Controls on the distribution of coal in the Campanian to Paleocene post-Wapiabi strata of the Rocky Mountain Foothills, Canada

Abstract

Coals in the post-Wapiabi strata of the Rocky Mountain Foothills are found in the upper Campanian (uppermost Belly River and lowermost St. Mary River formations), lower Maastrichtian (upper Brazeau Formation) and lower Paleocene (upper Coalspur Formation) stratigraphic sequences. Large-scale facies relationships within these sequences, combined with sedimentologic data for the coal-bearing strata and their correlatives, indicate that the coal-forming swamps originated in marginal marine, marginal lacustrine, and flood-plain enviornments. The coal-forming swamps developed only when there was a combination of appropriate diastrophic and favorable climatic conditions. This happened twice in the depositional history of the Rocky Mountain Foothills during phases of relative tectonic quiescence (early Maastrichtian and early Paleocene) in the northern, humid part of the basin. At those times the semiarid conditions in the southern part of the basin precluded the formation of coal-forming swamps. The semiarid conditions in this part of the basin were overridden in the late Campanian by the influence of the Bearpaw Sea, which led to the formation of thin coals in the marginal marine environment.

Stratigraphic architecture and coal character of Late Permian Fort Cooper Coal Measures, Bowen Basin, Queensland

“…For example, thin seams commonly develop in delta plains whereas thick coal seams can form in contiguous abandoned channels and floodplains (Flores, 1979;Hagelskamp et al, 1988;Hamilton, 1985;Hobday, 1987;Levey, 1985;Querol et al, 1992). However, on a regional basin scale, the distribution and thickness of coal seams may be influenced by tectonic factors that influence base level changes and accommodation space (McCabe and Parrish, 1992;Bohacs and Suter, 1997;Pashin, 1994; and climate (Flores and Sykes, 1996;Jerzykiewicz, 1992;McCabe and Parrish, 1992).…”

“…Case studies (for example, Hobday, 1987;Tibert and Gibling, 1999; have shown that differential subsidence in a basin can result in variable distribution of coal seams, with thicker seams often associated with stable palaeotopographic highs, and thin or split seams with topographic lows or high accommodation sites. Though tectonic setting of a basin and palaeotopography are primary controls on defining the extent of coal seams, the secondary controls are palaeodepositional systems (Cairncross, 1989), responding to eustatic fluctuations (Flores and Sykes, 1996) and climate (Flores and Sykes, 1996;Jerzykiewicz, 1992;McCabe and Parrish, 1992). In addition to that, the thickness of a coal seam can also be influenced by syndepositional deformation and thrusting (Charlesworth and Gagnon, 1985).…”