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.
