shale - dark gray Upper Cretaceous Mowry Shale from Utah - teaching hand specimen

The Mowry Shale is one of two important petroleum source rock shales in the northern Rocky Mountains. It is a siliceous shale, which makes it brittle. The Mowry is a self-contained petroleum system, since it’s a primary hydrocarbon source for Cretaceous petroleum reservoirs in the Powder River Basin and also a reservoir in itself. The keys to economically drilling, completing and producing wells in the Mowry have yet to be found, so few of the vertical and horizontal wells drilled directly in the Mowry have been economical. Even so, it remains an important petroleum source rock.

It was estimated that by 1984, the Mowry Shale, as a source rock for other Cretaceous reservoirs, had generated 11.9 billion barrels of oil in the southern Powder River Basin. There's a lot more left. 

These specimens were collected at the foot of the Uintah Range in Cottonwood Canyon on Highway 191 north of Vernal, Utah. Almost black on a fresh surface, the Mowry weathers to a light gray to tan. Some of these specimens intentionally were collected as weathered.  

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