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Title:
Timing of Incision Events Across the Upper Cumberland River System, Tennessee and Kentucky, USA, From Cosmogenic 26Al and 10Be in Cave Sediments
Authors:
Anthony, D. M.; Granger, D. E.
Affiliation:
AA(Purdue University, 1397 Civil Engineering Bldg, West Lafayette, IN 47907 United States ; ), AB(Purdue University, 1397 Civil Engineering Bldg, West Lafayette, IN 47907 United States ; )
Publication:
American Geophysical Union, Fall Meeting 2002, abstract #H21C-0845
Publication Date:
12/2002
Origin:
AGU
AGU Keywords:
1824 Geomorphology (1625)
Abstract Copyright:
(c) 2002: American Geophysical Union
Bibliographic Code:
2002AGUFM.H21C0845A

Abstract

Rivers across the unglaciated portion of the Ohio River basin are almost without exception deeply entrenched. The Upper Cumberland River is an excellent example, with more than 400 km of entrenched meanders as it crosses the Appalachian Plateau surfaces of the Cumberland Plateau and the Lexington-Highland Rim. Constraining the timing of incision events has not been possible in the past, given scant alluvial evidence that was not amenable to known dating techniques. We offer a new chronology of river incision based on the cosmogenic 26Al/10Be burial dating technique applied to multilevel caves alongside the Cumberland River and its tributaries. We interpret rapid incision in the Pliocene and Pleistocene to be a response eustacy and to glacial reorganization of the Mississippi and Ohio River drainage networks. A select group of multilevel caves found along the western margin of the Cumberland Plateau exhibit characteristics indicative of a common history related to river entrenchment. These caves each contain large, abandoned upper-level passages connected to lower, active levels by narrow canyons. The upper-level passages once carried water and sediment from the plateau uplands to a stable water table controlled by the Cumberland River. A wave of incision that migrated up the Cumberland River and its tributaries suddenly lowered the base-level at each of these major caves in turn, causing the sequential abandonment of upper-level conduits in favor of narrow canyons lower down. Sediments left behind in upper levels represent the onset of incision, and can be interpreted in much the same way as alluvium-mantled strath terraces on the surface. Quartzose cave sediments can be dated by the radioactive decay of cosmogenic 26Al and 10Be inherited from prior exposure at the surface. We used this burial-dating technique to date the onset of incision at 15 multilevel caves distributed throughout the Upper Cumberland River system, which show incision to have occurred at least twice over the past three million years. These data provide an important constraint for models of long-term incision into bedrock.
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