Abstract

Studies of the Lower Cretaceous Mannville Group in the Lloydminster Heavy Oil Area and beyond indicate that the group is pervaded by linear features that extend from the pre Mesozoic unconformity through the entire Mannville sequence, to the top of the overlying Colorado Group. Some of these features appear to be associated with basement magnetic anomaly lineaments and/or surface photolineaments. Northwest and northeast-striking linears are the most abundant, followed by those oriented ENE-WSW, NNW-SSE, NNE-SSW, WNW-ESE, N-S, and E-W.

The linears are interpreted as fractures, most commonly as high angle faults and joint zones. Mannville linears that have both magnetic anomaly and photolineament counterparts are thought to extend from the Precambrian crystalline basement through the entire Phanerozoic, to the surface. These features are believed to be established in early Precambrian time and, episodically reactivated; the association with photolineaments indicates that they may be active today.

Mannville linears in the Lloydminster area extend over distances of tens to hundreds of kilometres; they parallel or are apparent extensions of, well documented structural trends on the Canadian Shield and/or in other parts of the Western Canada Sedimentary Basin. Linears appear to have played a significant role in post Mannville structural developments. These features seem to have controlled, both spatially and temporally, interstratal karstification of the underlying Middle Devonian Prairie Evaporite beds.

Hydrocarbon migration and pooling in Mannville reservoirs of the Lloydminster area appear to be related to linears.