About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 674

Last Page: 675

Title: Retrogradational Shelf Sedimentation: Viking Sandstone (Lower Cretaceous), Central Alberta: ABSTRACT

Author(s): E. A. Beaumont

Article Type: Meeting abstract

Abstract:

The Viking Sandstone in the Joffre-Joarcam area of central Alberta consists of a series of overlapping sediment sheets becoming progressively younger westward toward the paleoshoreline. During the regression at the beginning of Viking deposition, streams meandered across the former shelf surface depositing sand in deltas (today's irregular-shaped reservoirs). An ensuing transgression, punctuated by minor regressions, reworked shoreline sediment deposited during the regressions into linear shelf sand bodies (today's linear reservoirs west of the irregular-shaped reservoirs). During the transgression, the retrogradational nature of the sediment sheets, which contain the sand bodies, was formed.

Well-log cross sections show that the Viking thickens westward, pinches out eastward, and that each sediment sheet contains several northwest-trending shoestring sandstone bodies. Cores of the sandstone bodies and their underlying beds exhibit a coarsening-upward succession of: (1) silty marine shale; (2) intercalated silty shale and rippled sand (locally a structureless bioturbated clayey sand); and (3) glauconitic cross-bedded sandstone. A polymictic pebble conglomerate occurs randomly within this sequence.

Submerged deposition on a shelf tens of miles from the paleoshoreline is documented by: (1) marine shale enclosing the Viking; (2) no consistent landward-seaward facies changes; (3) abundant glauconite; (4) an

End_Page 674------------------------------

"offshore" trace fossil assemblage; (5) coarsening-upward sequence of lithologies; and (6) position with respect to the strandline facies. Scarce evidence, such as coal partings and plant fragments, from irregular-shaped fields seems to be inconsistent with deposition offshore. All evidence, however, along with the shingling of the sediment sheets can be explained by retrogradational shelf sedimentation. Modern sediments of the New Jersey shelf are analogous.

End_of_Article - Last_Page 675------------

Copyright 1997 American Association of Petroleum Geologists