Due to the relative paucity of data, the Mannville sediments located at the western margin of the plains (T10-20, R27W4 to W5) have not been subjected to detailed study. However, recent exploration activity in this area has resulted in the acquisition of much core and drilling data. Using these data, together with those obtained from outcrop studies in the Foothills and from all the available core toward Range 20, a regional appreciation of the stratigraphy, sedimentology, and diagenesis of southern Alberta is now possible. Three major phases of sedimentation are recognized.

The first phase of Mannville sedimentation commenced with the deposition of coarse conglomerates in the Foothills (Cadomin) and chert-rich, often pebbly, sandstones in the plains (Basal Quartz, Cutbank, and Sunburst equivalents). These sediments were deposited as shallow braided or meandering stream deposits, often restricted to broad valleys on the Pre-Cretaceous unconformity. Fine-grained flood-plain deposits with well-developed pedogenic horizons are recognized within this interval.

The second, a transgressive phase of sedimentation, followed, with the deposition of bentonitic shales and fossiliferous limestones (Ostracod Member) and quartzose (Glauconitic) sandstones. The areally extensive sediments, which were primarily deposited in a complex of shallow restricted marine(?) environments, have a distinctive mineralogy compared to the underlying and overlying units. Changes in sediment provenance can account for this mineralogic diversity.

Thirdly, continental conditions returned to much of the area during post-Glauconitic time. This interval is represented by silts and shales intercalated with feldspathic and volcanic channel and crevasse sandstones. The textural and mineralogic immaturity of these sandstones is typical of the upper Mannville sediments of Alberta.

Complexities arise to the east of Range 22 where deep-channels originating during Ostracod, ?Glauconitic, and Upper Mannville times have cut through the underlying sediments. Recognition of the initiation point of these channels is important because reservoir quality is largely controlled by sediment composition. The most prospective reservoirs are quartz-rich sandstones which were not subjected to extensive silica cementation, a consequence of deep burial.

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