Maantang formation is of marine limestone

argillite and siltstone

while Xiaotangzi formation is mainly composed of delta-front deposit of tran sition zone from marine to land

rich in marine and terrigenous plant fossils.In the past

they were considered as one of the major source beds in northwestern Sichuan.On the basis of analyses by various mordern apparatus

the author made a study of geochemical features of kerogen in these two formations

we concluded that both of the two formations had been hydrocarbon-generating

but neither of them is a good source rock.In comparison between the two

Maantang formation is better than Xiaotangzi fomation.