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[[file:exploring-for-stratigraphic-traps_fig21-3.png|300px|thumb|{{figure number|3}}See text for explanation.]]

[[file:exploring-for-stratigraphic-traps_fig21-3.png|300px|thumb|{{figure number|3}}See text for explanation.]]

Raven Creek field (with 40 million BOE) illustrates the importance of a bottom seal. It is a paleotopographic trap in the Powder River basin of Wyoming. An unconformity overlying the “A” sandstone of the Permian Minnelusa Formation determines the primary trap geometry. This unconformity has paleotopographic relief, and the Opeche Shale red beds are sabkha deposits that infill an erosional valley forming the top and lateral seals to the “A” sandstone reservoir. The dolostone bed separating reservoir sandstones “A” and “B” provides the bottom seal.

Raven Creek field (with 40 million BOE) illustrates the importance of a bottom seal. It is a paleotopographic trap in the Powder River basin of Wyoming. An [[unconformity]] overlying the “A” sandstone of the Permian Minnelusa Formation determines the primary trap geometry. This unconformity has paleotopographic relief, and the Opeche Shale red beds are sabkha deposits that infill an erosional valley forming the top and lateral seals to the “A” sandstone reservoir. The dolostone bed separating reservoir sandstones “A” and “B” provides the bottom seal.

A trap would not form if the valley fill were composed of porous sand or if the bottom-sealing dolostone were absent (from unpublished data by Ralph Thompson, 1986).

A trap would not form if the valley fill were composed of porous sand or if the bottom-sealing dolostone were absent (from unpublished data by Ralph Thompson, 1986).