RADIOCARBON DATING OF ASH DEPOSITS
contain 3 layem of volcanic ash, each about 1-2 cm in thick-ness. Radiocarbon dates of discrete plant stems from these ash layers indicate that the age of the uppermost ash deposit ia 725 k260 years B.P. The two lower a & layem lie about 7 ern apart; the average of ltheir dates is 1,845 years B....
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.526.7700 http://www.avo.alaska.edu/pdfs/P0650B_p81to83.pdf |
| Summary: | contain 3 layem of volcanic ash, each about 1-2 cm in thick-ness. Radiocarbon dates of discrete plant stems from these ash layers indicate that the age of the uppermost ash deposit ia 725 k260 years B.P. The two lower a & layem lie about 7 ern apart; the average of ltheir dates is 1,845 years B.P. The amom * of peat above the ash layens indicates that avemge mites of ac-cumuhtion are approximately 0.2 cm/yr for fibrous to mucky peat, and 0.052 cm/yr for the more completely hnmified and compacted peat (muck). The totnil depth of peak a $ this loca-tion (2.8 m) indicates that about 3,400 yeam wa % required for the formation of this deposit. It is estimated, therefore, that this tableland has borne a vegetation mantle no longer than 4,000 yeare. Amohitka Island, the largest in the Rat Island group (Aleutian Islands), has an area of 114.1 square miles (Coats, 1956, p. 86), one-half of which is tableland of several segments at different altitudes ranging from about 135 to 500 feet (Powers and others, 1960, p. 526). These segments are largely mantled with a mat of liv-ing heath and bog vegetation which overlies deposits of peat and muck that are as much as 3 meters thick. Three layers of ash, each about 1-2 centimeters thick, can be recognized in profiles of bhis organic deposit. The vertical distance between the ash layers is pre-sumed to relate to the rate of peat deposition at a par-ticular site. Perennially frozen ground (permafrost) has not been reported in the Aleutian Islands, and no effects of cryogenic processes were evident in these peat deposits on Amchitka Island. There have been no vol-canoes on this island since its emergence from the sea, which was inferred by Powers, Coats, and Nelson (1960, p. 550) to have been before late Pleistocene time. The dating of these ash deposits allows one to deter- |
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