ABSTRA!CT COMPUTER PLOTTED lSOPACH AND STRUCTURE MAPS OF THE LOWER PALAEOZOIC FORMATIONS IN SASKATCHEWAN D. F. PATERSON, 1975 Nineteen maps on a scale of one inch to sixteen miles are presented. They cover all of Saskatchewan isouth of 57 degrees north latitude and comprise one isopach and one structure map for each of the nine Lower Palaeozoic rock units recognized within the Province. In addition, a structure map on top of the Precambrian Basement has been prepared. The text explains how the maps are made, discusses their quality, and includes short notes on each formation to aid in interpreting certain features. There is a table of rock unit data and a bibliography. l
Transcript
ABSTRA!CT
COMPUTER PLOTTED lSOPACH AND STRUCTURE MAPS
OF THE
LOWER PALAEOZOIC FORMATIONS IN SASKATCHEWAN
D. F. PATERSON, 1975
Nineteen maps on a scale of one inch to sixteen miles are
presented. They cover all of Saskatchewan isouth of 57 degrees
north latitude and comprise one isopach and one structure map for each of the nine Lower Palaeozoic rock units recognized within
the Province. In addition, a structure map on top of the Precambrian Basement has been prepared. The text explains how
the maps are made, discusses their quality, and includes short
notes on each formation to aid in interpreting certain features. There is a table of rock unit data and a bibliography.
The author thanks Don Schuster and Anne Greenberg of Saskatchewan Government Systems Centre for their invaluable
aid.
I also gratefully acknowledge the services of Pat Kydd and his colleagues in the Drafting Division, Department of Mineral Resources, for upgrading the computer drawn maps to publication standard and also for producing the new base map used in this
report.
Thanks are also due to the author's colleagues and friends
who contributed much data and helpful advice during the course
of thls project.
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LIST OF MAPS
CP-13b Computer Plotted Isopach Map of the Interlake Group in Saskatchewan.
CP-13a Computer Plotted Structure Map on the Interlake Group in Saskatchewan.
CP-12f Computer Plotted Isopach Map of the Upper Interlake Beds in Saskatchewan.
CP-12e Computer Plotted Structure Map on the Upper Interlake Beds in Saskatchewan.
CP-12d Computer Plotted Isopach Map of the Middle Interlake Beds in Saskatchewan.
CP-12c Computer Plotted Structure Map on the Middle Interlake Beds in Saskatchewan.
CP-12b Computer Plotted Isopach Map of the Lower Interlake Beds in Saskatchewan.
CP-12a Computer Plotted Structure Map on the Lower Interlake Beds in Saskatchewan.
CP-11 Computer Plotted Isopach Map of the Stonewall Formation in Saskatchewan.
CP-10 Computer Plotted Structure Map on the Stonewall Formation in Saskatchewan.
CP- 9 Computer Plotted Isopach Map of the Stony Mountain Formation in Saskatchewan.
CP- 8 Computer Plotted Structure Map on the Stony Mountain Formation in Saskatchewan.
CP- 7 Computer Plotted Isopach Map of the Red River Formation in Saskatchewan.
CP- 6 Computer Plotted Structure Map on the Red River Formation in Saskatchewan.
CP- 5 Computer Plotted Isopach Map of the Winnipeg Formation in Saskatchewan.
CP- 4 Computer Plotted Structure Map on the Winnipeg Formation in Saskatchewan.
CP- 3 Computer Plotted Isopach Map of the Deadwood Formation in Saskatchewan.
CP- 2 Computer Plotted Structure Map on the Deadwood Formation in Saskatchewan.
CP- 1 Computer Plotted Structure Map on the Precambrian Basement in Saskatchewan.
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PRODUCTION OF MAPS
Geological data in the files of the Department of Mineral Resources can be manipulated by computer and plotter in the Saskatchewan Government Systems Centre to yield maps of acceptable quality. The final results depend not only on the original data but also on controls introduced at intermediate stages of production.
PROCURING DATA
The first stage in map production entails making the computer search the tape-files of well data, and register pertinent data for wells containing the required formation. If maps are to be produced for several formations, data on all of them can be extracted in one run. For any one well the following data are printed out:
Well Identifier-as modified from the Saskatchewan Land Survey for the D.M.R. well file.
Latitude and Longitude-as entered in the well file.
X and Y rectangular coordinates-calculated internally to any specified scale from Latitude and Longitude.
Formation Top-calculated internally relative to Sea-Level Datum.
Formation Thickness-calculated internally from Formation Tops.
Kelly Bushing and Total Depth-as entered in the well file.
The data on the printout are reviewed at this point and checked with other data not on the well file ( e.g. Department Reports, see under "Bibliography"). Discrepancies are checked and any correction required is made, upgrading the original data.
Data derived from formation outcrops are included at this point after being transformed into a format analogous to the well data.
PREPARING A MAPPING MATRIX
The original information is irregularly distributed throughout the area of the map. In order to obtain, prior to contouring, a regular areal distribution of values, a matrix is superimposed over the area and a new value calculated for each matrix point. This is done by taking the irregularly distributed values around each matrix point, weighting them for distance and extrapolating. Two important constraints act at this stage.
1) The values used in evaluating each matrix point must lie within a specified distance from it. This distance ranges from 1 to 500 times the interval •between adjacent matrix points. If this
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scanning distance is set very low then the likelihood arises that matrix points will not be evaluated in regions of sparse well control because insufficient data will be encountered in the scanned area. Conversely, setting the scanning distance very high will result in all points being evaluated but some from well values which are very far away and only tentatively relevant. In this map series the distance has been set high enough to evaluate all points as a complete regional cover is preferred with no blank areas.
2) The number of matrix points may be specified between limits of 4 and 40,000. The greater the number, the less the distance between adjacent points (the grid interval). This distance controls the apparent resolution of detail in the map in that it corresponds approximately to the minimum size of geological structure detectable. However, the real resolution of detail depends on the distribution of the original data, not on the calculated matrix. If the original data is irregularly spaced, which is usual, then the real resolution possible will vary over the map. The apparent resolution cannot be varied on any one map and is of necessity a compromise. In this map series the scale of the maps is 1 inch to 16 miles and the grid interval has been set at one-half inch. Thus structures 8 miles across or larger are adequately resolved, within the limits of well control, whereas structures less than 8 miles across are portrayed as at least that size (if detected).
PLOTTING THE MAP
The plotting machine in the Saskatchewan Government Systems Centre requires tape input. Each set of data represented on the map requires that the computer produces a control tape. This map series uses two data sets, viz. contour lines and well positions.
The contour lines drawn by the plotter have their positions calculated by the computer from the previously evaluated matrix. The user must specify to the computer the contour interval, which contours to intensify (x2 is the only option) and which contours require written values. Other details, such as the suppression of negative values on isopach maps, may also require attention.
The well positions plotted are placed on tape by the computer using the original data, the X and Y coordinate values having been calculated at the first stage. The user needs only to specify the well symbol and the size he wishes it to be drawn. In this series the symbol "x" has been used.
Some specifications must be made directly to the plotter. They include paper type and size, pen size and colour of ink.
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PREPARING MAPS FOR PUBLICATION
When all data have been upgraded and acceptable maps plotted on paper a series of identical maps are plotted on mylar film. These mylar master maps are then upgraded to publication standards. Upgrading is done in four specific categories viz. contour lines, annotations, geographic data and title block.
Contour lines are erased where they have been drawn beyond the map limits. Conversely, contour lines which are not complete, usually because of insufficient well control, are extrapolated using trends present in the rest of the map. On isopach maps the contour line of zero thickness (if present) represents the limit of the formation. This line is transferred to the relevant structure map and structure contour lines are deleted beyond or extrapolated to it as they are at map boundaries.
Annotations on the present series of maps are minimal. On a structure contour map the limit of the formation has been labelled as such and the structure map on the Interlake Group has had the limits of the Upper, Middle and Lower Interlake Beds superimposed.
Geographic data in the form of major towns, Indian Reserves, Latitude-Longitude grid and Township and Range grid have been added by means of an overlay. This has been made possible by transforming the latitude and longitude values of the data to X and Y coordinates using a Lambert Conformal Conic Projection with standard parallels at 51 ° 30' 00" and 57° 30' 00". This is the standard projection now used for maps produced by the Department of Mineral Resources. The previous report in this series (Paterson, 1973) was plotted on a Polyconic projection. While it will be found that maps of the two reports will not superimpose exactly the distortion over small areas is not great.
The title block follows the standard format of the Department of Mineral Resources and includes map name and number, contour interval, scale, datum (if applicable), symbols present and the date to which the well data used can be considered valid. This last implies a certain incompleteness, in that new data may have become available while the map was being prepared but have not been added. The title block also contains reference to the number and title of this report along with the author's name and the year of publication.
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QUALITY OF MAPS
The maps produced by the computer are mathematical models based on geological data. Geological models based on the same data usually do not differ radically unless the mathematical model is geologicaily impossible or the geologist has more knowledge than the computer. In the first instance, negative thicknesses, for example, make sense mathematically but not geologically. In the second, the main source of disagreement is at the edges of map areas. The geologist will often draw on his knowledge of adjacent areas, which the computer cannot do unless given information beyond the map limits.
Situations such as the last arise from differences in interpretation. More adverse effects arise from errors in the input data. Specifically, those are errors in value of geological parameters and errors in location.
ERRORS IN VALUE OF GEOLOGICAL PARAMETERS
They can arise from mistaken identification of a formation top on a well log or from errors introduced while a genuine value is being placed in the computer file. Where a detailed study is made of any formation it is usual for the author to publish a list of depths to formation top. By comparing those lists with the values on the printout, errors in the latter can be detected, (assuming that the values reached in a detailed study are more accurate). In the present production, differences of less than ten feet were not considered errors and only those greater than ten feet were used to upgrade the values on the printout.
Scrutiny of the printout revealed several values which appeared to be anomalous in comparison with their neighbours. They were investigated and changed if incorrect. Some errors were also found by checking strong anomalies portrayed on the initial map.
ERRORS IN LOCATION
These can arise from erroneous procedure during the conversion from land survey location to latitude and longitude values and thence to X-Y coordinate values. Introduction of errors while the locations are being introduced into the computer is also possible.
Sampling of plotted well positions indicates that less than one per cent of the wells used in the present series are wrongly located on the maps. They are usually one-quarter to one-half mile displaced. This amounts to one thirty-second of an inch on the 1 inch to 16 miles mapping scale being used. As the minimum size of geological structure resolved is 8 miles across, errors from this source are ignored in the present series.
Errors arising from the second cause are not easily detected. Only if the erroneous location lies outside the boundaries of the map or if the value of the geological parameter is anomalous in its false location does the error show up on the initial map.
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NOTES ON INDIVIDUAL ROCK UNITS
INTERLAKE GROUP
The Silurian rocks of Saskatchewan are represented by the Interlake Group which has traditionally been subdivided into Upper,. Middle and Lower Interlake Beds. The only published data available for upgrading the computerised information were those of Kupsch (1952). Unpublished data came from Jamieson (1972, D.M.R. open file).
The structure map on the top of the Interlake Group shows a general dip from north to south with the major basinal structure of the Williston Basin appearing in the southeast. In the southwest, structural highs show up near Elbow and Swift Current. More minor flexures can be seen near Melfort, Prince Albert and Moose Jaw. The northeastern part of the map is poorly known owing to lack of data.
Superimposed on this map are the limits of the Upper, Middle and Lower Interlake Beds. Comparison of their individual structure maps with the equivalent areas thus delimited shows differences in the models. Both models are valid. In the individual maps, the computer only considered data relevant to the particular rock unit. In the delimited areas, the computer was considering a larger surface, thus data from beyond the limits of the rock unit were incorporated. This altered the structure, especially near the limiting line.
The isopach map shows the group to be thickest in the southeast, near Estevan, and a general thinning to the north and west. This regional picture is modified by numerous local thick and thin parts of the Group. Note that the formation is missing in the extreme west.
UPPER INTERLAKE BEDS
These beds are confined to the southeast of the province. They show a relatively simple structural dip to the south accompanied by a thickening trend from north and west towards the centre of the Williston Basin.
MIDDLE INTERLAKE BEDS
The Middle Interlake Beds are much more extensive than the Upper. The structure map shows them dipping generally south with the southeastern area conforming to the Williston Basin structure. Structural anomalies are apparent in the southwest around Swift Current, Elbow and Moose Jaw. Lesser disturbances can be seen around Saskatoon, Prince Albert and Melfort. The lack of data in the northeast makes the structural interpretation there speculative. The isopach map shows a gradual thickening from north and west towards the Williston Basin centre south of Estevan. This pattern is modified by a multitude of localities of
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thickening or thinning scattered over the entire range of the unit. As with the structure map, lack of data in the northeast makes interpretation tentative.
LOWER INTERLAKE BEDS
This unit is slightly more extensive than the Middle Interlake Beds. It shows great structural similarity, dipping generally south with local highs and lows in the southwest. The isopach map shows abrupt thickening of the unit close to its limits then a very gradual thickening towards the Williston Basin centre. Numerous areas of thickening or thinning distort this regional trend.
STONEWALL FORMATION
Information used to upgrade the computerised data came from Kupsch (1952), Kent (1960), Kendall (1975) and Jamieson (1972, D.M.R. open file).
The formation covers most of southern Saskatchewan, being absent only from a small area in the extreme southwest. The structure map shows a general southerly dip with the Williston Basin structure showing up in the Estevan area and other local structural lows and highs prominent in the southwest. Some less prominent anomalies appear near Prince Albert. The isopach map shows the formation thickening rapidly inward from its edge, then a very irregular thickening to the southeast. Markedly thick or thin bodies occur in the southwest and northeast.
STONY MOUNTAIN FORMATION
Data published by Kupsch (1952), Kent (1960) and Kendall (1975) were used to upgrade the formation picks.
The formation covers all of southern Saskatchewan except for a very small area in the extreme southwest. The structure map shows a generally southerly regional dip towards the centre of the Williston Basin. Minor flexures show up near Prince Albert and Nipawin. More prominent structural highs occur near Moose Jaw, Elbow and Swift Current. The isopach map shows a rapid thickening inward from the formation limits, then a more or less consistent value of about 100 feet over the rest of the area. This is modified by local thicks and thins, especially in the northeast and southwest.
RED RIVER FORMATION
Published information available for modifying the computerised data was extracted from Kupsch (1952), Kent (1960) and Kendall (1975).
The formation is present over the southern part of the province and its northeastern limit is coincident with the shield edge. There is a regional dip to the south with the Williston Basin
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structure showing in the southeast. Maj or anomalies are present near Elbow, Moose Jaw and Swift Current, minor ones near Prince Albert, Lloydminster and Nipawin. On the isopach map the formation thickens rapidly inward from its edge, then more slowly but consistently to the southeast. Sites of thickening coincide with the structural anomalies noted above. In the extreme southeast, the Imperial Lightning Creek 16-7-6-32 well (Twp. 6, Rge. 32 West of First Meridian) reflects a very thick (708 feet) section of Red River Formation. The value of 708 feet is thought to include a repeated section caused by faulting (Paterson, 1971, p. 8; Kendall, 1975). The computer mapping programme cannot allow for fault effects so this anomaly on the isopach map is invalid.
WINNIPEG FORMATION
Data on the Winnipeg Formation were upgraded using the reports of Kupsch (1952), McLean (1960), Fyson (1961) and Paterson (1971). The isopach map shows the formation absent in the west and northwest, to be very thin for some distance inside the limits and then to thicken in a general southwesterly direction. The thin portion in the west may be basal Red River Formation (Yeoman orthoquartzite of Kendall, 1975; see also Paterson, 1971, p. 14). Locally, the formation is thicker or thinner than expected. Conspicuous localities of thickening can be seen in approximate alignment from Yorkton, Wynyard, Melfort to Prince Albert. The anomaly of thinning in the extreme southeast is caused by the Imperial Lightning Creek well, 16-7-6-32Wl, where there is no Winnipeg Formation present. (Noted also on the structure map). As discussed under Red River, this is probably a fault structure. In the structure map there is a fairly regular regional dip to the south with the Williston Basin structure apparent in the southeast. Local anomalies can be seen near Moose Jaw, Elbow, Swift Current and Prince Albert.
DEADWOOD FORMATION
Well data pertaining to this formation were available in Kupsch (1952), McLean (1960), Fyson (1961) and Paterson (1971). The structure map shows the Deadwood to be absent in part of the east and part of the northwest of southern Saskatchewan. Recent work by the author, (unpublished), suggests that the limits in the extreme northwest should be drawn much farther south and that little Deadwood exists north of the Meadow Lake Escarpment which can be seen trending along a line from Molanosa to Meadow Lake. Lack of data in the northeast has also led to a generous interpretation of the formation's extent and in all likelihood it should be restricted there also. South of the Meadow Lake Escarpment there is a regional southerly dip, interrupted by local anomalies near Elbow, Moose Jaw, Swift Current and Prince Albert. The large scale Williston Basin structure shows in the southeast near Estevan. On the isopach map the most striking feature is the marked thinning of the formation over the Meadow
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Lake Escarpment. Otherwise, the formation thickens from its edge towards the west, reaching its maximum value near Lloydminster. There are few anomalous values of thickness, most of which are in the southwest of the Province.
PRECAMBRIAN
Values used for the Precambrian Basement map were upgraded from the reports of Kupsch (1952), McLean (1960), Fyson (1961) and Paterson (1971). Only the area below the Phanerozoic cover was treated. The structure contours indicate an even regional dip to the south-southwest over the northern part of the map. A minor structure shows up near Choiceland. In the southwest, structural highs and lows occur and in the southeast the Williston Basin structure can be seen.
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Table 1-ROCK UNIT DATA
Number of Wells*
Unit Approximate Approximate Thickness (feet ) entering completely area volume
unit penetrating (sq . miles) (cu. miles) Maximum Minimum Average
Precambrian ...... ............. ............. 157 . ... 149,946t .... I
. ... . .. . . ...
*The number of wells entering the unit is the number used in preparing the structure contour map. The number of wells completely penetrating the unit is the number used in preparing the isopach map. In both cases only one well per section was used, so re-entry and other closely spaced wells are not counted.
tArea of Precambrian beneath Phanerozoic cover.
PROGRAMMES USED
The programmes used in preparing this series of maps are stored in the Saskatchewan Government Systems Centre where all the computer work was done. Three programmes were used and are listed below:
Geology Plot Retrieval by J. V. Buller, Saskatchewan Government Department of Mineral Resources, Regina.
Coordinmte Transformations. Lambert Conformal Projection by G. S. Moppett, Computer Science Centre, Canadian Government Department of Energy, Mines and Resources, Ottawa.
Stampede PZotting Package by various authors of International Business Machines Corporation.
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BIBLIOGRAPHY
Fyson, W. K., 1961, Deadwood and Winnipeg Stratigraphy in South-Western Saskatchewan. Sask. Govt. Dept. Min. R es. R ept. 64L 37 pp.
Kendall, A. C., 1975, (In Preparation) , The Ordovician Carbonate Succession (Bighorn Group) of Southeastern Saskatchewan. Sask. Govt. Dept. Min. Res. Rept. 180.
Kent, D. M., 1960, The Evaporites of the Upper Ordovician Strata in the Northern Part of the Williston Basin. Sask. Govt. Dept. Min. R es. R ept. 46, 46 pp.
Kupsch, W. 0., 1952, Ordovician and Silurian Stratigraphy of East Central Saskatchewan. Sask. Geol. Surv. R ept. 10, 62 pp.
McLean, D. D., 1960, Deadwood and Winnipeg Stratigraphy in East-Central Saskatchewan. Sask. Govt. Dept. Min. R es. Rept. 47, 37 pp.
Paterson, D. F., 1971, The Stratigraphy of the Winnipeg Formation (Ordovician) of Saskatchewan. Sask. Govt. Dept. Min. R es. R ept. 140, 57 pp.
----- , 1973, Computer Plotted Isopach and Structure Maps of the Devonian Formations in Saskatchewan. Sask. Govt. Dept. Min. R es. R ept. 164, 15 pp.
