Depositional and Exploration Models for Cretaceous Lower Mannville Fluvial Sandstones of South-Central Alberta: ABSTRACT

Abstract

Production of hydrocarbons from fluvial strata of the lower Mannville Formation in the Taber-Milk River area of south-central Alberta occurs primarily from combination structural-stratigraphic traps situated on subtle north-northwest trending anticlinal features. Lower Mannville sediments were deposited in a north-trending valley that formed when sea level lowered and shorelines receded to the edge of the continent during the Late Jurassic and Early Cretaceous. The river that cut this valley shifted eastward in response to rising of the Cordilleran highlands, producing a west-facing escarpment. We regard this escarpment as a southward extension of the Fox Creek Escarpment of west-central Alberta. In latest Neocomian or earliest Aptian time, the river system began to aggra e as a result of southward transgression of the Boreal sea. The basal aggradational valley fill, the Sunburst Sandstone, is generally the coarsest, best sorted, and texturally most mature of the sandstones in the Mannville Group. Stratigraphic traps in the area are the result of: (1) updip pinch-out of the Sunburst Sandstone against the north-trending Fox Creek Escarpment (e.g., Horsefly Lake field); (2) general eastward-thinning of the Sunburst Sandstone within tributary valleys east of the Fox Creek Escarpment (e.g., Chin Coulee field); and (3) updip interruption of blanket fluvial sandstone units by clay-filled, abandoned reaches of the river system that deposited the lower Mannville sandstones (e.g., Taber field). A logical exploration strategy both in the Taber-Milk River area and i areas to the north and south would be to pursue the trends of the Fox Creek Escarpment and its tributary valleys. End_of_Article - Last_Page 543------------