1�� Geological Institute of Northwest Sichuan��Southwest Oil and Gas Field Branch��Jiangyou 643000��Sichuan��China; 2�� Department of Resources and Environment��Southwest Petroleum University��Chengdu 610500��China

The northern Longmenshan tectonic belt located at the egde of Upper Yangtze ancient land in Devonian�� inherited the continental shelf slope fault�� The depositional environment is controlled by Beichuan and Nanba faults in slope area��and divided into ocean trough��platform edge shoal��open platform and restricted platform areas from west to east at plane�� At the end of Silurian��Caledonian movement uplifted the whole Yangtze platform to be ancient land��which supplied massive terrestrial materials to Devonian deposition�� In Early Devonian��the crust declined and transgression started�� The depositional environment in Ganxi��Pingyipu and Liuhe between the Qingchuan--Nanba fault and Majiaoba --Yanmenba fault is of neritic carbonate rocks and shoreland clastic rocks�� In Middle Devonian��the transgression is more intensive with space of more extensive�� Tianjingshan ancient uplift is completely covered by sea water and reached to Chaotianyilongdongbei in the Hannan ancient land��while the geomorphic difference between Sichuan and Guizhou ancient lands became smaller with reduced provenance supply�� the sediments are mixed mainly by clastic and carbonate rocks�� In Late Devonian��the maritime space terminated inthe margin of Tianjingshan ancient uplift with the further expansion of transgression�� There was only carbonate deposition with no source supply in this area�� The evolution of depositional environment of Longmenshan in Devonian mainly experienced the Pingyipu��Ganxi --Guanwushan and Shawozi-Maoba sedimentary cycles�� The general pattern is long-time and slow-velocity transgression��and short-time��high-velocity and large-range regression��