Lithogeochemical Study of the Cretaceous in Central Saskatchewan -Preliminary Report

Colin E. Dunn 1

Dunn, D.E. (1990): Uthogeocttemlstry study of the Cretaceous in central Saskatchewan - Preliminary report; in Summary of In­vestigations 1990, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 90-4.

'Environmental geochemistry' is a new program being developed at the Geological Survey of Canada. One component of this program is the compilation of com­prehensive data bases of the Canadian landmass to pro­vide baseline information on the natural distribution of chemical elements. The program is an extension of on­going studies, such as the National Geochemical Recon­naissance (NGR), that have, over the past 20 years, been directed mostly toward mineral exploration (Friske and Hornbrook, in press).

Government agencies have had the foresight to careful­ly archive portions of samples collected during recon­naissance and exploration programs, and these materials are of immense value for further study in light of new knowledge and increasingly sophisticated analyti­cal instrumentation. The sample set used for this report is the rock cuttings from hydrocarbon exploration drill holes, that have been archived (in vials) and catalogued by Saskatchewan Energy and Mines over the past 50 years.

The purpose of the current study is to document the chemistry of the Cretaceous strata that subcrop beneath glacial deposits of the Prairies and, through collabora­tion with health specialists, examine the patterns of ele­ment distribution with respect to the quality of human, animal and crop health. At Henribourg, 20 km northeast of Prince Albert, an unusually high incidence of multip le sclerosis has been reported by Irvine et al. (1988, 1989). The authors have examined the chemistry of soils and well waters and noted a multi-element association which may be related to the disease. Other studies suggesting a link between trace elements in the environment and the incidence of multiple sclerosis include reports from British Columbia (Gould and Warren, 1980) and Finland (Hasanen et al., 1986).

The rationale for the present study is that the chemical composition of the subcropping sedimentary rocks is reflected in the overlying glacial deposits, and, therefore, in the ground waters and crops consumed by animals and the populace, particularly in rural areas. The provision of lithogeochemical maps will establish pat­terns of element enrichments, deficiencies or associa­tions for investigation by health, veterinary, and agricul­tural specialists to seek links with various diseases. Once a link is identified, then mitigating measures may be taken to alleviate the problem. Rocks, in effect, form the bottom end of the food chain, and their chemistry can have a significant bearing on man's environment and health.

(1) Geologleal Survey of Canaaa. 601 Booth St .. Ottawa, Ont.

Saskatchewan Geological Survey

1. Scope of Study The area examined is approximately 100 000 km2 of central Saskatchewan within which 107 exploration holes have been drilled (Figure 1). Work was contracted to experts on the Cretaceous of the Central Plains to col­lect well-cuttings for analysis, and provide a) an updated 1: 1,000,000 geology map of the Phanerozoic of the en­tire province beneath the Pleistocene cover, paying par­ticular attention to the Cretaceous of the study area; b) a compilation at the same scale of a hydrogeological map of the province, with respect to vectors of water movement, and zones of recharge and discharge at the subcropping Cretaceous surface; c) stratigraphic cross sections of the study area; d) annotated geophysical logs and sample descriptions of the 96 wells sampled; and e) a report on the stratigraphy of Cretaceous, Ter­tiary and Pleistocene strata (Christopher and Koziol, 1990).

2. Sample Materials and Methods In the 96 wells selected for study, each sample was a composite from two vials of well-cuttings over each 20 ft (6 m) interval throughout the top 200 ft (60 m) of the subcropping Cretaceous sedimentary rocks. This provided a maximum of 10 samples per well, although fewer were available from some wells such that a total of 720 (including standards and duplicates) were sub­mitted for analysis. Samples were retrieved in accord with the following specifications:

a) A 2 to 3 g sample of well-cuttings was collected from each of the storage vials that were present over specified 6 m intervals. The rock chips were ex· amined microscopically to select material repre­sentative of the stratigraphic interval (formation limits and lithologies were determined from geophysical well log signature).

b) A magnet was passed over each sample to remove any metallic contaminants derived from drilling and sample recovery operations. Plastic tweezers were used to make a composite sample, which was then split into two portions for different types of chemical analysis.

c) From the microscope examination of each com­posite sample a brief and systematic description was made of the lithology, grain size, colour, and any other noteworthy features. The well name, location,

193

110· 102·

GEOLOGY OF

CENTRAL SASKATCHEWAN

LEGEND

1111 Tertiary. undifferentiated

[==:] Cretaceous, Bearpaw

lfflffl Cretaceous, Judith River

EZ] Cretateous, Lea Park

~ Cretaceous. White Specks

[[[Il Cretaceous. Lower Colorado

E::] Cretaceous, Mannville

~ SUurian, ln18rlake

~ o«lovician, StonewalVStony Mt.

~ Ordovician, Red River/VVinnipeg

E±] Precambrian

S • Saskatoon PA • Prince Albert LR • La Ronge ML • Meadow Lake HS • Hudson Bay

200

Figun, 1 - Geology of central Saskatchewan showing locations of wells from which samples wen, collected. Map digitiz&d from compilation by Christopher and Koziol (1990).

stratigraphic formation, and depth below kelly bush­ing were also recorded.

d) A 1 to 1.5 g split of each sample was accurately weighed into a numbered plastic vial and submitted for instrumental neutron activation analysis (INAA) at Activation laboratories Ltd., Ancaster, Ontario. Analysis included Au, Ag, As, Ba, Br, Ca, Co, Cr, Cs, Fe, Hf, Hg, Ir, K, Mo, Na, Ni, Rb, Sb, Sc, Se, Sr, Ta, Th, U, W, Zn, and the rare-earth elements La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu.

e) A second 0.5 to 1 g split of each sample was placed into a small envelope and submitted for inductively­coupled plasma emission spectroscopy (ICP) at Acme Analytical Laboratories, Vancouver. Prior to in­strumental analysis each sample was hand-ground using an agate mortar and pestle, and a 0.5 g por­tion digested with 3 ml 3-1-2 HCI-HN03-H20 at 95°C for one hour then diluted to 10 ml with distilled water. The multi-element ICP package included some of the same elements provided by INAA, providing a comparison of the analytical methods. The ICP package included determinations for Mo, Cu, Pb, Zn, Ag, Ni, Co, Mn, Fe, As, U, Au, Th, Sr, Cd, Sb, Bi, V, Ca, P, La, Cr, Mg, Ba, Ti, B, Al, Na, K, and W. For some rock types this acid leach may be partial for Mn, Fe, Na, K, Al, Sr, Ca, P, La, Cr, Mg, Ba, Ti, B , and W. However, tor the shales compris-

194

ing this study many elements are bound to clay minerals and are released by this acid digest. Com­parison of ICP results with the INAA and standards results show that most analyses represent near total concentrations for elements other than those tightly bound in the crystal lattices of the aluminosilicate minerals, notably K, Al, and Ti, along with Ba, B. Sr, V and Cr.

f) The acid digest solutions obtained for ICP were analyzed separately for those elements that form hydrides, such as As, Sb, Se, Te, Bi, and Ge (par­tial) . Detection limits are considerably lower than can be achieved from the direct ICP scan, and were re­quired because of the environmental significance of these elements.

g) Within each batch of 20 samples a duplicate and a standard were inserted at random in the numerical sequence to provide control on the precision and ac­curacy of the analytical methods.

3. Geological Summary Cretaceous strata dip gently southwestward and from the northern flank of the the Williston Basin (Figure 1). Except for a few rare Cretaceous outcrops, sandy gla­cial deposits blanket the entire area. The glacial deposits, locally more than 100 m thick, are mostly

Summary of Investigations 1990

sandy tills and stratified drift that contain variable amounts of clay and minor carbonate (rarely more than 5 percent).

The lowermost strata of the study area are predominant­ly sandy deposits of the Lower Cretaceous Mannville Group. Sandstones vary from coarse and kaolinitic to bedded fine sands and silts, interdigitated with mudstones. In broad terms the sequence fines upward. The overlying sediments of the Lower Colorado Group are shales, divided by a thin sandy sequence known as the Viking Formation. The Lower Colorado can not be subdivided with confidence in some of the older wells for which geophysical logs have poor sensitivity. Conse­quently, in some wells samples from this sequence were picked simply as 'lower Colorado'. In others a lower se­quence of dark grey shales comprising the Joli Fou For­mation could be differentiated from an upper sequence of similar lithology known as the Big River Formation.

The White Speckled Shales (commonly known as the White Specks) form the basal sediments of the Montana Group. They constitute an important marker zone of kerogenous calcareous shale which, in the study area, can not be differentiated into the 'First' and 'Second' White Specks as it can farther to the south. The overly­ing sediments are open marine shales of the Lea Park Formation, overlain in turn by a cyclical sequence of glauconitic sandstones and shales comprising the Judith River Formation. Except for two isolated areas of Tertiary sediments east and south ot Saskatoon, the youngest sedimentary rocks of the study area are the cfaystones and sandstones of the Upper Cretaceous Bearpaw Formation.

Figure 1 shows the near parallel outcrop pattern of the eroded up-dip ends of the formations, the shape of which is modified by structural flexures and preglacial erosion (Christopher and Koziol, 1990). More details of the Cretaceous in the area are given in Christopher (1980, 1984), and Caldwell (1982) for example.

4. Current Status

All the contracted work has been completed, providing more than 50,000 analytical determinations (71 elements for each of the 720 samples). These data have been transferred to a microcomputer database (A-base Sys­tem V) and merged with the information provided for each sample (formation, lithology, colour etc.). The geological map and well locations have been digitized (Figure 1) and prepared for investigation using the SPANS (Tydac Corp., Ottawa) GIS system.

Summary statistics have been computed for the ICP and ICP-hydride data but not yet for the INAA determina­tions. Table 1 shows a compilation of the average ele­ment content of each stratigraphic interval. The most striking feature of this table is the relatively high level of many elements in the shales that comprise the White Specks. The main features of the table, in decreasing order of importance, are:

Saskatchewan Geological Suf\l'fly

1) The White Specks are strongly enriched in Mo, V, Ca, Sb and Se. There is also enrichment in Cu, Zn, Sr, Cd, and As.

2) The Mannville shows enrichment in Mn and Fe, with depletion in P, Al, Na, K, and Ba This composition reflects the dominance of sandstones in this basal sequence. The Mannville is the only stratigraphic Group to return W analyses above the detection level of 1 ppm.

3) The Bearpaw and Judith River Formations have rela­tive enrichment of Cr, Mg, Ba, and Ti.

It is noteworthy that 20 km northeast of Prince Albert the Henribourg 'cluster focus' for multiple sclerosis (Irvine et al., 1988, 1989) is located close to the subcrop of the metalliferous White Specks, at a site where there is a major structural flexure. Furthermore, this is an area of formation water discharge from the southwest (Chris­topher and Koziol, 1990). The coincidence of geological and geochemical conditions is, at present, merely an ob­servation for which no causal association is suggested, but which may warrant investigation from the standpoint of an epidemiologist.

5. Lithogeochemical Maps Sufficient data are available geographically and stratigraphically to be able to plot geochemical maps of a substantial part of central Saskatchewan, and the next phase of study will involve these compilations. The maps will provide a close prediction of the chemistry of the rocks at the Cretaceous/Pleistocene interface, and from first examination of the data it appears that the chemistry of each major stratigraphic interval is sufficient­ly uniform to extrapolate element contours from the Manitoba to the Alberta borders. Subsequently, input will be required from other professionals to seek associa­tions with areas exhibiting unusual incidence of disease in crops, livestock and humans.

6. Acknowledgements

Some geochemical information on the Cretaceous sup­plied by Malcolm Gent (Sask. Geol. Survey) sparked the idea for this data collection and compilation. The study has been made possible by the meticulous worl< ot Or. Jim Christopher and Brenda Koziol in compiling the in­formation required to provide the geological setting of the area, and in painstakingly collecting and recording representative samples of high quality for each stratigraphic interval. Thanks are extended to Kevin Beneteau for transferring the field and analytical data on to computer fifes, and to Rachael Cardinal for digitizing the maps. I thank, too, Wendy Spirito for advice and as­sistance on the computing aspects of this study.

7. References Caldwell, W.G.E. (1982): The Cretaceous System in the Willis­

ton Basin • A modern appraisal; in Christopher, J.E. and Kaldi, J. (eds.), 4th International Williston Basin Sym­posium, Sask. Geol. Soc., Spec. Publ. No. 6, p295-312.

195

Table 1 • A\'8,age Concentrations of Elements in Crr,taceous Sedimentary Rocks, Central Saskatchewan (ICP analysis of acid digest: detrmninations arr, partial for some elements - see text).

Bearpaw Judith Lea .... White . Viking Joli Fou Big Lower• Mann-River Park · Specks River Colorado ville

No. of 6 42 313 56 12 17 71 69 59 Samples

Fe% 2.8 2.1 3.5 2.5 2.0 2.1 2.1 2.0 5.3

Ca% 2.2 2.6 2.1 11.0 ··· 2.2 1.1 3.7 1.7 4.3

Al% 1.1 1.0 1.5 0.8 0.7 0.9 0.8 0.8 0.4

Na% 0.09 0.14 0.20 0.21 .. . 0.19 0.24 0.33 0.29 0.03

K% 0.20 0.16 0.22 0.22 . 0.16 0.20 0.23 0.18 0.08

Mg ppm 8600 7800 7700 3800 3500 3700 2900 4000 5900 ...

Pppm 590 460 930 / 820 ... ·· ... ·.· 890 720 1020 910 360

Mn ppm 600 558 596 .' 307 259 261 212 418 1368

Ti ppm 250 380 140 110 100 100 100 120 120

Cu ppm 24 29 31 50 16 20 23 18 14

Pb ppm· 13 11 20 15 16 23 22 18 12

Zn ppm 78 90 117 189 · 68 82 90 77 78

Ni ppm 27 25 33 68 18 19 26 20 14

Co ppm 10 9 11 . 11 . 8 8 9 8 9

Cr ppm 20 22 25 .. 18 11 11 9 10 10

Ba ppm 188 162 162 76 97 95 88 89 47

Sr ppm 78 76 97 ,170 76 88 113 77 80

V ppm 28 28 42 121 14 14 17 14 19

Cd ppm <l <l <1 4 <1 <1 < 1 <l < 1

Th ppm 5 6 6 5 10 9 8 8 4

B ppm 4 21 26 23 19 28 27 22 25

Wppm < 1 <1 <l <l <l <1 <1 <l 2

Mo ppm 1 1 2 . 34 1 1 5 2 1

Ag ppm 0.4 0.2 0.2 0.4 0.1 0.1 0.2 0.1 0.2

As ppm 8 7 12 22 9 8 11 8 8

Sb ppm 0.6 0.5 0.7 3.5 0.4 0.3 0.6 0.3 0.3

Bi ppm 0.2 0.3 0.3 0.4 0.4 0.4 0.5 0.3 0.2

Se ppm 0.4 0.3 0.9 11.7 0.4 0.2 1.2 0.6 0.2

Te ppm 0.4 0.2 0.2 0.2 0.2 0.3 0.2 0.2 0.2

Ge ppm 0.3 0.3 0.2 0.1 0.1 0.1 0.1 0.2 0.1

• undifferentiated

196 Summary of Investigations 1990

Christopher, J.E. (1980): The Lower Cretaceous Mannville Group of Saskatchewan - A tectonic overview; in Beck, L.S., Christopher, J .C. and Kent, O.M. (eds.), Uoydminster and Beyond, Sask. Geol. Soc., Spec. Pubf. No. 5, p3-32.

(1984): Depositional patterns and oil field trends in --t"'h_e...,L .... o-wer Mesozoic of the northern Williston Basin,

Canada; in Lorsong, J.A. and Wilson, M.A. (eds.), Oil and Gas in Saskatchewan, Sask. Geol. Soc., Spec. Pub!. No. 7, p83-102.

Christopher, J.E., and Koziol, B. (1990): Geological setting of Cretaceous strata in context of a geochemical sampling program, central Saskatchewan; Unpubl. report prepared under Oep. Supply and Services Contract # 23226-9-1559/01-SZ entitled Collection and preparation of geologi­cal samples in support of the environmental geochemistry program, 18p plus maps and annexes.

Saskatchewan Geological Survey

Friske, P.W.B., and Hornbrook, E.H.W. fin press): Canada's National Geochemical Reconnaissance program; Trant. Inst. Min. and Metall.

Gould, C.E. and Warren, H.V. (1980): Trace elements in human biology and a preliminary report on a possible relationship to multiple sclerosis; Sci. Total Environ., v15, 262-268.

Hasanen, E., Kinnunen, E. and Alhonen, P. (1986): Relation­ship between the prevalence of multiple sclerosis and some physical and chemical properties of soil. Sci. Total Environ., v58, p263-272.

Irvine, D.G., Schiefer, H.B. and Hader, W.J. (1988): Geotoxicol­ogy of multiple sclerosis: the Henribourg, Saskatchewan, cluster focus II. The soil; Sci. Total Environ., vn, p175-188.

(1989): Geotoxicology of multiple sclerosis: the --.-,Ae=n""ribE:'"ourg, Saskatchewan, cluster focus I. The water. Sci.

Total Environ., v84, p45-59.

197