PENNSYLVANIAN FLUVIAL SYSTEMS IN SOUTHWEST MISSOURI AND FLUVIO-DELTAIC SEDIMENTATION IN THE BOSTON MOUNTAINS

A network of Pennsylvanian channels with micaceous sandstone is present in southwest Missouri, north of the Boston Mountains. The channels are sub-parallel and oriented north to south; cross bedding and clast imbrication consistently indicate southerly flow. The exact age of the channels is unknown, but the sandstones are generally thought to be Desmoinesian (late Middle Pennsylvanian). Previous interpretations of provenance include the Canadian Shield, the Transcontinental Arch, and Missouri’s St. Francois Mountains.

The sandstones have very little feldspar with almost no igneous rock fragments but do contain significant amounts of metamorphic rock fragments. This composition points emphatically to the Appalachians as a major source area, and it is similar to those of pre-Desmoinesian fluvio-deltaic sandstones in the Boston Mountains. Morrowan (Early Pennsylvanian) and Atokan (earliest Middle Pennsylvanian) sandstones in the Boston Mountains were also deposited by southward flowing streams, and they have prominent Appalachian-sourced detrital zircon populations. Little interpolation is needed to connect these deposits and conclude that the channels in southwest Missouri supplied sediment at least as far south as the Boston Mountains. The presence of Appalachian sediment in southwest Missouri prior to the Desmoinesian would require new interpretations of sediment routes and timing for the Appalachian orogen.