Ardley Coal Zone

The Ardley Coal Zone is of Paleocene age and defines the upper part of the Scollard Formation. The Ardley Coal Zone can be subdivided into two distinct sub-zones: the upper Ardley and the lower Ardley. Because the strata dip toward the mountains, the Ardley Coal Zone is exposed along the eastern and northern edges of the Scollard Formation outcrop. Richardson et al. (1988) focussed on the coals to a depth of 400 m by examining 1408 oil and gas wells and 98 Alberta Research Council coal exploration drillholes. A recent report by Hughes et al. (1999) refines the characteristics of this coal zone.

The present study area formed part of the Medicine substudy area by Richardson et al. (1988) and many of the trends outlined in the present report are evident in the data presented by Richardson et al . (op. cit.).

Two prominent coal seams are generally recognized in the Ardley Coal Zone in outcrops along the Red Deer River, the Nevis (or No. 13) seam and the Ardley (or No. 14) seam from designations by Allan and Sanderson (1945; see also Gibson, 1977).

In the present study area, the Lower and Upper Ardley coal zones can be easily distinguished (Figure 4: Summary lithologic column for the Ardley Coal Zone). The Upper Ardley Coal Zone is about 10 m thick and is of the greatest economical importance in the study area. The Lower Ardley Coal Zone is more variable in thickness.

The structure on the top of the Ardley Coal Zone (Figure 5: Elevation on top of the Ardley Coal Zone (m)) shows a similar pattern as the top of the Battle Formation (Figure 3: Structural map of the top of the Battle Formation), but is slightly more irregular, probably because of variations in sandstone thickness between the coal seams. The top surface of the Ardley Coal Zone dips to the southwest at about 20 m/10 km. The basal surface dips in the same direction at about 25 m/10 km. The depth to the top of the coal zone varies between 330 and 470 metres (Figure 6: Depth to top of Ardley Coal Zone (m)). The ridge in the southern part of the area is a topographic high, formed by hills with elevations up to 1020 metres south of Buck Lake , which are about 150 metres higher than the lake. The Ardley Coal Zone thickness ranges from 48 to 74 metres and shows greatest thickness along a northwest to southeast trend, parallel to the mountain front (Figure 7: Ardley Coal Zone thickness (m)).

The total cumulative coal thickness (including coal and shaly coal intervals) of the Ardley Coal Zone (Figure 8: Total cumulative coal (m) of the Ardley Coal Zone) shows a prominent, east-northeast–west-southwest–trending, 15 to 19 metres thick band in the north-central part of the area between areas with 11 to 15 metres coal thickness. In addition, there is a northwest-southeast–trending band through the central part of the area with net coal thickness of 14 to 16 metres. These zones are related to peats that developed between fluvial channels. The orientation of these fluvial channels was probably determined by the tectonic environment of the Cretaceous-Tertiary molasse basin in front of the evolving mountains in the west. The map shows the orthogonal pattern that is also displayed by the face and butt cleats in the Highvale coal mine near Wabumun (Beaton et al., 2002) and the regional fracture pattern in the Alberta Plains (Babcock, 1973).

The number of coal seams (Figure 9: Number of Ardley coal seams) shows a similar trend as the cumulative coal (Figure 8: Total cumulative coal (m) of the Ardley Coal Zone), although the two perpendicular zones are less pronounced. The number of coal seams (including coal and shaly coal as separate seams) ranges from 12 to 20. The maximum concentration of coal seams is along a west-east direction within the central area and slightly northeasterly in most of Township 46.

Figure 10 (Upper Ardley Coal Zone; cumulative coal (m)) shows the cumulative coal of the Upper Ardley Coal Zone, which shows the same trend as the total Ardley Coal Zone cumulative coal (Figure 8: Total cumulative coal (m) of the Ardley Coal Zone). It shows a concentration of peat deposition in the southwestern area. The Lower Ardley Coal Zone (Figure 11: Lower Ardley Coal Zone; cumulative coal (m)) shows greatest cumulative thickness in the northeast. During this time, peat deposition was concentrated in the northern part of the study area. These maps show a migration of the peat deposition centres in time.

Paskapoo channel sands in the 20-metre interval above the Ardley Coal Zone are shown in Figure 12 (Cumulative sandstone (m) in the 20 m interval above the Ardley Coal Zone (in the lower part of the Paskapoo Formation). It shows a general blanket sand sheet, except for some shaly intervals in the central and northern part of the area.

Cumulative thickness of sandstones between the Lower and Upper Ardley coal zones is shown in Figure 13 (Cumulative sandstone (m) between Lower and Upper Ardley Coal zones). This figure shows a south-trending fluvial channel, which will be discussed under the section on ‘sedimentary environments.'

Cumulative thickness of sandstones in the Lower Ardley Coal Zone is shown in Figure 14 (Cumulative sandstone (m) of the Lower Ardley Coal Zone). This figure shows an east-trending meandering fluvial channel, which will be discussed under the section on ‘sedimentary environments.' The cumulative coal thickness is generally less in the area of the Lower Ardley channel (see Figure 11: Lower Ardley Coal Zone; cumulative coal (m)).

Cross-Sections

An east-west structural cross-section shows the regional southwest dip of all strata involved and indicates that the two coal zones can be correlated over the whole area (Figure 15: East-west cross-section through the Buck Lake area). The fluvial channels between the coal zones, which were discussed earlier, explain some of the thickening intervals on the cross-section.

A north-south cross-section also shows the regional dip and correlation of the coal seams (Figure 16: North-south cross-section through the Buck Lake area).

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Last modified: May 7, 2008