Abstract

The Upper Cretaceous (mid to late Coniacian) Bad Heart Formation consists of a ‘coarser’ clastic succession (i.e. comprised of sandstone and ooidal ironstone with lesser conglomerate and siltstone) that typically is about 5 to 15 m thick and exists within a much thicker shale succession. The Bad Heart Formation has long been of potential economic interest because in the eastern Clear Hills region it hosts the thickest and most regionally extensive ooidal ironstone deposit in the Western Canada Sedimentary Basin.

McLearn subdivided the Smoky River Group (then referred to by him as a formation) on a lithostratigraphic basis into three ‘members’: that is, “a lower shale [Kaskapau Formation], a middle sandstone — the ‘Bad Heart Sandstone’ [now a formation], and an upper shale [Puskwaskau Formation]”, with the type section for Bad Heart Formation being near the intersection of the Smoky and Bad Heart rivers. The data from this study have refined the previously published stratigraphic models, on a sequence stratigraphic basis, whereby three sequences encompass lithostratigraphic components of the uppermost Kaskapau, the entire Bad Heart and lowermost Puskwuskau formations. Each of the three sequences are underlain by a transgressive wave-ravinement surface. The two lower sequences are fully developed within the studied interval, each comprising a transgressive system tract that is overlain by a highstand system tract. The studied interval only includes the lower part of the uppermost sequence, represented by a transgressive system tract, based on the stratigraphic mapping herein.

Finally, the palynology results from this study indicate there is an important change in the depositional environment across the lowermost wave-ravinement surface because the first appearance datum for the dinoflagellate Chatangiella sp. cf. C. spectabilis occurs abruptly above this wave-ravinement surface.