Allostratigraphy of Stacked Prograding Coastal Sediments in the Lea Park-Belly River Transition (Campanian) of Central Alberta

POWER, BRUCE A., and ROGER G. WALKER, McMaster University, Hamilton, Ontario, Canada

The Lea Park-Belly River transition in central Alberta comprises a downlapping wedge of coastal sediments. The transition is characterized by numerous stacked shoreface successions that young in an eastward direction. They are very sharply based such that the transition between the mid/lower shoreface and the shelf sediments is either absent or very thin. The shoreface successions are laterally equivalent to incised fluvio-deltaic sediments and are interpreted to indicate forced regressions, where a relative drop in sea level causes the shoreline to move rapidly basinward. The most likely cause of these regressions is a change of subsidence rate due to active loading in the Cordillera acting in concert with a third-order relative drop in sea level. Subsidence due to tectonic loading w uld allow for the aggradation of coastal sediments. During periods of lesser subsidence or greater sea level drop, distributaries would incise and the position of the shoreline would move rapidly basinward, resulting in the subsequent sharp-based shoreface succession. This may indicate that in foreland basins, where subsidence acts to cancel relative drops in sea level, sequence boundaries due to third-order drops in sea level may be replaced by a stacked wedge of sharply based coastal successions.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)