities the fan may have a more elongate parabolic form similar in shape to the plane-jet (Hoyal et al., 2003). Identification of the appropriate jet model is important as the distribution, and flow parallel length scales are directly controlled by the depositional flow processes. This requires detailed sedimentological observations from either outcrops in the unsaturated zone or sedimentological logging of continuous core.

5.1.2 Confining Units

The Newmarket Till aquitard is estimated to underlie 75% of the ORM (Sharpe et al., 2002). The hydraulic conductivity of the till is likely between 10

-9 and 10

-10 m s

-1

(Gerber and Howard, 2002). Tunnel valleys eroded through the Newmarket Till and into underlying permeable sediment (e.g., Scarborough Formation sand units) represent important hydraulic windows. In places, however, tunnel channels have incised through the Newmarket Till into underlying mud of the Thorncliffe Formation (Sharpe et al., 2003). Additional barriers to downward flow may occur within erosional windows due to mud units deposited during basinal stages of ORM construction (Russell et al., 2004).

The Halton sediment forms a local confining unit along the flanks of the moraine. It is predominantly a massive to laminated mud unit with low stone count and local interbeds of sand and gravel. It is locally diamictic. Along the upper flanks of the ORM the unit is a 1-5 m thick and southward can increase in thickness up to 30 m. The variable thickness, in part reflects the variability in underlying sedimentary deposit geometry (subaqueous fan lobes) and the nature of Halton sediment to fill depressions and thin over highs (Russell et al., 2004). Geotechnical studies indicate a range in K of 10

-3 to 10

-9

m s-1

(Fenco MacLaren Inc., 1994; Golder and Associates, 1994).

Figure 6. Conceptual subqueous fan model with insets showing approximate hydraulic conductivity values for sedimentary facies (Russell et al., 2007). Hydraulic conductivity (K) values in m s

-1 (from Freeze and Cherry,

1979)

5.1.3 Hydrology Annual precipitation in the ORM area is approximately 860 mm, E/T is 530 mm and infiltration is 300 plus mm with local estimates reaching 400 mm (Gerber and Howard, 2002). Discharge from springs along the flanks of the ORM above 275 m, from which headwater streams develop, is thought to account for almost half (43%) of the groundwater discharged from the ORM recharge (Gerber and Howard, 2002). In the western ORM, Hinton et al. (1998) record local discharge values up to 176 l s

-1 from

stream baseflow surveys. This discharge is spatially variable, which reflects the control of the heterogeneous facies architecture within the ORM and the confining effect of Halton sediment. The effect of the confining Halton sediment on groundwater discharge to streams is further highlighted by two stream baseflow measurements for similar sized areas. Where streams are floored by the Halton, baseflow is below 36 ls

-1; however, where ORM

sediment outcrops baseflow is 790 ls-1

(Hinton et al., 1998). To sustain baseflow of this magnitude requires K values of 10

-4 m s

-, K values which equates with medium

sand of the proximal to mid fan setting. Groundwater that does not discharge from headwater

stream springs sourced in the ORM likely follows one of several flow paths: (i) it can move through the ORM aquifer and enter streams south of the headwater area; (ii) it can move within the ORM aquifer and flow into lower

aquifers in the Thorncliffe and Scarborough formations, then discharge as springs along deep river valleys where the river has eroded into or beneath the Newmarket Till; and (iii) it can migrate through the complete sediment column to discharge at Lake Ontario (Gerber and Howard, 2002). These discharge pathways are controlled primarily by the distribution of permeable subaqueous fan elements within the western ORM, secondly by confining aquitards (Halton), and thirdly by regional hydrostratigraphy (e.g. underlying Newmarket Till vs tunnel valleys). 6 SUMMARY The petroleum play concept is a well established scheme used to assess patterns in the petroleum occurrence within sedimentary basins that can help improve exploration success and aid the prediction of future exploration targets (Doust, 2010). The play is commonly developed within the context of basin analysis studies, which provides the predictive framework—an understanding of the basin history—for the play schema. The principal components of the play definition – source (charge), reservoir, seal, and trap – are adaptable to groundwater aquifer classifications with minimal modification. One potential groundwater schema is aquifer (reservoir), confining unit (trap), and hydrology.

The play concept can provide a national scheme for aquifer classification, one in which large amounts of hydrologic, geological, and hydrogeological data contained in local case studies are synthesized into an easily understood conceptual framework. Using a relatively standardized approach the play can provide a means of assessing risk when developing different types of aquifers in the different hydrogeological regions of Canada. In this context it affords the same opportunity as in the hydrocarbon context of providing an analogue for aquifers that may have received less study but have similar characteristics. Additionally, the play concept provides an ability to better compare and even quantify groundwater extraction from different areas based on similar aquifer and hydraulic conditions. ACKNOWLEDGEMENTS An internal GSC review by Marc Hinton is much appreciated. This is a contribution of the Groundwater Geoscience Program and the National Aquifer Evaluation and Accounting Project. ESS Contribution 20100444. REFERENCES Barnett, P.J, Sharpe, D.R., Russell, H.A.J ., Brennand,

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