May 2, 2017
Paul Link, Geosciences Department, Idaho State University.
Some of the most dramatic rocks in Jackson Hole, the Harebell Formation, are located in a rather remote, NE corner of the valley, and have been seen by few local residents. Wyoming’s most famous geologist, Dave Love (the “father” of Jackson Hole geology) considered their origin to be something of a mystery. The Harebell Conglomerate, long known for its “cannonball” cobbles of quartzite, with their dimples and concentric fractures, remains a geologic conundrum of Jackson Hole. This unit, which contains fine-grained detrital gold, is exposed on Togwotee Pass and in other localities of the Absaroka and Gros Ventre Mountains. It contains quartzite roundstones that, according to Dave Love, came from the Targhee Uplift, a feature that if it existed must now lie buried beneath the northeastern Snake River Plain in Idaho. Studies of detrital zircon grains in this conglomerate suggest that although the sandstone matrix was sourced in the Late Cretaceous “Idaho River”, that drained the Idaho batholith and Belt Supergroup of central Idaho, the larger rock components are not from the Belt Supergroup, but rather from the younger (Neoproterozoic, 600 million year old) Brigham Group, exposed today in the thrust belt of southeast Idaho. Paul Link will discuss these conflicting bits of evidence for the Harebell and associated conglomerates of Jackson Hole, and work to provide insights to solve Dave Love’s “conundrum”.