Brian A. Zaitlin1,
Marian J. Warren1,
(1) PanCanadian Petroleum Ltd, Calgary, AB
(2) Mannville Group Inc, Calgary, AB
(3) The University Of Newcastle
Abstract: Sequence stratigraphy in low accommodation Foreland Basins: an example from the Lower Cretaceous "Basal Quartz" Formation of southern Alberta
An intensive regional study including more than 9000 wells and 1350 core has shown the Basal Quartz ("BQ") Formation in the Western Canada Sedimentary Basin to occur in a low accommodation setting with sediment accumulation rates varying from 1.25 to 11.1 m/Ma. North-south and east-west variations in accommodation derived from tectonic processes resulted in a spectrum of terrestrial depositional styles in the BQ, ranging from sheet sandstones to incised valleys and paleosols. These changes in accommodation appear to 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 have been mapped on the basis of detailed petrographic variation and changing channel forms, and illustrate application of sequence stratigraphic methods in non-marine sediments. 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 sheet-dominated deposits. As accommodation increases, systems aggrade and sandbodies become more "ribbon-like" and separated between off channel deposits. Changes in accommodation at BQ time can be attributed to the interplay between eustacy and along-strike changes in deep basin structure and tectonic loading. Major variations in accommodation here result from differential foreland basin loading of contrasting basement terranes.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana