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

Abstract

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 26 Al and 10 Be 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 Lafayettetype gravels on the Eastern Highland Rim deposited between c. 5·7 and c. 3·5 Ma; (2) initial incision of the Cumberland River into the Eastern Highland Rim after c. 3·5 Ma; (3) formation of the Parker strath between c. 3·5 Ma and c. 2·0 Ma; (4) incision into the Parker strath at c. 2 Ma; (5) formation of a major terrace between c.2·0 Ma and c. 1·5 Ma; (6) shorter cycles of accelerated incision and base level stability beginning at c. 1·5 Ma; and (7) regional aggradation at c. 0·85 Ma. Initial incision into the Appalachian uplands is interpreted as a response to eustasy at 3·2-3·1 Ma. Incision of the Parker strath is interpreted as a response to eustasy at 2·5-2·4 Ma. A third incision event at c. 1·5 Ma corresponds with glacial reorganization of the Ohio River basin. Widespread aggradation of cave passages at c. 0·85 Ma is interpreted as the beginning of intense glacial-interglacial cycling associated with global climate change.

Origin and interpretation of knickpoints in the Big South Fork River basin, Kentucky–Tennessee

“…However, the Cumberland River is a tributary of the Ohio River, which has been influenced by ice sheets and glaciofluvial outwash. About 1.5 Ka, ice displaced the ancestral Teays River southward to the valley of the modern Ohio River, shortening the distance to base level of major tributaries, thus increasing slope gradients and triggering incision (Teller and Goldthwait, 1991;Granger et al, 2001;Andrews, 2004;Ward et al, 2005;Anthony and Granger, 2007b).…”

Surface and subsurface drainage evolution of the Corfino and Soraggio karst areas (Tuscany, Italy)

“…A comparison between orograp�y and t�e altimetric distribution of cave passages is often very useful to understand t�e evolutionary p�ases of a karst system, (Piccini 1998;Piccini et al 2003;Mayer et al 2003;Ant�ony & Granger 2007). For t�is reason, a geomorp�o-logical survey of t�e w�ole area was performed by aerial p�oto interpretation and by field surveys.…”

Landscape evolution space and the relative importance of geomorphic processes and controls

“…Streams of the study area began the most recent episode of incision about 1.5 Ma, in response to glacially-driven reorganization of the Ohio River drainage system (Andrews, 2004;Anthony and Granger, 2007). Topography is typical of a dissected plateau, with topographically accordant ridgetops and peaks, and deeply incised stream valleys with steep hillslopes.…”