a. General paleogeography of the Western Interior Seaway during the Cenomanian (modified after Williams and Stelck, 1975).
b. General paleogeography of the Western Canada Sedimentary Basin during Dunvegan deposition (mid-Cenomanian). A larger version of this map is shown in Smith (this volume, Chapter 17). Dunvegan paleogeography to the northwest is based on Stott (1982). Regional cross section H-H'is shown in Figure 22.4. Outlined area is described in detail in Bhattacharya (1989a), and is enlarged in Figure 22.10. Reference wells are shown in Figures 22.6 and 22.8; S.R., Imperial Spirit River #1 well (12-20-78-6W6m); B.M., Triad Pan Am Big Mountain Creek well (3-26-66-7W6m).
Structure map on the top of the Dunvegan, showing the overall dip to the southwest. At the scale of the map, the overall trend approximates the dip of time-line surfaces within the Dunvegan, although the map does not coincide with any real physical surface. Outcrop geology is taken from Stott (1982) and Green (1972). Dunvegan and Doe Creek oil and gas fields, and the accompanying summary tables, are derived from Hay (this volume, Chapter 32).
Isopach map of the interval from the top of the Dunvegan to the Base of Fish Scales marker, showing the overall shape of the Dunvegan clastic wedge, thinning to the southeast. The top of the Dunvegan represents a diachronous and interfingering facies change, whereas the Base of Fish Scales approximates a time line. The diachronous nature of the top of the Dunvegan introduces some distortion of the shape, although at the scale of the map, it is probably not extreme. A more detailed isopach is shown in Figure 22.10. Lithofacies designations are based on standard Atlas methodologies, as described in Mossop and Shetsen (this volume, Chapter 1).
Regional cross section H-H' through the Dunvegan and related strata of Alberta. The northwestern end of H-H'is in the Peace River valley where the Dunvegan is exposed. The cross section illustrates the wedge-shaped nature of the Dunvegan and its diachronous boundaries, and shows the interfingering relations with the Shaftesbury and Kaskapau formations. The Dunvegan prograded to the southeast and downlaps onto the FSU and Fish Scales markers, producing a prominent condensed section in the east and south. This is also indicated by the loss of lower Cenomanian strata farther southeast. The Dunvegan comprises shoreline-related sandstones (yellow) and heterolithic nonmarine facies to the northwest (orange-yellow). Silty progradational marine mudstones (green) are distinguished from dominantly transgressive, bentonitic to marly mudstones (gray). This section is based on correlations in cross section H-H' in Chapter 20 (Leckie et al., this volume). All correlation lines are interpreted as representing chronostratigraphically significant surfaces. Facies changes are indicated with a jagged line. Designation of lettered allomembers in the Dunvegan is based on correlations shown in Figures 22.7 and 22.9. Location of the cross section is shown in Figure 22.1b.
Time-stratigraphy (Wheeler Diagram; Wheeler, 1958) of Dunvegan and related strata showing condensed sections, hiatuses and erosional intervals, based on cross sectional relations shown in Figure 22.4. Major paraconformities in the Cemomanian and at the base of the Turonian coincide with major condensed sections. Ages and eustatic curve from Haq et al. (1987) indicate that the Dunvegan correlates in part with a third-order lowstand between 94 and 93.5 Ma. The Fish Scales and Second White Specks coincide with times of peak transgression.
Reference well, Imperial Spirit River #1 12-20-78-6W6M (S.R.; Fig.20.1b). The Dunvegan consists of a series of interbedded sandstones and mudstones, with thin coaly horizons. The facies are arranged into a series of coarsening- and fining-upward cycles capped by marine flooding surfaces. These are tentatively correlated with Dunvegan allomembers defined farther south. Halliburton's SP\Resistivity log is shown. No other types of well logs were run. Core shows the facies of the Fish Scales and FSU markers in the Shaftesbury Formation, and radioactive markers at the top of the Pouce Coupe and Howard Creek intervals in the Kaskapau Formation. The radioactive nature is inferred on the basis of correlation with adjacent wells in which a gamma-ray log was run. Location of this reference well (S.R.) is shown in Figure 22.1b. Note that the vertical scale (1:1800) differs from Atlas standard (1:3000).
Well-log cross section J-J', oriented along depositional dip, illustrating correlation of flooding surfaces. All log traces represent long-scale gamma-ray logs. Major marine flooding surfaces (thick correlation lines) separate sets of offlapping shingled units (allomembers A to G). The cross section shows how the correlation surfaces downlap to the southeast. Numbers within the allomembers refer to the offlapping shingles. Figure from Bhattacharya and Walker (1991a). Location of cross section shown in Figure 22.10.
Reference well, Triad Pan Am Big Mountain Creek, 3-26-66-7W6M (B.M.; Fig. 20.1b). Typical coarsening-upward facies successions capped by marine flooding surfaces are apparent in allomembers of the Dunvegan Formation. Note increase of nonmarine facies upward. The radiation and resistivity logs show the typical log response across the Fish Scales, FSU, top of the Doe Creek, and top of the Howard Creek equivalents. No Pouce Coupe-equivalent sediments are present in this well and only the shaly equivalents of the Howard Creek sandstones are present in the Kaskapau Formation. The K1 marker is a silty bioturbated zone immediately above the Dunvegan in the lower Kaskapau. It correlates with Dunvegan shoreline strata farther north. TSE, transgressive surface of erosion; MjFS, major marine flooding surface (corresponding to an allomember boundary); MnFS, minor marine flooding surface (generally corresponds to a shingle boundary). Figure modified after Bhattacharya and Walker (1991a). Legend is as in Figure 22.6. Note that the vertical scale (1:1800) matches Figure 22.6, but differs from Atlas standard (1:3000).
Well-log cross section K-K', oriented along depositional strike, illustrating a number of channel fills. Successive channels in allomembers E, D, and C are offset from each other. Shingles E1 and D1 are represented by channels. The associated deltaic systems lie in a seaward position and are indicated in Figure 22.7. Location of cross section is shown in Figure 22.10. Figure from Bhattacharya and Walker (1991a).
Isopach of K1 to FSU marker in area studied by Bhattacharya (1989a), showing overall southeast thinning of the Dunvegan clastic wedge. The geometry is similar to that in Figure 22.3. Dots indicate data points. Dots on lines of cross sections indicate well logs only; squares indicate cored wells. Figure from Bhattacharya and Walker (1991a). Indicated cross sections are shown in Figures 22.7 (J-J') and 22.9 (K-K').
Figure 22.11
Summary paleogeographic facies maps of area studied in detail by Bhattacharya (1989a). Maps are based on sand isolith maps and facies relations documented in Bhattacharya (1989a,b; 1991) and Bhattacharya and Walker (1991b); a,i,k and l modified after Bhattacharya and Walker (1991b); f,g,h and i after Bhattacharya (1991). Discussion of maps is in the text. Location of study area shown in Figure 22.1b.
Table 22.2a (as text) (as image)
Oil production from the Dunvegan.
Table 22.2b (as text) (as image)
Gas production from the Dunvegan.
