ABSTRACT

The Rocky Ridge pool, Billings County, North Dakota, was discovered in January, 1957. The field, a stratigraphic trap, produces from a lower Pennsylvanian sandstone lens and is important primarily because of the stratigraphic implications of the producing horizon. The pool is in the earliest stages of development with three producing wells and four dry holes defining the pool limits.

The producing interval is believed to be a bar-type sand buildup deposited in a shallow sea in early Pennsylvanian time. A widespread black shale-sandstone sequence resting on truncated Otter (Mississippian) formation in the Rocky Ridge area, represents a marker-defined operational unit lying between the truncated Mississippian and a gray limestone marker bed in the Amsden formation.

Preliminary paleontological examination of the lower Amsden operational unit reveals a lower Pennsylvanian fresh water faunal assemblage including ostracods considered to be a marker of the true Amsden (Pennsylvanian) formation of Wyoming.