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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


The Mesozoic of Middle North America: A Selection of Papers from the Symposium on the Mesozoic of Middle North America, Calgary, Alberta, Canada — Memoir 9, 1984
Pages 205-219
Regional Synthesis and Concepts

Stratigraphic Framework of the Niobrara Formation (Upper Cretaceous) in North and South Dakota

G. W. Shurr, J. Reiskind

Abstract

The Upper Cretaceous Niobrara Formation in North and South Dakota can be subdivided into three distinct stratigraphic/geographic areas. In the western Dakotas, chalk and calcareous shale, approximately 120 m (400 ft) thick, grade westward into the non-calcareous Gammon Ferruginous Member of the Pierre Shale which is over 370 m (1,200 ft) thick. In eastern North Dakota, the Niobrara, approximately 60 m (200 ft) thick, consists of a lower calcareous shale and an upper chalk and shaly chalk. In central South Dakota, the Niobrara, about 60 m (200 ft) thick, consists of two separate chalk tongues which merge eastward into a single massive chalk unit.

The top of the Niobrara is marked by an unconformity throughout most of eastern North Dakota and central South Dakota. Well logs indicate that erosional channels are present on this surface and in central South Dakota the unconformity is exposed along the Missouri River.

Published depositional and paleotectonic models for the Niobrara are refined as a result of interpretations produced by this study. A carbonate ramp which sloped westward into deeper water in the western Dakotas was subdivided into two different depositional settings. On the shallow-water part of the ramp in eastern North Dakota, some terrigenous material was mixed with the chalks and paleoslopes were probably very low. Near the crest of the Transcontinental Arch in central South Dakota, water depths on the ramp were at a minimum and chalk, protected from clastic dilution, was deposited.

Exploration potential for biogenic gas is poor in the western Dakotas, intermediate in eastern North Dakota, and best in central South Dakota.


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