ABSTRACT: Stratal Geometry and Facies Distribution in the Dunvegan Deltaic Wedge (Cenomanian, Alberta Basin): Sedimentary Response to Sea Level Oscillation and Foreland Basin Subsidence

PLINT, A. GUY, University of Western Ontario, London, Ontario, Canada

The Cenomanian Dunvegan Formation of northeastern British Columbia and northwestern Alberta forms a clastic wedge that thins from about 250 m to under 30 m from northwest to southeast. The Dunvegan was deposited as a deltaic complex that prograded at least 900 km southeast, parallel to the axis of the foreland basin. A regional allostratigraphic framework has been defined, primarily from abundant subsurface data, supplemented by sections measured in outcrop in the Foothills and Peace River Plains. The allostratigraphy is based on regionally extensive marine flooding surfaces that can be correlated for hundreds of kilometers. Allomembers bounded by these key surfaces downlap to the southeast and can be traced from distal offshore areas, updip through the shoreline and 100-200 km back o to the coastal plain. Fluvial channels, commonly incised between 20 and 30 m are widely recognized immediately below major marine flooding surfaces. These channels, in conjunction with the widespread occurrence of erosively based shoreface sandbodies, suggest that cycles of transgression (accompanied by coastal plain aggradation), coastal progradation, and subsequent fluvial incision took place in response to high-frequency (<1 m.y.) relative sea level oscillations. Allomembers may therefore be considered as sequences in the EXXON sense. The correlation of marine flooding surfaces far onto the coastal plain may permit some quantification of differential subsidence rates between areas proximal and distal to the foreland thrust belt.

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