The stratigraphic accumulation of oil in the upper Red River Formation of the Lake Alma-Beaubier region of southern Saskatchewan, Canada, is controlled by textural variations in the medial "argillaceous or earthy" dolomite member which separates the underlying, mottled, extensively burrowed, skeletal micrograined, dolomitic limestone of the Yeoman beds from the overlying interior anhydrite-carbonate rhythms of the Herald beds.

Lenses of oil-saturated, coarse chalk to finely microgranular, calcareous dolomite (grain size 15-25 µ) pass vertically and laterally into micrograined (silt and clay intermixture) carbonate, and finally to cryptograined (less than 5 µ), commonly varved, dolomite.

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