Sedimentology and Ichnology of Shallow-Water Deltaic Complex: Lower Cretaceous Sparky Formation, Wainwright Heavy Oil Pool, Alberta, Canada

Leslie A. Brodylo

Much of the 2.5 billion bbl of recoverable reserves in the Lloydminster heavy oil area lie within the Sparky Formation. In the Wainwright pool, the Sparky is 20-30 m thick and comprises three stacked parasequences interpreted to have formed during progradation of a shallow-water deltaic complex into the Cretaceous epicontinental Boreal Sea.

Two 4 to 7 m-thick coarsening-upward parasequences comprise the lower Sparky member and are interpreted as progradational, brackish-water, delta lobe deposits. Intensely bioturbated prodelta mudstones grade up into delta-front siltstones/very fine sandstones, which contain low-angle stratification (HCS?), graded-laminated storm beds, and convex ripples, capped by abundant fair-weather wave ripples. Shoaling is reflected in the vertical succession of ichnofacies: Zoophycos(?)-Cruziana-Skolithos-Psilonichnus. Each parasequence is truncated by a flooding surface and overlain by a thin transgressive shale unit deposited within a bay following lobe abandonment.

The 10 to 15 m-thick upper Sparky parasequence exhibits a complex three-dimensional arrangement of mudstones, siltstones, sandstones, and coals and is interpreted to have formed in a mosaic of bay, marsh, and swamp environments on the lower delta plain. Two 20 to 30 m-thick upper Sparky channels that cut into lower Sparky strata are interpreted as distributaries.

Following abandonment of the entire deltaic complex, peat-forming environments were established resulting in the formation of a regionally extensive 2 to 3 m-thick coal seam that caps the Sparky succession.

Delta-front sublitharenites were cleaned, sorted, and laterally redistributed by storm processes, and form better reservoir facies than feldspathic litharenites of the distributaries.

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