Abstract

Uranium-lead geochronology of zircon from five subaqueous ash-flow tuffs distributed throughout the Stanley Group of the Ouachita Mountains in Oklahoma and Arkansas define eruption ages that range from 328.5 ± 2.7 Ma near the base to 320.7 ± 2.5 Ma near the top. Biostratigraphy indicates that the oldest age of the Stanley Group is likely to be between 345.3 and 338 Ma. From these age constraints and stratigraphic positions of the tuff units, calculated deposition rates are 1–40 m/My in the Lower Tenmile Creek Formation (< 326 to 322.4 ± 2.4 Ma) and increase to 300–1400 m/My for the overlying Moyers and Chickasaw Creek formations (322.4 ± 2.4 to 320.7 ± 2.5 Ma). Ages of zircons representing detrital components in the tuffs indicate that they are derived mainly from Laurentian sources. The flysch units in the Stanley Group were deposited in a remnant ocean basin flanked by the Alleghenian orogen to the east, which supplied west-southwest-flowing submarine fan systems. These fans likely incorporated material cycled through a growing offshore allochthonous prism in front of a northward-encroaching volcanic arc system to the south of the Laurentian margin in the late Mississippian.