Study on the middle Permian sequence stratigraphy of Sichuan basin

Through considerable drilling and logging data,com-bined with the outcrop section and so on,we carried on research on the sequence boundary of middle Permian in Sichuan basin and the characteristics of each sequence,estab-lished stratigraphic framework and divided into 5 third-or-der sequences(SQ1-SQ5),the average delay time is about 4 Ma.In this period Sichuan basin was a stable neritic facies carbonate deposition,and is in the mature stage of the basin.The thickness of each sequence was gradually increasing tendency and in the period of SQ4 the thickness of is maxi-mum.The sequence style is mainly of TST>HST,reflects the process of a slow transgression-rapid regression in this period.From the period of SQ4HST the basin began to rise and accept denudation,to the period of SQ5,the area of denudation was up to the maximum and could be extended to the center of basin.