Abstract:

1.It is proved that the Miocene Series is featured with stable heavy minerals,and the Pliocene with unstable minerals.Common augite bed appeared in the middle of Pliocene is the counterpart croped out on the earth's surface,i.e.augite sandstones,and constitutes a key bed.2.The unconformity between the Xiyu Formation conglomerate and the under-lying Artux Formation are found very often at the margin of the basin,but itchanges gradually into conformity inside the basin.Large amounts of pyro-clasts are discovered in the gravels of the Xiyu Formation,whereas in the Ar-tux Formation,pyroclasts are very few.Common augite bed found above theuncomformity interface in Taiss section proves that this key bed is located at the basal of the Xiyu Formation.The gravels under the key bed of augite sand-stones in Pusa section are composed mainly of sedimentary and metamorphicrocks,but pyroclasts increases greatly above the key bed,showing that the boundary between the Xiyu Formation and the Artux Formation should be lo-cated properly under the key bed in successive sections.The same result is obtainedwhen seismic reflective waves are used to trace the boundary.Abundant ostracod and charophyte fossils—generally Candoniella-Cypridopsis-Cyclocyprisfossil assemblage—are collected above the key bed both on ground and in boreholes.In correlation with regional strata,it is appropriate to consider the XiyuFormation to be in Middle to Late Pliocene.3.In wells,the basal of the Pliocene Artux Formation site in 4,800-5,400m deep in Guman structure,4,500m in Yengisar structure and 1,600-1,800m in Kokyar anticline.It is obvious that there are very thick sediments of the Xiyu Formation in Guman and Yengisar structures,that is why the Miocene Serieshad not been drilled in well Guman-2 though this well had drilled in 7,002m.4.The oil reservoir of Kokyar anticline sites generally below 3,000-4,000min depth.It is coarse grained,rich in argillaceous gravels and stable heavy minerals,Corresponding with that of Karato anticline in the west of Kashi City,it should be considered as the lower part of the Pakabrak Formation.Oil shows have been found in well Qibei-1,So it is believed to be an important target reservoir of the Tertiary System in this region.