Cosmogenic 26Al/10Be burial ages and 40Ar/39Ar formation ages for cave sediments and manganese oxide ores in Greenbrier and Monroe Counties, West Virginia and Giles County, Virginia

Caves preserve useful archives of fluvial sediments, especially in mountainous landscapes that hinder the preservation of thick, dateable terrace deposits. We used cosmogenic ²⁶Al and ¹⁰Be to date the burial of sediments in four caves along tributaries of the New River: Windy Mouth Cave along the Greenbrier River in West Virginia, Haynes Cave along Second Creek in West Virginia, Bone-Norman Cave along Stony Creek in West Virginia, and Starnes Cavern along Walker Creek in Virginia. Windy Mouth Cave featured the oldest sediment, with a burial age of 4.71 ± 0.09 Ma. Haynes Cave contained two overlapping sediment burial ages of 2.08 ± 0.39 Ma and 2.29 ± 0.50 Ma. Eight samples were measured in Bone-Norman Cave, with major burial age clusters near 1.3 Ma and 2.2 Ma. Starnes Cave yielded the youngest burial ages, ranging from 0.34 ± 0.06 Ma to 0.13 ± 0.06 Ma. All cosmogenic nuclide burial ages are reported at 1-sigma uncertainty. While the Windy Mouth Cave sediments are the oldest dated in the New River Basin, we observe overlapping burial ages between the rest of the caves in this study and others dated along the New River at ~2.2 Ma, ~1.3 Ma, and ~0.2 Ma. Notably, the ~1.3 Ma age cluster coincides with a major ice advance and reorganization of the Ohio River. To examine the erosional history of this area over longer timescales, we also dated the formation of supergene manganese oxide ores using 40Ar/39Ar geochronology of cryptomelane, a K-bearing manganese oxide. Three samples collected on ridges in Giles County, Virginia (n = 2) and Monroe County, West Virginia (n = 1) yielded plateau ages of 30.4 ± 0.2 Ma, 16.40 ± 0.14 Ma, and 8.0 ± 0.3 Ma. All 40Ar/39Ar ages are reported at 2-sigma uncertainty. These ages provide evidence for gradual denudation of valleys and relative stability of ridges throughout the later Cenozoic, while rapid local incision has occurred along the New River and its network of tributaries during the Pleistocene.