1. College of Earth Sciences��Jilin University��Changchun 130061��China; 2. Land ��esources Survey and Planning ��esearch Institute of Jilin Province��Changchun 130061��China; 3. Jilin Natural Gas Branch��China Petrochemical Marketing Co�� ��Siping 136108��Jilin��China

Based on systematic geological survey and sampling analysis��this paper restores the palaeoenviron- ment of dark mudstone of Lower Cretaceous largely developed in Fujin uplift of Sanjiang Basin�� The geochemical characteristics show that ratio of Sr/Ba varies from 0. 08 to 0. 20 and coefficient of carbon and oxygen isotopes va- ries from 106. 62 to 116. 03��which indicates the Lower Cretaceous developed in a freshwater sedimentary environ- ment with stable salinity�� Content of Ti varies from 3 183 ×10 ^��6 to 5 239 ×10 ^��6 ��ratio of Sr/Cu varies from 2. 53 to 35. 84 and ratio of Fe/Mn varies from 21. 15 to 96. 95��which indicates the Lower Cretaceous developed under warm humid climate conditions�� And��ratio of Cu/Zn varies from 0. 09 to 0. 21��ratio of V/ (V + Ni) varies from 0. 77 to 0. 81 and abnormal index of Ce varies from ��0. 06 to 0. 01��which indicates the Lower Cretaceous devel- oped in a reducing environment�� The palynological fossils��Protopodocarpus sp�� and Aratrisporites fischeri (Klaus) Playford et Dettmann indicate warm and humid environment for the plants growing�� Geochemical characteristics of source rocks indicate a prospect for gas generation��and the warm and humid reductive environment provided fa- vourable condition for organic matter��