Discovery and significance of Qrebake and Yijianfang Fomations of Ordovician in well GL1, Tarim Basin

The Qrebake Formation of the Upper Ordovician and the Yijianfang Formation of the Middle Ordovician have been found for the first time in well GL1 of the Guchengx? Uplift of the Tarim Basin.They have the same lithologic association,electrical property and conodont zone as name-sections and typical wells in the Tahe and Shaxi regions.Unique stratigraphic sequence has been found in the study region.According to studies of petrology,sedimentary structure and palaeontology,the Qrebake Formation belongs to slope facies sediments.The Qrebake and the Yijianfang Formations distribute stably in the west of Guchengx? Uplift and are favorable for trace comparison on seismic profiles.The 2 formations mainly locate in the lower positions of uplift margin and the intermediate zone of slope.On the uplift,sedimentary gap and degradation vacuity are found respectively.The studies may help the stratigraphic correlation of Ordovician and the analyses of sedimentary environment and tectonic movement in the Guchengx? Uplift,the Katkke uplift,the Tangusbas Sag,and the Tahe and Shaxi regions.