The Devonian Period is generally understood to be one of uniformly warm climate without significant polar ice caps or continental glaciation. As a result, sea level was much higher than it is today, and epeiric seas covered much of the continental interior of North America. Fringing the continents beneath these epeiric seas were extensive reefs that were situated just landward of the major ocean basins. Fossil reefs from the Devonian Period are found in Alberta, Canada where the climate is currently much too cool for this to occur.
Within the shallow seas that covered the continent, regional bathymetric lows acted as intracontinental basins which collected fine-grained silt and clay. Organic matter from the upper, light-intensive parts of the water column rained down to the deeper, anoxic parts of the basins and was preserved as black shale.