40Ar / 39Ar geochronology and provenance of detrital K-feldspars, Ordovician, Upper Mississippi Valley

These shale-bed-partings can be interpreted in two ways: as pulses of terreginous material entering the system and overwhelming carbonate deposition, or as background sediment, accumulating during pauses in carbonate deposition. While the older Glenwood and Platteville samples can be interpreted in either way, the samples from the Galena are better interpreted as condensed background sediment.