Examination of nearly 4,000 m of core from more than 180 wells clearly demonstrates that fluvial processes were insignificant in deposition of the Mannville Group (Lloydminster member and above) in the Lloydminster area of Saskatchewan (R18W3-28W3, T44-54). Previous fluvial models are based primarily on the presence and geometry of channels interpreted from geophysical well logs. With rare exceptions, however, well spacing and core data are inadequate to prove a fluvial origin of such features, if they exist at all. A notable exception is an unequivocal channel deposit in the Waseca Formation in the Pikes Peak-Lashburn area. However, the nature of adjacent strata, the presence of numerous clay drapes within the deposit and its dimensions (≤= 40 m thick, 1.6 to 2.7 km wide, but only 30 km long) are inconsistent with fluvial deposition in a terrestrial setting. The most compelling argument against a fluvial origin of the Mannville is the presence in every core studied of numerous sedimentary structures that are extremely difficult to reconcile with fluvial deposition and the paucity of possible fluvial structures or sequences of structures. The former include swash-zone cross lamination; oscillation ripples; and hummocky cross-stratification; and flaser, wavy, lenticular, and pin-stripe bedding. Cored intervals of strata which can be equivocally interpreted to represent fluvial or other channels (such as massive or ripple cross-laminated sands) are nearly everywhere less than 5 m thick. Even if such an interpretation is applied in every example, channel deposits are volumetrically insignificant. Finally, many undoubtedly marine or brackish assemblages of foraminifera and dinoflagellates have been recovered in the study area. Ubiquitous wave-generated sedimentary structures, essentially tabular geometries of sand bodies, and microfossils in the Mannville Group clearly demonstrate deposition in a coastal, rather than fluvial, setting.

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