Preliminary Report on Conodont and Sm-Nd Isotope Data from Upper Ordovician Red River Strata (Herald and Yeoman Formations) in the Williston Basin, Berkley et al Midale 12-2-7-11W2, Southeastern Saskatchewan
F.M. Haidl, C. Holmden 1, G.S. Nowlan 2, and K.C. Fanton 1
Haidl, F.M., Holmden, C., Nowlan, G.S., and Fanton, K.C. (2003): Preliminary report on conodont and Sm-Nd isotope data from Upper Ordovician Red River strata (Herald and Yeoman formations) in the Williston Basin, Berkley et al Midale 12-2-7-11W2, southeastern Saskatchewan; in Summary of Investigations 2003, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.1, CD-ROM, Paper A-1, 13p.
Abstract Recent research indicates that conodont and Nd isotope data are useful in interpreting the depositional history of Upper Ordovician epeiric sea carbonates in Saskatchewan and Iowa. Detailed analysis of an additional core (Berkley et al Midale 12-2-7-11W2) was undertaken to further document the usefulness of these tools in the interpretation of Red River strata in Saskatchewan. This paper reports the results of 74 Sm-Nd isotope analyses and 62 conodont analyses obtained from this core.
Four conodont biofacies, based on conodont genera believed to be benthic or nektobenthic, are recognized for the Late Ordovician of Saskatchewan. These are, from shallowest to deepest: 1) Rhipidognathus biofacies; 2) Aphelognathus-Oulodus biofacies; 3) Plectodina biofacies; and 4) Phragmodus biofacies. In the Midale well, Aphelognathus-Oulodus biofacies and Plectodina biofacies dominate the Yeoman Formation and Coronach Member of the Herald Formation. Rhipidognathus specimens were recovered from only the top two samples in the Redvers Unit of the Herald Formation. Panderodus bergstroemi, believed to be a pelagic organism, is the only conodont species recovered from the Lake Alma Member.
Values for ε Nd in the Midale well range from -10.8 to -7.1 indicating that the Nd isotope balance in seawater was primarily controlled by the relative contributions of Nd weathered from the highlands of the Taconic Orogen (εNd = -6 to -9) and possibly the extension of the Appalachian-Caledonian Orogen in the Arctic (εNd = -6 to -9), and that Precambrian rocks of the Transcontinental Arch and the Canadian Shield (εNd = -22 to -15) were not exposed on the margins of the Williston Basin during deposition of the Red River carbonates and anhydrites sampled in this well. The two samples with values of ε Nd less than -9.5 (in the lower Herald Formation) may be indicative of a contribution of Nd from weathered older Ordovician strata which, in other Saskatchewan cores, have more negative ε Nd values. Previous work has shown that, in circumstances in which increasing distance from paleo-shoreline is associated with increasing water depth in the basin, Sm/Nd chemostratigraphy can serve as an indicator of seawater paleo- depth. Sm/Nd ratios in the Midale well range from 0.145 to 0.234. Preliminary interpretation of Midale data suggests a correspondence between conodont paleoecology, Sm/Nd ratios, and lithological data: stratigraphic increases in Sm/Nd ratios reflect increasing water depth, whereas stratigraphic decreases in Sm/Nd ratios indicate decreasing water depth. Examples of these correlations include: 1) Two major shifts associated with kukersitic beds in the Yeoman Formation are interpreted to reflect deepening- shallowing events. Sm/Nd ratios increase below the kukersitic beds and then decrease within this facies. The Plectodina conodont biofacies below the kukersitic beds is replaced by a mixed Aphelognathus-Oulodus and Plectodina fauna within and above these organic-rich beds. 2) Isotope and conodont data adjacent to the contact of lower burrow-mottled Yeoman rocks with the overlying “transitional unit” suggest that a major relative sea-level change may be reflected by this lithologic change. 3) In the Lake Alma Member, shifts in the Sm/Nd ratios, the complex distribution of dolostone and anhydrite, and the paucity of conodonts suggest several changes in paleo-water depth in a saline to hypersaline environment. Keywords: Upper Ordovician, Saskatchewan, Red River, Herald, Yeoman, carbonates, anhydrite, conodonts, Sm and Nd isotopes.
1 Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2. 2 Geological Survey of Canada, 3303 - 33rd Street NW, Calgary, AB T2L 2A7.
Saskatchewan Geological Survey 1 Summary of Investigations 2003, Volume 1 1. Introduction The relationships between sedimentology, conodont biofacies, εNd values, and Sm/Nd ratios are the subject of earlier studies conducted by the authors in Iowa and Saskatchewan (Nowlan and Haidl, 2001; Fanton et al., 2002). In order to further document the usefulness of these tools in the interpretation of depositional environments of oil-producing Red River strata in southeastern Saskatchewan, detailed sampling of a core from the Berkley et al Midale 12-2-7-11W2 well (Figure 1) was undertaken. This paper reports the results of 74 Sm-Nd isotope analyses and 62 conodont analyses obtained from this core which encompasses the upper 38.7 m of the Yeoman Formation and all but the upper 3.5 m of the Herald Formation.
2. Lithostratigraphy of Red River Strata in Berkley et al Midale 12-2-7-11W2
Middle to Upper Ordovician strata in southeastern Figure 1 - Map of southeastern Saskatchewan showing Saskatchewan comprise a basal clastic unit (Winnipeg locations of the Berkley et al Midale 12-2-7-11W2 well Formation) and an overlying sequence characterized by (star) and of four wells (solid circles) reported on in repetition of carbonate and evaporite lithologies Nowlan and Haidl (2001) and Fanton et al. (2002). (Yeoman, Herald, Stony Mountain, and Stonewall formations, Figure 2).
The stratigraphic nomenclature established for Red River strata in the study area (Figures 2 and 3) reflects the interpretation that the repetition of carbonate and evaporite strata represents three brining-upward cycles. The Yeoman Formation and the lower Herald (Lake Alma Member) form the oldest cycle, the middle part of the Herald Formation is the middle cycle (Coronach Member), and the Redvers Unit encompasses the youngest cycle (Kendall, 1976). The evaporite unit at the top of the youngest cycle is present only in North Dakota (Longman and Haidl, 1996). New core and geophysical log data from the more than 300 wells drilled into the Red River since 1976 suggest a more complex depositional history than the current stratigraphic breakdown implies (Pratt et al.,1996; Haidl et al., 1997; Canter, 1998; Kent and Kissling, 1998; Kreis and Kent, 2000). Conodont and isotope data from previous studies by the authors and from this study also support the interpretation of a complex depositional history (Nowlan and Haidl, 2001; Fanton et al., 2002). a) Yeoman Formation
Burrow-mottled Unit
The Yeoman is 90.9 m thick in the Berkley et al Midale 12-2-7-11W2 well. Only the uppermost 38.7 m of this formation are cored of which the lower 35.4 m are composed primarily of fossiliferous lime mudstones and wackestones characterized by abundant trace fossils and varying degrees of dolomitization (Figure 3). The mottled texture that characterizes much of the Yeoman in southeastern Saskatchewan and in stratigraphically equivalent rocks in adjacent areas dominates this core from 2570 m to the base (2605.4 m) (Figure 4). This mottling is primarily the result of Thalassinoides burrows that commonly contain secondary Planolites, Paleophycus, and Chondrites burrows (Pak and Pemberton, this volume). Macrofossils identified include corals, brachiopods, bryozoans, echinoderms, stromatoporoids, and gastropods. Kukersitic laminae/beds are preserved in several limestone intervals, the thickest of which occurs at 2577.5 to 2578.8 m (Figures 3 and 5). The micro-alga Gloeocapsomorpha prisca, of probable cyanobacterial origin (Stasiuk and Osadetz, 1991; Stasiuk et al., 1993), is the primary component of these organic-rich rocks.
“Transitional” Unit The uppermost 3.32 m of the Yeoman in this well are composed of interbedded dolowackestone, dolopackstone, and dolograinstone with abundant skeletal material, coated grains, and peloids (Figures 3 and 6). Lithologic variations at this stratigraphic interval in other wells in southeastern Saskatchewan include stromatoporoid dolorudstone, microbial doloboundstone, oolitic dolograinstone, and dolomudstone/wackestone (Pratt et al., 1996; Haidl et al., 1997; Kreis and Kent, 2000) The contact of this “transitional unit” with the overlying Lake Alma Member of the Herald Formation is difficult to pick in core and on geophysical logs. In this well, the contact is
Saskatchewan Geological Survey 2 Summary of Investigations 2003, Volume 1 placed at the base of a peloidal unit that is interpreted to correlate with a bed characterized by high gamma reading on geophysical logs. Other workers place the “transitional unit” in the Lake Alma (e.g., Kreis and Kent, 2000).
b) Herald Formation
Lake Alma Member A thin (0.2 m) peloidal bed at the base of the Lake Alma is overlain by a unit of laminated to bedded dolomudstones. The overlying Lake Alma Anhydrite comprises a lower unit dominated by nodular anhydrite (Figure 7), a middle unit of dolomudstone with anhydrite laminae, and an upper unit of laminated to bedded anhydrite with abundant dolostone beds and laminae (Figure 3). The contact with the overlying Coronach Member is placed above a thin (1.0 cm) bed of intraclasts.
Coronach Member
Figure 2 - Stratigraphic correlation chart of Lower Paleozoic strata in southeastern The Coronach comprises, in Saskatchewan. Numeric values for isotopic ages from Okulitch (2003). ascending order: 1) laminated argillaceous dolomudstone (0.2 m thick); 2) fossiliferous burrow- mottled limemudstone/wackestone; 3) mottled dolomudstone/dolomitic lime mudstone; 4) lime mudstone/ wackestone with abundant skeletal debris including laminar stomatoporoids; 5) laminated lime mudstone; laminated dolomudstone with stromatolitic intervals (Figure 8); and 6) an anhydrite bed (Figure 3). The contact with the overlying Redvers Unit is placed at the top of the Coronach Anhydrite.
Redvers Unit
The basal 0.5 m of the Redvers is composed of laminated dolomudstone. This is overlain by a brecciated unit of uncertain origin (Figures 3 and 9). Kreis and Kent (2002) suggest that this may be the product of subaerial exposure. Alternatively, brecciation may be the result of seismic activity (Pratt, pers. comm., 2003). The upper 0.5 m of the cored interval is laminated lime mudstone. The topmost 3.5 m of the Redvers are not cored in this well.
3. Conodont Biofacies Fifty-three of the sixty-two samples collected from the Midale 12-2-7-11W2 well produced over 1900 conodont specimens. Table 1 shows the numerical distribution of genera in this well. The relative abundance of significant genera is summarized in Figure 3. All samples are reported, but clearly those with only a few specimens should not be given much validity or used to argue strongly for biofacies interpretations. The fact that the distribution of Ordovician conodont genera and species are affected by facies distribution was first recognized by Seddon and Sweet (1971). A study specific to Upper Ordovician biofacies was completed by Sweet and Bergström (1984) in which they recognized six conodont biofacies for the Edenian-Maysvillian of North America. Their biofacies are modified herein to reflect local faunas and other biofacies work on the Late Ordovician by Nowlan and Barnes (1981). The biofacies recognized for the Late Ordovician of Saskatchewan (Nowlan and
Saskatchewan Geological Survey 3 Summary of Investigations 2003, Volume 1 Figure 3 - Lithology of Herald and Yeoman formations in cored interval (2544.3 to 2605.4 m) from Berkley et al Midale 12-2- 7-11W2 is illustrated in left-hand column. The middle column shows relative abundance of conodont genera in this core; numbers on the right indicate number of specimens recovered from each sample. The right-hand column illustrates stratigraphic variations in ε Nd (left curve) and Sm/Nd ratios (right curve). All sample depths are corrected to geophysical log depths.
Saskatchewan Geological Survey 4 Summary of Investigations 2003, Volume 1 Figure 6 - Skeletal wackestone/packstone at base of Figure 6 - Skeletal wackestone/packstone at m). Fm., 2569.9 transition zone (Yeoman Figure 5 - Burrowed limestone with kukersitic with Figure 5 - Burrowed limestone m). Fm., 2577.53 (Yeoman laminae burrows that contain secondary Figure 4 - Borrow-mottled dolomitic limestone with limestone dolomitic Figure 4 - Borrow-mottled Thalassinoides burrowsm). (Yeoman Fm., 2585.7
Saskatchewan Geological Survey 5 Summary of Investigations 2003, Volume 1 a interpreted as a product interpreted as a a is and Kent, 2000) or of is and Kent, 2000) att, pers. comm., 2003) comm., att, pers. Figure 9 - Dolostone brecci of subaerial exposure (Kre seismic activity (B. Pr m). (Redvers Unit, Herald Fm., 2544.9 stone (Coronach Member, Figure 8 - Partially oil-stained, laminated oil-stained, Partially Figure 8 - (stromatolitic ?) dolomud Herald Fm., 2548.2 m). 2548.2 Herald Fm., Figure 7 - Horizontal to vertical elongate nodular Figure 7 - Fm., Herald Member, Alma anhydrite (Lake 2560.8 m).
Saskatchewan Geological Survey 6 Summary of Investigations 2003, Volume 1
2572.7
2571.5
2570.1 2569.9
1911
2569.6 2605.3
2568.9 2603.5
2568 2602.3
2567.2 2600.7
Yeoman
2566.8 2599.5
og depths and indicate depth at centre of indicate depth depths and og
2566.6 2598.1
2566 2596.4
2565.3 2595.6
2564.8 2595
2563.9 2593.6
ed to geophysical l ed
2562.6 2591.9
2558.9 2591.3
2556.4 2591
2555.7 2588.9
2555.3 2588.6
le depths are correct
2554.5 2588.3
2553.9 2588
Yeoman (cont'd)
2553.1 2585.7
Herald 2552.2 2584.3
2550.8 2582.7
2550.1 2581.6
2549.7 2580.8
2549.1 2580.2
2548.2 2579.5
2547.4 2578.9
2546.5 2578.2
2545.2 2577.7
2544.9 2577.5
2574.8 2544.6 00 000000 0 000 0100000000000 011031 000000 0 000 0001 0000000000000 0000 0000 00 000100 0 201 35410648374438111316 00 000000 0 000 0000000000000 0000 300861130000000039 27423 033493 00 000010 0 200 0000000000000 0000 010003 000080631716330305000000000 0037 1005 00 000000 0 000 0000000000000 000000 00007035142026000000000000 0000 1004 100 600174312400000 62 102195210 82 100979 0 361 1429186333201 1231 00 000000 0 000 0000000000000 0000 00 000000 0 000 0100000000000 0000 40 062735 1 914911257827262102531328235 Redvers Coronach Lake Alma 73005213810200113 475471148 048795 37135000250271631851104270008101130 27292146373376368879173716281858102232085 541051277425594 4 0004305020000 12210412 011202 500090145300250012000000000 249 0290 0000 40100008101130 00000028000 100 36 6 3 6 3 38 10 24 3 12 9 10 25 25 22 33 17 46 27 5 17 7 17 12 36 61 18 11 59 are 10 to are 20 10 to cm in length). Total Total and others and others Table 1 - Numerical distribution of conodont genera by sample depth in metres. All samp in conodont genera by sample depth Numerical distribution of Table 1 - sampled interval (samples sampled interval (samples Rhipidognathus Rhipidognathus Aphelognathus-Oulodus Drepanoistodus Phragmodus Aphelognathus-Oulodus Panderodus B Panderodus GGP Panderodus B Plectodina Pseudobelodina Drepanoistodus Panderodus GGP Phragmodus Plectodina Pseudobelodina
Saskatchewan Geological Survey 7 Summary of Investigations 2003, Volume 1 Haidl, 2001), in order from shallowest to deepest, are based on conodont genera believed to be benthic or nektobenthic: 1) Rhipidognathus biofacies; 2) Aphelognathus-Oulodus biofacies; 3) Plectodina biofacies; and 4) Phragmodus biofacies. The genera Panderodus and Drepanoistodus and many of the rastrate element-bearing genera such as Pseudobelodina are believed to be pelagic and, therefore, less likely to show strong biofacies partitioning. However, because of the unusual exclusive occurrence of Panderodus bergstroemi in the Lake Alma Member, it has been separated out as “Panderodus B” in Table 1 and Figure 3 to distinguish it from the remaining species of Panderodus that are characterized as Panderodus GGP. a) Yeoman Formation Representatives of the Plectodina and Aphelognathus-Oulodus biofacies dominate the Yeoman Formation. The lowermost sample at 2605.3 m contains a mixed Aphelognathus-Oulodus and Plectodina fauna. Samples from 2603.5 to 2595 m are exclusively within the Plectodina biofacies, suggestive of somewhat deeper conditions. A return to a mixed Aphelognathus-Oulodus and Plectodina fauna is documented from 2593.6 to 2588.9 m but specimens of Plectodina are much more numerous than Aphelognathus-Oulodus in two of the samples (Table 1, Figure 3). Below a kukersitic bed at 2588.12 m, another deepening event is suggested by the return to the Plectodina biofacies in a sample at 2588.6 m and by the single occurrence of Phragmodus in a sample at 2588.3 m that also contains some Plectodina, but no Aphelognathus-Oulodus. The Phragmodus species represented here may not be an indicator of deep water like the related species P. undatus that signals the deepening event at the base of the Stony Mountain Formation (see Nowlan and Haidl, 2001), but its occurrence with some Plectodina, but no Aphelognathus-Oulodus in a sample with a very high Sm/Nd ratio (see below) suggests that this specimen may be a deep-water indicator. Representatives of the genus Phragmodus are extremely rare in the Yeoman and Herald formations in other Saskatchewan cores. A mixed Aphelognathus-Oulodus and Plectodina fauna was recovered from the sample immediately above the kukersitic bed at 2588.12 m. Specimens of the Plectodina biofacies characterizes the samples above and below another kukersitic bed at 2585.2 m.
With the exception of one sample in a kukersitic interval (2581.6 m) from which only four specimens of Plectodina were recovered, samples from 2582.7 to 2578.9 m are assignable to a mixed Aphelognathus-Oulodus and Plectodina biofacies. A thick kukersitic bed (2578.8 to 2577.5 m) yielded conodonts assignable to the Plectodina biofacies just above the base (2578.2 m) and to the Aphelognathus-Oulodus biofacies from overlying samples (2577.7 m; 2577.5 m). From 2574.8 to 2571.5 m, there is a return to a mixed Aphelognathus-Oulodus and Plectodina biofacies.
Samples from 2569.9 to 2568 m are assignable to the Aphelognathus-Oulodus biofacies. Conodonts recovered from near the top of the Yeoman in other wells (Nowlan and Haidl, 2001) are also assignable to the Aphelognathus- Oulodus biofacies, indicative of deposition in shallower water than underlying strata which contain Plectodina. No conodonts were recovered from the two samples at the top of the Yeoman. b) Herald Formation
Lake Alma Member
Only four of eight samples from the Lake Alma Member yielded conodonts. All of the conodonts recovered from the productive samples are assignable to Panderodus bergstroemi Sweet (2566.58 to 2563.86 m). This species was originally described from the Bighorn Group in Wyoming and Colorado by Sweet (1979) where it occurs in an interval approximately equivalent in age to the Herald Formation. There is no evidence in the literature, nor in our data from the Saskatchewan part of the Williston Basin, to suggest that the species was an ecological specialist, but its exclusive occurrence here in the Lake Alma Member suggests that it might have been more tolerant of evaporitic, perhaps hypersaline, conditions than other species. Specimens of P. bergstroemi occur in the Yeoman Formation and the Lake Alma Member of the Herald Formation in Holdfast 14-12-23-26W2, at the base of the Lake Alma Member in Oungre 15-9-2-14W2, and within the Coronach Member in Hartaven 2-11-10-9W2 (Nowlan and Haidl, 2001). It is not reported as occurring alone in conodont samples recovered from other wells. The absence of conodonts from samples of featureless beige dolostone closely associated with evaporites in the Lake Alma Member is strong support for the idea that conodonts did not occupy areas that presumably experienced truly hypersaline conditions.
Coronach Member We have much more detailed sampling available for the Coronach Member in this well than in any previously studied well. Samples from the lower part of the Coronach Member are very sparse (Table 1, Figure 3). The middle
Saskatchewan Geological Survey 8 Summary of Investigations 2003, Volume 1 part of the Coronach is characterized by samples that are dominated by specimens of Aphelognathus-Oulodus but also contain a moderate proportion (10 to 24%) of specimens of Plectodina. Presumably this indicates a shallow to moderately deep depositional setting for the middle part of the Coronach Member. The barren interval at the top is within the laminated dolomudstone unit below the Coronach Anhydrite.
Redvers Unit Conodonts from the Redvers Unit are closely similar to those recovered from this interval elsewhere in Saskatchewan. The mixture of the shallow-water Aphelognathus-Oulodus biofacies and of the Rhipidognathus biofacies, the shallowest water biofacies (2544.87 to 2544.56 m) has been found in three other wells in Saskatchewan (Hartaven 2-11-10-9W2, Holdfast 14-12-23-26W2, and Oungre 15-9-2-14W2) (see Nowlan and Haidl, 2001).
4. Isotope Data Fanton et al. (2002) demonstrated that: 1) Nd isotope ratios can be used to track the submergence of the interior craton during deposition of Ordovician sediments in Iowa and Saskatchewan, and 2) the fractionation of rare earth elements (REE), represented by the Sm/Nd ratio, behaves as a chemostratigraphic indicator of relative paleo-depth of seawater. This study adds isotope data from 74 samples from the Berkeley Midale 12-2-7-11W2 core. a) Neodymium Isotope Ratios (εNd) The Nd isotope balance in Late Ordovician epeiric seas was primarily controlled by the relative contributions of Nd weathered from the highlands of the Taconic Orogen (εNd = -6 to -9), Precambrian rocks of the Transcontinental Arch and the Canadian Shield (εNd = -22 to -15), and possibly the extension of the Appalachian-Caledonian Orogen in the Arctic (εNd = -6 to -9). In the Midale well, ε Nd values range from -10.8 to -7.1 (Table 2, Figure 3) indicating that the Transcontinental Arch and the Canadian Shield were not exposed on the margins of the Williston Basin during deposition of Red River strata cored in this well. This is consistent with values from other Saskatchewan cores from this part of the stratigraphic succession (Fanton et al., 2002). Values of ε Nd lower than -9.5 from two samples from the lower Lake Alma (Table 2, Figure 3) may be indicative of a contribution of Nd from weathered older Ordovician strata which have more negative ε Nd values (see Figure 2 in Fanton et al., 2002). b) Sm/Nd Ratios Stratigraphic changes in Sm/Nd ratios are attributed to aqueous fractionation of heavier REE from lighter REE during transport from source to depositional site (Fanton et al., 2002). With increased distance from the paleo- shoreline, dissolved Sm is enriched over dissolved Nd in the seawater due to the preferential adsorption and sedimentation of the LREE by particulates. This aqueous signature is then imparted to the sediments on metalliferous coatings and in biogenic phosphate. In circumstances in which increasing distance from paleo- shoreline is associated with increasing water depth in the basin, Sm/Nd chemostratigraphy can serve as an indicator of seawater paleo-depth. Fanton et al. (2002) showed a correspondence between conodont paleoecology, sea-level curves, and Sm/Nd ratios in Ordovician carbonates in Iowa: stratigraphic increases in Sm/Nd ratios of carbonates reflect increasing water depth, whereas stratigraphic decreases in Sm/Nd ratios indicate decreasing water depth.
Sm/Nd ratios in samples from the Midale well range from 0.145 to 0.234 (Table 2, Figure 3). Interpretation of the complex relationships between Sm/Nd ratios, lithologies, and conodont biofacies is ongoing. Some preliminary observations are summarized below.
Yeoman Formation The distribution of Sm/Nd ratios, conodont biofacies, and lithologies suggest a complex depositional history for Yeoman rocks, including several changes in paleo-water depths. Data indicate that two major shifts in the Sm/Nd ratio in the Yeoman Formation are associated with kukersitic beds. A kukersitic limestone bed from 2588.05 to 2588.20 m (not analyzed) is located above a dolomitic limestone sample at 2588.34 m which yielded a high Sm/Nd ratio (0.234) and the single occurrence of Phragmodus, the deepest water conodont biofacies identified in this well. The kukersitic bed is overlain by a dolomitic limestone sample at 2587.97 m with an Sm/Nd ratio of 0.185. Kukersitic limestones from 2577.5 to 2578.8 m are also associated with a decrease in Sm/Nd ratios and a change from a mixed Aphelognathus-Oulodus and Plectodina biofacies to Aphelognathus-Oulodus biofacies. A marked increase in Sm/Nd ratios underlies this uppermost kukersitic bed with values increasing from 0.173 in a burrow-mottled limestone (2580.75 m) to 0.229 in a dolostone dominated by horizontal burrows (2578.93 m).
Saskatchewan Geological Survey 9 Summary of Investigations 2003, Volume 1 Table 2 - Sm and Nd isotope and concentration data from Berkley et al Midale 12-2-7-11W2. All sample depths are corrected to geophysical log depths and indicate depth at centre of sampled interval (samples are 10 to 20 cm in length).
Herald Formation Sample Depth 147 144 143 144 Member (m) [Sm] (ppm) [Nd] (ppm) Sm/Nd Sm/ Nd Nd/ Nd εNd(450Ma) Redvers 2544.56 0.307 1.63 0.180 0.1140 0.511978 -8.1 Redvers 2544.87 0.684 3.52 0.185 0.1174 0.511973 -8.4 Redvers 2545.22 0.550 2.26 0.232 0.1473 0.512113 -7.4 Coronach 2546.17 0.0354 0.18 0.191 0.12140 0.512011 -7.6 Coronach 2546.54 0.046 0.21 0.208 0.1317 0.512038 -8.0 Coronach 2547.39 0.027 0.12 0.222 0.1407 0.512042 -8.4 Coronach 2548.17 0.037 0.16 0.218 0.1381 0.512059 -8.0 Coronach 2549.08 0.085 0.41 0.198 0.1254 0.511970 -8.9 Coronach 2549.68 0.076 0.43 0.167 0.1059 0.511932 -8.6 Coronach 2550.07 0.085 0.42 0.190 0.1208 0.511969 -8.7 Coronach 2550.76 0.065 0.32 0.194 0.1232 0.512002 -8.2 Coronach 2552.22 0.049 0.27 0.171 0.1084 0.511920 -8.8 Coronach 2553.06 0.058 0.31 0.181 0.1146 0.511954 -8.6 Coronach 2553.85 0.080 0.44 0.173 0.1099 0.511930 -9.0 Coronach 2554.58 0.084 0.45 0.176 0.1117 0.511948 -8.6 Coronach 2555.34 0.083 0.48 0.166 0.1051 0.511922 -8.7 Coronach 2555.73 0.104 0.58 0.171 0.1083 0.511942 -8.5 Lake Alma 2556.38 0.036 0.16 0.219 0.1390 0.512065 -7.9 Lake Alma 2556.71 0.0324 0.15 0.199 0.12641 0.511995 -8.3 Lake Alma 2557.17 0.1782 0.73 0.233 0.14763 0.512063 -8.2 Lake Alma 2557.41 0.1540 0.70 0.211 0.13362 0.512045 -7.7 Lake Alma 2557.69 0.0283 0.14 0.187 0.11874 0.511979 -8.2 Lake Alma 2557.88 0.0665 0.32 0.199 0.12594 0.512015 -8.2 Lake Alma 2558.10 0.1232 0.63 0.188 0.11900 0.511954 -8.6 Lake Alma 2558.27 0.5800 2.94 0.188 0.11929 0.511940 -9.1 Lake Alma 2558.67 0.1465 0.71 0.197 0.12524 0.512003 -8.1 Lake Alma 2558.88 0.103 0.49 0.201 0.1274 0.512012 -8.2 Lake Alma 2559.27 0.0629 0.31 0.196 0.12438 0.512004 -8.0 Lake Alma 2559.37 0.0025 0.01 0.195 0.12380 0.511969 -9.1 Lake Alma 2560.66 0.0030 0.02 0.182 0.11577 0.511926 -9.0 Lake Alma 2561.63 0.0106 0.05 0.189 0.11963 0.511950 -9.1 Lake Alma 2562.63 0.066 0.29 0.216 0.1372 0.512019 -8.5 Lake Alma 2563.86 0.051 0.21 0.231 0.1466 0.512071 -8.2 Lake Alma 2564.77 0.046 0.19 0.228 0.1444 0.512031 -8.8 Lake Alma 2565.34 0.051 0.22 0.221 0.1403 0.511918 -10.8 Lake Alma 2566.00 0.028 0.12 0.225 0.1427 0.511970 -9.9 Lake Alma 2566.58 0.066 0.30 0.208 0.1320 0.512014 -8.3 Yeoman Formation Sample Depth 147 144 143 144 Member (m) [Sm] (ppm) [Nd] (ppm) Sm/Nd Sm/ Nd Nd/ Nd εNd(450Ma) - 2566.79 0.033 0.15 0.215 0.1367 0.512035 -8.4 - 2567.16 0.036 0.16 0.210 0.1330 0.512037 -8.0 - 2568.02 0.109 0.47 0.221 0.1403 0.512003 -9.1 - 2568.9 0.029 0.14 0.198 0.1255 0.512016 -8.0 - 2569.55 0.355 1.68 0.202 0.1281 0.512047 -7.4 - 2569.9 0.100 0.51 0.187 0.1187 0.511995 -8.1 - 2570.09 0.085 0.56 0.145 0.0923 0.511923 -8.0 - 2571.45 0.066 0.38 0.166 0.1054 0.511970 -7.8 - 2572.68 0.074 0.38 0.187 0.1189 0.512041 -7.1 - 2574.83 0.072 0.37 0.184 0.1170 0.512017 -7.6 - 2577.53 0.084 0.45 0.180 0.1145 0.511940 -8.7 - 2578.23 0.123 0.58 0.203 0.1285 0.511979 -8.9 - 2578.93 0.101 0.42 0.229 0.1455 0.512014 -9.6 - 2579.45 0.086 0.37 0.224 0.1419 0.512040 -8.6 - 2580.15 0.271 1.24 0.207 0.1313 0.511973 -9.0 - 2580.75 0.064 0.35 0.173 0.1098 0.511933 -8.7 - 2581.6 0.082 0.42 0.185 0.1174 0.511949 -8.9 - 2582.74 0.053 0.27 0.186 0.1181 0.511985 -7.9 - 2584.32 0.371 1.91 0.185 0.1171 0.511936 -9.0 - 2585.71 0.489 2.13 0.219 0.1388 0.512013 -9.0 - 2587.97 0.112 0.58 0.185 0.1173 0.511944 -9.0 - 2588.34 0.225 0.92 0.233 0.1475 0.512023 -9.0 - 2588.58 0.119 0.52 0.219 0.1390 0.512028 -8.5 - 2588.91 0.109 0.51 0.203 0.1291 0.511982 -8.8 - 2591.02 0.101 0.50 0.191 0.1212 0.511961 -8.7 - 2591.32 0.090 0.43 0.199 0.1264 0.511999 -8.3 - 2591.92 0.127 0.52 0.234 0.1485 0.512052 -8.3 - 2593.58 0.111 0.47 0.225 0.1425 0.512055 -7.9 - 2594.97 0.126 0.57 0.211 0.1338 0.511973 -9.2 - 2595.59 0.168 0.85 0.189 0.1199 0.511942 -9.2 - 2596.44 0.122 0.53 0.221 0.1402 0.512016 -8.9 - 2598.05 0.115 0.54 0.203 0.1291 0.511978 -9.0 - 2599.5 0.308 1.42 0.207 0.1311 0.511992 -8.8 - 2600.66 0.111 0.52 0.201 0.1277 0.511961 -9.3 - 2602.28 0.096 0.47 0.193 0.1226 0.511973 -8.5 - 2603.48 0.098 0.48 0.193 0.1224 0.511945 -9.0 - 2605.32 0.144 0.68 0.200 0.1270 0.511996 -8.4
Saskatchewan Geological Survey 10 Summary of Investigations 2003, Volume 1 Another major shift in the Sm/Nd ratio is associated with a change from lime mudstone with a Sm/Nd ratio of 0.145 (2570.09 m) to skeletal dolowackestone with an Sm/Nd value of 0.187 (2569.9 m). The contact between these two lithologic units is interpreted as the base of the “transitional unit”. Within the “transitional unit”, Sm/Nd ratios range from 0.187 at the base to 0.221 in the middle to 0.215 in the sample from the uppermost Yeoman. The lower portion of this unit is characterized by the Aphelognathus-Oulodus biofacies; no conodonts were recovered from the upper section.
Herald Formation
Lake Alma Member In the Lake Alma Member, shifts in the Sm/Nd ratios, the complex distribution of dolostone and anhydrite, and the paucity of conodonts suggest several changes in paleo-water depth in a saline to hypersaline environment. Sm/Nd ratios in the lower Lake Alma laminated to bedded dolomudstone unit range from 0.225 at the base to 0.231 at 2563.9 m and then decrease to 0.216 in the uppermost sample (Table 2, Figure 3). Sm/Nd values continue to decrease in the lower nodular anhydrite portion of the Lake Alma Anhydrite and then increase again to a value of 0.201 in the dominantly dolomudstone bed that separates the two anhydrite units. A shift to lower values in the upper section of the dolomudstone bed reverses as values of the Sm/Nd ratio increase into the upper bed of the Lake Alma Anhydrite which is composed of laminated to bedded anhydrite with abundant thin beds and laminae of dolostone. This upper evaporite unit may represent replacement of carbonate by anhydrite (A.C. Kendall, pers. comm., 2002). Conodonts are sparse in the Lake Alma and are present only in the basal 2.8 m. All specimens are assignable to Panderodus bergstroemi Sweet; this species may be indicative of hypersaline conditions (see discussion in conodont section above).
Coronach Member
Changes in Sm/Nd ratios and in conodont biofacies suggest that several changes in paleo-water depth and salinity are associated with deposition of the Coronach Member.
A decrease in the Sm/Nd ratio is recorded between the upper Lake Alma Anhydrite (0.219) and the Coronach burrow-mottled limestone unit in which Sm/Nd ratios range from 0.166 to 0.194. Conodonts are sparse in the lower 2 m of the Coronach. Large increases in total conodont specimens, including Plectodina, at 2553.9 m and 2550.07 m are associated with increases in the Sm/Nd ratios in underlying rocks. An absence of conodonts at the base of a laminated limestone bed (2549.7 m) is correlated with a decrease in the Sm/Nd ratio in this sample (0.167) compared to a Sm/Nd ratio of 0.190 in the sample from the underlying skeletal wackestone (2550.1 m) from which 271 conodont specimens were recovered. A positive shift in Sm/Nd values occurs from 0.167 at the base of the laminated limestone unit to 0.222 at 2547.4 m in the middle of the overlying laminated dolostone unit. Sm/Nd ratios then decrease through the upper part of the laminated unit into the Coronach Anhydrite. A mixed Aphelognathus- Oulodus and Plectodina conodont biofacies is present in the upper portion of the laminated limestone bed; conodonts are absent from the overlying laminated dolostone and anhydrite.
Redvers Unit
Sm/Nd ratios increase from 0.191 in the Coronach Anhydrite to 0.232 in laminated dolostone near the base of the Redvers Unit and then decrease to 0.185 in the overlying brecciated unit and to 0.180 in the laminated limestone at the top of the core. The only specimens of Rhipidognathus, representative of the shallowest water Late Ordovician conodont biofacies present in Saskatchewan, are found in the two samples from the uppermost 1.6 m of this core. This occurrence correlates well with the Sm/Nd ratios to indicate marked shallowing at the top of the Redvers that has been noted in other wells (Nowlan and Haidl, 2001; Fanton et al., 2002).
5. Discussion The correlation between Sm/Nd ratios and conodont biofacies in several intervals in the Berkley et al Midale 12-2- 7-11W2 core provides additional evidence that these tools are useful as paleo-water depth indicators in interpretation of the depositional history of these rocks. More in-depth interpretation of relationships between conodont, isotope, and lithologic data, and paleo-water depth is ongoing. Tentative plans include detailed sampling of at least one more core of the Herald and Yeoman formations to provide conodont, isotope, and sedimentology data from another location in southeastern Saskatchewan.
Saskatchewan Geological Survey 11 Summary of Investigations 2003, Volume 1 Integration of all data types from all Saskatchewan cores will provide a better understanding of the paleogeography of this intracratonic basin during deposition of carbonate-evaporite sequences in the Late Ordovician.
6. Acknowledgments The authors thank Megan Opseth for assistance in preparation of the diagrams for this paper, Tim Prokopiuk and Daphne Cordeiro for technical support in the Saskatchewan Isotope Laboratory, and Karen Paull (Geological Survey of Canada) for processing the conodont samples. D.M. Kent, B.R. Pratt, and A.C. Kendall are thanked for sharing their expertise in carbonate and evaporite rocks.
7. References
Canter, K.L. (1998): Facies, cyclostratigraphic and secondary diagenetic controls on reservoir distribution, Ordovician Red River Formation, Midale Field, southern Saskatchewan; Eighth International Williston Basin Symposium, Core Workshop Volume, Regina, October 1998, Sask. Geol. Soc./N. Dakota Geol. Soc./Montana Geol. Soc., p41-65.
Fanton, K.C., Holmden, C., Nowlan, G.S., and Haidl, F.M. (2002): 143Nd/144Nd and Sm/Nd stratigraphy of Upper Ordovician epeiric sea carbonates; Geochim. Cosmochim. Acta, p241-255. 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.(comp.), CSPG-SEPM Core Conference, Calgary, p5-39.
Kendall, A.C. (1976): The Ordovician carbonate succession (Bighorn Group) of southeastern Saskatchewan; Sask. Miner. Resour., Rep. 180, 185p.
Kent, D.M. and Kissling, D.L. (1998): Covert facies of the Red River C Laminated Member, northern Williston Basin; in Christopher, J.E., Gilboy, C.F., Paterson, D.F., and Bend, S.L. (eds.), Eighth International Williston Basin Symposium, Sask. Geol. Soc., Spec. Publ. No. 13, p24.
Kreis, L.K. and Kent, D.M. (2000): Basement controls on Red River sedimentation and hydrocarbon production in southeastern Saskatchewan; in Summary of Investigations 2000, Volume 1, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2000-4.1, p21-42.
Longman, M.W. and Haidl, F.M. (1996): Cyclic deposition and development of porous dolomites in the Upper Ordovician Red River Formation, Williston Basin; in Longman, M.W. and Sonnenfeld, M.D. (eds.); Paleozoic Systems of the Rocky Mountain Region; Rocky Mount. Sec., SEPM, p29-46.
Nowlan, G.S. and Barnes, C.R. (1981): Late Ordovician conodonts from the Vaureal Formation, Anticosti Island, Quebec; Geol. Surv. Can. Bull., No. 329, p1-49.
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. Okulitch, A.V. (2003): Geological Time Chart 2003; Geol. Surv. Can., Open File 3040 (National Earth Science Series, Geological Atlas) – REVISION. Pratt, B.R., Bernstein, L.M., Kendall, A.K., and Haidl, F.M. (1996): Occurrence of reefal facies in Red River strata (Upper Ordovician), subsurface Saskatchewan; in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p147-152. Seddon, G. and Sweet, W.C. (1971): An ecologic model for conodonts; J. Paleont., v45, p869-880. Stasiuk, L.D. and Osadetz, K.G. (1990): The life cycle and phyletic affinity of Gloeocapsomorpha prisca Zalessky 1917 from Ordovician rocks in the Canadian Williston Basin; in Current Research, Part D, Geol. Surv. Can., Pap. 89-1D, p123-137.
Saskatchewan Geological Survey 12 Summary of Investigations 2003, Volume 1 Stasiuk, L.D., Kybett, B.D., and Bend, S.L. (1993): Reflected light microscopy and micro-FTIR of Upper Ordovician Gloeocapsomorpha prisca alginite in relation to paleoenvironment and petroleum generation, Saskatchewan, Canada; Org. Geochem. v20, p707-719. Sweet, W.C. (1979): Late Ordovician conodonts and biostratigraphy of the western Midcontinent Province; Brigham Young University Geology Studies, v26, p45-86. Sweet W.C. and Bergström, S.M. (1984): Conodont provinces and biofacies of the Late Ordovician; in Clark, D.L. (ed.), Conodont Biofacies and Provincialism, Geol. Soc. Amer., Spec. Pap. 196, p69-87.
Saskatchewan Geological Survey 13 Summary of Investigations 2003, Volume 1