The Characteristics of Organic Matter in Permafrost Bog Sediments of Qinghai-Xizang(Tibet)Plateau

Key words: 
• Organic matter /
• Bog secliment /
• Permafrost /
• Qinghai-Xizang plateau

Abstract: The characteristics of organic matter in permafrost bog sediments of Qinghai-Xizang (Tibet) Plateau may provide special in-formation on geochemistry and environment history. In this work, sedimentary facies and organic matter of shallow frozen lacus-trine sediments from a depth of 1 .4m, which is the upper limit of permafrost to 4. 5m have been studied systematically. In thisprofile, clay, silt and fine sand layers occur alternatively. The layers of clay contain the highest content of organic matter and thoseof fine sand contain the least. The important characteristics of organic matter in these frosted bog deposits are shown as follows; 1)the organic matter was of simple source which came from local grasses and subjected to little effect of sedimentation; 2) the compo-nents were relatively stable once after frozen in the sediments. In this profile, the Corg and HI range from 0.11 to 4. 77 and 0 to369 in the section of 20 to 40cm respectively and the contents of extracts vary from 108 to 3630ppm. In soluble extracts, contentof alkane, aromatic, non-hydrocarbon and asphaltene groups are from 0.21 to 15.6296，0 . 79 to 19 . 2 96，3. 8 to 46. 55 96 and 2 .0 to 26.996 respectively. In section from 20 to 40cm, the Corg, HI(hydrogen index), content of extracts by CH₂₂2 andmethanol (8:2), groups of extracts have the same variations with the depth and,can imply the paleoenvironmental changes. TheOEP and Pr/Ph high than 2 and 1 respectively, Indicating that the sedimentary environment was in oxidation. The distribution ofditerpane and hopane vary clearly with the depth and may be a good indicator to environment. Especially, the biomarkers such aspigment and diterpane may help reconstruct the paleoenvironment and imply the change of environment