ABSTRACT

The Bad Heart Formation of northwestern Alberta is a coarsening-upward package of marine siltstone and sandstone of the Upper Cretaceous Smoky Group. It rests erosionally on the Muskiki and Marshybank formations, the contact being marked by a sideritized pebble bed. It is disconformably overlain by the Dowling Member of the Puskwaskau Formation.

The Bad Heart is present in outcrop in two regions: to the south, it outcrops along the Smoky River, where thirteen sections have been measured. Here the Bad Heart is characterized by numerous, closely-spaced, erosional

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surfaces and local facies changes, making correlation difficult. To the north of the Peace River, the Bad Heart outcrops in the Clear Hills. More than a thousand well logs have been used to determine the subsurface stratigraphy of the Bad Heart.

Along the Smoky River, the Bad Heart is capped by a persistent oolitic ironstone layer a few metres thick; in the Clear Hills however, this ironstone is much more extensive, forming low-grade deposits of several million tons, which have attracted interest in the past as an economically viable source of iron ore.

Subsurface work has revealed a marked lithological variation within the Bad Heart. To the west, the sandy oolitic sediments of the Clear Hills and Smoky River areas pass laterally into a siltstone facies. This may be the result of an underlying structural control on sedimentation during Bad Heart time.

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