DETRITAL ZIRCON GEOCHRONOLOGY OF THE CAMBRIAN FLATHEAD AND DEADWOOD SANDSTONE OF WYOMING AND SOUTH DAKOTA: AN ANALYSIS OF PROVENANCE AND SEDIMENT DISPERSAL PATTERNS

Cambrian sandstones were sampled for detrital zircon U-Pb analysis from two stratigraphically distinct locations in the Bighorn Mountains of Wyoming (Flathead Formation) and one location in the Black Hills of South Dakota (Deadwood Formation) in order to evaluate provenance and sediment dispersal patterns. The Flathead Formation U-Pb zircon age spectra (n=149) from the Steamboat Point sample (northern Bighorn Mountains) includes prominent age peaks with modes at 1787 Ma and 1836 Ma and a smaller age peak at 2730 Ma. The Flathead Formation U-Pb zircon age spectra (n=136) from the Steerhead Ranch sample (central Bighorn Mountains) yields an age peak of 1798 Ma and two smaller age peaks at 2751 Ma and 2980 Ma. The Deadwood Formation (eastern Black Hills) U-Pb zircon age spectra (n=128) includes a major age peak at 1775 Ma and minor age peaks of 2600 Ma to 3320 Ma. K-S analysis of age peak spectra indicates that each detrital age population is statistically distinct from each other. We find that all of the samples are dominated by Yavapai and Trans Hudson age zircons, which indicates sediment derivation from the south and east. Archean age zircons present in the Flathead samples were most likely derived from the Cambrian Wyoming province that was situated in northern Wyoming and parts of western South Dakota. The absence of Grenville age zircons in all of the samples indicates that by middle Cambrian the Transcontinental Arch emerged as a barrier to sediment transport in the Laurentian midcontinent.