Figure 27.1

Unconformity-bounded slices of the Phanerozoic succession in the northern Williston Basin, schematically demonstrating the relative extent of basin enlargement and the effect of peripheral stripping. Note specifically the expanded distribution of Devonian strata in the Elk Point Basin. The vertical component is the thickness for each slice.

Figure 27.2

Well-log cross section H-H' through the centre of the Williston Basin. Depositional thinning toward the peripheries of the basin is demonstratable in the carbonate rock portion of the Ordovician, lower part of the Silurian, and the Mississippian. It is also apparent that erosianal attenuation influenced the thickness of the upper parts of both the Silurian and Mississippian. Well locations for numbers 1 to 10 are, respectivily: 1) NE SW 10 T139R101W, 2) NW NE 6T152N R94W/NE SE 1 T152N R95W, 3) NE 2 T155N R96W, 4) SE SW 16 T156N R95W, 5) 15-7-3-8W2, 6) 6-18-6-10W2, 7) 14-11-14-16W2, 8) 4-2-14-21W2, 9) 1-3-19-26W2, 10) 14-10-27-25W2 (After Carlson, 1967, and Hutch, 1967).

Figure 27.3

Well-log cross section J-J' of Devonian and lower Paleozoic rocks through southern Alberta. Note pronounced truncation of the latter over an ancestral Sweetgrass Arch (after Herbaly, 1974).

Figure 27.4

Well-log cross section K-K' of Jurassic and Lower Cretaceous rocks in southern Alberta. Datum is Base of Fish Scales. Note depositional thinning of Jurassic strata over the Sweetgrass Arch (from Herbaly, 1974).

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Figure 27.5

Structure map of the Devonian, and tectonic elements of the Williston Basin and Sweetgrass Arch region of Canada and the United States.

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Figure 27.6

Lithotectonic basement elements identified from geological, geophysical and geochronological data (after Green et al., 1985, and Hoffman, 1989).

Figure 27.7

Middle Paleozoic axes of maximum sediment thickness in the northern Great Plains (after Kent, 1987).

Figure 27.8

A tabulation of recognizable basement positive features in the structurally defined Williston Basin or on the flanks of the expanded basin. Locations are identified by the townships and ranges in which the structures occur, except for Moose Lake, where the location is the centre of the structure.

Figure 27.9

Seismic profile through the 3-17-3-21W2 well in the Minton Field, demonstrating relief on the Devonian Winnipegosis and the Ordovician Winnipeg formations, related to an elevated Precambrian basement block (from Potter and St. Onge, 1991).

Figure 27.10

Sloss's (1963) sequences and transgression/regression plots for the Williston Basin.

Figure 27.11

Schematic illustrations of typical shallowing-upward carbonate-evaporite sequences for the Williston Basin.

Figure 27.12

Idealized shallowing-upward and brining-upward sequences for the Devonian of the Williston Basin area. a. Dawson Bay and Duperow brining-upward sequence, and a stromatoporoid proto-reef (Kent, 1987). b. brining-upward parasequence for the rest of the sedimentary succession.

Figure 27.13

Isopach map of the Mississippian Madison Group in the Williston Basin and Sweetgrass Arch (after Craig, 1972, and Macauley et al., 1964).

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Figure 27.14

Isopach map of the Triassic Spearfish, Lower Watrous and Lower Amaranth units of the Williston Basin and Sweetgrass Arch (after Maclachlan, 1972, Springer et al., 1964).