Skip to Main Content
Book Chapter

Recognition and Significance of an Intraformational Unconformity in Late Devonian Swan Hills Reef Complexes, Alberta

By
Jack Wendte
Jack Wendte
Institute of Sedimentary and Petroleum Geology Geological Survey of Canada Calgary, Alberta, Canada
Search for other works by this author on:
Iain Muir
Iain Muir
Wascana Energy Inc. Calgary, Alberta, Canada
Search for other works by this author on:
Published:
January 01, 1995

Abstract

Swan Hills reef complexes are isolated buildups up to 75 m thick that occur on an underlying drowned carbonate platform (approximately 60 m thick) in the subsurface of west-central Alberta and were studied in detail at the Judy Creek and Snipe Lake oil fields. Although these two reef complexes are 85 km apart, 8 to 10 m thick megacycles can be correlated between them. The top of the fourth reefal megacycle is a widespread subaerial unconformity (the intraformational Swan Hills unconformity [ISHU]) that separates an underlying rimmed-reef complex from an overlying ramp-bounded shoal complex.

Emergence at the ISHU was a result of a low-magnitude, relative sea level fall. This is substantiated by the following observations: (1) this surface exhibits a lithified nature continuously across both reefs; (2) shallower-water, mainly tidal-flat deposits overlie relatively deeper-water subtidal limestones at the contact; (3) solution vugs filled with marine sediments occur down to 2.3 m below the ISHU; and (4) oxidation of sediments occurs in some cores immediately beneath the unconformity

Distinct and unique lithologie changes occur in lagoonal successions in the fourth megacycle below the ISHU. The middle and upper parts of this megacycle consist entirely of shallow lagoonal deposits and totally lack the "deep"-water lagoonal deposits that typify portions of the first three reefal megacycles. These distinct changes record the gradual and progressive loss of accommodation space prior to emergence and suggest that the withdrawal of the sea was not due to a Pleistocene-like, glacial eustatic lowering of sea level. This sea level fall and resulting emergence had little effect on reservoir quality of the limestones underlying the ISHU.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

AAPG Memoir

Unconformities and Porosity in Carbonate Strata

David A. Budd
David A. Budd
Search for other works by this author on:
Arthur H. Saller
Arthur H. Saller
Search for other works by this author on:
Paul M. Harris
Paul M. Harris
Search for other works by this author on:
American Association of Petroleum Geologists
Volume
63
ISBN electronic:
9781629810843
Publication date:
January 01, 1995

GeoRef

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now