Three troughs

namely Guangyuan-Wangcang

Chengkou-Exi

and Kaijiang-Liangping

in Sichuan basin and its adjacent areas

is filled with deep water carbonates of the Upper Permian-Lower Triassic of Feixianguan Formation.The Dalong Formation in the upper part of the Upper Permian in the area is a condensed succession of 12.5-29m in thickness deposited in the troughs in the chasmic stage.It is composed of silicalite

siliceous mudstone

and siliceous limestone

with fossils such as radiolarans and foram.While the lower part of the Triassic Feixianguan Formation is a filled succession of 50-300m in thickness deposited in the troughs in post-chasmic stage.It is deep water carbonates consisting of a pelagic melanic mudstone and microcrystalline calclithite

as well as turbidites and breccia limestone from gravity flow.The Dalong Formation was deposited at the end of the late Permian when the maximum flooding surface occurred in the trough area.And the deep water carbonates of Feixianguang Formation were deposited during slow regression.The Upper Permian-Lower Triassic Feixianguan Formation constitutes a complete third-order sequence.The deep water carbonates are source rocks of excellent quality with TOC up to 6.21%.But no organic reefs were developed in the Upper Permian and the Feixianguan Formation is lack of oolite.