Abstract

Statistical measurements of organic and inorganic parameters in thin sections reveal that the Swan Hills Member of the Beaverhill Lake Formation in the Shell Swan Hills 10-17 well is made up by the rhythmical alternation of 8 carbonate microfacies. These rock-types are closely related and interpreted as a continuous sequence representing fore-reef, reef and back-reef conditions. The fore-reef environment shows dark-colored calcarenites whereas the reef itself consists of dark-colored bioconstructed limestones made up by cabbage-type stromatoporoids followed in shallower water by branching colonies of Amphipora. With these 2 organically constructed deposits are associated several types of biocalcarenites. The back reef environment is represented by light-colored calcilutites containing scattered colonies of Amphipora and of mat-type stromatoporoids. The vertical superposition of these microfacies displays 7 rhythms of sedimentation during which an Amphipora-stromatoporoid reef community was established over a carbonate platform, developed and eventually disappeared. The rhythms seem to correspond to tectonically controlled phases of depth decrease.

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