Depositional Surfaces in the Eagle Sandstone at Billings, Montana

Route

Start point

No route; this field guide describes two stops in Billings, MT. One of the two stops provides a panoramic view of the sandstone units; the other stop provides an opportunity to study the outcrop.

End point

No route.

Roads (and Trails)

Various roads in Billings, Black Otter Trail at Swords Park

Total distance

No route.

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Geology

Summary

Marine shelf sandstones and barrier bars are commonly formed by lateral accretion of sand bodies with time lines inclined to the formation boundaries. Shelton (1965) described low-angle inclined bedding in the lowermost sandstone unit of the Eagle Sandstone at Billings, Montana. He recognized these beds as shoreface accretion surfaces of a barrier bar and likened them to those found on present-day Galveston Island, Texas. The Billings location provides an excellent opportunity to examine an important hydrocarbon reservoir rock of the Northern Rocky Mountain region.

Key Lithologic Features

• Lower and middle members of the Eagle Sandstone

Structures

• sedimentary structures and burrows

Landforms

• sandstone cliffs (rimrocks)

Other Features

• observation of an important hydrocarbon reservoir

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Reference

Hansen, W.B., and Kendrick, K.R., 1987, Depositional surfaces in the Eagle Sandstone at Billings, Montana, in Beus, S.S., ed., Centennial Field Guide Volume 2: Rocky Mountain Section of the Geological Society of America , p. 79-82.

Availability

Out of print. Check Amazon.com. Digital access to this publication is available via the links in the references section above.