Eocene-Pliocene Stratigraphy Along the Southern Margin of the Wind River Range, Wyoming: Revisions and Implications from Field and Fission-Track Studies

The established mid-Tertiary stratigraphy along the southern margin of the Wind River Range is of questionable chronologic validity because of the difficulty in discriminating among the several tuffaceous units and because lithologic criteria have been used as chronostratigraphic indicators. Field observations and zircon fission-track ages suggest certain revisions of, and additions to, this stratigraphy. These include: 1) recognition of the Cathedral Bluffs Tongue of the Wasatch Formation at Reds Cabin monocline, 2) establishment of a late Oligocene or early Miocene age for the South Pass Formation and 3) recognition that there are middle Miocene deposits previously mapped as Arikaree that consist of reworked Arikaree shed off the upthrown side of the Continental fault. The implications of these findings are that the Continental fault, now a collapse feature, was a tear fault during the early Eocene, that there are most likely Oligocene rocks north of the Continental fault, that there was late Oligocene or early Miocene uplift in the core of the Wind River Range and that the range collapsed in the middle Miocene.