HIGH-RESOLUTION SEQUENCE STRATIGRAPHY AND PALEOGEOGRAPHY OF THE INTERVAL 6 OF THE UPPER TRIASSIC YANCHANG FORMATION IN THE JIYUAN REGION,ORDOS BASIN

The Jiyuan region is located in the western Ordos Basin where the Anbian delta in the north and the Huanxian delta in the west of the basin converged during theLate Triassic.Through a comprehensive analysis of cores,well logs and seismic interpretation data,and using the principles of high-resolution sequence stratigraphy,the characteristics of multi-order sequence boundaries and lacustrine flooding surfaces in the Interval 6 of the Yanchang Formation in the studied area are documented.This interval includes 20 supershort-term,10 short-term,three middle-term cycles,and one long-term cycle.On the basis of these data,the architecture,stacking pattern and the distribution of different sequences are discussed in detail.According to the high-resolution chronostratigraphic correlation of the boundaries of base-level changes,the sequence stratigraphic and chronostratigraphic framework have been established on the scale of supershort-term base-level cycle.The results are useful in hydrocarbon exploration,particularly in the stratigraphic correlation of small sandstone horizons.