Regional setting of Niobrara formation in Northern Great Plains

Journal Article · Tue May 01 04:00:00 EDT 1984 · AAPG Bull.; (United States)

OSTI ID:5161596

Shurr, G W

In North Dakota and South Dakota, 2 Niobrara chalk tongues grade into calcareous shales, which in turn intertongue northward and westward with thick noncalcareous shales of the Pierre Shale. In Nebraska, 3 Niobrara chalk tongues and intervening calcareous shales thicken southward as a unit. An isopach map of the interval from the Niobrara base to the Ardmore Bentonite Bed in the overlying Pierre Shale shows an oblate area of thin sediments extending from southwest to northeast out of the Nebraska Panhandle and into central South Dakota. Erosion along the basal Niobrara unconformity is greatest in the area of thin strata and an unconformity is locally developed on the top of the Niobrara in that same area. Structural contours of the Ardmore Bentonite Bed suggest that the area of thin Niobrara strata presently approximates the south flank of the Williston basin and north flank of the Denver and Kennedy basins.

• Research Organization: U.S. Geological Survey, Denver, CO
• OSTI ID: 5161596
• Journal Information: AAPG Bull.; (United States), Journal Name: AAPG Bull.; (United States) Vol. 68:5; ISSN AABUD
• Country of Publication: United States
• Language: English

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