New 26Al/10Be and (U-Th)/He constraints on the age of the Upland Complex, central Mississippi River Valley

The Upland Complex is a widespread terrace of the ancestral Mississippi River. It has played a central role in studies of the Pliocene Mississippi River drainage, as well as uplift and seismicity in the central Mississippi River Valley. Previous efforts to date the Upland Complex have yielded a range of age estimates spanning the Miocene through Pleistocene. We dated gravels and Fe-oxide cements from quarries of the Upland Complex in Arkansas, Kentucky, Mississippi, and Tennessee using 26Al/10Be burial dating and (U-Th)/He geochronology. Our 26Al/10Be burial dates revealed possible Pliocene-to-Pleistocene depositional ages, while (U-Th)/He dating showed that the onset of weathering dates to at least the Pliocene. Taken together, the 26Al/10Be and (U-Th)/He age constraints demonstrate that the Upland Complex is at least Pliocene in age, and likely formed during a prolonged period of base level stability that preceded Pleistocene glaciations.