A new chronology for the age of Appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments

摘要

The relative chronology of landscape evolution across the unglaciated Appalachian plateaus of Kentucky and Tennessee is well documented. For more than a century, geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide-valley straths and smaller terraces. Constraining the timing of river incision into the Appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials. Today, burial dating using the differential decay of cosmogenic 26Al and 10Be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground. Multilevel caves linked hydrologically to the incision history of the Cumberland River contain in situ sediments equivalent to fluvial deposits found scattered across the Eastern Highland Rim erosional surface. Cave sediments correlate with: (1) thick Lafayette-type gravels on the Eastern Highland Rim deposited between c. 5? and c. 3? Ma; (2) initial incision of the Cumberland River into the Eastern Highland Rim after c. 3? Ma; (3) formation of the Parker strath between c. 3? Ma and c. 2? Ma; (4) incision into the Parker strath at c. 2 Ma; (5) formation of a major terrace between c. 2? Ma and c. 1? Ma; (6) shorter cycles of accelerated incision and base level stability beginning at c. 1? Ma; and (7) regional aggradation at c. 0?5 Ma. Initial incision into the Appalachian uplands is interpreted as a response to eustasy at 3?-3? Ma. Incision of the Parker strath is interpreted as a response to eustasy at 2?-2? Ma. A third incision event at c. 1? Ma corresponds with glacial reorganization of the Ohio River basin. Widespread aggradation of cave passages at c. 0?5 Ma is interpreted as the beginning of intense glacial-interglacial cycling associated with global climate change. Copyright ? 2006 John Wiley & Sons, Ltd.