Distributive Characteristics of Bio-markers in Modern Sediments of Dachaidan Lake, Qaidam Basin

Modern mud of Dachaidan Lake and the mudstone of the Pliocene sampled from Well Nan-4 both were formed under drought climate. GC and GC-MS had been used to the saturated fraction of hydrocarbons of the samples and the results revealed that;the distribution of bio-markers of the two types sediments are very similar,revealed the similarity of sedimentary environment of them. From the view point of the distribution of saturated hydrocarbon, the maturity parameter of the samples are all very low,OEP and CPI value of mudstone are 4. 5 and 4. 4 respectively,and those of rock samples are 0. 924 and 1. 743 correspondingly. Preference of phytane over pretane are seen in the two sorts of samples also,whereas the Pr/Ph value of mudstone is 0.66 and that of rock profile is 0. 309,and both of them shows the predominance of C₂₂. Diterpanes are simple and featured by m/e 123,predominanted by drrimane and homodr-rimane while long chain triterpanes that characterized by m/e 191 are abundant in the two samples and show a comparatively complete homologues that predominated by C₂₁ and C₂₃. Moreover,except for the triterpane of 13β14α type that normally occurrenced, there is an iso-13β14β triterpane after each peak,the content of which is about half of its hemologue of the same carbon number. Gamacerane that occurrences ordinarilly with high concentration is low in the two samples and the value of Gamacerame over C^H+M₃₀ ratio of mud and rock is 0. 203 and 0. 113 respectively. To the distribution of stroid,regular C₂₉ sterane predominance are shown in the samples, this phenomenon is probaly resulted from the halophilic bactera and algea such as diatom under the saline lake facies,rather than the input of higher plants. The innomal variation of the maturitional parameters of sterane and terpane,such as that of mordern mud can even higher than rock,is related with two raesons.i. e., the difference of existing form of bio-markers in the samples;the contents and sorts of mineral matrix can also effect the maturational evolution process of organic matters,for instance,carbonate minerals can postpone the maturational evolution process.