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The southeastern margin of the Devonian Miette reef complex exposed in the Miette thrust sheet near Marmot Cirque has been reexamined and the geometric arrangement of strata from the reef margin to the basin established by tracing units laterally and by detailed examination of several closely spaced stratigraphic sections.
These observations, together with those from other reef-margin exposures in the Miette and Ancient Wall reef complexes, provide a model for reef-margin sedimentation.
The reef margin at Marmot Cirque (which comprises a series of dolomitized units built up as successive layers) remained "passive" throughout its history; i.e., sediments seaward of the reef complex for the most part do not grade into the reef complex, but rather lap onto it. Reef-derived sediment in the offreef position came from lateral "active" reef margins where sediment from the reef was carried into the basin.
Sedimentation at the margin of the reef complex is a function of 4 important processes: (1) sea-level fluctuations and stillstands, (2) production rates and nature of materials building the reef complex, (3) local currents and wave action, and (4) rate of influx of fine terrigenous sediment. The last process has not been stressed in the past and is thought to be particularly important.
Availability and volume of fine terrigenous sediment in the surrounding basin at any particular time influenced the nature and form of reef development. Part of the Miette reef complex and the subsurface Leduc reefs may be explained on this basis.
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