DATING TERRACE DEPOSITS ALONG THE TENNESSEE RIVER USING COSMOGENIC 26AL AND 10BE

River incision in the south-central United States has been variously attributed to climate change and drainage reorganization (Granger et al., 2001), eustatic base level drop (Anthony and Granger, 2006), and Neogene mantle dynamics (Gallen et al., 2013; Miller et al., 2013). Although terrace gravels have been mapped along much of the Tennessee River, there are few dates available with which to constrain the various models. Terrace gravels are abundant in western Tennessee, where evidence exists for capture and incision events during the late Cenozoic. Downstream of Counce, Tennessee, the Tennessee River curiously flows north parallel to the Mississippi River for >300 km. The presence of quartzose Appalachian gravels in the nearby Hatchie River valley suggests that the Tennessee River once took a more direct path to the Mississippi River, perhaps until the late Miocene-early Pliocene (Self, 2000). Upstream of Counce, a prominent 25 m high knickzone is developed on the Fort Payne chert at Muscle Shoals, Alabama. Profile reconstructions indicate that the knickzone may be correlative with the terraces at Counce as well as with Pliocene terraces along the Mississippi River mapped by Van Arsdale et al. (2007).

To help constrain the late Neogene incision history of the Tennessee River, we sampled gravels at 30 m above river level near Counce for dating with the isochron ²⁶Al/¹⁰Be burial dating method. The terraces near Counce feature a wide variety of lithologies, but only quartzose Appalachian gravels were selected from the deposit. Evidence of deep weathering was found in the deposits, including manganese cements and nodules. The date obtained from this site will be compared to previously obtained terrace ages along other tributaries of the Mississippi River to evaluate the potential influence of climatic or eustatic drivers of incision.