Recent Glacial History of an Alpine Area in the Colorado Front Range, U.S.A.: I. Establishing a Lichen-Growth Curve

摘要: A lichen-growth curve has been developed for dating Recent glacial and periglacial deposits in the Indian Peaks area of Colorado Front Range. Rhizocarpon geographicum was selected study because its long life span consistent size-age relationship. The species grows at different rates micro-environments, with moisture, stability substrate length snow-free growing season having greatest effect. Growth were determined indirectly, by measuring maximum diameters circular or nearly thalli on surfaces known exposure age. Measurements made 24 historically dated surfaces, ranging age from 25 to 69 yr., three radiocarbon-dated including (1) mudflow levees younger than 180 (2) a rock wall built prehistoric Indians about 970 yr. ago, (3) ground moraine deposited retreating valley glacier 2,460 radiocarbon years ago. R. geographicurrz very rapidly (14. mm./100 yr.) during First 100 life. then slows an average rate 3.3 completed growth is believed be suitable least as old 3,000