An abundance of heavy oil resources is contained in the North western Margin of Junggar Basin. Given GC/MS analyses of saturates and aromatics within its mainly developed areas, it shows a different biodegradation in place to place and ocrresponding to its differential compositions. To the former, an analysis with GC/MS suggests that most degradutions for n-alkanes and branched alkanes occurred, but steroids and terapane and so on cyclic hydrocarbon are well preserved in it in these areas except Feng-cheng area and Tuzigou area. To the latter, a similar feature occured with the saturates, also having an alternative microbial erosion to it from the features of Naphthalene, Phenanthrene, Tri-aromatic steroids （fragment） that is absorbed in order in preference of light aromatics followed by heavy aromatics. In identical numbers of carbon to them, they have more poweful biodegra dation-resisted capability than that of the saturates.
Based on the distribution of each biomarker in the heavy oils existing variable degradstious, these biomarkers in the saturates and aromatics of this capability successivly as follows:n-alkanes, alkyl-cyclo hexne （methyalkyl-cyclohexhe）, isoprenoids hydrocarbons steroids（20R）,γ-carotane, β-carotane, Bicyclic sesquiterpenes light aromatic （Naphtalene）,steraids （20S）,steroids （αββ）, weight aromatic （phenanthrene）,C2l - steroids （C22 - steroids）, hopanes,tricyclic terapane, rearranged, sterane,deme thyaled hopanes, with more poweful capability of garmacerane, and tri-aromatic steroids.
In view of this order integrated with the features of the heavy oil studied,a classification of its biodegradation into following five ranks:
1 ) Stight biodegradation. It occured in district Ⅳ - 2 and Heiyonshan （Triassic）, having 22. 5-27. 5°API oil.
2) Low biodegradation.It occured in district Ⅵ（Jurassic）, having 19-24°API oil.
3) Intermediate biodegradation.It occured in district Ⅸ （Juraasic）,having 16-21° API oil.
4) High biodegradation.It occured in Fengcheng（Jurassic）, having 11.5-17. 5°API oil.
5) Superhigh biodgradation.It occured in Thou（Jurassic）, the tar sand has a gravity below 13° API.
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