Three-Dimensional Facies Architecture of River-Dominated Deltas, Upper Cretaceous Dunvegan Formation, Alberta Subsurface

Janok Bhattacharya

The Dunvegan Formation comprises a thick clastic wedge deposited into the West Alberta Foreland basin. This wedge consists of a complex series of interbedded shales and sandstones and has been divided into seven allomembers (A to G), each separated by widespread flooding surfaces.

Member E consists of four shingled sandstone bodies that progressively step out into the basin. Detailed mapping of each of these sandstones reveals they consist of several architectural components. These include well-developed, birdfoot-shaped lobate sand bodies that narrow landward and correlate with northwest-southeast-oriented shoestring-shaped linear sand bodies. Cores through the lobes show well-developed coarsening-upward sandy facies successions, typical of prograding river-dominated delta fronts. Cores and cross sections indicate that the shoestring sandstones are fluvial channels. They are erosively based, and the facies successions fine upward and are typical of sandy channel fills. Facies successions through interlobe areas shallow upward but do not contain thick sandstone .

The association of lobes and channels and the facies associations within these components suggest deposition as river-dominated deltaic lobes fed by major distributary channels. Superposition of sand bodies within each shingle reveals the fashion in which the sedimentary basin was filled. The areal pattern and scale of overlapping depositional delta lobes is similar to the Mississippi delta during the last 5,000 years.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.