Organic Geochemical Characteristics And Its Paleoenvironmental Significance Of The Middle Permian Oil Shale In The Southern Junggar Basin

Junggar Basin Permian oil shale formation has more characteristics such as age early,high oil quality and large thickness.Based on the research objects,the methods and the means of tracing the ancient sedimentary environment by outcrop observation,profile measurement and organic geochemical data,preliminarily recovered the ancient sedimentary environment.The oil shale of Junggar basin is mainly deposited in Permian strata assigned with the Jingjingzigou,Lucaogou and Hongyanchi Formations,The Jingjingzigou Formation consists of thin oil shale,siltstone and fine sandstone.The Lucaogou Formation is composed of laminated oil shale,dolomitic mudstone and little gravity flow sedimentation.In contrast,The Hongyanchi Formation is constituted by oil shale,mudstone,siltstone and conglomerate.Oil shale mainly deposited in semi deep lacustrine environment.The organic matter of oil shale in II₁-II₂ kerogen,has a lowercarbon preference index,Odd-Even Predominance and Regular alkane isomerization index.Rock pyrolysis parameters shows that oil shale has high source capacity.The reflectance vitrinite is in the range of 0.5-1.0%,which shows the low maturity and the degree of thermal evolution.Oil shale terpane compounds mainly tricyclic terpane and pentacyclic terpane,smaller tetracyclic terpane content.???regular steranes showed that C₂₈>C₂₉>C₂₇7 carbon number distribution,Diasteranes in low abundance or lack.The deposition of the Permian oil shale in Junggar basin is corresponded with paleo-climate transition from cool aridity to warm moisture condition.The Jingjingzigou Formation oil shale is deposited under plankton organic origin,saline paleo-lake water conditions.The Lucaogou Formation oil shale is deposited under algae and plankton organic origin,semi-saline stratified water conditions,The Hongyichi Formation is deposited under high plant origin,fresh and oxidate paleo-lake water conditions.