Red River Carbonates (Saskatchewan): Major Facies, Lithological, and Spatial Controls on Rock Magnetism – Preliminary Observations

Erika Szabo 1 and Maria T. Cioppa 2

Szabo, E. and Cioppa, M.T. (2003): Red River carbonates (Saskatchewan): Major facies, lithological, and spatial controls on rock magnetism – preliminary observations; in Summary of Investigations 2003, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.1, CD-ROM, Paper A-2, 9p.

Abstract Preliminary results from ten wells in the Saskatchewan portion of the reveal significant lithological, facies, and spatial controls on the natural remanent magnetization (NRM) intensity in Red River carbonates. High NRM intensity values are recorded within the sequences, intermediate values are seen in burrowed/fossiliferous dolostone, and the lowest values of NRM intensity are measured in laminated/bedded dolostones associated with anhydrite. The NRM intensity tends to increase towards the centre of the Williston Basin suggesting that the most probable variables affecting NRM intensities are: 1) depth of sampling and 2) proximity to the North American Central Plains Conductivity Anomaly. With a few exceptions, the magnetite grain-size distribution determined from partial anhysteretic remanent magnetization (pARM) spectra seems to be unaffected by facies and other lithological variations, or by spatial position. Well 0210, in the northwestern part of the Williston Basin, however, has magnetite grain-size values that are predominantly in the pseudosingle domain range whereas samples from the other wells display a mixed pseudosingle and single domain grain-size distribution. These findings suggest that fluid flow from the Alberta Basin may have influenced this portion of the Williston Basin.

Keywords: Upper , Williston Basin, Red River, Yeoman Formation, Herald Formation, Saskatchewan, rock magnetism, carbonates, facies control, lithological control, spatial control.

1. Introduction Paleomagnetic studies of several formations in the Alberta Basin indicate that paleomagnetic components of different ages can be correlated with lithological facies, and that detailed paleomagnetic and rock magnetic analyses can determine the order and timing of diagenetic events (Cioppa et al., 2001). Information on paleomagnetism in the Williston Basin is limited (e.g. Enkin et al., 2001; Cioppa, 2003); however, reliable paleomagnetic data obtained from preliminary studies in the basin (Cioppa, 2002, unpubl. data) suggest that further research is warranted. This paper presents preliminary results from a detailed paleomagnetic and rock magnetic investigation of Red River carbonates in Saskatchewan. We examine the potential for facies or spatial controls of paleomagnetic patterns in these rocks which are characterized by several different lithological facies and dolomitization events.

2. Geology The Williston Basin is ~800 km in diameter. It covers much of southern Saskatchewan and Manitoba in and extends southward through Montana, North Dakota, and South Dakota in the United States (Figure 1). The Precambrian basement, which is reached at a maximum depth of ~5 km in North Dakota, features several structures that influence the generation and migration of hydrocarbons in the Williston Basin (Osadetz et al., 1992). The North American Central Plains Conductivity Anomaly (NACPCA, Figure 1), a 2000 km long and 80 km wide structure at a depth of 10 to 20 km, is characterized by basal heat flow that is ~20% higher than elsewhere in the basin (Jones and Craven, 1990; Jones and Savage, 1986).

1 Earth Sciences, University of Western Ontario, London, ON N6A 5B7; E-mail: [email protected]. 2 Department of Earth Sciences, University of Windsor, Windsor, ON N9B 3P4.

Saskatchewan Geological Survey 1 Summary of Investigations 2003, Volume 1 Figure 1 - Distribution of Ordovician and strata within the Williston Basin with locations of sampled wells (NACPCA- North American Central Plains Conductivity Anomaly) (after Norford et al., 1994 and Morel-a-l’Huissier et al., 1990). Upper Ordovician Red River carbonates comprise the Yeoman and Herald formations (Norford et al., 1994). Within conformable limits, these formations are underlain by clastics of the Winnipeg Formation and overlain by carbonates of the . The Yeoman Formation is the thickest formation of the Red River carbonates. Various fossils and traces of different burrows are found in the Yeoman. The larger burrows are Thalassinoides-like structures that are thought to have been re-burrowed, as indicated by the smaller included burrows (i.e. Planolites, Chondrites) (Kendall 1976, 1977; Haidl et al., 1997; Canter, 1998; Pak et al., 2001). Several types of dolomitization are present in the Yeoman Formation. The burrows are commonly dolomitized, and may be associated with either a limestone or dolostone matrix. Also, minor saddle dolomite cement has been precipitated in vugs, fractures, and geopetal structures (Carroll, 1979; Qing et al., 2001). The Herald Formation is divided into the Lake Alma and Coronach members, and the overlying Redvers unit (Kendall, 1976). Laminated to bedded dolostones and calcareous dolostones, sometimes interbedded with burrowed or fossiliferous dolostones, lie beneath nodular, bedded, and laminated anhydrite with anhydritic dolostone

Saskatchewan Geological Survey 2 Summary of Investigations 2003, Volume 1 interbeds in the Lake Alma Member (Nowlan and Haidl, 2001). From bottom to top, the Coronach Member is composed of argillaceous dolostones, fossiliferous and burrowed and dolostones, laminated dolostones that are locally limestones, and an upper anhydrite (Kendall, 1976; Nowlan and Haidl, 2001). The base of the Redvers unit is argillaceous dolostone, which is overlain by an upper laminated dolostone or limestone (Nowlan and Haidl, 2001). In the Lake Alma Member of the Herald Formation, dolomitization is recognized in the form of non- porous cryptocrystalline and porous crystalline dolostone (Qing et al., 2001).

3. Methodology Systematic sampling, utilizing the paleomagnetic sampling procedure described by Lewchuk et al. (1998) and Cioppa et al. (2000), was carried out on core from ten wells in southern Saskatchewan (Table 1). Nine wells are located along two cross-section lines: one east-west (A-A’) and the second (B-B’) north-south (Figure 1). The tenth well (0210) was sampled in the west-central part of the province, removed from the other sampling locations (Figure 1). Detailed macroscopic lithological observations were made of each core. A total of 152 plugs, each 2.5 cm in diameter, were drilled from the well cores. From the core plugs, 434 specimens were cut. As the first phase of this project, we measured the natural remanent magnetization (NRM) of all specimens using a vertical- configuration 2G cryogenic magnetometer with a lower sensitivity limit of ~2x10-6 A/m. Thirty pilot specimens (2 to 4 specimens per well) were subjected to alternating field (AF) demagnetization before any rock magnetic experiments were performed. Results of these measurements will be presented in the near future. We also measured stepwise partial anhysteretic remanent magnetization (pARM) on the pilot samples by treating the specimens in steps of 10 mT up to 100 mT using the procedure introduced by Everitt (1961) and a Sapphire Instruments SI-4 Alternating Field (AF) demagnetizer. The AF and pARM demagnetization procedures differ in that the pARM procedure has a small biased direct circuit (DC) field applied over a section of the AF demagnetizing field (i.e. DC between 10 and 20 mT over AF demagnetization from 100 mT). The procedure is performed because coercivity is a function of grain size and by doing a step sequence of DC biases (0 to 10 mT, 10 to 20 mT, ... , 90 to 100 mT) an estimate is obtained of the relative amounts of magnetic grain sizes. The percentage of the different ranges of magnetic grain sizes is approximated by the measured pARM values and their corresponding grain size ranges as defined by Jackson et al. (1988). Thus, the magnetization intensity values for the untreated specimens are considered to represent the amount of multidomain (MD) size grains, the sum of pARM values obtained over the intervals 0 to 10 mT to 30 to 40 mT represent the amount of pseudosingle domain (PSD) particles, and the sum of the pARM values for the remaining intervals (40 to 50 mT to 90 to 100 mT) represent the amount of single domain (SD) magnetic particles. All experiments were done in a magnetically shielded room in the Paleomagnetics Laboratory at the University of Windsor (Canada).

4. Results and Preliminary Observations a) Natural Remanent Magnetization (NRM) The NRM intensities vary from well to well across the study area and also within individual wells with values ranging from 10-6 A/m to 10-2 A/m. NRM intensities of specimens cut from the outside of most plugs were systematically higher than those cut from the interior of the plug (e.g. for ~12% of the plugs, the outside specimens exceeded twice the NRM values from specimens from the middle of the plug). It is considered that the outer surface of a core, which would have been in direct contact with the core barrel, is much more likely to acquire a drilling- induced viscous magnetization than the interior of the core. Therefore, the analysis of the NRM intensity distribution was carried out only on specimens cut from the middle of the core plugs.

Table 1 - List of sampled cores. Well Well Name Location Logged Interval (m) Formation Sampled 0201 Pan American White Bear Cres. 5-15-10-2W2 2148.1 to 2482.6 Herald and Yeoman 0202 Ceepee Annette 10-25-36-5W2 3083.0 to 3103.0 and Yeoman 3154.0 to 3164.0 0203 Esso Bromhead 6-28-3-12W2 2875.6 to 2893.6 Yeoman 0204 PCP Scurry et al Lake Alma 5-29-01-17W2 3071.0 to 3089.5 Herald and Yeoman 0205 Trilink Hazelwood 4-14-11-5W2 2225.0 to 2243.0 Yeoman 0206 Mark Saskoil Minton 1-10-3-21W2 2856.0 to 2874.0 Yeoman 0207 T.W. Wapella Cr. 12-34-14-1W2 1677.5 to 1692.8 Herald and Yeoman 0208 Imp. Long Range 4-31-1-27W2 2669.7 to 2683.5 Herald 0209 B.A. Baciu 15-36-6-4W3 2333.3 to 2339.4 Yeoman 0210 Ceepee Reward 4-28-38-24-W3 1517.1 to 1526.2 Herald and Yeoman

Saskatchewan Geological Survey 3 Summary of Investigations 2003, Volume 1 The NRM intensity of specimens from the plug interiors was plotted as a function of burial depth and macroscopic lithology. There was little to no correlation between the NRM intensity and the burial depth or macroscopic lithology in wells 0202, 0203, 0206, and 0209. However, significant NRM intensity variations with depth and lithology were seen in the other wells (Figure 2 and Figure 3). A significant observation is that the lowest NRM (~10-6 to 10-5 A/m) values are observed in the laminated/bedded dolostone and anhydrite (0201, 0204, and 0208) or laminated dolostones with anhydrite-filled fractures (0207) from the Herald Formation. Similarly, the Yeoman Formation samples with anhydrite-filled vugs have low NRM values (0205). Limestones seem to have higher NRM values than dolostones when they occur in the same well (0204, 0207, and 0208); this is the reverse of observations in Alberta (Cioppa et al., 2001). These differences are better defined in some wells than in others. Two examples, one from the Herald and one from the Yeoman, are discussed below (Figure 2 and Figure 3).

Figure 2 - Correlation between lithological variations and NRM distribution in well 0208 (Herald Formation).

Saskatchewan Geological Survey 4 Summary of Investigations 2003, Volume 1 Figure 3 - Correlation between lithological variations and NRM distribution in well 0205 (Yeoman Formation).

Saskatchewan Geological Survey 5 Summary of Investigations 2003, Volume 1 NRM Distribution in Well 0208 (Imperial Long Range 4-31-1-27W2) Portions of both the Coronach and Lake Alma members of the Herald Formation are cored in well 0208 (Figure 2). Figure 2 illustrates the relationship between major macroscopic lithological characteristics and the distribution of NRM intensity values. The uppermost samples (2670 to 2673 m, interval I in Figure 2), composed of wavy laminated/bedded dolostone intermixed with anhydrite, record the lowest intensity values. A slight increase in the NRM intensity occurs between ~2673 to 2679 m (II and III) where anhydrite is minor. There is a significant jump in the NRM intensity values as the lithology changes from the laminated/bedded dolostone to unlaminated, burrowed and fossiliferous dolostones (2673 to 2675 m, interval II). Where wispy are more pronounced and show a wavy impression (2675 to 2676.5 m, interval III), the NRM intensity decreases. NRM values increase as the lithology changes (at ~2678.5 m, interval IV) to fossiliferous and burrowed limestone, and then decrease again where bedded and laminated dolomites are observed (~2678.8 to 2683 m, interval V).

NRM Distribution in Well 0205 (Trilink Hazelwood 4-14-11-5W2) An example from the Yeoman Formation is depicted in Figure 3. There is a trend towards increasing NRM intensity with depth. The burrowed dolostone in the lower part of the section (2236 to 2242 m interval) has higher intensity values than the unburrowed dolostone in the upper section (2225 to 2231 m). We note that there are also anhydrite- filled vugs in this upper section. The lowermost sample in this core (Figure 3) is from a unit with intermixed clasts (probably dolostone). The rusty colour of this unit may indicate the presence of hematite which may account for the slightly increased intensity value seen at this depth. b) Partial Anhysteretic Magnetization (pARM) Results Data from pARM experiments plot as well defined curves with broad peaks between 20 to 40 mT (see 021002 and 040101 in Figure 4 for examples), indicating that magnetization in magnetite is carried by PSD and SD size grains (Jackson et al., 1988, Figure 4). Three specimens produce curves with more than one peak: 1) a sample from a unit of laminated/bedded dolostone interbedded with anhydrite (well 0208), 2) a sample with anhydrite-filled vugs from well 0205, and 3) a sample with anhydrite-filled vertical fractures from well 0207 (see 070101 in Figure 4). In general, however, pARM values reveal minimal variations as a function of depth or lithology, or between different wells.

In well 0210 , curves from two treated samples from the top and the bottom of the Herald-Yeoman sequence both define a distinct peak between 10 and 20mT, with a more dramatic decrease in pARM acquisition thereafter (see curve for sample100101, Figure 4). This indicates the presence of magnetite, predominantly in the PSD size range. There are two possible causes for this distinctive ARM behaviour: 1) a reddish tint within the wispy shales and in the burrow and vug infills in the dolostone may indicate the presence of other magnetic minerals; and 2) the location being considerably closer to the eastern margin of the Alberta Basin than the other samples in this study.

c) Comparison of Results in Cross-section Wells The average NRM intensity values for each well along the two cross-sections are illustrated in Figure 5 and indicate that NRM intensity increases towards Figure 4 - pARM patterns in Red River carbonates. 021002 and 040101 illustrate the centre of the basin. The representative pARM behaviour in the Red River carbonates. Sample 070101 is intensities, however, are composed of laminated dolostone with vertical fractures filled with anhydrite. 100101 is a sample from well 0210 located in the northwestern part of the Williston Basin (the significantly greater on the east- numbers on the AF axis represent an interval, i.e. 10 mT = 0 to 10 mT - the AF west cross-section than on the interval over which a DC biased field was applied; J - magnetization intensity; Jmax - south-north section. A potential maximum magnetization intensity; and AF - alternating field).

Saskatchewan Geological Survey 6 Summary of Investigations 2003, Volume 1 explanation for the marked difference in NRM is that Red River carbonates of the east-west cross-section were sampled at greater depths than were those of the north-south cross-section. We note that wells 0204 and 0203 show anomalously high intensity values, and also show higher percentages of limestone than the other wells. Furthermore, these wells are also the closest to the NACPCA (Figure 1). However, NACPCA influence on the pARM spectra seems to be minimal as there is a negligible increase in the percentage of SD magnetite at the expense of MD magnetite on the east-west profile (Figure 5a).

5. Preliminary Conclusions Preliminary observations from this study suggest there is a lithological control over the NRM intensity in Red River carbonates. Except for anhydrite and laminae, however, the magnetite grain-size distribution indicated by the pARM spectra seems to be unaffected by the lithological variations. Also, on a vertical profile, NRM intensity seems to be higher in deeper wells whereas the magnetite grain-size distribution remains unchanged. Other factors such as proximity to the NACPCA could also potentially influence the data in a similar way. Moreover, preliminary interpretation of data from the western margin of the Williston Basin (well 0210) suggests that fluid flow from the Alberta Basin, where paleomagnetic studies have recorded different diagenetic and fluid-flow events, may also control magnetic properties of strata in this area.

6. To Be Continued … Work will continue on these specimens, focusing on the analysis of paleomagnetic directions and performing detailed rock magnetic investigations such as pARM and saturation isothermal remanent magnetization. Geochemical and microscopic petrographic analyses will also be completed and correlated to magnetic data. The area of investigation will be expanded to include Manitoba and the north-central United States, in an attempt to better define magnetic variations in the Williston Basin and to compare oriented outcrop samples with the initially unoriented samples from cored wells. The main goal is to establish whether there is a substantial facies or spatial control on the paleomagnetic and magnetic signatures. Of Figure 5 - NRM arithmetic average values and arithmetic average of magnetite grain- particular interest are the origin size distribution along east-west (a) and north-south (b) profiles. Note the higher NRM and timing of dolomitization values exhibited eastward and southward (southeastern Saskatchewan, central events. The resultant data will Williston Basin), and the relative constant values of the averaged grain-sizes along provide us with a better these profiles (NRM - natural remanent magnetization; MD - multidomain grain size; understanding of the geological PSD - pseudosingle domain grain size; and SD - single domain grain size). The history of Red River carbonates. standard deviation of the NRM values is represented by bars.

Saskatchewan Geological Survey 7 Summary of Investigations 2003, Volume 1 7. Acknowledgments We wish to thank the personnel from the Saskatchewan Industry and Resources Subsurface Laboratory for their helpful assistance in accessing the cores. This research was funded by an NSERC grant to Maria Cioppa.

8. References Canter, K.L. (1998): Facies, cyclostratigraphic, and secondary diagenetic controls on reservoir Midale Field, southern Saskatchewan; Eighth International Williston Basin Symposium, Core Workshop Volume, Sask. Geol. Soc./N. Dak. Geol. Soc./Montana Geol. Soc., Regina, October 1998, p41-65. Carroll, W.K. (1979): Depositional environments and paragenetic porosity controls, Upper , North Dakota; North Dakota Geol. Surv., Report of Investigation, no66, 51p. Cioppa, M.T. (2003): Magnetic evidence for the nature and timing of fluid migration in the , Williston Basin, Canada: A preliminary study; J. Geochem. Explor., v78-79, p349-354. Cioppa, M.T., Symons, D.T.A., Gillen, K.P., and Lewchuk, M.T (2000): Paleomagnetism provides alternative; Oil & Gas J., May 22, p46-53. Cioppa, M.T., Lonnee, J.S., Symons, D.T.A., Al-Aasm, I.S., and Gillen, K.P. (2001): Facies and lithological controls on paleomagnetism: An example from the Rainbow South field, Alberta, Canada; Bull. Can. Petrol. Geol., v49, no3, p393-407.

Enkin, R.J., Baker, J., and Osadetz, K.G. (2001): Paleomagnetic indications for a Late Paleozoic Age for part of the Watrous Formation, Williston Basin, southern Saskatchewan; in Summary of Investigations 2001, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2001-4.1, p72-76.

Everitt, C.F.W. (1961): Thermoremanent magnetization I: Experiments on single-domain grains; Philos. Mag., no6, p713-726.

Haidl, F.M., Longman, M.W., Pratt, B.R., and Bernstein, L.M. (1997): Variations in lithofacies in Upper Ordovician Herald and Yeoman formations (Red River), North Dakota and southeastern Saskatchewan; in Wood, J. and Martindale, B. (comps.), Can. Soc. Petrol. Geol./Soc. Econ. Paleont. Mineral., Core Conference, Calgary, p5-39.

Jackson, M., Gruber, W., Marvin, J., and Subir, K.B. (1988): Partial Anhysteretic Remanence and its anisotropy: Applications and grainsize-dependence; Geophys. Resear. Lett., v15, no5, p440-443.

Jones, A.G. and Craven, J.A. (1990): The North American Central Plains conductivity anomaly and its correlation with gravity, magnetic, seismic, and heat flow data in Saskatchewan, Canada; Phys. Earth Planet. Inter., v60, no1-3, p169-194.

Jones, A.G. and Savage, P.J. (1986): North American Central Plains conductivity anomaly goes east; Geophys. Resear. Lett., v13, p685-688. Kendall, A.C. (1976): The Ordovician Carbonate Succession (Bighorn Group) of Southeastern Saskatchewan; Dep. Miner. Resour., Rep. 180, 185p. ______(1977): Origin of dolomite mottling in Ordovician limestones from Saskatchewan and Manitoba; Bull. Can. Petrol. Geol., v25, p480-504. Lewchuk, M.T., Al-Aasm, I.S., Symons, D.T.A., and Gillen, K.P. (1998): Dolomitization of Mississippian carbonates in the Shell Waterton gas field, southwestern Alberta: Insights from paleomagnetism, petrology and geochemistry; Bull. Can. Petrol. Geol., v46, no3, p387-410. Morel-a-l’Huissier, P., Green, A.G., Jones, A.G., Latham, T., Majorowicz, J.A., Drury, M.J., and Thomas, M.D. (1990): The crust beneath the Williston Basin from geophysical data; in Pinet, B. and Bois, C. (eds.), The Potential of Deep Seismic Reflection for Hydrocarbon Exploration, Edition Technip., Paris, p141-160. Norford, B.S., Haidl, F.M., Bezys, R.K., Cecile, M.P., McCabe, H.R., and Paterson, D.F. (1994): Middle Ordovician to Lower Strata of the Western Canada Sedimentary Basin; in Mossop, G.D. and Shetsen,

Saskatchewan Geological Survey 8 Summary of Investigations 2003, Volume 1 I. (eds.), Geological Atlas of the Western Canada Sedimentary Basin, Calgary, Can. Soc. Petrol. Geol./Alta. Resear. Counc., Calgary, p109-127. Nowlan, G.S. and Haidl, F.M. (2001): Biostratigraphy and paleoecology of Late Ordovician conodonts from a composite section in the subsurface of Saskatchewan; in Summary of Investigations, 2001, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2001-4.1, p14-31. Osadetz, K.G., Brooks, P.W., and Snowdon, L.R. (1992): Oil families and their sources in Canadian Williston Basin (southeastern Saskatchewan and southwestern Manitoba); Bull. Can. Petrol. Geol., v40, p254-273. Pak, R., Pemberton, S.G., and Gingras, M.K. (2001): Reservoir characterization of burrow-mottled carbonates: The Yeoman Formation of southern Saskatchewan – preliminary report; in Summary of Investigations 2001, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep., 2001-4.1, p10-13. Qing, H., Kent, D., and Bend, S. (2001): Preliminary results of isotopic geochemistry of Ordovician Red River carbonates, subsurface of southeastern Saskatchewan: Implications for process of dolomitization and diagenetic modification of dolomites; in Summary of Investigations 2001, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep., 2001-4.1, p3-9.

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