Although accounting for a small proportion of the cap rocks all over the world

the saline deposit is of vital importance for accumulation and preservation of hydrocarbons

for it serves as seal to most of the discovered hydrocarbon reserves and is also the major cap rock in many huge and giant oil and gas fields.The close relationship between the Middle-Lower Triassic saline deposit cap rock and the distribution of natural gas in Sichuan basin suggests that distribution of saline deposit is crucial to the understanding and evaluation of the gas preserve conditions in southern China.Saline deposit forms mostly during the middle and late stages of basin development.In southern China

saline deposit cap rock are mainly developed in Middle-Lower Cambrian

Car-boniferous

Middle-Lower Triassic

and Cretaceous-Paleogene

but they are unevenly distributed and have different sealing importance.Under the influence of deposition

tectonic settings

and late destruction

the saline-deposit rock of Middle-Lower Cambrian mainly distribute in the eastern and southern parts of Sichuan basin and the northwestern part of Guizhou province;the Carboniferous saline deposit mainly distributed in the central of Hunan province

and the Cretaceous-Paleogene saline deposit mainly occurs in Jianghan basin.The Middle-Lower Triassic Saline-deposit

with the widest distribution and the biggest thickness

plays an important role in the sealing of natural gas in Sichuan basin

northern Guizhou Province

Chuxiong basin

and parts of the Middle-Lower Yangtze.