Brian A. Zaitlin1, Dan Potocki1, Marian J. Warren1, Lorne Rosenthal2, Sophie Lemieux3, Ron Boyd4
(1) PanCanadian Petroleum Ltd, Calgary, AB
(2) Mannville Group Inc, Calgary, AB
(3) PanCanadian Petroleum Limited
(4) University of NewCastle, New South Wales, Australia
ABSTRACT: Basement Controls on the Sequence Stratigraphic Development of Low Accommodation Foreland Basins: An Example from the Lower Cretaceous "Basal Quartz" Formation of Southern Alberta
A major regional subsurface study (>9000 wells; ~1350 core) of the L. Cret. Basal Quartz ("BQ") Formation was undertaken in Southern Alberta portion of the Western Interior Seaway, and is equivalent to the Lakota/Kootanai interval in the northern plain states. The BQ was deposited in an overall low accommodation setting (net sediment accumulation rates ~ 1.25 to 11.1 m/Ma), with significant variations in accommodation and depositional styles occurring across key tectonic elements and basement terrains. These variations in accommodation have a profound effect on fluvial style, porosity type and preservation, stratigraphic complexity, reservoir/trap distribution, reservoir continuity and field size distribution.
Individual sequences within the BQ were mapped on the basis of detailed petrographic variation and changing channel geometries, and illustrate application of sequence stratigraphic methods in non-marine strata. Incised valley systems and thin lowstand system tracts dominate the non-marine sequence stratigraphy in low accommodation settings such as the BQ. These deposits are characterized by multiple, closely spaced sequence boundaries and a strong influence from underlying paleotopography. Reservoir distribution is best and most continuous at the base of incised valleys where sand bodies tend not to aggrade, but instead laterally migrate, forming amalgamated sheet deposits. As accommodation increases, systems aggrade and sandbodies become more "ribbon-like" and separated by floodplain deposits. Changes in accommodation at BQ time can be attributed to the interplay between eustasy and along-strike changes in deep basin structure/rigidity and proximity to tectonic loading of contrasting basement terranes.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado