ABSTRACT: Cretaceous Sequence Stratigraphy in Nebraska

Harold M. DeGraw

Cretaceous strata make up a significant part of the sedimentary rock section in Nebraska, but surface exposures are so localized that subsurface studies are required to correlate and interpret the regional stratigraphy. This may be possible now that deep petroleum exploration wells, many with electric logs, have been drilled in most areas of the state.

The Cretaceous consists of multiple unconformity- and disconformity-bounded depositional sequences that contain nearly every sedimentary rock type, deposited in a wide range of marine and nonmarine environments.

Earlier workers divided Cretaceous strata in the Great Plains Region into five major lithologic groups. From oldest to youngest, these were named Dakota, Benton, Niobrara, Pierre, and Fox Hills.

In Nebraska, five regional unconformity-bounded stratigraphic sequences are recognizable, although all of the unconformities are not yet traceable across the state. In general, four of the lithologic groups correspond with the regional stratigraphic sequences even though lithologic and unconformity contacts commonly diverge.

The Dakota consists of two stratigraphic sequences, and the Benton, Niobrara, and Pierre each consist of one. Additionally, a stratigraphic sequence that occurs in the upper part of the Cretaceous and is restricted to the southwestern part of the Nebraska panhandle corresponds to the Fox Hills (Laramie). Each group contains numerous smaller depositional sequences, but only the Niobrara and the Benton contain depositional sequences that appear to extend across the state.

Much of the regional structural framework in Nebraska seems largely to have been inherited from Pierre and Laramie times.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990