| The Mannville Group is subdivided into a lower "Transgressive Systems Tract" and an upper "Highstand Systems Tract" at the transition from dominantly retrogradational to progradational stratal geometry.;The "Transgressive Systems Tract" is subdivided by three major flooding events. The initial flooding event is associated with the transgression of the Boreal Sea during which time paleo-valleys on the sub-Cretaceous unconformity were filled with fluvial deposits. The flooding of broad fluvial plains formed broad embayments separated by a chain of north-northwest trending Paleozoic highlands. Embayments on the western side of the Paleozoic Highs and closer to the foredeep of the foreland basin were more sediment-starved compared to those on the east. The flooding event was followed by a major drop in sea-level contributing to deep incision. The second flooding event transformed incised valleys into long estuaries which later formed broad estuaries as sea-level continued to rise. During the relative still-stand of the sea, the progradation of the shoreline results in the deposition of a widespread, 10 to 15 m thick, sandstone sheet. The third flooding event marks the time of maximum transgression, during which an open marine environment covered the northern half of the Alberta Foreland Basin.;The "Highstand Systems Tract" is subdivided by at least six major flooding events. In the south, each succession generally consists of a 15 to 25 m thick, upward-shoaling, muddy to sandy facies often capped by a thin 0.5 to 2 m thick coal. (Abstract shortened by UMI.)... |
