Chapter 20 Figures
Cretaceous Colorado/Alberta Group of the Western Canada Sedimentary Basin

Figure 20.1

Stratigraphic terminology of the Colorado/Alberta Group.

Figure 20.2

Isopach map of the Colorado Group from the top of the Milk River Formation to the top of the Mannville Group. The bulk of the petroleum production from the Colorado Group is from the Viking, Dunvegan and Cardium formations, illustrated in chapters 21, 22 and 23 (this volume), but major gas fields in the Milk River, Medicine Hat and Second White Specks are shown here. Note that the tabulation of gas production (Table 20.2a) includes data from fields in overlying Belly River Formation strata (see Fig. 24.16).

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Figure 20.3

Structure map constructed on the base of Fish Scales Zone. Note that in Saskatchewan, the Base of Fish Scales is not commonly picked and contours in Saskatchewan reflect the (stratigraphically higher) Lower Colorado marker.

Figure 20.4

Structure map constructed on top of the Milk River Formation (Milk River shoulder).

Figure 20.5

Regional cross section A* - A'. Logs are gamma ray and SP.

Figure 20.6

Regional cross section D - D*. Logs are gamma ray and SP.

Figure 20.7

Regional cross section F - F". Logs are gamma ray and SP.

Figure 20.8

Regional cross section G - G*. Logs are gamma ray and SP.

Figure 20.9

Regional cross section H - H'. Logs are gamma ray and SP.

Figure 20.10

Regional cross section J - J'. Logs are gamma ray and SP.

Figure 20.11

Isopach map of the interval from the base of the Fish Scales Zone to the Viking-Bow Island; Lower Colorado to Viking in Saskatchewan.

Figure 20.12

Isopach map of the interval from the top of the Cardium Formation to the Second White Speckled Shale.

Figure 20.13

Isopach map of the interval from the First White Speckled Shale to the top of the Cardium Formation.

Figure 20.14

Isopach map of the interval from the Milk River shoulder to the First White Speckled Shale.

Figure 20.15

Isopach map of the interval from the base of the Fish Scales Zone to the top of the Mannville Group; Lower Colorado to Mannville in Saskatchewan.

Figure 20.16

Isopach map of the interval from the Second White Speckled Shale to the base of the Fish Scales Zone.

Figure 20.17

Isopach map of the interval from the First White Speckled Shale to the Second White Speckled Shale.

Figure 20.18

Reference well logs through the Colorado/Alberta Group (continued overleaf). Note that all logs are standard 1:3000 vertical scale, except a. Pex Valhalla (1:4000), which is condensed to fit the page.

Figure 20.19

Cross section illustrating the retrogradational, backstepping pattern of linear sandstone bodies within the lower Kaskapau formation (modified from Wallace-Dudley and Leckie, 1993).

Figure 20.20

Map showing the location of the Marshybank reference section on Mistanusk Creek, and the type section of the Bad Heart exposed on the west bank of the Smoky River. The locations of wells used in Figure 20.21 are also shown.

Figure 20.21

Cross section (located in Fig. 20.20) tracing the Marshybank and Muskiki formations eastward from Mistanusk Creek into the plains. Note the continuity and parallelism of markers in the Muskiki, and the abrupt resistivity log deflection that marks the base of the Marshybank Formation. The type section of the Bad Heart can be closely correlated with the most easterly well (after Plint et al., 1990).

Figure 20.22

Measured section of the Muskiki and Marshybank formations on Mistanusk Creek, British Columbia, and correlation with the gamma-ray log from well a-23-A, 93-I-16 which lies 10 km to the north-northeast. Note the marked negative (i.e., sandier) deflection of the gamma-ray log that corresponds to the base of the Marshybank Formation (after Plint et al., 1990).

Figure 20.23

Summary stratal geometry of the Muskiki and Marshybank formations. In sequence stratigraphic terms, the Muskiki plus Marshybank unit A make up a transgressive systems tract, Marshybank units B through L make up a broadly progradational highstand systems tract that downlaps onto the top surface of unit A. Major relative sea-level fall following deposition of the Marshybank resulted in deep regional erosion that truncated the Marshybank and Muskiki toward the northwest. The Bad Heart Formation was deposited above this erosion surface and probably constitutes a lowstand systems tract.

Figure 20.24

Map showing progradational limits for shoreface sandstones in Marshybank units F, J and L (see Fig. 20.23), based on data in Plint and Norris (1991).

Figure 20.25

Location maps.

a. Generalized paleogeography of prograding shorelines of the Chungo, Milk River, and Chinook. Shelf sandstones of the Alderson Member are probably younger than the Milk River shoreline sandstones farther south (Braman, pers. comm.).
b. Northern limit of Milk River/Chungo shoreline sands and locations of detailed cross sections (modified after Rosenthal and Walker, 1987, and Meijer Drees and Myhr, 1981).

Figure 20.26

Cross section through Milk River based on well logs (after Meijer Drees and Myhr, 1981). The cross section emphasizes the downlapping nature of the Milk River onto the First White Speckled Shale and shows the interfingering nature of the Milk River with the Alderson Member. The Virgelle sandstone is diachronous, with indication of at least two offlapping shorefaces. Cross section located on Figure 20.25b.

Figure 20.27

Cross section through Chungo Member (outcrop sections taken from Rosenthal and Walker, 1987). The Chungo consists of three offlapping shoreface sandstones that pass landward (south) into non-marine facies and interfinger north with the Hanson and Thistle members. Bioturbated sandy mudstones of the Hanson Member, at Ghost Dam, correlate with non-marine facies of the Chungo farther south. This is also supported by the biostratigraphy (Sweet and Braman, 1990). The base of the Nomad represents a transgressive unconformity, indicated by the chert-pebble horizon and shown by the biostratigraphic relations (Sweet and Braman, 1990). This is used as the datum.

Figure 20.28

Generalized geochemical characteristics of the shales of the Colorado Group. K2WS refers to Second White Speckled Shale; FSMB refers to Fish Scales Zone; TOC is Total Organic Carbon content, based on Rock-Eval pyrolysis; HI is Hydrogen Index, based on Rock-Eval pyrolysis.