Abstract:

In western part of Tarim Basin,the Miocene is represented by a sequence of clastic sediments which can be divided in ascending order into three forma-tions:the Kezilouyi,Anjuan and Pakabulake Formations.The Kezilouyi andAnjuan Formations are composed of continental sediments deposited on a Paleo-gene erosion surface or abandoned lagoonal basin,containing a few of continen-tal Ostracoda and Charophyta.The 3rd to 5th members of the Anjuan Formationare characterized by abundant Cyprideis and Ammonia,with some horizonscontaining Ostracoda and Charophyta common to continental fresh water,suggesting a transitional facies.According to the variation of microfossils,12 sedimental environments of the Anjuan Formation are recorded.Five ofthem are transgressional,represented by fine-grained sediments,well-developedmarine fossils,enriched salinity;while those of regression horizons arerepresented by retired lacustrine basin,coarse-grained sediments,decreasedsalinity and appearance of fresh water fossils.All the ransgressive horizons are rich in organic matters,have higher rate of deposition and plenty of darkargillites with larger thickness of single bed.They are mainly distributed in Wuqia region,totalling about 200m thick.Organic matters are not quite developed in abnormal continental sediments,but they occupy large areas.The Pakabulak Formation comprises entirely clastic sediments.