Abstract: The Opal Hinge, Green River Basin, Wyoming: Lineament Controls on Facies and Thickness Variations

John R. Forster, John C. Horne, Alan J. Scott, Ernest Gomez

Recurrent differential movements of basement blocks during the tectonic evolution of foreland basins create lineaments at block boundaries. Differential movements along these lineaments throughout the developmental history of the basins influence paleostructuring and sediment dispersal patterns. Structural and stratigraphic changes as well as differences in the production characteristics between the Moxa Arch and the La Barge Platform have long been recognized in the western Green River basin, Wyoming. The separation of these features is particularly evident throughout the Lower and middle Cretaceous where rapid thickness and facies changes occur along a southwest to northeast trending linear feature called the Opal Hinge. Thickness and facies variations in the Dakota, Mowry, Frontier and Hilliard intervals provide evidence that the La Barge area, northwest of the Opal Hinge. was rapidly subsiding relative to the areas of the Moxa Arch, southeast of the hinge.

Paleostructural analysis of the Green River basin indicates the development of the Moxa Arch began with deposition of the Frontier Formation. Frontier sediments thin over the Moxa Arch. While thick, predominantly nonmarine Frontier deposits accumulated in the more rapidly subsiding La Barge area, northwest of the Opal Hinge. This provides evidence for the influence of the Opal Hinge on structural development of the western Green River basin. The structural development of the La Barge Platform, as it is presently characterized, post-dates the lower Hilliard since associated thinning with that structural feature is not evident until middle Hilliard sedimentation. The Opal Hinge separates the paleostructural development of The La Barge Platform and The Moxa Arch.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994