DETRITIAL ZIRCON GEOCHRONOLOGY OF PENNSYLVANIAN CHANNEL SANDS AND "PENNSYLVANIAN" SINK FILL DEPOSITS IN MISSOURI

The Missouri USGS has historically mapped certain "sink fill" deposits as Pennsylvanian in age because of some fossil identifications. These are overlain by Mississippian age rocks and found within Ordovician formations. The Moberly and Warrensburg formations have been mapped and conclusively identified as Pennsylvanian channel sandstones. Their provenance is unclear as possible connections have been wiped out by modern fluvial processes. We have conducted U-Pb detrital zircon geochronology on these formations by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the most likely source(s) of these rocks and determine if the "sink fill" deposits are in fact Pennsylvanian in age. Based on the presence of garnet, tourmaline, muscovite, and metamorphic rock fragments observed in these rocks we conclude that the Pennsylvanian channel deposits represent first cycle detritus sourced from high grade basement rocks, most likely the Canadian shield to the north or the Appalachians to the east. The nearly identical zircon cumulative probability plots indicate that the Warrensburg and Moberly formations share the same provenance and were likely anciently connected. The sink fill deposit zircon probability plots are very different from the Warrensburg and Moberly, leading to the conclusion that they are definitely not Pennsylvanian in age. They do appear to have similar plots to the Ordovician aged rocks and thus likely represent reworked Ordovician formations.