Paleofire indicated by triterpenes and charcoal in a culture bed in eastern Kunlun Mountain, Northwest China |
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Authors: | Dan Jiao Shucheng Xie Huan Yang Shuyuan Xiang and Xinjun Wang |
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Abstract: | A series of biomarkers were analyzed in the 4000 a B.P. loess sediments in Balong, Dulan County at the north of the eastern
Kunlun Mountain in Northwest China using gas chromatography-mass spectrometry. Olean-2,13 (18)-ene, olean-2,12-ene, urs-2,12-ene
and 5α14α17 α20R-stigmasterane identified in an ancient culture bed were observed in association with charcoal grains, believed
to be the products of paleofire due to the anthropogenic activity in Qijia culture. These triterpenes were proposed to be
derived from dehydration of oleanolic acid and ursolic acid present in angiosperms, and 5α14α17α20R-stigmasterane was derived
from stenols; they both were formed during incomplete combustion. The n-alkane distributions show a shift in the dominant carbon from C27 or C29 to C31, indicative of the abrupt change in paleovegetation from woody to herbaceous plants driven by the changing paleoclimate at
4000 a B.P. after the Holocene Optimum. Coincidently, the Qijia agriculture culture began to collapse during the 200-year
cooling and dryness, and was replaced by nomadism in the mountainous area. The paleofire identified is such a record as to
document the change of ancient culture induced by paleoclimate change. |
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