Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Dag Nummedal

Abstract

The tectonic subsidence history recorded in middle Cenomanian to early Campanian (96 to 80 Ma) strata in the U.S. Cretaceous Western Interior basin was studied by applying two-dimensional flexural backstripping techniques to six regional stratigraphic sections across different segments of the basin. Results indicate that tectonic subsidence over the 16 m.y. study interval consists of two distinct components: a westward-increasing flexural subsidence confined within a few hundred kilometers of the thrust belt, and a spatially uniform "residual" subsidence that affected the entire basin. The residual subsidence does not represent signals of eustatic sea level changes but instead reflects epeirogenic movements specific to the North American Western Interior. The flexural component exhibits significant spatial and temporal variations along the strike of the Sevier thrust belt. The greatest cumulative subsidence occurred in southwestern Wyoming and northern Utah, whereas concurrent subsidence in northwestern Montana and southern Utah was insignificant. Temporal trends in subsidence also show a distinct regional pattern. From middle Cenomanian to late Turonian (96 to 90 Ma), subsidence rates were high in Utah and much lower in Wyoming and Montana. In contrast, during the Coniacian and Santonian stages (90 to 85 Ma) subsidence accelerated rapidly in Wyoming, increased slightly in Montana, and decreased in Utah. The observed variations in flexural subsidence were probably manifestations of basement structures, particularly those zones of crustal weakness inherited from the Precambrian rifting and early Paleozoic passive margin development.

Pages

217

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