Print this pageABSTRACT: Platy Stromatoporoid Reefs of the Upper Devonian Jean Marie Formation of Northeastern British Columbia
WENDTE, JACK, D. CADENHEAD, D. L. STURROCK, and S. W. DAWSON, Canadian Hunter Exploration Ltd., Calgary, Alberta, Canada
Recent drilling in the Helmet and July Lake areas of northeastern British Columbia has found sizeable reserves of natural gas in the Upper Devonian (latest Frasnian) Jean Marie Formation. Patch reefs form a principal reservoir facies in this limestone. These reefs more closely resemble Carboniferous aged Phylloid-algal mounds than the more typical Givetian and Frasnian age buildups.
The patch reefs attained a maximum thickness of 25 m and had a maximum relief above the sea floor of approximately 13 m. The dominant reef formers were platy stromatoporoids which grew in an upright, interconnected manner similar to that of phylloid algae. Renalcis typically grew on the underside of these stromatoporoids, partially filling the shelter cavities while finer sediment accumulated on the tops of these stromatoporoids in a geopetal fashion.
Regionally, four distinct upward-shoaling cycles of carbonate deposition were mapped in the Jean Marie. The lowermost cycle consists of widespread open-marine carbonates. Successive cycles either shoal up into a platy stromatoporoid reef or remain as a deeper water facies, depending on the paleotopography of the Cycle 1 carbonate. The reefs grew at a faster rate than the surrounding off-reef sediments were deposited, resulting in progressively greater relief above the sea floor. The reefs were subsequently drowned and covered by prograding shales of the Redknife Formation.
The evolution of these unusual buildups provides another example of the interaction of relative sea level, organic growth, and relic topography on the control of reef growth.
AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)