--> Carson Creek Reef, Alberta, Canada: A Case for Tectonic Heredity, by D. J. Edwards; #90986 (1994).

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Abstract: Carson Creek Reef, Alberta, Canada: A Case for Tectonic Heredity

Darran J. Edwards

The Carson Creek oil field in west-central Alberta is an Upper Devonian undolomitized reef complex. A case for basement tectonics as a contributing factor toward carbonate sedimentation within this area has been suggested by many workers, but with little direct evidence. Clearly, knowledge of basement structure would provide valuable insight regarding whether any such enigmatic relationships may have existed.

Interpretation of a seismic dataset recorded to 16 seconds across this area yielded a well defined basement fabric, apparently dipping 20° to 30° SW. These imbricate structures are thought to represent zones of weakness in the crust and impose marked offsets on distinctive Proterozoic layering within the basement, serving as deep marker horizons for discerning later reactivations. Work in progress suggests deep profiles situated 100 km to the SE display similar basement geometries. The horizontal gradient vector of total magnetic field illustrates lineament cluster trends that correlate with these features. The Precambrian surface has a gently undulating, peneplanar topography, punctuated in places by discrete grabens and half-grabens. These high-angle normal faults appear t sole into the low-angle basement fabric, implying partial reactivation. Industry seismic data confirm the areal, sub-vertical nature of Phanerozoic faulting in this region.

Long-wavelength arching of the Phanerozoic cover is present to the NE, an effect of the Laramide Orogeny. Flattening of this broad fold reveals a number a Precambrian irregularities interpreted as faults, apparently coincident with the overlying reef margin. From the available well data, palaeotopographic features just prior to reef growth suggest prominent, structurally high lobes underlying the reef complex. Although actual Devonian reactivation cannot be easily demonstrated seismically, it can be postulated that pre-Devonian differential compaction and erosion over these irregularities created the subtle relief that promoted reef

growth. Differential subsidence controlled by lines of weakness in the basement complex has been an important factor for reef and platform initiation in this area. Through revealing structural grains in basement terranes in this area, deep seismic reflection profiling has made a major contribution to recognizing geological inheritance, a relationship of great proven economic importance.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994