ZIRCON U-PB GEOCHRONOLOGY OF LATE CRETACEOUS STRATA IN THE ELK BASIN ANTICLINE, NORTHERN BIGHORN BASIN: UNDERSTANDING THE TIMING OF PALEOSEISMITE DEVELOPMENT ASSOCIATED WITH LARAMIDE DEFORMATION

Paleoseismites in the form of clastic dikes, convolute-bedding, and sub-vertical vents associated with overturned laminae are present in Late Cretaceous strata along the western and eastern flanks of the Elk Basin anticline. Previous work linked these features with initial Laramide basement deformation in the northern Bighorn Basin of Wyoming and Montana. To establish a quantitative age for paleoseismite formation, we present detrital zircon U-Pb geochronology from the Mesa Verde Group.

The Mesa Verde Group consists of Late Cretaceous (Campanian) strata that is subdivided based on environments of deposition. In the fluvial depositional environment facies (Eagle Formation), paleoseismites are expressed as clastic dikes and convolute-bedding, while in shallow marine facies (Telegraph Creek, Claggett, and Judith River formations), paleoseismites are expressed as sub-vertical vent structures bounded by overturned laminae.

Zircon U-Pb geochronology from a sand-source bed in the Eagle Formation, sandstone bed in the Claggett Formation, and a bentonite layer at the contact between fluvial and shallow marine facies change will reveal the maximum depositional ages throughout the Late Cretaceous strata containing paleoseismites. Therefore, providing timing estimates for early Laramide deformation in the northern Bighorn Basin. Results from this work will be integrated into regional spatial and temporal tectonic models focused on the development of the Laramide Orogeny throughout the Western Cordillera.