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.