Abstract

Lichenometrical, pedological, and geological evidence are used to establish a Neoglacial chronology in Fourth of July Cirque, Colorado Front Range. Glacial and periglacial deposits are assigned ages based on a growth-rate curve developed for Rhizocarpon geographicum (Benedict, 1967). Three ages of deposits are recognized. The earliest deposits are Temple Lake till dating from about 4,500 to 2,700 yrs B.P. Younger deposits of till, locally termed Audubon, have a minimum age of 950 B.P. The most recent deposits are talus of Gannett Peak age dating from 300 to 100 B.P.

Rock-stratigraphic units in the cirque have distinctive weathering features, vegetation cover, and maximum diameters of crustose lichen thalli indicative of their age. Changes in soil-profile development suggest that soils can be utilized to correlate deposits within the cirque; recent field investigations in the Colorado Front Range indicate that long-range correlations are possible.

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