Glacial sequence near McCall, Idaho: Weathering rinds, soil development, morphology, and other relative-age criteria

Abstract

The sequence of glacial deposits near McCall, Idaho, previously assigned to the Pinedale and Bull Lake glaciations, contains deposits of four different ages. These ages are defined by multiple relative-age criteria, including weathering rinds, soil development, surface-rock weathering, morainal morphology, and loess stratigraphy. The thickness of weathering rinds on basaltic clasts is statistically representative and reproducible and can be used to estimate numerical ages. Following in order of decreasing relation to age are soil development, surface-rock weathering, and moraine morphology. The glacial deposits near McCall appear to correspond to times of high worldwide ice volume indicated by the marine oxygen-isotope record. Pilgrim Cove and McCall deposits, both assigned to the Pinedale glaciation, are late Wisconsin in age, perhaps 14,000 and 20,000 years, respectively. They represent a rare case in which deposits of Pinedale age can be separated by relative-age data. Timber Ridge deposits, assigned to the Bull Lake glaciation, have subdued, but well-preserved morainal morphology; relative-age data indicate that they are pre-Wisconsin in age, probably about 140,000–150,000 years old, although we cannot exclude an older age. Williams Creek deposits are clearly distinct from, and intermediate in age between, McCall and Timber Ridge deposits. Weathering rinds and the inferred ages of the other deposits suggest an early Wisconsin age for Williams Creek deposits.