Figure 25.1

Dunvegan cross sections, a. west-to-east lithostratigraphic cross section, illustrating sandstone of the Dunvegan Formation passing eastward into shale of the La Biche Formation with some intertonguing (modified after Singh, 1983); b. northwest-to-southeast cross section showing subdivision into allomembers (lettered A to G) and shingles (numbered). Cross section based on correlation of chronostratigraphically significant well-log markers interpreted as time lines (based on Fig. 22.7, Bhattacharya, this volume; and Bhattacharya and Walker, 1991b). SB, Sequence Boundary; TSE, Transgressive Surface of Erosion; LST, 3rd-order lowstand systems tract. See text for further details.

Figure 25.2

Wheeler diagram of Dunvegan cross section shown in Figure 25.1b. Deposition of the Dunvegan took place over about 1.5 m.y. Each of the 19 shingles is assumed to have been deposited in about the same interval of time (80 k.y.). Cycle chart shows 3rd- and 4th-order transgressive-regressive cycles. Dunvegan time-stratigraphy is compared with the eustatic chart of Haq et al. (1987) and suggests correlation with a global lowering of sea level. H, hiatus; C.S., condensed section.

Figure 25.3

Definition diagram showing sequences, key surfaces, and systems tracts.

Figure 25.4

Formation and abandonment of a lowstand delta during a rise and fall of sea level. 1. normal regression in the highstand systems tract (HST), 2. a fall in sea level causes valley incision and a seaward jump in the shoreline (forced regression). The lowstand systems tract (LST) overlies a Sequence Boundary (SB). 3. During early transgression, delta-plain sediments accumulate landward. 4. During later transgression, the valley is backfilled as an estuary, and parts of the older SB are cut by a ravinement surface overlain by a thin veneer of diachronous, transgressive sediments. The final panel shows a hypothetical well-log cross section through the arrangement shown above. FS, flooding surface.

Figure 25.5

Basin-fill patterns in: a. foreland basin with a ramp margin, and b. passive margin with a shelf/slope break. P, pod-shaped lowstand units; W, wedge-shaped highstand units.

Figure 25.6

a. Viking allostratigraphy (after Boreen and Walker, 1991). b. Comparison of Viking with global sea level curves of Haq et al. (1987) (modified after Pattison, 1991).

Figure 25.7

Cardium allostratigraphy, based on recognition of seven erosion/ transgression surfaces (E/T surfaces). Lowstand shoreface conglomerates (Waskahigan, Burnstick, Carrot Creek, and Amundson) overlie transgressively modified sequence boundaries. Transgressive erosion (ravinement) is interpreted as having removed the evidence of the channels that fed these shorefaces, resulting in basinally isolated lowstand conglomerates encased in highstand mudstones and sandstones. The conglomerates have been previously interpreted as offshore bars (from Plint et al., 1988).

Figure 25.8

Viking sequence stratigraphy of Joarcam shoreface showing well-log cross sections (above) and schematic of the resulting geometry (below). Note the offlapping shingled geometry. Joarcam is also interpreted as being deposited by the process of forced regression. Compare with Figure 25.5 (after Posamentier and Chamberlain, in press).