Research on Outcrop Sequence Stratigraphy of Permian in the Middle-Lower Yangtze Region

According to the latest International Chronostratigraphic Scheme (ICS, 2000), the Permian in the middle-lower Yangtze region of South China traditionally can be divided into three series and nine stages or relevant to six stages. From Assellian to Changxingian of Permian, 44 Ma in age range, the strata are composed of 14 third-order sequences, 3.14 Ma in average age range of each third-sequence. There is one third-order sequence in Zisongian, equivalent to middle and upper Chuanshan Formation or equal to Assellian and two thirds of Sakmarian. There are two third-order sequences, corresponding to Liangshan Formation or Zhenjiang Formation. And upper Chuanshan Formation, which are assigned to Longlingian, coinciding with Artinskian and one third of Sakmarian. In addition, three of them, equal to Qixia Formation, are attributed to Qixian, corresponding to Kubergandian and one third of Roadian. Five of them, comprising Kuhfeng Formation, Maokou Formation, Yanqiao Formation, Yinping Formation and Wuxue Formation, are assigned to Maokouan, equivalent to two thirds of Roadian, Wordian and Capitanian. Two of them, equal to Lungtan Formation or Wujiaping Formation, are included in Wujiapingian. Other two of them, corresponding to Changxing Formation or Talung Formation, are assigned to Changxingian. In brief, these above third-order sequences can be incorporated into 4 sequence sets.