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Rivers across unglaciated portions of the Appalachian Plateaus of Tennessee and Kentucky are deeply entrenched, almost without exception. Widespread gravel deposits on upland surfaces, combined with broad straths and terraces inset beneath the highlands indicate a history of base-level stability punctuated by periods of river incision. Determining the exact timing of episodic incision historically has been difficult due to a combination of unsuitable dating methods and poorly preserved surface materials. Recently, advances in analytical techniques have allowed researchers to constrain the incision history by utilizing the hydrologic link between multilevel cave systems and regional rivers. In this study, we date clastic sediments deposited in caves associated with the Cumberland River using cosmogenic 26Al and 10Be, and show that they correspond to: (1) deposition of upland (Lafayette-type) gravels between ca. 5.6 Ma and ca. 3.5 Ma; (2) initial incision of regional rivers into the Highland Rim after ca. 3.5 Ma; (3) development of the Parker strath during the interval between ca. 3.5 Ma and ca. 2 Ma; (4) incision of the Parker strath at ca. 2 Ma; (5) shorter cycles of incision after ca. 1.3 Ma associated with terraces above the modern floodplain; and (6) regional aggradation at ca. 0.8 Ma. Burial ages of cave sediments record more than 5 m.y. of incision history within the unglaciated Appalachian plateaus and constrain the time needed to develop multilevel cave systems on plateau margins.

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