Pliocene−Pleistocene incision of the Green River, Kentucky, determined from radioactive decay of cosmogenic 26Al and 10Be in Mammoth Cave sediments


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July 2001


Cosmogenic 26Al and 10Be in sediments washed into Mammoth Cave, Kentucky, record the history of 3.5 m.y. of water-table position, governed by incision and aggradation of the Green River, a tributary of the Ohio River. Upper levels of the cave formed during a period of slow river incision and were later filled with sediment due to river aggradation at 2.3–2.4 Ma. A brief surge of river incision ca. 2 Ma was followed by river stability and cave-passage formation at a lower level. Rapid incision through 15 m of bedrock ca. 1.5 Ma was prompted by repositioning of the Ohio River to its present course along an ice-sheet margin. Renewed incision ca. 1.2 Ma and aggradation at 0.7–0.8 Ma correlate with major ice advances in the Ohio River basin. Measurements of 26Al and 10Be also indicate that sandstone-capped uplands have maintained slow erosion rates of 2–7 m/m.y. for the past 3.5 m.y., despite accelerated Pleistocene river incision rates of ∼30 m/m.y.


Absolute Age, Al-26, Alkaline Earth Metals, Aluminum, Be-10, Beryllium, Burial, Caves, Cenozoic, Clastic Sediments, Climate Change, Cosmogenic Elements, Dates, Edmonson County Kentucky, Erosion Rates, Fluvial Features, Green River, Ground Water, Incised Valleys, Isotopes, Karst, Karst Hydrology, Kentucky, Landform Evolution, Mammoth Cave, Metals, Neogene, Ohio River Basin, Paleoclimatology, Plateaus, Pleistocene, Pliocene, Quaternary, Radioactive Decay, Radioactive Isotopes, Rivers, Sediments, Solution Feat

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GSA Bulletin, Vol. 113, no. 7 (2001-07-01).