--> Abstract: From Platform to Buildup: A Stratigraphic Feedback System of Bathymetric Profile, Physical Processes and the Carbonate Factory (the Miette and Ancient Wall Reef Complexes, Canadian Rocky Mountains), by P. Homewood, M. T. Whalen, F. Van Buchem, G. Eberli, and E. Mountjoy; #90987 (1993).

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HOMEWOOD, PETER, Elf Aquitaine Production, Pau, France; MICHAEL T. WHALEN, RSMAS University of Miami, FL; * FRANS VAN BUCHEM, Institut Francais du Petrole, Reuil-Malmaison, France; GREGOR EBERLI, RSMAS, University of Miami, FL; and ERIC MOUNTJOY, McGill University, Montreal, Canada

ABSTRACT: From Platform to Buildup: a Stratigraphic Feedback System of Bathymetric Profile, Physical Processes and the Carbonate Factory (the Miette and Ancient Wall Reef Complexes, Canadian Rocky Mountains)

Basic questions such as why, how, when and where carbonate buildups form on acarbonate shelf have not so far received a general answer. We propose a model that, based on the interaction and feedback of four parameters (depositional processes, bathymetric profile, development of the carbonate ecosystems and the basin environment) predicts a typical, three-phased development of carbonate systems.

It is based on the Late Devonian Miette and Ancient Wall buildups (Calm and Peechee) which were formed on the regionally extensive Flume platform. The following phases in their development have been distinguished:

1. Initially the bathymetric profile was bevelled flat (Flume platform) with sediment planed off by storm and wave activity (`wave-base razor'). Seaward stepping genetic units show a more highly diversified faunal association than backward (buildupward) stepping units.

2. The more pronounced bathymetric profile created by the backstepping units of the overlying Maligne, led in the next seaward stepping phase (base of Cairn) to the development of significant clinoforms and the occurrence of turbidites--graded beds of coral and stromatoporoid debris. Small (meter scale) buildups occur at the foot of the clinoforms, showing further diversification of the ecosystem, while the depositional processes became more varied (gravity flows, storms and waves).

3. Finally the lower Peechee forms a large, intensely dolomitized reefal buildup structure with a high diversity of tabular, branching and bulbous stromatoporoids. It has an overall backstepping architecture, and partly interfingers with well-bedded basinal sediments. Contemporaneously developed source rocks suggest conditions in the basin were dys- to anaerobic. The onlapping Perdrix storm deposits and turbidites (shales, HCS calcarenites, graded beds of reefal debris) overlie a conglomerate possibly resulting from erosion during transgression of the Peechee.

This documentation of a rimmed platform progressively building up over a deeper shelf or ramp, reveals a complex stacking pattern of seaward and backward stepping genetic units, leading to a more and more pronounced bathymetric profile and more varied depositional processes. The ecosystems become progressively more complex and niche-specific, while conditions in the basin become dys-/anaerobic. The successive geometries going from low-angle ramp to reef-rimmed platform may be seen on exploration seismics, even though they depend upon genetic units which are below the normal scaleof seismic resolution.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.