ABSTRACT: Allostratigraphy and Depositional Environments of the Basal Belly River Formation (Campanian) in Central Alberta

AL-RAWAHI, ZUWENA, and R. G. WALKER, McMaster University, Ontario, Canada

In the Western Interior foreland basin of Alberta, the lower 50 m of the Belly River Group show a transition from the marine shales of the Lea Park into continental deposits. This transition is defined by an intertonguing geometry of fluvial and shoreface sediments related to shoreline progradation. Such sandstone facies geometries have to be recognized for efficient oil exploration and recovery.

The shales of the Lea Park grade up into wave-dominated coarsening-upward shoreface sandstones, and associated beach facies that inturn are overlain by fluvial/deltaic fining-upward sandstones, floodplain sediments, and coal. Fluvial channel progradation cut out part of the shoreface sequence. In the east, in Davey (TW 34 Rge 28W4) and Tindastoll (TW 36 Rge 1W5) fields, the fluvial sandstones are truncated by a 25 cm thick, transgressive coarser sand or by a shell lag, overlain by marine mudstones and siltstones. Above the transgressive unit, a second shoreface prograded to the northwest, either with a gradational base above marine mudstones or with a sharp erosive contact over the underlying coal. In contrast, to the southwest at Innisfail (TW 34, Rge 1W5), there is no evidence of th s transgression; instead, channelized fluvial sandstones cut out part or all of the first shoreface succession, and continental conditions prevailed thereafter. These facies relationships have been used to map out the limits of transgression and the intertonguing nature of this transition.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)