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ABSTRACT

The exceptional exposure of the margin of the Upper Devonian Miette (Frasnian) buildup in the Canadian Rockies provides a representative example of the sequence-stratigraphic framework of the Late Devonian for the subsurface of Alberta, Canada. The dominant eustatic sea level control during the Frasnian allows a comparison between the outcrop and subsurface buildups. A synthetic seismic section across the Miette buildup outcrop is used for calibrating and comparing the outcrop geometries and facies with seismic and log data across the subsurface Redwater reef complex. The results of this case study illustrate that if the seismic geometries and characteristics are well calibrated with detailed geology, even lower-frequency seismic data can be used to predict platform architecture and large-scale stratigraphic sequences. The outcrop-derived sequence-stratigraphic framework is the basis for the impedance model for constructing synthetic seismic sections at various frequencies. The synthetic sections document the seismic characteristics of the platform, margin, and basinal areas. Two types of seismic-scale geometries are also found in the subsurface Redwater reef complex: a rimmed platform margin and clinoforms of a prograding platform. The iterative interpretation of seismic data and well logs with outcrop data results in a reinter-pretation of the platform architecture of the Redwater reef complex in the subsurface.

This reinterpretation is based on the identification of four sedimentological phases in a platform construction and the six third-order depositional sequences in outcrop that can be correlated to facies in core and the geometries observed on the seismic data from the Redwater reef complex. Phase I is a regional carbonate ramp/platform and is characterized by a ramp platform architecture. Phase II is characterized by the retro-gradation of the platform and the initiation of buildups and can contain low-angle progradation in the retrograding platforms. Phase III is characterized by platform aggradation and basin starvation. This phase generates a steep-rimmed platform margin. Phase IV is characterized by basin infill followed by platform progradation.

These four phases form in a second-order sea level cycle, in which Phases I–III are deposited during the transgressive part and Phase IV during the regressive part of the cycle. Such a coherent model can enhance both exploration and development and can be used or modified to fit analogous areas where data is lacking. Because this second-order sea level change in the Frasnian is mostly eustatic in nature, the resulting platform architecture is expected to be found in other age-equivalent isolated carbonate buildups in Canada or around the world.

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